In recent years, cultivation of leafy vegetables such as lettuce and spinach using hydroponic systems in closed plant factories under light-emitting diodes (LEDs) lamps is becoming popular. Unfortunately, these vegetables may accumulate high level of nitrate which pose serious human health implications, upon being consumed by consumers. Finding solutions to lower the nitrate content through environmental control is important for vegetable quality control. Therefore, strategies are leaning towards to minimize the nitrate accumulation in leafy vegetables for agricultural product security. The aim of this review is to understand the factors leading to nitrate accumulation in a closed plant factory, to study the factors affecting nutrient ions management in hydroponic system, to review the cultural measures that may lead to minimize the nitrate content in leafy vegetables under controlled environment. Genetic, agronomic (e.g. supply, composition, timing, and form of nitrogen fertilizer), and environmental factors (e.g. temperature, light quality, intensity and photoperiod, carbon dioxide concentration) can significantly impact the nitrate level in leafy vegetables. To produce high quality vegetables especially in low nitrate content, regulatory methods during cultivation including light quality and other aspect of nutrient solution, can Improve the value-added product.

1. Impact Factors Influencing the Nitrate Accumulation of Leafy Vegetables in Plant Factory
IJHSOP
Impact Factors Influencing the Nitrate Accumulation of
Leafy Vegetables in Plant Factory
1Khurshied Ahmed Khan, 1Zhengnan Yan, 2Adnan Abbas, *1Dongxian He
1
Key Lab of Agricultural Engineering in Structure and Environment of Ministry of Agriculture, College of Water
Resources and Civil Engineering, China Agricultural University, Tsinghua East Rd. 17, Haidian, Beijing 100083,
China
2
College of Engineering, China Agricultural University, China
In recent years, cultivation of leafy vegetables such as lettuce and spinach using hydroponic
systems in closed plant factories under light-emitting diodes (LEDs) lamps is becoming popular.
Unfortunately, these vegetables may accumulate high level of nitrate which pose serious human
health implications, upon being consumed by consumers. Finding solutions to lower the nitrate
content through environmental control is important for vegetable quality control. Therefore,
strategies are leaning towards to minimize the nitrate accumulation in leafy vegetables for
agricultural product security. The aim of this review is to understand the factors leading to nitrate
accumulation in a closed plant factory, to study the factors affecting nutrient ions management
in hydroponic system, to review the cultural measures that may lead to minimize the nitrate
content in leafy vegetables under controlled environment. Genetic, agronomic (e.g. supply,
composition, timing, and form of nitrogen fertilizer), and environmental factors (e.g. temperature,
light quality, intensity and photoperiod, carbon dioxide concentration) can significantly impact
the nitrate level in leafy vegetables. To produce high quality vegetables especially in low nitrate
content, regulatory methods during cultivation including light quality and other aspect of nutrient
solution, can Improve the value-added product.
Keywords: Environmental control, LED lighting, light intensity, nitrate reductase
INTRODUCTION
A plant factory with artificial lighting (PFAL) or indoor
vertical farming system are a substitution for traditional
greenhouses or open-field production and also the
foundation of new markets and business opportunities. It’s
a modern form of agriculture where the growth conditions
of plants are carefully controlled. PFAL as a
comprehensive agricultural production way is vital for
profitable vegetable production to solve global concern.
Contrary to the conventional vegetable cultivation, PFAL
can extend the growing season to provide offseason
vegetables (Kozai et al., 2015). This type of agricultural
activity has been highly developed in many western and
Asian countries since the 1970s, especially in Japan,
China, Netherland, Israel, and the United States (Kozai et
al., 2015) with advanced planting and pollution control
technologies. The industry is interested in controlling the
growth and quality of plants by fluctuating the biotic and
abiotic factors such as light, temperature, carbon dioxide,
and nutrient solution (Fang, 2015).
*Corresponding author: Dongxian He, Key Lab of
Agricultural Engineering in Structure and Environment of
Ministry of Agriculture, College of Water Resources and
Civil Engineering, China Agricultural University, Tsinghua
East Rd. 17, Haidian, Beijing 100083, China. E-mail:
hedx@cau.edu.cn
International Journal of Horticultural Science and Ornamental Plants
Vol. 4(1), pp. 064-073, April, 2018. © www.premierpublishers.org, ISSN: 2141-502X
Review Article

2. Impact Factors Influencing the Nitrate Accumulation of Leafy Vegetables in Plant Factory
He et al. 065
Vegetable production in plant factory is about two to four
times faster than by typical outdoor conventional system
due to controlled of indoor conditions (Jones, 2004). In
addition, vertical cultivation shelves (a multi-shelf system)
are used in plant factories and in a small biological
controlled facilitated cultivation space (Alejandro et al.,
2016). Leafy vegetables are affluent in vegetarian diet and
are commonly consumed as ready to eat salad foods in
dietary intake of huge population. The sales of ready-to-
use fresh vegetables have increased rapidly in recent
decades as a result of changes in consumer preferences,
especially in the consumption of prepared salads with
fresh-cut vegetables. Loose-leaf lettuce which has
become particularly popular over the last decade in
Europe and is increasingly consumed as a side dish either
without any other accompaniment or as part of ready-to-
eat mixed salads. Lettuce contains high contents of
vitamin C and antioxidants such as phenolic compounds
and is also rich in dietary fiber. Red lettuce is becoming
more popular than green lettuce in salad mixes because
red lettuce is richer in anthocyanin (Blekkenhorst et al.,
2017).
But unfortunately, it accumulates considerable amounts of
nitrate which have both positive and negative effects on
the human health (Danijel et al., 2017). Persistence
solution to nitrate content in leafy vegetables is important
because in the intellectual and academic community there
are still conflicting evidence regarding potential long-term
health risk of nitrate encountered in human diet
(Santamaria, 2006; Sindelaar and Milkowski, 2012), such
as “dietary nitrate – harmful or beneficial?” (Gilchrist et al.,
2010) or “life-giving or death-dealing”? (Weightman and
Hudson, 2013). Therefore, the European Union prescribed
regulation (No. 1822/2005), became foundation stone to
limit the nitrate content in leafy vegetables. Some
investigations have recorded that a high nitrate
accumulation is harmful to plant growth (Reddy and
Menary, 1990) as well as to human health (Ishiwata et al.,
2002).
The substantial nitrate content of leafy vegetable in plant
factory depends on many factors, since there may be a
significant difference in the level of nitrate between the
same types of a vegetable which grew at same
environmental conditions (Colonna et al., 2016). Factors
responsible for higher nitrate accumulation in plant
factories are connected with environmental, biological,
nutritional, and physiological components. Among them
light quality, lower light intensity and excessive nitrogen
fertilization identified as major possible factors in affecting
the process of nitrate accumulation in protected
horticulture. Therefore, the nitrate content increases
significantly when the rate of uptake exceeds the rate of its
chemical reduction. This situation usually occurs in low
light intensity and high level of nitrate in the medium
(Cometti et al., 2011), which is specific to horticultural
crops under covers, especially in autumn and winter time
because light is the main factor stimulating the nitrate
uptake and its reduction in plant tissues (Shao et al.,
2007), supplemental illumination of horticultural plants
during periods with shortage of sunlight improves the
quantity and nutritional quality of yield. It is important to
follow relevant strategies and determine the role of
individual physiological factors in the process in order to
limit accumulation of nitrate in vegetables, and important
to optimize the use of nitrogen fertilizer (Santamaria et al.,
1998). This review focuses on the input and contribution of
leafy vegetables towards the dietary nitrate intake and its
effects of nitrate on human health, and factors responsible
for nitrate accumulation in plant factory. It also suggests
and reviewed different approaches to decrease the nitrate
content in leafy vegetables and its connected consumption
by human beings.
