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ABIOTIC STRESS RESPONSES IN TEA [Camellia

sinensis L (O) Kuntze]: AN OVERVIEW
Hrishikesh Upadhyaya1 and Sanjib K Panda 2
1
Department of Botany and Biotechnology, Karimganj College, Karimganj 788710, Assam, India
2
Plant Molecular Biotechnology Laboratory, Department of Life Science and Bioinformatics, Assam University, Silchar 788011, Assam, India

ABSTRACT
Abiotic stress is limiting to tea productivity. The severity and duration of the abiotic stress are critical, as it has multifarious effects
on crop plants. The tea plant is commonly grown in rain-fed ecosystems and thus it encounters seasonal water deficit conditions that
induce loss in crop yield. In this review, we have highlighted the effects of abiotic stress (drought, metal etc.) on the growth, mineral
nutrition, reactive oxygen species (ROS), and antioxidant metabolism in tea plants. This article also highlights the mechanism of
drought stress amelioration in tea plants on a physiological and biochemical basis. Drought stress caused increased water loss rate (WLR)
and decrease in relative water content (RWC), dry mass, chlorophyll, carotenoid, and total phenolic contents of leaf and antioxidants
like ascorbate and glutathione in tea. Leaf antioxidant enzymes (e.g., SOD, CAT, GR, etc.) showed differential activities whereas there
was increase in ROS and lipid peroxidation with decreased POX activities with progressive stress. Drought stress altered antioxidative
response with apparent decrease in mineral nutrient (Zn, Ca, Na, Fe, Mg, and K) contents of leaves suggesting that mineral deficiency
mediated drought stress induced oxidative damage in tea. Tea plants exposed to heavy metals (e.g., Cd, Cu, Al) also showed reduction
in growth and antioxidative responses. Further, a post-drought recovery study in tea also reveals that drought induced biochemical
damages are not permanent, as the plant recovers on rehydration. Mineral nutrients play an important role in post-drought recovery in
tea. The process of recovery was significantly influenced by foliar spray of K, Ca, Zn etc., leading to improved antioxidant potential.
Thus, drought tolerance and post-drought recovery can be improved by application of nutrients like K, Ca, Zn, B etc. However,
molecular mechanisms of abiotic stress amelioration and post stress recovery mediated by these nutrients need to be explored in future.
Keywords:Abiotic stress, Drought, Post-drought recovery, Metal stress, Tea

Introduction tropical countries, tealeaves are harvested all year round, whereas
Tea is second only to water as the most consumed drink in in temperate countries harvesting is seasonal. Tea is an evergreen,
the world. It has been used medicinally for centuries in India and perennial, cross-pollinated, C3 plant and in nature, the tea tree can
China. Green tea is comparatively healthier than black and Oolong attain a height of 20–30 m. However, under cultivated condition,
tea. Literature also suggests polyphenols as potential indicators the bush height of 60–100 cm is maintained for harvesting the
of drought tolerance in Camellia sinensis (Cheruiyot et al., 2007) tender leaves, which continues flashing even more than 100 years.
because of variation of shoot epicatechin and epigallocatechin Abiotic stresses cause considerable loss to agricultural
contents in response to water stress (Cheruiyot et al., 2008). Tea production worldwide. Abiotic stress conditions such as drought,
plants are grown in a wide range of latitudes in the world ranging salinity, heat, or heavy metal, etc., have been the subject of intense
from 45° N (Russia) to 30° S (South Africa) and longitude from researches. In plants, osmotic stress generated by either drought
150° E (New Guinea) to 60° W(Argentina). In India, it is grown and/or salinity or heavy metal stress represents the most common
in Barak/Brahmaputra valley/Dooars and other hilly terrains environmental hazard for the plant's growth and productivity.
of India (i.e., Darjeeling, Himachal, Nilgiri, and Uttaranchal). In addition, it has been reported that when combined, multiple
In general, the plant is kept as an evergreen shrub by pruning. abiotic stresses may interfere with nutrient accumulation, thereby
The first two leaves and a bud are plucked for tea processing. In further contributing to growth inhibition.Consequently, it seems a

