Physiological responses of crops to light and moisture

1. Presented by
K. Poojitha
PALB-8044

2. Introduction
 Response : Reaction to an event
 Physiology: Branch of biology that deals with the functions
and mechanisms which work within a living system.
 Physiological response of crops refers to changes in the plant
mechanism or metabolism due to an stimuli (may be light,
water, CO2, nutrients etc..).
 A better understanding of physiological response of crops to the
factors of crop production helps in altering the management
practices such as to improve the crop yields.

3. Basic needs of plants
In order to live and grow, plants need four basic
elements:
Soil
Water
Sunlight
Air

4. Light
 Light is a form of electromagnetic radiation, a type of
energy that travels in waves.
 The word usually refers to visible light, which is
the visible spectrum that is visible to the human eye and
is responsible for the sense of sight.
 Visible light is usually defined as having wavelengths in
the range of 400–700 nanometres (nm). The main source
of light on Earth is the Sun.

5. Fig. 1: Absorption pattern of light by plant pigments

6. Effects of different electromagnetic spectrums
In general, different colors have different effects on plants:
 Ultraviolet Light: Ultraviolet light causes DNA damage, reduces
photosynthesis rate, flowering and pollination and affects seed
development. Ultraviolet A (a subcategory of ultraviolet light) can
cause plant elongation.
 Blue Light: It corresponds to one of the absorption peaks;
therefore, the photosynthetic process is more efficient when
there is blue light. Blue light is responsible for vegetative and leaf
growth and is important for seedlings and young plants because it
helps reduce plant stretching.
 Red Light: This is the other peak of light absorption by the leaves.
Phytochrome (a photoreceptor) within the leaves is more
sensitive and responds to red light. This light is important in the
regulation of flowering and fruiting. It also helps increase stem
diameter and promotes branching.

7.  Far Red Light: This light can cause plant elongation and
trigger flowering in long-day plants.
 Red: Far Red Ratio: Plant elongation results when this
ratio is low. In other words, plants are more exposed to
far red than red. In nature, we see this phenomenon
when plants are shaded by neighbouring plants; the
shaded plants receive a higher ratio of far red light and
tend to grow taller to reach more light. This can become
a problem with greenhouse crops that are shaded by
overhead baskets or are planted too close together.

9. Phytochrome
 Phytochromes are proteins with a light
absorbing pigment attached to it, which is
known as chromophore.
 Phytochrome is synthesized as the Pr form,
which accumulates in dark-grown tissue
and is generally considered to be
physiologically inactive.
 When Pr absorbs red light, it is converted
to the Pfr form, which is the physiologically
active form of the pigment for most known
responses
 Exposure of Pfr to far-red light returns the
pigment to the Pr form.

10. Functions of phytochrome
Seed germination
Flowering time (photoperiodism)
Entraining (setting) the biological clock
Leaf expansion
Chloroplast development
Stem elongation
Pigment synthesis

11. Role of phytochrome in seed germination
 The germination of many seeds is influenced by light.
Some plants, by red light
Some plants, by far-red light
 Based on the requirement of light for germination plants
are categorized into three types.
1. Positive photoblastic: Require light for inducing
germination. Pfr promotes germination.
EX: Lettuce, Tobacco
2. Negative photoblastic: Do not germinate when exposed
to light. Pfr inhibits germination.
Ex: Onion, Amaranthus, Lilly
3. Non photoblastic: Germinate either in dark or light

12. Fig. 2: Lettuce seed germination (positively photoblastic)

13. Phototropism
Photo means light and
Tropism means turning movement or growth in
response to.
 The growth of or the movement of an organism towards
light is called Phototropism.
 Positive phototropism: If the plant grows towards light.
 Negative phototropism: If the plant grows away from
light.
 Phototropism allows the plants to be in a position to get
sunlight for photosynthesis.

14. East facing At noon West facing

15. Photoperiodism
• The influence of relative duration of day and night on the
flowering response of plants is called Photoperiodism.
• This phenomenon was first discovered by Garner and
Allard (1920).
In short day plants, Pr promotes flowering.
In long day plants, Pfr promotes flowering.