HEALTH ASSESSMENT OF LEAFY VEGETABLE AS A
SOURCE OF NITRATE DIETARY INTAKE
Leafy vegetables are ultimate and an important part of the
human diet, approximately 80% of dietary nitrates are
derived from vegetable consumption which means that
human exposure to nitrate is usually associated with intake
through vegetables (Temme et al., 2011). The vegetarian
diets are rich in vital bioactive phytochemicals and as
important source of consumption. These vegetables
contain considerable amounts of nitrate, which can have
both positive and negative effects on the human health.
Leafy vegetable well-thought out to be a highest source of
nitrate accumulation upon being consumed in dietary
intake (Zhong et al., 2002), computing for 72%–94% of the
total nitrate intake of humans (Walker, 1990; Dich et al.,
1990; Umar and Iqbal, 2007). It has been postulated that
the potential daily dietary intake of nitrate has significant
effect on human health (Satnamand Andrew, 2013). This
viewpoint is sustained by a large body of evidence (results
and conclusions of a number of experimental and clinical
studies) showing that dietary nitrate has a magnitude of
beneficial cardiovascular effects (Tang et al.,2011)
including reducing blood pressure (Larsen et al., 2005),
improving platelet build-up (Bahra et al., 2012; Bonik et al.,
2001), safeguard or repairing endothelial dysfunction
(Webb et al., 2008), amplify the exercise performance in
healthy and patients with secondary arterial disease
(Sobko et al., 2010; Machha and Schechter, 2011). The
valuable effects of nitrate also include reduction
cardiovascular diseases and hypertension (McKnight et
al., 1999). The book published in (2002) “Nitrate and man:
Toxic, harmless or beneficial?” by L’hironde briefly
described the various effects of nitrate on human health. A
study reported by McKnight et al. (1999), dietary nitrate is
an effective potential defensive shield defense against
gastrointestinal pathogens. Nitrate have biological effects
on human body (Duncan et al., 1997; McColl, 2005), it acts
as mediator in digestion of food. Nitrate is relatively non-

3. Impact Factors Influencing the Nitrate Accumulation of Leafy Vegetables in Plant Factory
Int. J. Hort. Sci. Ornam. Plants 066
toxic but its reaction products and metabolites such as
nitrite, nitric oxide and N-nitroso compounds, have raised
concern because of their implications for adverse health
effects. Thus, documentation with reference to the effect
of nitrate on human health is conflicting. It should be noted
that nitrate to some extent by itself is nontoxic; however, it
may be endogenously switch to nitrite, which rebound with
amines and amides to produce N-nitroso compounds
(Knobeloch et al., 2000; Yordanovet et al., 2001). Their
harmful effects are linked with the occurrence of
methemoglobinemia, and some carcinogen effects have
been held responsible to them as well (Keszei et al., 2013;
Della et al., 2013). Nitrate is rapidly and effectively
absorbed from the upper part of the small intestine in
humans after digestion (Iijima et al., 2003).
Approximately estimated dietary exposure accounts in
human daily diet ranged 11%-41% of daily intake, and
Scientific Committee on Food (SCF) in 2002 estimated
acceptable daily intake (ADI) for adult of weighing 60 kg
ranged from 0 to 3.7 mg/kg body weight per day, which is
equivalent to the intake of 222 mg nitrate per day.
(Speijers, 1996; FAO/WHO, 2013). The European
Commission adopted Regulation No. 1822/ 2005 has set
the harmonized maximum levels of nitrate for fresh lettuce
(Lactuca sativa L.) (protected and open-grown lettuce) in
2500-4500 mg/kg. Unfortunately, indoor cultivated leafy
vegetables under different light conditions and systems
accumulate more nitrate to potentially harmful contents
(Vieira et al., 1998).
.
FACTORS AFFECTING THE PROCESS OF NITRATE
ACCUMULATION IN PLANT FACTORIES
The world is facing global challenges in agriculture due to
climatic changes, environmental and soil degradation,
shortages of water, and quality concern in food products
(Kozai, 2013). The stable supply food chain demand of
products will be endangered due to these issues if
concerns remained unsolved (Rosenzweig and Liverman,
1992). Quality of product, the safety and security of food in
market is based on consumer requirement. Plant factory
applications in controlled environment seem possible
solution to meet the global food demand in future. Plant
factories usually use hydroponic system including medium
culture, in which nitrogen is considered as the essential
nutritional demand, for proper metabolic control on the
nitrate content and other nitrogen compounds. In this
regard, nitrogen is an essential element required for
successful plant growth (Chen et al., 2014). Nitrate
accumulation in plants is affected greatly by environmental
factors. Plant nitrate content is commonly viewed as an
outcome of imbalance between its net absorption and
assimilation rates (Cardenas et al., 1998). Light
environment and nitrogen fertilization are distinguished
major factors that influence nitrate accumulation in
vegetables (Seginer et al., 1998).
Whereas on the other hand, nitrate uptake in aerial parts
depends on availability of nutrition, and nitrate assimilation
depends exclusively on photosynthetic photon flux density
(PPFD), as it is partially a photosynthetic process in
controlled environment (Ferrario et al., 1997).
Alternatively, plant nitrate content in controlled
environment might be either fixed through osmotic
potential regulation (McIntyre, 1997) or regulated through
negative feedback on its transport systems (Kacjan and
Osvald, 2002). Therefore, in this regard, focusing on the
environmental factors (light, temperature, photoperiod,
composition of nutrient solution) and analyzing the effect
of differences in nitrate ion can improve the quality of leafy
vegetables. When these factors fluctuate plants have
ability of adjusting morphological and physiological as well
as their mineral composition and secondary metabolites
(Niu et al., 2015).