Received: January 22, 2013, Accepted: February 27, 2013, Published online: June 5, 2013. 1
Correspondence to H.U.: hkupbl_au@rediffmail.com
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prerequisite for plant species selected for their use in these areas i． Cold (chilling and frost)
to have adaptations that confer abiotic stress resistance through ii． Heat (high temperature)
notably the optimized utilization of water and nutrients. However, iii．Salinity (salt)
in nature, tea and other crop plants are routinely subjected to iv．Drought (water deficit condition)
a combination of different abiotic stresses.Recent studies have v． Excess water (flooding)
pointed out that drought may exacerbate the advers eeffects of vi．Radiations (high intensity of ultraviolet and visible light)
abiotic stress on the plant nutrient status, but only a few attempts vii．Chemicals and pollutants (heavy metals, pesticides, and aerosols)
have been made to quantify the combined effect of drought, viii．Oxidative stress (reactive oxygen species, ozone)
mineral nutrients, and other abiotic stress. Camellia sinensis (L.) ix．Wind (sand and dust particles in wind)
O. Kuntze is a perennial plant growing in rain-fed ecosystems x． Nutrient deprivation in soil
and has several medicinal values attributed to high polyphenol Abiotic stresses include salinity, drought, nutrient deficiency,
contents having tremendous impact on human health (Cabrera et floods, metal, temperature, high light intensity, pollutants etc. Crops
al., 2006). Growth and productivity of tea plants largely depends including tea and their varieties differ in their responses to various
on their capacity to adapt to abiotic stress, namely temperature, abiotic and biotic stresses due to differences in their inherent
drought, metal, and nutritional disturbances. Although the effects antioxidant potential (Upadhyaya and Panda, 2004b). Among the
of some individual environmental factors on the tea plant are abiotic stresses, temperature, heavy metal, and drought stresses are
well documented (Handique and Manivel, 1990; Chakraborty of special significance. As most of the plant processes are influenced
et al., 2002; Panda et al., 2003; Upadhyaya and Panda, 2004a; by these stresses, their effect depends on the dose, duration of stress,
Jeyaramraja et al., 2005; Sharma and Kumar, 2005; Cheruiyot et and developmental stages of plants. During abiotic stress, signaling
al., 2007; Cheruiyot et al., 2008; Upadhyaya et al., 2008; Yadavand stress is first perceived by the receptors present on the membrane
Mohanpuria, 2009; Upadhyaya et al., 2011; Upadhyaya et al., of the plant cells (Fig.1); the signal is then transduced downstream
2012; Das et al., 2012; Gupta et al., 2012), the effects of interacting resulting the generation of second messengers including calcium,
abiotic factors remain poorly investigated.Therefore, the objective reactive oxygen species (ROS), and inositol phosphates. These
of this review is to highlight the effects of drought, heavy metal second messengers, such as inositol phosphates further modulate
stress, and their interaction on growth, water relationships, the intracellular calcium level. This perturbation in cytosolic Ca2+
nutrient status, and antioxidative responses during abiotic stress level is sensed by calcium binding proteins, also known as sensory
and its recovery in the tea plant. proteins, which change their conformation in a calcium dependent
manner and then interact, initiating a phosphorylation cascade
Abiotic stress and the tea plant regulating stress responsive genes (e.g., drought responsive genes)
Plants grow in almost any part of the world under diverse climatic or the transcription factors controlling these genes, as shown in
conditions differing in temperature, light quantity, and quality and Fig.1. The products of these stress genes ultimately lead to plant
availability of water. Plants that grow in a specific environment are adaptation and help the plant to confer abiotic stress tolerance.Thus,
adapted to these conditions, and can also cope with changes that the plant responds to stresses as individual cells and synergistically
might be adverse for their growth and development.Adaptation is as a whole organism. Stress induced changes in gene expression in
required because plants cannot escape unfavorable conditions due to turn may participate in the generation of hormones like abscisic acid
their sessile growth habit. This implies that species differ genetically (ABA), salicylic acid, and ethylene. These molecules may amplify
in their adaptation and resistance to abiotic stresses. Abiotic stress is the initial signal and initiate a second round of signaling that may
in fact the principal cause of the loss of crop productivity worldwide, follow the same pathway or use altogether different components
reducing average yields for various crops by more than 50%. Abiotic of the signaling pathway. The most common features of abiotic
stresses cause losses worth hundreds of millions of dollars each year stress represent the regeneration of ROS in tea plants resulting in
due to reduction in crop productivity and crop failure. a condition of imbalance between oxidants and antioxidants called
Any external constraint that reduces the ability of a plant to oxidative stress. Abiotic stress causes various morphological,
develop to its genetically predetermined level is called stress. physiological, biochemical, and molecular alterations in plants as
Plant species are highly variable in their optimum environments outlined in Figs.1 and 2. Tea being perennial, encounters occasional
and tolerance to abiotic stress conditions (e.g., drought, salinity, drought, temperature change, various metals, etc. that affect the
metals, temperature, etc.) Principal abiotic stresses that can affect growth and productivity of crops growing in an agro-ecosystem.
growth and productivity of the tea plant include the following

