International Journal of Photochemistry - Vol 2_Issue 2

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 Photoelectrochemical cell
 Photochemical and photobiological sciences
 Photochemistry and photobiology
 Photochemical logic gate
 Photoreceptor systems in plants
 Blue light systems
 Etiolated and de-etiolated growth pattern of plants
 Blue light photoreceptors
 Phytochromobilin
 Photomorphogenetic mutants
 Chloroplast development
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From the Editor's Desk
Dear Readers,
We would like to present, with great pleasure, the inaugural volume of a new scholarly
journal, International Journal of Photochemistry. This journal is part of the Applied
Sciences, and is devoted to the scope of present Photochemistry issues, from theoretical
aspectstoapplication-dependentstudiesandthevalidationofemergingtechnologies.
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Journal of Photochemistry focuses on original high-quality research in the realm of Atmospheric
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Maximum entropy thermodynamics, Non-equilibrium thermodynamics, Maximum entropy
thermodynamics, Non-equilibrium thermodynamics, Reaction's mechanism, Gas phase kinetics, Solution
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It is our hope that this fine collection of articles will be a valuable resource for Photochemistry readers and
willstimulatefurtherresearchintothevibrantareaofPhotochemistry.
PuneetMehrotra
ManagingDirector

1. Development of Continuous Photocatalytic Reactor: Effect of Various Parameters
Sharad M. Sontakke, Priyanka H. Kamble 1
2. Light Sensing Photoreceptors
Zeanut Akoijam 9
3. Plant Responses to Light Stress
Amit Agnihotri 11
4. Gibberellin and Seed Germination
Vishal Jain 13
5. Light Dependent Processes in Plants
Amit Agnihotri 16
Contents

IJP (2016) 1-8 © JournalsPub 2016. All Rights Reserved Page 1
International Journal of Photochemistry
Vol. 2: Issue 2
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Development of Continuous Photocatalytic Reactor: Effect of
Various Parameters
Sharad M. Sontakke*, Priyanka H. Kamble
Department of Chemical Engineering, Institute of Chemical Technology, Mumbai, India
ABSTRACT
Water purification by heterogeneous photocatalysis is one of the rapidly growing areas of
interest amongst the researchers. For mass application of the technology, efficient and
economic reactor design is necessary which should address two important parameters,
namely, light distribution inside the reactor and high surface area of irradiated catalyst per
unit volume of reactor. The present study reports design of a continuous photocatalytic
reactor using an easy-to-apply and economic TiO2 paste. TiO2 obtained by four different
sources were studied and based on photoactivity as well as economy a suitable material was
shortlisted. A paste of TiO2 was synthesized using the shortlisted material and coated on two
different substrates, namely, glass and acrylic. Effect of various parameters such as choice of
substrate, number of layers and number of coated slides on the photocatalytic degradation of
Methylene blue was investigated in a batch photocatalytic reactor. The optimum conditions
from the batch studies were used to design a continuous photocatalytic reactor. Degradation
of Methylene blue was investigated in the continuous mode and it was observed that the
reactor displayed same degradation efficiency for at least three cycles.
Keywords: continuous reactor, Methylene blue, photocatalysis, titanium dioxide
INTRODUCTION
Advanced oxidation processes (AOPs),
such as photocatalysis, have shown a great
promise as an alternative to the
conventional water treatment
technologies. TiO2, due to its superior
properties, is a preferred material in the
photocatalytic degradation studies.[1]
The
catalyst can be used in two ways namely,
suspended and immobilized. The
advantage of suspended catalyst is the
availability of large surface area for the
reaction, however, the separation and
reuse of the catalyst are the serious
disadvantages associated with it.[1]
On the
other hand, the available surface area for
the reaction in case of immobilized
catalyst is less compared to the equivalent
amount of slurry catalyst. Suspended
catalyst (or in slurry form) is extensively
studied in the literature however, a very
limited attention is given to the
immobilized (or supported) catalyst.
Several substrates have been used for
immobilization of catalyst which includes
glass beads, glass tubes, glass fiber,
semipermeable membranes, ceramic
membranes, porous filter pipes, stainless
steel, etc.[1–3]
The immobilization of the
catalyst is reported by various techniques
such as spray coating, dip coating,
chemical vapor deposition, sol–gel and
electrophoretic deposition.[3]
However,
most of the immobilization techniques
reported in literature are costly and require
use of a sophisticated instrument.