EFFECT OF LIGHT QUALITY ON NITRATE CONTENT
OF LEAFY VEGETABLE
The factors responsible for nitrate accumulation in closed
plant factory system are mainly connected with
environment, one of them is light (Gruda, 2005; Xiao and
Kozai, 2004). Plants perceive changes in their lighting
environment by sensing light quality using signal of
photoreceptors (Smith, 2000). Light quality, mostly refers
to the effects of red and blue lights on plant growth and
development, recently it attracts more of the attentions due
to the fact that these wavelengths are primarily absorbed
by photosynthetic pigments and have the biggest influence
on plant architecture and development (Goto, 2003; Abidi
et al., 2013). Light quality impacts the formation of the key
enzyme related to nitrate and its activity (Appenroth et al.,
2000; Nemie et al., 2013). The phytochromes via
photoreceptor involved in this process increases the
activity of nitrate reductase as a result of
dephosphorization of the enzyme. It has been
demonstrated by Ohashi et al. (2006). When plants
exposed to red and blue lights, the light quality stimulates
the process of nitrogen assimilation in comparison to the
exposure to only red or blue light. This means that the
addition of blue light to red radiation results in increasing
the activity of nitrate reductase. Nitrite reductase is
regulated (NO3−, NO2−), with regards to the amount of the
enzyme and its activity (Aslam and Huffaker, 1989; Luo et
al., 1993). The regulative effect of light quality on nitrate
reductase activity, phytochrome potential aid in this
phenomenon has been demonstrated too light quality
regulates the nitrate uptake, translocation and
incorporation into organic compounds (Lillo, 2004). Nitrate
accumulation is directly or indirectly affected by light
quality in indoor production facilities (Qi et al., 2007). It’s
reported that illumination cycle of 12 h of blue light
increased nitrate reductase activity more than red light
(Sasakawa and Yamamoto, 1979).
Harmonizing/regulating/adjusting the red to blue light ratio

4. Impact Factors Influencing the Nitrate Accumulation of Leafy Vegetables in Plant Factory
He et al. 067
(R/B ratio) on photon flux density could significantly
improve plant growth and development (Maevskaya and
Bukhov, 2004). Previous results about quality control
revealed that nitrate content in lettuce grown under the
light with R/B ratio of 8 was lowest. The control of light
quality usually is achieved by combining different kinds of
lamps and regulating their relative intensities (Wen et al.,
2009). Nitrate reductase activity is affected by light quality
and blue light promotes stomatal opening which increases
transpiration, and this phenomenon may promote nitrate
uptake. Therefore, it may be strained to regulate nitrate
content by only light quality (Hall et al., 2015).
EFFECT OF LIGHT INTENSITY ON NITRATE CONTENT
IN PROTECTED LEAFY VEGETABLES
Light intensity seems to be among the environmental
factors that most influences nitrate accumulation in plants,
because nitrate accumulation in leafy vegetable is strongly
affected by light intensity. Low light intensity is often
reported in many studies to enhance nitrate accumulation.
In contrast under high light intensity also increases the
nitrate content when the temperature is high (Chadjaa et
al., 2001). It has been reported in many studies that both
light quality and intensity can influence the nitrate contents
in vegetables. Nitrate content of leafy vegetables depends
upon photosynthetic photon flux density (PPFD) because
it is transported in the xylem through cell vacuoles (Fan et
al., 2013). The xylem transports water and minerals from
the roots zone to the leaves, whereas the phloem carries
the products of photosynthesis (carbohydrates) from the
leaves to the growth points of the plant. This mechanism
affects the diffusion of nitrate between the leaves and cell
vacuoles. The combination of nitrogen metabolism and
photosynthetic electron transport in leaves signify that light
intensity is the key factor in determining nitrate contents in
leafy vegetables. Different PPFD in light intensity caused
variations in nitrate contents of lettuce grown in plant
factories (Yorio et al., 2001). Low light cycle has generally
higher nitrate content than plants in the same environment
with high PPFD. These differences can be explained by
sampling lettuce at higher irradiance in tends to reduce
nitrate content which coincide with periods of high
irradiance and high temperatures (Di et al., 2008). The
optimization of light quality and intensity influences also
the nitrate level when vegetables are produced under
glasshouse conditions (Pinto et al., 2014), this means e.g.
shelter/shading of vegetables should be avoided.
EFFECT OF NITROGEN FERTILIZER ON NITRATE
CONTENT
In plant factory, nitrogen fertilization is commonly used for
maintaining proper green pigment retention and leaf
growth. However, lettuce is characterized by its ability to
accumulate high level of nitrate. The nitrate content in
commercial lettuce vary considerably. Acceptable nitrate
levels ranging from 1000 to 4500 mg/kg in fresh weight
according to cultivation mode. Plants grown in hydroponic
systems showed higher levels of nitrate compared to those
grown in conventional systems (Gromaz et al., 2017).
Nitrate in plant tissues occurs high when there is an
imbalance between the absorption and assimilation of this
ion or ammonium, and surplus quantities are stored in the
vacuoles to be assimilated later (Andriolo, 1999). Nitrogen
fertilization facilitates accumulation of nitrate in plant
tissues as a result of an excess of nitrogen uptake over its
reduction. When taken up in excess of immediate
requirement, it is stored as free nitrate in the vacuole and
can be remobilized subsequently when nitrogen supply is
insufficient to meet the demand (Branimir et al., 2017). An
adequate fertilization program may ensure sufficient plant
growth without any risk of plant nitrate levels going too high
(Vieira et al., 1998). Plants accumulate more nitrate as the
nitrogen fertilization level increases (Nazaryuk et al., 2002;
Leigh et al., 2016), whereas limiting the nitrogen
availability reduces nitrate content significantly and
nutritional quality of vegetables (Guo, 2016).
EFFECT OF TEMPERATURE ON NITRATE CONTENT
Temperature is one of the critical factors determining the
growth rate of plants, and the nutrient solution and air
temperatures impact a variety of physiological processes.
Literatures concerning the effect of temperature on nitrate
content of vegetables are conflicting, this might due to
inability to distinguish between uptake of nitrate and its
reduction at particular temperatures of solution and
atmosphere. Photosynthetic functions and most enzymes
are also influenced by temperature which then in response
affect nitrate uptake. It has been reported in many studies
that temperature of nutrient solution affects uptakes of
water and nutrient ions. Generally, more uptake of NO3
- is
reported with cold solution due to less water uptake,
whereas high temperature with high light intensity also
increases the NO3
- uptake rate. Temperature also affects
solubility of fertilizer and uptake capacity of oxygen, by
roots which ultimately affect the nitrate uptake. Many
studies demonstrated significant interaction between
temperature and nitrate supply, which means nitrate
uptake is temperature dependent (Liu et al., 2016).
EFFECT OF PHOTOPERIOD ON NITRATE CONTENT
Nitrate content in leafy vegetables is not constant
throughout the day, it increases during the dark period and
decreases during the photoperiod. Photoperiod plays an
important role in nitrate assimilation. It was observed in
many studies that nitrate content found in higher when
plants treated with low cycle of photoperiod. It means that
lengthening the photoperiod decreases the nitrate content.
Nitrate uptake in leafy vegetables is sensitive to light and
dark cycles, plants tissues accumulate more nitrates
especially when grown in high NO3-N availability and long

5. Impact Factors Influencing the Nitrate Accumulation of Leafy Vegetables in Plant Factory
Int. J. Hort. Sci. Ornam. Plants 068
dark cycle. It was observed that with low nitrogen supply
and long continuous light for 72 h reduce the nitrate
content significantly. Growing cycle and nitrate
concentration of nutrient solution has been demonstrated
in a number of studies that carried out in field and growth
chamber studies on changes in nitrate contents over a 24
h period for spinach, sweet basil, and scallions (Wen et al.,
2009). The authors demonstrated that the nitrate content
fluctuated over the 24 h period, and these variations were
strongly correlated to the changes in light intensity over the
same period and were also species dependent. The
authors concluded that the reduction of nitrate content
could be possible, by harvesting the vegetables at the right
time of the day. Nevertheless, little information is available
concerning the effect of light intensity at the time of harvest
on desirable and undesirable compounds in baby leaf
vegetables, especially under greenhouse conditions (Zhou
et al., 2013).