16. Fig. 3: Phytochrome control of flowering by red (R) and far-red (FR) light.
Short day (long night)
plant
Long day (short night)
plant
A flash of red light during the dark period induces flowering in an
LDP, and the effect is reversed by a flash of far-red light. This response
indicates the involvement of phytochrome. In SDPs, a flash of red light
prevents flowering, and the effect is reversed by a flash of far-red light.
----- Critical day length

17. Examples
Short day plants Long day plants Day neutral
plantsQualitative
(Absolute)
Quantitative
(Facultative)
Qualitative
(Absolute)
Quantitative
(Facultative)
Rice Cotton Barley Lettuce Tomato
Tobacco Sunhemp Wheat Clover Sunflower
Soybeans Sugarbeet Castor Cucumber
Xanthium Spinach Peas Buckwheat
Cocklebur
Sugarcane

18. Phytochrome also control Apical dominance and
branching
Pr – Apical growth
Pfr – Branching
In light: Pr → Pfr = Branching
In shade: Pfr → Pr = Apical growth

19. Problems with Excess and Deficit Light
Excess light
 Scorching of leaves.
 Chlorophyll content is reduced. This reduces the rate of
light absorption and the rate of photosynthesis.
 Excess light intensity is associated with increase in the
temperature of leaves which in turn induces rapid
transpiration and water loss.
 Stomatal conductance declines in response to declining leaf
water potentials.
 High leaf temperature inactivates the enzyme system that
changes sugars to starch.

20. Deficit light
 Etiolation, a morphological manifestation of the adverse effect
of inadequate light: it develops white, spindly stems, elongated
internodes, leaves that are not fully expanded, and a stunted
root system.
 Stems will be leggy or stretched out
 Leaves turn yellow
 Leaves are too small
 Leave or stems are spindly
 Brown edges or tips on leaves
 Lower leaves dry up
 Variegated leaves lose their variegation

21. Treatments Light intensity (mol m−2 s−1) Peak wavelength (nm)
R + B (1:1) 50 658 + 460
R + B (1:1) 150 658 + 460
R + B (1:1) 200 658 + 460
R + B (1:1) 300 658 + 460
R + B (1:1) 450 658 + 460
R + B (1:1) 550 658 + 460

22. Table 1: Effect of different light intensities on morphology of young tomato plants

23. Table 2: Effects of different light intensities on structure in young tomato
plants leaves
Fig. 4: Effects of different light intensities
on anatomical structure in young tomato
plants leaves.
(A: 50 mol m−2 s−1, B: 150 mol m−2 s−1,
C: 200 mol m−2 s−1, D:300 mol m−2 s−1,
E: 450 mol m−2 s−1, F: 550 mol m−2 s−1).
PT, palisade parenchyma; SPT, spongy
parenchyma. Scale bar is 25 micron.

24. Table 3: Effect of different light intensities on stomata traits
Fig. 5: Effects of different light intensities on
stomata traits in young tomato plants
leaves.
(A: 50 mol m−2 s−1, B: 150 mol m−2 s−1, C:
200 mol m−2 s−1, D:300 mol m−2 s−1, E: 450
mol m−2 s−1, F: 550 mol m−2 s−1). S,
stomata; E, epidermis. Scale bar is 25 m.

25. Fig . 6: Effects of different light intensities on net photosynthetic rate
of young tomato plants

26. Table 4: Plant growth characteristics and grain yield of PBNT and T5
generation PHY A transgenic lines (PA26, PA41 and PA53). Data are the means
± SD from at least 40 plants/line
a. Differences in plant
architecture between
non transgenic and
PHY A over-expressing
transgenic lines.
Ajay et al., 2006USA

27. b. Two tillers of each representative rice line showing differences in the
internode length. length length length length length length length lengthlength.
c. SEM analysis from the fourth internode fixed tissue of PBNT and PA41
representative lines. The cross section (XS) and longitudinal section (LS) of the
sample from each line showing differences in parenchyma cells
such as cell width and length, cell number, and density in the zone between the
two vascular bundles as indicated by an overlay of a semi-transparent box.
Ajay et al., 2006USA

28. Importance of water in plants
 It is a constituent of protoplasm. More than 80% of plant
tissue is made of water.
 Imparts turgidity to plant cell, which is responsible &
essential for cell multiplication.
 Involved in various metabolic activities like
• Photosynthesis
• Transpiration –maintenance of body temperature
• Translocation – Photosynthates to storage / growing tissue
• Respiration - gas exchange, TCA Cycle
• Enzymatic action – synthesis, translocation and their
function
• Hormonal activity
Moisture

29.  Agent for absorption of plant nutrients
 Integral part of metabolism
 Essential for germination
 It is the medium through which the excess dissolved salts in
soil can be flushed out.
 Opening and closing of stomata
 Water also decides the microclimate of the plants and
incidence of pests and diseases.