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Responses of drought stress in tea Jeyaramraja et al., 2005; Upadhyaya et al., 2008). However, there is
Drought denotes a period without rains during which soil water a dearth of information on the effect of drought on mineral nutrition
content is reduced and plants suffer from water deficit. Drought in tea. Drought caused osmotic stress and affects mineral nutrition
affects the morphology (Fig.2), anatomy, and physiology of the (Fig.3). Drought stress may be perceived by plants through various
plants. Physiological, biochemical, and anatomical responses, osmosensors, and signal transduction involving various cascades
however, occur much earlier than the usual symptoms of wilting (MAPKs, Ca2+, etc.) activates stress responsive genes responsible
(Fig.2), which may be permanent or temporary depending on the for detoxification (Fig.1), osmoprotection, chaperone function, and
availability of soil moisture. Drought stress results in stomatal water and ion movements in plants. Nutrient imbalance resulting
closure and reduced transpiration rate, a decrease in water potential from drought or other abiotic stress may cause oxidative stress
of plant tissues, decrease in photosynthesis and growth inhibition, in plants. We studied the impact of drought stress changes in the
accumulation of ABA, proline, mannitol, sorbitol, formation of nutrient status of the tea plant and the result reveals that drought
radical scavenging compounds (ascorbate, glutathione, tocopherol, stress caused reduction in leaf mineral content (Fig.2), which varies
etc.), and synthesis of protein. Drought stress caused decreased in different clones (data not shown). Drought induces an increase in
mineral uptake (Fig.3), stomatal conductance, and photosynthetic ROS production and inactivation of the antioxidant system (Fig.1),
rate (Jeyaramraja et al., 2005) and ultimately reduced the growth resulting in various degrees of oxidative damage in different clonal
rate of tea plants. There are reports of various physiological varieties of tea (Upadhyaya et al., 2008). Drought induced decrease
and biochemical responses of various tea clones to drought in mineral nutrients modulates oxidative stress in tea.
(Fig.1.) (Chakraborty et al., 2002; Upadhyaya and Panda, 2004a; Growth and yield of tea is greatly influenced by the seasonal

Fig.1. Morphological, physiological, molecular and biochemical basis of drought stress responses in tea. Reactive oxygen species (ROS),
catalase (CAT), superoxide dismutase (SOD), peroxidase (POX), glutathione (GR), ascorbate peroxidase (APX), ascorbate (Asc),
glutathione (GSH), mitogen activated protein kinases (MAPKs) and drought responsive protein (DR protein)

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Fig.2. Morphological changes in Camellia sinensis in response to drought and rehydration. Control (well irrigated), 7 days drought (D1)
and 14 days drought (D2) conditions and 15 days of post drought rehydration (PDR). [Original photograph by H Upadhyaya],