NUTRIENT IONS MANAGEMENT IN SOILLESS
SYSTEM
High quality products with low nitrate content in soilless
system are only possible if nutrition is optimized. This
prevail upon accurate management of all factors involved
in nutrition, which include nutrient solution composition,
electrical conductivity (EC) and pH, dissolved oxygen, and
temperature of nutrient solution, water supply (Bongekile
et al., 2017). Plants may suffer inconsistency in nutrient
uptake, if these factors are under non-optimal conditions.
In order to diagnosis distortion in yield and quality due to
incorrect management in controlled environment, these
above-mentioned factors need to be focused.
Plant factories practice hydroponics as growing plants
substrate with the addition of essential nutrients and
considered as a successful used method in nutrient-
delivery systems. Excessive amount of nitrogenous
fertilizers is applied against yield loss, when inputs of
nitrogen increases the demand, plants are no longer to
absorb it, this causes imbalance in nutrient uptake in
nutrient solution. That’s why among factors affecting
nitrate accumulation in plant factories, the nutrient solution
is considered to be one of the most important determining
factors in terms of quality control. The fundamental
component in hydroponic system is represented by the
nutrient solution. The concentration control of nutrient
solution, referred as EC or osmotic pressure, allows the
culture of a great diversity of species. Moreover, the
accurate control of nutrient supply to the plant represents
the main advantage of soilless culture. Additionally, the
regulation of pH, root temperature among others factors,
leads to increased yield and quality. Nitrate accumulation
in leafy vegetables often depends on, nitrogenous
fertilizers, mainly of nitrate variety (Wang, 2004). An
adequate program of applying nitrogen at once at the
beginning based on potassium, ammonia, or mixture of
potassium, ammonium nitrate is effective in controlling
nitrate accumulation In addition, it is essential to have a
good knowledge of plant mineral requirement in order to
formulate optimum nutrient solution. Several studies have
documented that when nitrite content is too high or low
quality and yield may even be decreased. Therefore, it is
crucial to formulate nutrient solution with balanced
relationship among the different ions. Some ions in excess
can cause nutrient deficiencies by interfering with the
uptake of other ions, which is called antagonism. Studies
of antagonism highlights the importance of nutrient ions
management instead of monitoring EC level in nutrient
management. In order to formulate the optimum nutrient
solution for particular leafy vegetable, it’s necessary to
understand the factors that regulates nutrient ions
absorption by that particular vegetable, and first step is
measuring that vegetable nutrient absorption under
different conditions. In soilless system, many studies
reported that nutrient uptake is proportional to nutrient
supply and plants regulates its uptake according to its
needs.
In commercial production of plant factories, symptoms of
specific deficiencies by limited nutrient ions supply may
appear in plant tissues. Therefore, visual symptoms are
not the correct method to diagnose nutrient deficiencies,
because limiting level of specific nutrient ions affect
metabolic process in which they involved. Therefore, many
nutrient ions are having been identified in literatures such
as calcium, chlorides, potassium, phosphorus, sulfate, are
involved in nitrate accumulation.
CULTURAL MEASURES TO REDUCE NITRATE
The availability of current technologies makes it possible
to expand an optimal control of nitrate contents for leafy
vegetables grown in plant factories and some of
approaches can help to maintain an acceptable limit. The
impact of nitrogen dressings on the nitrate contents in leafy
vegetables has been studied in several countries in indoor
experiments conducted both in greenhouses and growth
chambers. Nitrate content in plants is commonly reported
as result of imbalance between endogenous and
exogenous factors in both uptake and assimilation and that
seems genetically determined. Therefore, in plant factory,
the factors affecting of nitrate uptake and its assimilation
are totally dependent on nutritional, environmental and
physiological factors. Therefore, for indoor cultivation to
limit the nitrate accumulation in vegetables, it’s important
to adopt appropriate strategies and determine the role of
individual physiological factors in the process. Regulatory
methods to produce low nitrate vegetables depend on light
quality, light intensity, and composition aspects of nutrient
solution. Light intensity is the key factor of nitrate
accumulation during the cultivation process. Light quality
also plays a significant role to drive biochemical
photosynthetic activity (Du et al., 2007; Liu et al., 2016).

6. Impact Factors Influencing the Nitrate Accumulation of Leafy Vegetables in Plant Factory
He et al. 069
Arrangements for good agriculture practice (GAP) with
regard to nitrate were established to aid grower respond to
the European nitrate rules and the need to curtail nitrate
contents in vegetables. These policies were shaped by the
agronomist or commercial growers. Each GAP includes an
assembly of presently existing knowledge, including
reference based on experiments, and is projected to
address agricultural, economic, and health issues in on-
farm production and the processing of produce beyond the
farm gate.
Previous studies highlighted following culture measures to
avoid nitrate accumulation in lettuce by dosed nitrogen
supply of nutrient solution (Kowalska, 1997; Santamaria
et al., 1997), inhibiting the nitrogen supply of solution with
growth stages (Andersen and Nilsen, 1992; McCall and
Willumsen, 1999; Seginer, 2003), withdrawal of nitrate in
fertilization prior to harvest (Stagnari et al., 2015),
replacing and balancing nitrate ions with chloride before
crop maturity (Gunes et al., 1994), optimization of
environmental factors with respect to nitrate accumulation
(Gaudreau et al., 1995; Nazaryuk et al., 2002). Predicting
and manipulating nitrate deficiency in relation to other
fertilization chemicals (Ahmed et al., 2000; Chen et al.,
2014). It is reported in several studies that stopping the
nitrogen supply in growth medium few days before crop
maturity, resulted in yield losses and poor leaf quality.
Many authors have suggested that additions of moderate
amount of chloride to the growing medium replacing
nitrogen supply during the last week prior to harvest
decreases nitrate content (Maynard et al., 1976; Cerezo et
al., 1990; Urrestarazu et al., 1998). Increase rate of
potassium and phosphorus application facilitates and
promotes metabolism accompanied by nitrate assimilation
(Buwalda and Warmenhoven, 1999; Ahmed et al., 2000).