30. Hydrotropism
 The movement or the growth of a plant in relation to the
stimulus of water are called Hydrotropism.
 Positive Hydrotropism: when the roots grow towards water
 Negative Hydrotropism: when roots grow away from water
 Hydrotropism makes sure the plant gets enough water from
soil for photosynthesis.

31. Plant response to moisture deficit
Moisture deficit alters the following activities in plants:
1. Water relations
2. Photosynthesis
3. Respiration
4. Metabolic reactions
5. Hormonal relationship
6. Nutrition
7. Growth and development
8. Yield

32. Physiological response due to water deficit

33. Crop Adaptations to moisture stress
The ability of crop to grow satisfactorily under water stress is
called drought adaptation.
Adaptation is a structural or functional modification in plants
to survive and reproduce in a particular environment
1. Escaping drought
2.Drought resistance
(a) Drought avoidance
(1) Conserving water ( Water stress).
( 2) Improving water uptake ( water spenders ) .
(b) Drought tolerance.
( 1) mitigating stress
( 2) High tolerance.

34. RSA of ideotypes for well-watered and water-deficit conditions

35. Excess moisture
 Reduced growth and in some cases death of plants.
 Water logging causes injury to the plant due to low oxygen
supply to the root system and accumulation of toxic substances
in soil and plant.
 Several morphological, anatomical and physiological changes
take place in plants subjected to water logging.
 Production of adventious roots
 Poor root growth and nutrient absorption
 Senescence and abscission
 Permeability of roots reduces
 Flower and fruit drop

36. • Development of aerenchymatous tissue
• Increased porosity of the shoot base
• Replacement rooting
• Fast upward shoot elongation
• In rice activation of alcohol dehydrogenase system to
reduce the accumulation of ethanol, alcohols and
aldehydes
Crop Adaptations to excess moisture
A. Maize; B. Sunflower
(2 weeks after water logging)

37. Fig. 7: Summary of possible stages in aerenchyma formation in roots of Zea
mays induced by partial oxygen shortage external to the root and mediated by
increased synthesis of ethylene that in turn induces a form of programmed cell death
in target cells of the cortex.
Michael B. Jackson

38. Fig. 9: Effect of water logging on rice
Fig. 8: Effect of water logging on ragi
control 4 days 8 days 12 days
control 4 days 8 days 12 days
Kulkarni and Chavan (2014)Maharashtra, India

39. Fig. 10: Effect of water logging on calcium contents of roots of ragi and rice
a. Control ragi roots contain 682 mg/g dry weight
b. Control rice roots contain 104.2 mg/g dry weight
Kulkarni and Chavan (2014)Maharashtra, India

40. Table 5: Yield loss in some crops caused by moisture deficit
Crop Yield loss (%) Reference
Rice 53-92 Lafitte et al., 2007
Wheat 57 Balla et al., 2011
Maize 63-87 Kamara et al., 2003
Soybean 46-71 Samarah et al., 2006
Sunflower 60 Mazahery et al., 2003
Chickpea 45-69 Nayyar et al., 2006

41. Fig. 11 : Soil moisture stress
effects on soybean seed
protein and oil content.
1.6
Fig. 12 : Effect of soil moisture stress on the uptake
of nutrients like Nitrogen, Phosphorus, Potassium
and Calcium
Chathurika et al., 2019USA

42. Conclusion
 Both light and moisture plays an important role in the
crop growth, development and yield.
 Phytochrome plays a crucial role in regulating most of
the plant physiological functions.
 Extremities (too high and low) of light and moisture
affects the crop growth and hence optimum is best.
 Water logging increases the development of
aerenchyma tissues in roots.
 Soil moisture deficit reduces the uptake of nutrients like
Nitrogen, Phosphorus, Potassium and Calcium.

43. Future line of work
 More research is needed in order to find the interactions
of light, moisture and nutrients.
 Developing transgenic phytochrome varieties to produce
high yielding, semi-dwarf plants that can be used as a
donor in breeding programs towards the creation of
varieties or as a variety that are fully integrated with the
demands of modern cultivation.