fluctuations in weather variables such as rainfall, temperature, enzymes and as the key structural motif in transcriptional regulatory
drought, and mineral nutrients etc. Drought stress is an important proteins. The level of zinc nutrition may affect plant water
abiotic stress, which induces oxidative damage in the tea plant and relations and alter stomatal conductance. Stomatal conductance
affects antioxidant systems, altering different physiological and and transpiration rates also declined under zinc deficiency. Gas
biochemical processes as outlined in Fig.1 (Upadhyaya and Panda, exchange data presented by Hu and Sparks (1991) and Sharma et al.
2004a) and causes significant crop losses. As shown in Fig.3, even (1994) indicated that zinc deficiency reduces transpiration efficiency
after 7 and 14 day of water withholding RWC of leaves significantly of leaves. However, it has been reported that zinc fertilization and
decreased, which is correlated with decreased leaf dry mass in a water stress affects plant water relations (Khan et al., 2004). Leaf
stressed plant with respect to control. Drought induced degradation Fe2+content also decreased with progressive dehydration stress
of both total chlorophyll and carotenoid in tea plants. Decrease (Fig.3). Na+ content of leaf decreased in tea under drought stress.
in chlorophyll and carotenoid in response to drought stress in tea Osmotic adjustment has been considered as beneficial to the drought
was reported earlier (Upadhyaya and Panda, 2004a; Upadhyaya et tolerant mechanism in field crop species. Na+ and K+ contents of
al., 2008). Such damage to chlorophyll pigments may eventually leaf affect and regulate the osmotic potential of the plant during
decrease photosynthetic efficiency in plants, which might be one of stress conditions and hence the Na+ /K+ ratio should be adequate
the potent causes of reduction in growth of the tea plant. However, for stress acclimatization by plants through osmotic adjustment.
some studies also provide evidence for a significant positive Both Mg and K content decreased in leaves of drought induced tea
relationship between transpiration efficiency and leaf chlorophyll seedlings (Fig.3). Mg nutrition is essential for the function of many
concentration in plants (Sheshshayee et al., 2006). enzymes, including adenosine triphosphatases (ATPases), RNA
Our previous experiment suggests that proline content polymerases, phosphatases, protein kinases, glutathione synthase,
increased in leaves of stressed tea plants (Fig.1). Proline acts as an and carboxylases (Shaul, 2002). In higher plants, Mg is essential for
osmoprotectant and accumulation of proline suggested genotypic chloroplasts, in the development of the chlorophyll molecule, and a
tolerance of tea to water deficit stress, as this helps in maintaining bridging element for the aggregation of ribosome subunits necessary
water relations, prevents membrane distortion, and acts as a for protein synthesis (Beale, 1999). Although K concentration of
hydroxyl radical scavenger (Bohnert and Jensen, 1996; Yoshiba et leaf is significantly correlated with increased proline content and its
al., 1997; Matysik et al., 2002). RWC, proline might not be sufficient to maintain leaf water status
The data obtained from the previous study suggest that there with concomitant decreased K content under drought stress (Fig. 3).
is a close relationship between leaf nutritional status and drought Potassium is one of the major nutrients, essential for plant growth
stress induced oxidative damage in the growing seedlings of tea. and development. Literature suggests that improving K status of
Zinc content of leaves in stressed tea plants also decreased. Zinc plants can greatly lower ROS production, imparting beneficial
is an essential nutrient that plays important roles in numerous effects when plants are subjected to abiotic stress (Cakmak, 2005;
physiological processes in plants, serving as a cofactor for many Ashley et al., 2006). Potassium is one important mineral regulating

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Fig.3. Biochemical changes in Camellia sinensis in response to drought. Control (well irrigated), 7 days drought (D1)and 14 days
drought (D2) conditions. Data presented are mean of three independent repeats.

leaf osmotic potential, affecting the water use efficiency in plants. and enzyme inactivation and affects nucleic acid and almost every
Osmotic adjustment is an essential stress-acclimatizing feature component of cell, leading to cell death (Panda, 2002; Upadhyaya
of stressed plants. The effects of potassium on drought resistance and Panda, 2004b; Jeyaramaraja et al., 2005; Cheruiyot et al., 2007;
of plants have also been reported (Egilla et al., 2001). Calcium is Cheruiyot et al., 2008; Upadhyaya et al., 2008).
another important nutrient that is well established as a secondary Drought stress caused reduction in ascorbate and glutathione
messenger and is also known to ameliorate water stress effects contents with differential responses of enzymic antioxidants in
(Nayyar and Kaushal, 2002). In the present study, leaf Ca2+ content various clones of Camellia sinensis resulting in an oxidative stress
of growing tea seedlings decreased under drought stress. Calcium is situation. Drought induced oxidative stress was also evident from
known to be involved in oxidative stress signaling, participating in increased MDA, O2-, and H2O2 content in drought imposed plants.
linking H2O2 perception and induction of antioxidant genes in plants TV-1 clones showed less decrease in antioxidants; higher activities
(Renteland Knight, 2004). Calcium is a player in most cellular of POX, GR, CAT with higher phenolic contents suggested their
signaling processes (Sanders et al., 2002) and interacts strongly better drought tolerance potential. On the other hand, higher
with ROS (Evans et al., 2005). Decreasing water availability under ROS and membrane oxidation with decrease in phenolic content
drought stress generally results in reduced total nutrient uptake and during stress in S3A3 and TV-29 proved their drought sensitivity.
frequently leads to reduced concentrations of mineral nutrients in We reported variation in antioxidant efficiency and biochemical
crop plants as reported by Baligar et al. (2001). The most important tolerance in response to drought stress in various clones of
effects of water deficits are on the transport of nutrients to the root Camellia sinensis (Upadhyaya et al., 2008).
and on root growth and extension. Reduced absorption of inorganic
nutrients results from interference with nutrient uptake, unloading Responses of heavy metal stress in tea
mechanisms, and reduced transpiration flow (Gunes et al., 2007). Heavy metal stress is a major threat to crop production. Heavy
Imposition of drought stress may increase generation of ROS, metal stress reduces crop yield and adversely affects consumers
such as superoxide radicals (O2-), hydrogen peroxide (H2O2), hydroxyl who are using that crop as food. Tea is grown in hilly areas like
radical (.OH), alkoxyl radical (RO), and singlet oxygen (.1O2) within the northwestern region of the Himalayas and weathering of
the cell, particularly within the chloroplasts of water stressed leaves. rocks contributes a lot toward enhancing levels of metals such as
Such ROS generation leads to lipid peroxidation, protein degradation, cadmium. Plant exposure to high levels of Cd causes reductions in