Furthermore, the increased light intensity supplied more
energy to fix carbon dioxide to accelerate nitrate
assimilation in plant leaves (Demsar et al., 2004). In
hydroponic culture broken nitrogen treatment before
harvest can decline the nitrate accumulation in leafy
vegetables (Liu and Yang, 2012; Zhou et al., 2013). The
morphological, physiological adaptation of plants depends
on light quality, the spectral composition of light sources
must be adjusted to physiological requirements of plants
to drive photosynthesis efficiently for growth and
development (Lee et al., 2007). The nitrate content of leafy
vegetable is negatively correlated with photosynthetic end
product (carbohydrates). The amount of said product can
be uplifted by higher light intensity whereas nitrate stored
in vacuoles (Abidi et al., 2013). In term of light quality that
refers to effect of red and blue lights on plant architecture
and development attracts more attention due to specific
wavelength and color (Johkan et al., 2010), which
ultimately affects plants photosynthetic capacity and CO2
assimilation to reduce nitrate content (Yorio et al., 2001;
Dougher and Bugbee, 2004; Hernandez and Kubota,
2016). Nitrate content in indoor facilities is greatly affected
by environmental factors, interaction between light quality,
light intensity, temperature, and nitrogen supply.
Unfortunately, different experimental conditions and
designs restraint an efficient comparison of the listed
methods.
CONCLUSIONS
Leafy vegetable production in plant factory using
hydroponics represents substitute to traditional farming
with benefits for producers, consumers and environment.
Leafy vegetables are the main source of nutrition and
contributes to 80% of dietary intake of human diet. Leafy
vegetables especially grown in indoor need further studies
to understand the specific role of nitrate and its derivatives
with respect to human health because ingestion of high
nitrate level though vegetables may lead to carcinogenic
effects. Leafy vegetables such as lettuce grown under
distinctive production systems may accumulate different
nitrate content which may reach to the levels potentially
toxic to humans. Thus, uncertainty to human health due to
nitrate intake may be minimized according to European
commission regulation No. 1822/2005 by determining the
exact mechanism for nitrate accumulation in leafy
vegetables. It is more important to educate the farmer and
consumer to understand the human health implications of
nitrate in dietary intake. They must be motivated to adopt
relevant agricultural practices that help in minimizing
nitrate content. Nitrate and nitrite levels in raw agricultural
commodities can be influenced by a number of factors
such as storage time and conditions (i.e. ambient,
refrigerated, frozen), and food processing (i.e. washing,
peeling, blanching, boiling). Therefore, various
approaches are suggested and may be adopted to
decrease the nitrate level.
• Leafy vegetables grown in hydroponic system needs
balanced fertilization scheme according to supply and
release of nutrient ions. Nutrient management
strategies should be implemented with simulation
models for proper uptake and its reduction, because the
time variation of nitrate content in whole lettuce plants
during photoperiod and dark period throughout
cultivation is different. Controlled nutrition results in
sufficient reduction in leaf nitrate of leafy vegetables.
• Nitrate uptake in aerial parts of leafy vegetables may be
reduced by partial adjustment of nitrogen solution with
chloride before harvest, under controlled environmental
conditions increasing the light intensity over diluted
nitrogen solution to standard effects the nitrate content.
• A computerized system is proposed which supplies
different light condition (slight, medium, strong) in
accordance with growth stages and changeable nitrate
content. Effect of light quality on micronutrients, cultural
conditions, physiological mechanism need to be
investigated by molecular tools to understand the over
expression of nitrate.

7. Impact Factors Influencing the Nitrate Accumulation of Leafy Vegetables in Plant Factory
Int. J. Hort. Sci. Ornam. Plants 070
ACKNOWLEDGMENTS
The research is supported by the National Key Research
and Development Program of China (2017YFB0403901).
REFERENCES
Abidi F, Girault T, Douillet O, Guillemain G, Sintes G,
Laffaire M, Leduc N. (2013). Blue light effects on rose
photosynthesis and photomorphogenesis. Plant Biol.
15(1): 67–74.
Ahmed H, Khalil MK, Farrag AM. (2000). Nitrate
accumulation, growth, yield and chemical composition
of Rocket (Eruca vesicaria sub sp. sativa) plant as
affected by NPK fertilization, kinetin and salicylic acid.
in: Proceedings of ICEHM 2000. Cairo University,
Egypt, pp. 495–508.
Alejandro I, Luna M, Juan A, Vidales C, Humberto R.
(2016). Advances and trends in development of plant
factories. Front Plant Sci. 7: 1848.
Andriolo JL. (1999). Fisiologia das culturas protegidas.
Santa Maria: UFSM, pp.142.
Andersen L, Nilesen NE. (1992). A new cultivation method
for production of the vegetables with low content of
nitrate. Scientia Hort. 49: 167–171.
Appenroth K, Mec R, Jourdan V, Lillo C. (2000).
Phytochrome and post-translational regulation of
nitrate reductase in higher plants. Plant Sci. 159: 51–
56.
Aslam M, Huffaker RC. (1989). Role of nitrate and nitrite in
the induction of nitrite reductase in leaves of barley
seedlings. Plant Physiol. 91: 1152–1156.
Bahra M, Kapil V, Pearl V, Ghosh S, Ahluwalia A. (2012).
Inorganic nitrate improves vascular compliance but
does not alter flow mediated dilatation in healthy
volunteers. Nitric Oxide. 26: 197–202.
Blekkenhorst LC, Prince RL, Ward NC, Croft KD, Lewis
JR, Devine A, Shinde S, Woodman RJ, Hodgson JM,
Bondonno CP. (2017). Development of a reference
database for assessing dietary nitrate in vegetables.
Mol. Nutri. Food Res. 61(8).
http://dx.doi.org/10.1002/mnfr.201600982.
Boink A, Speijers G. (2001). Health effects of nitrate and
nitrites: a review. Acta Hortic. 563: 29–36.
Bongekile Z, Mpumelelo N, Hintsa A, Wonder N,
Fhatuwani N. (2017). Nutritional quality of baby spinach
(Spinacia oleracea L.) as affected by nitrogen,
phosphorus and potassium fertilization. South African
Journal of Plant and Soil. 34(2): 79-86.
Branimir U, Maja J, Christine B, Hans Kl, Angelika K,
Smiljana B, Dietmar S. (2017). Effect of NO3 and NH4
concentrations in nutrient solution on yield and nitrate
concentration in seasonally grown leaf lettuce. Acta
Agriculturae Scandinavica, Section B - Soil & Plant
Science. 67(8): 748-757.
Buwalda F, Warmenhoven M. (1999). Growth-limiting
phosphate nutrition suppresses nitrate accumulation in
greenhouse lettuce. J. Exp. Bot. 50: 813–821.
Cardenas NR, Adamowicz S, Robin P. (1998). Diurnal
nitrate uptake in young tomato (Lycopersicon
esculentum Mill.) plants: test of a feedback-based
model. J. Exp. Bot. 49: 721–730.
Cerezo M, Garcia-Agustin P, Serna MD, Primo-Millo E.
(1997). Kinetics of nitrate uptake by citrus seedlings
and inhibitory effects of salinity. Plant Sci. 126: 105–
112.
Chadjaa H, Vezina L, Dorais M, Gosselin A. (2001). Effects
of lighting on the growth, quality and primary nitrogen
assimilation of greenhouse lettuce (Lactuca sativa L.).
Acta Hortic. 559: 325–331.
Chen WT, Yeh YF, Liu TY, Lin TT. (2016). An automated
and continuous plant weight measurement system for
plant factory. Front Plant Sci. 7: 392.