Vol. 2: Issue 2
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Light Sensing Photoreceptors
Zeanut Akoijam*
Department of Chemistry, Manipur University, Manipur, India
ABSTRACT
Light is a vital factor for plant growth and development. Plant responds to light in different
ways. Plants consist of special receptors that perform various mechanisms in multi-steps to
regulate different aspects of plant growth and development. Here, in this short article, an
overview of these light harvesting photoreceptors is given.
Keywords: COP1, phytochrome, photoreceptors, phototropin
BACKGROUND
Light is undoubtedly a vital abiotic factor
regulating plant growth and development
throughout their life-cycle. Several light
sensing mechanisms have been developed
in plants for regulating their responses
towards light quality, intensity, duration of
exposure or periodicity, direction or
movement, etc.[1]
Plants contain several
photoreceptors that play important role in
mediating different developmental
processes in response to light. These
photoreceptors consist of multiple steps of
transduction chains that regulate different
aspects such as gene expression,
interaction among the plant hormones,
developmental changes in plant cell
membrane etc. Some of the plant
photoreceptors involved in regulation of
these activities is briefed here.
Phytochrome
It is a protein molecule consisting of
covalently attached chromophore.
Phytochrome may exist in two different
based on absorption spectra from light.
The active form is the Pfr that absorbs red
light of the spectra. The other form, Pr
absorbs red light. These two forms are
interconvertible, i.e., absorbtion of red
light converts Pr to Pfr while absorbtion of
far red converts Pfr to Pr.[2]
Since, these
forms of the phytochrome are
interconvertible; the plant response is
largely regulated by this red/far red
reversibility. A typical example is the
phenomenon of germination in lettuce.
Germination is induced when the lettuce
seeds are exposed to red light. However, if
the red light is followed by even a short
pulse of far red light, germination is
inhibited.
Since, phytochrome can exist in two forms
depending on red or far-red light; this
photoreceptor is often used as an indicator
of light quality.[2–4]
Besides germination,
phytochrome also mediates other
photomorphogenic phenomena such as
leaf expansion and inhibition of stem
elongation. Phytochrome also undergoes
autophosphorylation, owing to the
presence of protein kinase receptors.
Phototropin
Phototropin is the blue light receptor of
plants. Phototropism is controlled mainly
by blue/UVA light. It brings directional
growth of the stem. In other words, it
causes shoots to grow towards light,
referred as positively phototropic. Roots
on the other show negative phototropism

Vol. 2: Issue 2
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Plant Responses to Light Stress
Amit Agnihotri*
Department of Chemical Engineering, ITM Institute of Technology and Management, Gwalior,
Madhya Pradesh, India
ABSTRACT
Light is crucial for several physiological processes that control growth and development in
plants. However, though crucial, excessive light can be harmful and detrimental for the plant
causing photo-damage. Plants have adapted several mechanisms in order to respond against
the light stress. Such protective response adapted by the plant depends upon the intensity and
duration of the light stress.
Keywords: light stress, photo-inhibition, photosynthetic quantum conversion
Light is considered to be an essential
ingredient for good plant growth. Inspite
of being crucial for growth, exposure to
excess levels of light can cause detrimental
effects on plant function and development.
Light is primarily required by plants to
carry out photosynthesis, a process
whereby plants turn the energy of light
into their own building materials i.e.,
sugars. More the light is available, more
energy is absorbed and consequently more
sugars are formed. This enhances the
overall plant growth including flowers
growing bigger, fruits becoming sweeter,
crops flourishing rapidly, etc. If plants are
exposed to light intensities beyond their
photosynthetic capacity, there is potential
for photo-damage.[1–4]
Light stress has been the least
characterized and studied among the
various types of abiotic stresses
encountered by the plants. Plants being
immobile cannot escape and have to face
the light stress. In order to overcome the
detrimental consequences of such hostile
circumstances, plants have developed
certain protective and adaptive stress
responses such as[5]
:
(1) Lowering the cross-sectional area of
plant surface exposed to light, thereby
reducing the amount of light absorbed.
(2) Increasing the rate of photosynthetic
quantum conversion in chloroplasts.
(3) Increasing heat emission such as by
de-epoxidation of violaxanthin to
zeaxanthin.
(4) Rise of non-photochemical de-
excitation of absorbed light quantum.
(5) Photo-inhibition of the photosynthetic
pigment apparatus.
During stress exposure, plants undergo
through different phases which have been
categorized into 4 parts viz.
(1) Response phase (alarm reaction)
(2) Resistance phase
(3) Exhaustion stage
(4) Regeneration phase, in which the
physiological function is gradually
restored once the source of stress is
removed
The length (hours, days) of the
regeneration phase to take the plant back
to a normal physiological function depends
on the strength and duration of the stress.
The light stress either directly or