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photosynthesis, water uptake, and nutrient uptake (Sanita di Toppi and Cu. In tea and other plants, enzymatic antioxidant cellular
and Gabbrielli, 1999). Plants grown in soil containing high levels of machinery comprises a diverse array of enzymes including
Cd show visible symptoms of injury reflected in terms of chlorosis, superoxide dismutase, catalase, peroxidases, and enzymes of
growth inhibition, browning of root tips, and finally death. Unlike ascorbate glutathione cycle, while nonenzymatic antioxidants
Cd, Cu is an essential micronutrient required by the tea plant include low molecular weight nonprotein thiols like cysteine and
for various physiological functions, but excess Cu may lead to glutathione that are involved in detoxifying ROS.
oxidative stress in the tea plant. Any imbalance in cellular redox Al is a major limiting factor for crop production and quality in
homeostasis can be defined as oxidative stress, and imbalance in acid soil (Kochian 1995), resulting in ROS generation and enhancing
which the redox steady state of the cell is altered in the direction of lipid peroxidation in crop plants. It is known that tealeaves can
pro-oxidants can result in the potentially dangerous ROS and is very accumulate large amounts of Al from 8,700 to 23,000 mg kg-1,
common in tea plants subjected to heavy metal stress. ROS such as and even up to 30,000 mg kg-1 without experiencing Al toxicity
O2-, H2O2, and .OH are commonly generated under stress conditions (Matsumoto et al. 1976). Li et al. (2011) demonstrate the adaptation
and act as strong oxidants that can damage biomolecules. In fact, mechanisms in the leaves of the tea plant with an increasing capacity
these oxygen species represent intermediates emerging during the to overcome ROS via antioxidative enzyme systems (SOD, CAT,
successive reduction of O2- to H2O2. Plants exposure to certain GPX, APX, and GR) at low Al concentration with CAT and GPX
heavy metal ions shifts the balance of free radical metabolism activities of tealeaves playing a more important role. At 0.53 mM Al
toward an accumulation of H2O2. In the presence of redox active concentration, the balance between the formation and detoxification
transition metals such as Cu and Fe2+, H2O2 can be converted to the of ROS is lost, leading to accumulation of H2O2 , which is responsible
highly reactive -OH molecule in a metal-catalyzed reaction via the for destruction of cell ultrastructure. Exposure of tea to high contents
Fenton reaction. The oxidized metal ions undergo a re-reduction in of Cu, Cd, Hg, and Ni causes decrease in chlorophyll and increase in
a subsequent reaction with superoxide radicals (O2-). An alternative proline content (Fig.4). Reduction in the chlorophyll content of tea
mechanism of -OH formation directly from H2O2 and O2- is the has also been reported during Cd stress (Mohanpuria et al., 2007).
metal-independent Haber Weiss reaction. Thus, heavy metal stress caused oxidative stress drastically affecting
growth and productivity of the tea plant.
Fenton reaction:
H2O2+ Fe2+ /Cu+ → •OH + OH- + Fe3+ /Cu2+ Effect of mineral nutrition in abiotic stress responses in tea
• 2-
O + Fe3 /Cu2+ → Fe2 /Cu++ O2 Mineral deficiency reduced crop productivity under various
environmental conditions, as limited mineral nutrition greatly
Haber Weiss reaction: affects plants performance and their response to abiotic
H2O2 + O2- →-OH + OH- + O2 stress. Mineral deficiencies exert unpredictable responses in
plants growth, chemical composition, and functioning of the
The •OH molecule is one of the most reactive with its ability antioxidative system, particularly abiotic stress tolerance of
to initiate radical chain reactions and is responsible for irreversible plant. Thus mineral deficiencies result in increase of intensity
damage of various cellular components. Another ROS that might of abiotic stress induced damages in plants. Several studies
be involved mainly in lipid peroxidation is the protonated form suggest a significant effect of mineral nutrients on plant growth
of • O2-, the hydroperoxyl radical ( • O2- H). These species exist in and productivity under optimum environmental conditions and
equilibrium. The metal ions inhibit the activities of antioxidative thus mineral nutrients alleviate abiotic stress induced injuries
enzymes, especially of glutathione reductase, and also raise a (Upadhyaya et al., 2008; Upadhyaya et al., 2011; Upadhyaya et
transient depletion of GSH leading to ROS accumulation. Heavy al., 2012). Tea, being an evergreen perennial shrub, is subjected to
metals like Cu, Zn, Cd, Pb, Al, etc. under toxic concentration various abiotic stresses, particularly drought and metal stress. Our
inactivate the enzymic antioxidant defense system (Fig.4.) in tea previous study suggests that drought stress results in decreased
plants resulting in increased ROS signaling, generally leading leaf mineral content as shown in Fig.3; Zn, Fe, Ca, Na, and K
to death of a plant. As shown in Fig.4, metals like Cd, Cu, etc. content particularly significantly decreased with progressive
induce decrease in total chlorophyll and carotenoid, consequently stress imposition. Thus, drought stress induced mineral deficiency
reducing photosynthetic rate and increase in proline content of mediated oxidative stress in the tea plant.
tealeaf. Cd is more injurious than Cu as Cd induces decrease in
leaf dry mass. However, antioxidant enzymes like SOD, CAT, Abiotic stress recovery responses in tea: An insight
POX, and GR showed differential activities in response to Cd
Studies on post-drought stress recovery on rehydration reveal