Chen XL, Guo WZ, Xue XZ, Wang LC, Qiao XJ. (2014).
Growth and quality responses of ‘Green Oak Leaf’
lettuce as affected by monochromic or mixed radiation
provided by fluorescent lamp (FL) and light-emitting
diode (LED). Scientia Horticulturae. 172: 168–175.
Colonna E, Rouphael Y, Barbieri G, Stefania DP. (2016).
Nutritional quality of ten leafy vegetables harvested at
two light intensities. Food Chemistry 199: 702–710.
Cometti N, Martins MQ, Bremenkamp CA, Nunes JA.
(2011). Nitrate concentration in lettuce leaves
depending on photosynthetic photon flux and nitrate
concentration in the nutrient solution. Horticultura
Brasileira. 29: 548-553.
Danijel B, Martina B, Andrea G, Dario L, Aleksandar R,
Ana M, Natalija T. (2017). Nitrate in leafy green
vegetables and estimated intake. Afr. J. Tradit.
Complement Altern. Med. 14(3): 31–41.
Della CT, Daniel CR, Aschebrook B, Hollenbeck AR,
Cross AJ, Sinha R, Ward MH. (2013). Dietary intake of
nitrate and nitrite and risk of renal cell carcinoma in the
NIH-AARP diet and health study. Br. J. Cancer. 108:
205–212.
Demsar J, Osvald J, Vodnik D. (2004). The effect of light-
dependent application of nitrate on the growth of
aeroponically grown lettuce (Lactuca sativa L.). Journal
of the American Society for Horticultural Sciences. 129:
570-575.
Dich J, Jivinen R, Knekt P, Pentill PL. (1996). Dietary
intakes of nitrate, nitrite and NDMA in the finish mobile
clinic health examination survey. Food Addit. Contam.
13: 541–552.
Di XR, Jiao XL, Cui J, Liu XY, Kong Y, Xu ZG. (2008).
Effects of different light quality ratios of LED on growth
of chrysanthemum plantlets in vitro. Plant Physiology
Communications. 44: 661–664. (in Chinese with
English abstract).
Du ST, Zhang YS, Lin XY. (2007). Accumulation of nitrate
in vegetables and its possible implications to human
health. Agricultural Sciences in China. 6(10): 1246–
1255.

8. Impact Factors Influencing the Nitrate Accumulation of Leafy Vegetables in Plant Factory
He et al. 071
Duncan C, Li H, Dykhuizen R, Frazer R, Johnston P,
MacKnight G, Smith L, Lamza K, McKenzie H, Batt L,
Kelly D, Golden M, Benjamin N, Leifert C. (1997).
Protection against oral and gastrointestinal diseases:
importance of dietary nitrate intake, oral nitrate
reduction and enter salivary nitrate circulation. Comp.
Biochem. Phys. 118: 939–948.
Du ST, Zhang YS, Lin XY. (2007). Accumulation of nitrate
in vegetables and its possible implications to human
health. Agricultural Sciences in China. 6(10): 1246-
1255.
Dougher T, Bugbee B. (2004). Long-term blue light effects
on the histology of lettuce and soybean leaves and
stems. J. Am. Soc. Hortic. Sci. 129: 467–472.
Fan X, Xu ZG, Liu XY, Tang C, Wang LW, Han XL. (2013).
Effects of light intensity on the growth and leaf
development of young tomato plants grown under a
combination of red and blue LED. Sci. Hortic. 153: 50–
55.
FAO/WHO. (2013). Nitrate and potential endogenous
formation of N-nitroso compounds: WHO Food Additive
Series World Health Organization. (Geneva 2003, 50).
Farina E, Allera C, Paterniani T, Palagi M. (2003).
Mulching as a technique to reduce salt accumulation in
soilless culture. Acta Horticulturae. 609(1): 459-466.
Ferrario S, Murchie E, Hirel B, Galtier N, Quick WP, Foyer
CH. (1997). Manipulation of the pathways of sucrose
biosynthesis and nitrogen assimilation in transformed
plants to improve photosynthesis and productivity. In:
Foyer CH, Quick WP. (Eds.), A molecular approach to
primary metabolism in higher plants, Taylor and
Francis, London, pp. 125–153.
Fang W. (2015). Status of PFAL in Taiwan. (Eds) Plant
Factory an Indoor Vertical Farming System for Efficient
Quality Food Production, Academic Press, pp. 129–
140.
Gaudreau L, Chorbonneau LP, Vezina, Gosselin A.
(1995). Effects of photoperiod and photosynthetic
photon flex on nitrate content and nitrate reductase
activity in greenhouse grown lettuce. J.Plant
Nutr.18:437-453.
Gilchrist M, Winyard PG, Benjamin N. (2010). Dietary
nitrate - good or bad? Nitric Oxide. 22: 104–109.
Goto E. (2003). Effects of light quality on growth of crop
plants under artificial lighting. Environ. Control in Biol.
41(2): 121-132.
Gromaz A, Torres F, San Bautista A, Pascual B, Lopez G,
Maroto V. (2017). Effect of different levels of nitrogen in
nutrient solution and crop system on nitrate
accumulation in endive. Journal of Plant Nutrition.
40(14): 2045-5053.
Gruda N. (2005). Impact of environmental factors on
product quality of greenhouse vegetables for fresh
consumption. Crit. Rev. Plant Sci. 24: 227–247.
Gunes A WHK. Post EA Kirk, Aktas M. (1994). Influence
of partial replacement of nitrate by amino acid nitrogen
or urea in the nutrient medium on nitrate accumulation
in NFT grown winter lettuce. J. Plant. Nutr. 17: 1929–
1939.
Guo MS. (2016). Various types of nitrogen and light levels
on Brassica chinensis yield and quality parameters
under water stress. Communications in Soil Science
and Plant Analysis. 47(15): 1721-1730.
Hall MKD, Jobling JJ, Rogers GS. (2015). Effect of
nitrogen supply and storage temperature on vitamin C
in two species of baby leaf rocket, and the potential of
these crops for a nutrient claim in Australia. Journal of
Plant Nutrition. 38(2): 246-259.
Hernandez R, Kubota C. (2016). Physiological responses
of cucumber seedlings under different blue and red
photon flux ratios using LEDs. Environ. Exp. Bot. 121:
66–74.
Hirondel JL. (2002). Nitrate and Man. Toxic, Harmless or
Beneficial? Wallingford, UK: CABI Publishing. pp. 84-
92.
Iijima K, Fyfe V, McColl L. (2003). Studies of nitric oxide
generation from salivary nitrite in human gastric juice.
Scand. J. Gastroentero. 38: 246–252.
Ishiwata H, Yamada T, Yoshiike N, Nishijima M,
Kawamoto A, Uyama Y. (2002). Daily intake of food
additives in Japan in five age groups estimated by the
market basket method. Eur. Food Res. Technol. 215:
367–374.
Jones JBJ. (2004). Hydroponics: A Practical Guide for the
Soilless Grower, 2nd Edn Boca Raton, FL: CRC Press
.pp. 32-52.