Vol. 2: Issue 2
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Gibberellin and Seed Germination
Vishal Jain
MM College, Modinagar, Uttar Pradesh, India
Plants undergo several developmental
processes throughout their life-cycle.
Several plant hormones participate in these
growth and developmental processes. Plant
hormones are chemical signals that are
produced by cells in one area such as
leaves, stems or root, and transported to a
different area of the plant, where it
generates a specific response. In this way,
hormones co-ordinate different parts of the
plant and regulate various physiological
activities. Five major plant hormones are
known: auxin, ethylene, cytokinin, abscisic
acid and gibberellin. Though required in
very small quantities, all of these play
countless important functions in plants.
This review describes the importance of
gibberellin hormone in plants with main
emphasis on its role in seed germination.
Gibberellin was first isolated in 1938 from
the metabolite product of rice pathogenic
fungus Gibberella fujikuroi; the causal
agent of the ‘foolish-seedling’ disease of
rice.[1,2]
Gibberellins are synthesized from
geranyldiphosphate by a specific pathway
including several enzymes. Gibberellins
regulate diverse developmental processes
throughout the plant life cycle such as
stem elongation, leaf expansion, influence
transition from juvenile to mature stage,
pollen maturation, induction of flowering,
fruit ripening, trichome development, sex
determination and various aspects of seed
germination such as breaking dormancy,
mobilization of endosperm reserves.[3–5]
Seed germination, an important step in the
plant life cycle, is a complex mechanism
wherein physiological and morphological
alterations take place resulting in
activation of the embryo. The pathways
leading to seed germination is initiated
with the release of coat dormancy,
‘weakening of endosperm’, and ‘expansion
of embryo cell’. Many researchers have
evaluated the processes involved in seed
germination, and how they are affected by
plant hormones in different plant families
like Brassicaceae.[6,7]
It has been indicated that there is an
intimate interaction between gibberellins
metabolism and gibberellins response
pathways. This kind of interaction, along
with other pathways in the plant, results in
the regulation of plant growth and
development. Some reports suggest that
gibberellins stimulate the synthesis and
production of hydrolases particularly α-
amylase that leads to the germination of
seeds. While there are some others that
though confirms the role of gibberellin in
seed germination, rule out the opinion that
gibberellin promotes seed germination via
amylase production.[8]
Using proteomic
analysis, Gallardo et al. (2002) indicated
the way via which the germination of
Arabidopsis seeds is regulated by
gibberellins.[9]
In a view to identify the
proteins whose abundance depends on the
action of gibberellin during different
stages of seed germination, Gallardo et al.
pointed out that the gibberellin do not
directly participates in the processes
leading to seed germination. Instead, the
hormone is involved in controlling the
accumulation level of proteins associated
with radicle protrusion and post-
germination processes. An example of
such protein being the cytoskeleton
component, α-2,4 tubulin.[9]

Vol. 2: Issue 2
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Light Dependent Processes in Plants
Amit Agnihotri
Department of Chemical Engineering, ITM Institute of Technology and Management,
Gwalior, Madhya Pradesh, India
Light is vital for the survival of all living
organisms on Earth. It is hard to imagine
life without light. The source of light, the
Sun, is the universal source of energy for
all life on Earth. It helps the human beings
to carry out daily routine work very easily.
It is also required for growth and
development of plants; bacteria such as
cyanobacteria, green sulfur bacteria. In
plants, the solar energy or light is absorbed
and converted into another useful form,
i.e., chemical energy. This review gives a
brief insight into the various growth and
developmental processes in plant that are
controlled or regulated by light.
Plants show different responses in
presence to light. This phenomenon is
called phototropism. A classic example is
the bending of a plant stem towards light.
Anyone who has grown a plant near a
window would have observed that the
plant usually bends toward the window
where the light is stronger than inside the
room. Another commonly experienced
example of tropic response is
gravitropism, where the plant grows in
such a way so as to stay oriented relative
to the source of gravity (the earth). Thus,
in case a plant is knocked down, the shoot
will grow faster on the lower side until the
shoot is more-or-less standing up again.
Such phototropic responses are regulated
by specific blue-light photoreceptors
called phototropins. Gravitropism is
dependent on the presence of starch-filled
plastids called amyloplasts in specialized
cells. When the orientation of cells change,
the mass of amyloplasts causes them to
sink and tumble towards lower end of the
cell. As a result, differential growth occurs
causing curvature in the plant.
Several reports are available in literature
that have described in detail how light
effects the movement and/or functioning
of different plant parts/cellular organelles.
Light-dependent changes in the leaflet
movement rhythm of Desmodium gyrans,
the Indian telegraph plant was studied in
detail by Sharma et al.[1]
The movements
and oscillations of the lateral leaflets of
this plant were analyzed in response to
different chemicals, DC currents, and
static magnetic fields. It showed that the
frequency of oscillations was more and
rapid in presence of bright light, while low
light intensity slowed down the
oscillations. short period oscillations of the
lateral leaflets actually was an adaptive
response of the plant in order to optimize
the amount of light falling on the leaflets
thereby facilitating transpiration of water
through stomata.
Mimosa pudica is a highly sensitive and
unique plant that shows rapid leaf
movement. In response to any physical
disturbance, this species folds its leaves in
a fraction of seconds. Under conditions of
high light, the plant immediately closes its
leaves.
This action is opposite of what is expected
from the principle of energetics, according
to which, the plant in high light, having
abundant energy available to them should
more rapidly open its leaves to allow
capturing of more and more solar energy.

International Journal of Photochemistry - Vol 2_Issue 2

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