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Fig.4. Biochemical changes in Camellia sinensis leaf in response to 7 days of CuSO4 (100μM) and CdCl2 (100μM) treatment. Control plants are not
treated with Cu or Cd. Data presented are mean of three independent repeats.

that tea plants have the potential to retrieve growth and antioxidant plant relative to a drought stressed plant. Concurrently, rehydration
function when subjected to normal growth conditions and the recovery improves antioxidant activity with respect to CAT, POX, SOD, GR
potential varies in different clones of tea (Upadhyaya et al., 2008). etc., in the tea plant along with increased photosynthetic pigments
During post-drought recovery, the tea plant showed differential (chlorophyll and carotenoid) and leaf dry mass (Fig.5). Further, the
response in activating and enhancing the coordinated antioxidant post-drought recovery was enhanced by foliar spray of K, Ca, Mn,
defense system to recover and resume growth after rehydration.In the and B (Upadhyaya et al., 2011; Upadhyaya et al., 2012). Differential
drought acclimatization as well as during the recovery process several activities of enzymes like SOD, CAT, POX, GR, and PPO in response
antioxidant enzymes play an important role in resuming the normal to foliar spray of nutrients in rehydrated plant improved the recovery
growth of the tea plant. Such studies help us understand the drought process. We also observed that foliar spray of Zn and its combination
tolerance potential of various clones of the tea plant better. In this with K, Ca, and B improves growth and antioxidative responses,
process, some of them can be recommended for growing in drought resulting in enhancement of post-drought recovery potential in the tea
prone areas and in particular for the benefit of the tea industry at large. plant (data unpublished). Such studies reveal that the mineral nutrients
In the process of abiotic stress, particularly drought stress recovery, the play a significant role in influencing growth and antioxidative responses
role of mineral nutrients, particularly K, Ca, Mn, B, Zn, etc., has been during post stress recovery in the tea plant. However, the detailed
emphasized (Upadhyaya et al.,2012). Decrease in RWC, dry mass of mechanism of abiotic stress amelioration and post stress recovery at
leaf, and antioxidants such as ascorbate and glutathione in tea has been molecular level needs to be worked out in future.
reported (Upadhyaya et al., 2012) as a consequence of drought but the
damage was not permanent (Fig.5). Increase in phenolic content with Molecular physiology of abiotic stress responses in tea
decreasein O2-, H2O2 , and lipid peroxidation was an indication of the
The molecular physiology of abiotic stress is well understood
recovery of stress induced oxidative damage following the post stress
in various model plants. However, the molecular mechanism of
rehydration (Upadhyaya et al., 2008). As depicted in Fig.5, various
abiotic stress, particularly drought and heavy metal in tea, is poorly
biochemical changes occurred during post stress rehydration. After 15
investigated. Wang et al. (2009) use a suppression subtractive
days of rehydration (PDR), RWC of leaf increased to 89% relative to a
hybridization analysis approach to identify genes involved in cold
stressed plant with 52%. Post-drought rehydration studies also showed
acclimation of tea [Camellia sinensis (L.) O. Kuntze]. A total of 10
revival of mineral uptake (e.g., Zn, Mg, Ca, K, etc.) as evidenced by
complementary DNA (cDNA) clones, induced by low temperature
increased micro and macro nutrient levels in the leaf of a rehydrated
in tealeaves, were identified. Das et al. (2012) identified a total of 123