Johkan M, Shoji K, Goto F, Hashida S, Yoshihara T.
(2010). Blue light-emitting diode light irradiation of
seedlings improves seedling quality and growth after
transplanting in red leaf lettuce. HortSci. 45: 1809–
1814.
Kacjan MN, Osvald J. (2002). Nitrate content in lettuce
(Lactuca sativa L.) grown on aeroponics with different
quantities of nitrogen in the nutrient solution. Acta
Agronomica Hungarica. 50(4): 389–397.
Ohashi K. (2016). Plant Factory: An Indoor Vertical
Farming System for Efficient Quality Food Production.
Elsevier Inc., pp. 177–185.
Keszei AP, Schouten LJ, Driessen AL, Huysentruyt CJ,
Keulemans YC, Goldbohm RA, Van Den Brandt PA.
(2013). Dietary N-nitroso compounds, endogenous
nitrosation, and the risk of esophageal and gastric
cancer subtypes in the Netherlands cohort study. Am.
J. Clin. Nutr. 97: 135–146.
Kowalska I. (1997). Effect of urea, ammonium, and nitrate
nitrogen on the yield and quality of greenhouse lettuce
grown on different media. Folia Hort. 9: 31–40.
Kozai T. (2013). Resource use efficiency of closed plant
production system with artificial light: Concept,
estimation and application to plant factory. Proc Jpn
Acad Ser B Phys Biol Sci. 11 (10): 447–461.
Kozai T, Niu G, Takagaki M. (2015). Plant Factory: An
Indoor Vertical Farming System for Efficient Quality
Food Production. Academic Press. pp. 3-5.

9. Impact Factors Influencing the Nitrate Accumulation of Leafy Vegetables in Plant Factory
Int. J. Hort. Sci. Ornam. Plants 072
Knobeloch L, Salna B, Hogan A, Postle J, Anderson H.
(2000). Blue babies and nitrate-contaminated well
water. Environ Health Perspec. 108(7): 675–678.
Larsen FJ, Ekblom B, Sahlin K, Lundberg JO, Weitzberg
E. (2005). Effects of dietary nitrate on blood pressure in
healthy volunteers. New England J. Med. 355: 2792–
2793.
Leigh J, Whittinghill D. Bradley R, Mathieu N, Bert M.
(2016). Evaluation of nutrient management and
mulching strategies for vegetable production on an
extensive green roof. Agroecology and Sustainable
Food Systems, 40(4): 297-318.
Lee SH, Tewari RK, Hahn EJ, Pack KY. (2007). Photon
flux and light quality induce changes in growth, stomatal
development, photosynthesis and transpiration of
Withania Somnifera (L.) dunal. plantlets. Plant Cell
Tissue Organ Cult. 90: 141–151.
Lillo C. (2004). Light regulation of nitrate uptake,
assimilation and metabolism. In: Amancio, S. and I.
Stulen (eds.). Plant ecophysiology. Vol. 3. Nitrogen
acquisition and assimilation in higher plants. Kluwer
Academic Publisher, Dordrecht, The Netherlands. pp.
149–184.
Lillo C. (2008). Signalling cascades integrating light-
enhanced nitrate metabolism. Biochem. J. 415: 11–19.
Liu CW, Sung Y, Chen BC, Lai HY. (2014). Effects of
nitrogen fertilizers on the growth and nitrate content of
lettuce (Lactuca sativa L.). Int. J. Environ. Res. Public
Health. 11: 4427-4440.
Liu H, Fu YM, Yu J, Liu H. (2016). Accumulation and
primary metabolism of nitrate in lettuce (Lactuca Sativa
L. Var. Youmaicai) grown under three different light
sources. Communications in Soil Science and Plant
Analysis. 47(17): 1994-2002.
Liu WK, Yang QC. (2012). Effects of short-term treatment
with various light intensities and hydroponic solutions
on nitrate concentration of lettuce, Acta Agriculturae
Scandinavica, Section B — Soil & Plant Science. 62(2):
109-113.
Luo J, Lion Z, Yan X. (1993). Urea transformation and the
adaptability of three leafy vegetables to urea as a
source of nitrogen in hydroponic culture. J. Plant Nutr.
16: 797–812.
Machha A, Schechter A. (2011). Dietary nitrite and nitrate:
a review of potential mechanisms of cardiovascular
benefits. Eur. J. Nutr. 50: 293–303.
McCall D., Willumsen J. (1998). Effects of nitrate,
ammonium and chloride application on the yield and
nitrate content of soil-grown lettuce. J. Hortic. Sci.
Biotech. 73: 698–703.
McCall D, Willumsen J. (1999). Effects of nitrogen
availability and supplementary light on the nitrate
content of soil grown lettuce. J. Hortic. Sci. Biotech. 74:
458–463.
Maevskaya SN, Bukhov NG. (2004). Effect of light quality
on nitrogen metabolism of radish plants. Russ. J. Plant
Physiol. 52: 349–356.
Maynard DN., Barker AV., Minotti PL., Peck NH. (1976).
Nitrate accumulation in vegetables. Adv. Agron. 28: 71–
118.
McKnight GM, Duncan CW, Leifert C, Golden MH. (1999).
Dietary nitrate in man: friend and foe? Brit. J. Nutr. 81:
349–358.
McColl KL. (2005). When saliva meets acid: chemical
warfare at the esophagogastric junction. Gut. 54: 1–3.
McIntyre GI. (1997). The role of nitrate in the osmotic and
nutritional control of plant development. Aust. J. Plant
Physiol. 24: 103–118.
Nazaryuk VM, Klenova MI, Kalimullina FR. (2002). Eco
agrochemical approaches to the problem of nitrate
pollution in agroecosystems. Russ. J. Ecol. 33: 392–
397.
Nemie D, Krolicka A, Forland N, Hansen M, Heidari B, Lillo
C. (2013). Post-translational control of nitrate reductase
activity responding to light and photosynthesis evolved
already in the early vascular plants. J. Plant Physiol.
170: 662–667.
Niu G, Kozai T, Sabeh N. (2015). Physical environmental
factors and their properties. (Eds) Plant Factory: An
Indoor Vertical Farming System for Efficient Quality
Food Production, Academic Press, pp. 129–140.
Ohashi K, Goji K, Matsuda R, Fujiwara K, Kurata K. (2006).
Effects of blue light supplementation to red light on
nitrate reductase activity in leaves of rice seedlings.
Acta Hortic. 711: 351–356.
Pinto E, Fidalgo F, Teixeira J, Aguiar A., Ferreira IM.
(2014). Influence of the temporal and spatial variation
of nitrate reductase, glutamine synthetase and soil
composition in the N species content in lettuce (Lactuca
sativa). Plant Sci. 219–220(1): 35–41.
Qi LD, Liu SQ, Xu L, Yu WY, Liang QL, Hao SQ. (2007).
Effects of light qualities on accumulation of oxalate,
tannin and nitrate in spinach. Transactions of the
CSAE. 23: 201–205. (in Chinese with English abstract).
Reddy KS, Menary RC. (1990). Nitrate reductase and
nitrate accumulation in relation to nitrate toxicity in
Boronia mega stigma, Physiol. Plantarum. 78: 430–
434.
Rosenzweig C, Liverman D. (1992). Predicted effects of
climate change on agriculture: A comparison of
temperate and tropical regions. In Global Climate
Change: Implication, Challenges and Mitigation
Measures, Philadelphia (ed. Majumdar, S.K.).
Pennsylvania Academy of Sciences. pp. 342–361.
Santamaria P, Elia A, Gonnella M. (1997). Changes in
nitrate accumulation and growth of endive plants during
light period as affected nitrogen level and form. J. Plant
Nutr. 20: 1255–1266.
Santamaria P, Elia A, Parente A, Serio F. (1998). Nitrate
and ammonium nutrition in chicory and rocket salad
plants. J. Plant Nutr. 21: 1779–1789.
Santamaria P. (2006). Nitrate in vegetables: toxicity,
content, intake and EC regulation. J. Sci. Food Agric.
86: 10–7.

10. Impact Factors Influencing the Nitrate Accumulation of Leafy Vegetables in Plant Factory
He et al. 073
Sasakawa H, Yamamoto Y. (1979). Effects of red, far red,
and blue light on enhancement of nitrate reductase
activity and on nitrate uptake in etiolated rice seedlings.
Plant Physiology. 63: 1098–1101.
Satnam L, Andrew J. (2013). Vascular effects of dietary
nitrate (as found in green leafy vegetables and
beetroot) via the nitrate‐nitrite‐nitric oxide pathway. Br
J. Clin. Pharmacol. 75(3): 677–696.
Seginer I, Buwalda F, Van G. (1998). Nitrate concentration
in greenhouse lettuce: A modeling study, Acta Hortic.
456: 189–197.
Seginer I. (2003). A dynamic model for nitrogen-stressed
lettuce. Ann. Bot., 91: 623–635.
Shao HB, Guo QJ, Chu LY, Zhao XN, Su ZL, Hu YC,
Cheng JF. (2007). Understanding molecular
mechanism of higher plant plasticity under abiotic
stress. Bio interfaces. 54(1): 37-45.
Sindelaar JJ, Milkowski AL. (2012). Human safety
controversies surrounding nitrate and nitrite in the diet.
Nitric Oxide. 26: 259–266.
Smith H. (2000). Phytochromes and light signal perception
by plants-an emerging synthesis. Nature. 407: 585-591.
Sobko T, Marcus C, Govoni M, Kamiya S. (2010). Dietary
nitrate in Japanese traditional foods lowers diastolic
blood pressure in healthy volunteers. Nitric Oxide. 22:
136–140.
Speijers GJA. (1996). Nitrate in World Health Organization
(Eds.), Toxicological evaluation of certain food
additives and contaminants in food, Food Additive
Series 35, Geneva, pp. 325–360.
Stagnari F, Galieni A, Pisante M. (2015). Shading and
nitrogen management affect quality, safety and yield of
greenhouse-grown leaf lettuce. Sci. Hort. 192: 70–79.
Tang Y, Jiang H, Bryan NS. (2011). Nitrite and nitrate:
cardiovascular risk-benefit and metabolic effect. Curr
Opin Lipidol. 22(1): 11–15.
Temme EH, Van S, Vinkx C, Huybrechts I, Goeyens L, van
Oyen H. (2011). Average daily nitrate and nitrite intake
in the Belgian population older than 15 years. Food
Addit Contam Part a Chem Anal Control Expo Risk
Assess. 28: 1193–2004.
Umar S, Iqbal M. (2007). Nitrate accumulation in plants,
factors affecting the process, and human health
implications: a review. Agron Sustain Dev. 27: 45–57.
Umar S, Iqbal M, Abrol Y. (2007). Are nitrate
concentrations in leafy vegetables within safe limits?
Curr. Sci. 92: 355-360.
Urrestarazu M, Postigo A, Salas M, Sanchez A, Carrasco
G. (1998). Nitrate accumulation reduction using
chloride in the nutrient solution on lettuce growing by
NFT in semiarid climate conditions. J. Plant Nutr. 21:
1705–1714.
Vieira IS, Vasconselos EP, Monteiro AA. (1998). Nitrate
accumulation, yield and leaf quality of turnip greens in
response to nitrogen fertilisation. Nutr. Cycl.
Agroecosys. 51: 249–258.
Walker R. (1990). Nitrates, nitrites and N-nitroso
compounds, a review of the occurrence in food and diet
and the toxicological implications. Food Addit. Contam.
7: 717-768.
Wang ZH, Li SX. (2004). Effects of nitrogen and
phosphorus fertilization on plant growth and nitrate
accumulation in vegetables. Journal of Plant Nutrition.
27(3): 539-556. DOI: 10.1081/PLN-120028877.
Webb AJ, Patel N, Loukogeorgakis S. (2008). Acute blood
pressure lowering, vasoprotective, and anti-platelet
properties of dietary nitrate via bioconversion to nitrite.
Hypertension. 51: 784–790.
Weightman RM, Hudson EM. (2013). Noxious or
nutritious? Progress in controlling nitrate as a
contaminant in leafy crop species. Food and Energy
Security. 2(2): 141–156.
Wen J, Bao SH, Yang QC, Cui H X. (2009). Influence of
R/B ratio in LED lighting on physiology and quality of
lettuce. Chinese Journal of Agrometeorology. 30: 413–
416. (in Chinese with English abstract).
Xiao Y, Kozai T. (2004). Commercial application of
photoautotrophic micropropagation system using large
vessels with forced ventilation,plant growth and
production cost. HortScience. 39(6): 1387-1391.
Yorio NC, Goins GD, Kagie HR, Wheeler RM, Sager JC
(2001). Improving spinach, radish and lettuce growth
under red light emitting diodes (LEDs) with blue light
supplementation. HortScience. 36: 380–383.
Yordanovet N, Novakova E, Lubenova S. (2001).
Consecutive estimation of nitrate and nitrite ions in
vegetables and fruits by electron paramagnetic
resonance spectrometry. Anal. Chim. Acta. 437: 131-
138.
Zhou WL, Liu WK, Yang QC. (2013). Reducing nitrate
content in lettuce by pre-harvest continuous light
delivered by red and blue light-emitting diodes. Journal
of Plant Nutrition. 36(3): 481-490. DOI:
10.1080/01904167.2012.748069.
Zhong W, Hu C, Wang M. (2002). Nitrate and nitrite in
vegetables from north China, content and intake. Food
Addit. Contam. 19: 1125-1129.
Accepted 23 February 2018
Citation: Khan KA, Yan ZN, Abbas A, He DX (2018).
Impact Factors Influencing the Nitrate Accumulation of
Leafy Vegetables in Plant Factory. International Journal of
Horticultural Science and Ornamental Plants 4(1): 064-
073.
Copyright: © 2018. He et al. This is an open-access
article distributed under the terms of the Creative
Commons Attribution License, which permits unrestricted
use, distribution, and reproduction in any medium,
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