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Fig.5. Biochemical changes in Camellia sinensis in response to post drought and rehydration. Control (14 days drought) and 15 days of post drought
rehydration (PDR). Data presented are mean of three independent repeats.

putative drought responsive genes that include candidate genes of in reduction of oxidized glutathione (GSSG) to reduced glutathione
ubiquitin-proteasome, glutathione metabolism, and sugar metabolism (GSH), also showed up-regulation under Cd stress. Such studies
pathways and several transcription factors. In order to determine the suggest that Cd exposure induces oxidative stress in Camellia sinensis
possible expression, 10 genes associated with drought responsive and the up-regulation in transcript levels of glutathione metabolic genes
pathways were further analyzed by reverse transcription polymerase except GSH indicated the role of these enzymes in the protection of
chain reaction. Their study provides a basis for studying the drought plants from Cd stress. Although there are few reports on molecular
tolerance mechanism of the tea plant, which will also be a valuable aspects of abiotic stress in tea, there is a dearth of information on the
resource for the functional genomics study of woody plants in future. molecular physiological aspect of abiotic stress amelioration and post
Rana et al. (2008) reported that expression of tea cytosolic glutamine stress recovery in tea, which needs to be taken up in future.
synthetase in tissue specific glutamine synthetase transcript by both
salinity and Cd indicates that abiotic stress can induce the expression Conclusion and future perspectives
of this gene; thus, it contains stress responsive elements in its promoter The tea plant is commonly grown in rain-fed ecosystems and
region. Glutamine synthetase is an enzyme that plays an important thus it encounters abiotic stress conditions that induce loss in crop
role in nitrogen assimilation, growth, and development of plants. yield. Abiotic stress affects the growth, mineral nutrition, ROS,
Expression of glutathione biosynthetic enzymes γ-glutamyl cysteinyl and antioxidant metabolism in tea plants. Drought stress caused
synthetase (γ-ECS) and glutathione synthetase (GSHS) was reported changes in leaf antioxidant enzymes (e.g., SOD, CAT, GR, etc.) and
to be elevated under Cu and Al stress (Yadav and Mohanpuria, 2009). there was increase in ROS, and lipid peroxidation with decreased
Phytochelatin synthase (PCS) was up-regulated at its transcript level POX activities with progressive stress. Hence, drought stress
more in the Chinary than in the Assamica variety of tea, suggesting that altered antioxidative response with apparent decrease in mineral
Chinary could be more tolerant than Assamica (Yadav and Mohanpuria, nutrient (Zn, Ca, Na, Fe, Mg, and K) contents of leaves, suggesting
2009). Mohanpuria et al. (2007) also reported that Cd induced oxidative that mineral deficiency mediated drought stress induced oxidative
stress influence on glutathione metabolic genes of Camellia sinensis damage in tea. Heavy metal (e.g., Cd, Cu, Al) stress also caused
(L.) O. Kuntze.The transcript levels of glutathione biosynthetic genes, reduction in growth and antioxidative responses. Further, post
namely γ-glutamyl cysteine synthetase (γ-ECS) and glutathione stress recovery study in tea also revealed that the tea plant recovers
synthetase (GSHS) increased upon Cd exposure. Furthermore, on post stress rehydration and the post stress recovery potential
transcript levels of glutathione reductase (GR), an enzyme involved

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