Physiology and Molecular Biology of Stress ... - KHAM PHA MOI

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164 A.R. Reddy and A.S. Raghavendra Table 1. Localization, half-life and target sites of different ROS in plant cells (Mittler , 2002; Perl-Treves and Perl, 2002) ROS LOCALIZATION HALF-LIFE TARGET SITE Dioxygen Chloroplasts, Mitochondria > 100 Possibly not clear Singlet oxygen Chloroplasts 1 x 10 -6 Chlorophyll destruction, membrane lipid peroxidation Superoxide radical Chloroplasts, 1 x 10 -6 Chlorophyll Mitochondria, destruction, Plasma membrane, membrane lipid Peroxisomes, peroxidation, Cell wall, D1 protein Endoplasmic reticulum, Glyoxysomes Hydrogen peroxide Peroxisomes, Not known Calvin cycle enzymes, Apoplast, cross linking to D1-D2, Cell wall damage to Mn-cluster in PSII Hydroxy radical Chloroplasts, 1 x 10 -9 All loci in cell Cell wall several strategies in plants for mitigation of photoinhibition which primarily involve the removal or detoxification of reactive oxygen molecules inevitably generated during photosynthesis. 5.1. Non-Enzymatic Antioxidants- Role of Plant Pigments 5.1.1. Pigments The generation of 1 O 2 under high light stress and other stressful conditions is highly deleterious to plant cell if it is not instantly removed. The toxicity of ROS arises from their ability to initiate radical cascade reactions that lead to protein damage, lipid peroxidation, DNA damage and finally cell death. Plants have evolved a range of avoidance and tolerance strategies employing versatile tools against photooxidative stress.
Photooxidative Stress 165 The use of solar energy in photosynthesis primarily depends on the ability to safely dissipate excess light energy to avoid photoinhibition. The dissipation process employed by plants in their natural environment is mediated by different groups of plant pigments which are known as photoprotective pigments. Carotenoids play an important role in the photoprotection of plant cell against over excitation in excess light and thus dissipate the excess of absorbed energy (Frank, 1999; Strzalka et al., 2003; Edreva, 2005a). Even under low light, carotenoids act as energetic antenna, harvesting light at the wavelength not absorbed by chloroplast and transferring electron excitation states towards photochemical reaction centers. Carotenoids are now known as intrinsic components of the chloroplast, involved in quenching the 1 O 2 under excess light (Mittler, 2002). This quenching ability of the carotenoids was attributed to chain of isoprenic residues with numerous conjugated double bonds with delocalized Ð-electrons which allows easy energy uptake from excited molecules and dissipation of excess energy as heat (Edge et al., 1997; Edreva, 2005b). Also, â-carotein, lutein and neoxanthine are known to protect the photosynthetic apparatus against photoexcitation damage by quenching the triplet states of chlorophyll molecules (Frank, 1999). Carotenoids are thus potent scavengers of ROS, protecting pigments and lipids from oxidative damage (Edge and Truscott, 1999). Carotenoids also protect plants from photooxidative stress by modulating physical properties of photsynthetic membranes with an involvement of xanthophyll cycle (Demings-Adams and Adams, 1996).The quenching by exchange electron transfer to produce the carotenoid triplet state ( 3 Car) is the principle mechanism of carotenoid photoprotection against 1 O 2. Carotenoids fluidize the membrane in its gel state and make it more rigid in its liquid crystalline state. Changes in the membrane fluidity play an important regulatory role in the de-epoxidation of violaxanthine to antheraxanthine which influences the rate of xanthophyll cycle under high light stress (Havaux and Niyogi, 1999; Strzalka et al., 2003) (Figure 3). Under excess light, a rapid change in the carotenoid composition of LHCs is a common phenomenon. The diepoxide xanthophyll violaxanthin is rapidly and reversibly converted to epoxide- free zeaxanthin via the intermediate antheraxanthin by the activity of violaxanthin deepoxidase and the reverse reaction is mediated by zeaxanthin epoxidase under low light regimes (Havauex and Niyogi, 1999). Zeaxanthin is known to quench the singlet excited states of chlorophylls or could favour protein – induced aggregation of the LHCs of PSII leading to energy dissipation, thus protecting the reaction centers from overexcitation and photoinhibition. Chloroplast membranes are sensitive targets for photodestruction by different ROS. The xanthophylls cycle is thus significant in scavenging the free radicals that otherwise would interact with the lipids surrounding the photosystems.The higher number of conjugated double bonds in antheraxanthin and zeaxanthin can be presumed to be better protectors than violaxanthin with a higher efficiency for deexciting 1 O 2 . The xanthophylls cycle is thus a ubiquitous light-controlled antioxidant system in which a simple chemical substitution in xanthophylls molecule elicits profound changes in the photostability of the chloroplast membrane system.
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PHYSIOLOGY AND MOLECULAR BIOLOGY OF
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A C.I.P. Catalogue record for this
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About the Editors K.V. Madhava Rao
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LIST OF CONTRIBUTORS K. AKASHI Grad
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List of Contributors xiii NAVINDER
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PREFACE Increasing agricultural pro
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2 K.V. Madhava Rao Abiotic stresses
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4 K.V. Madhava Rao SOME O THE PROMI
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6 K.V. Madhava Rao 2. WATER STRESS
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8 K.V. Madhava Rao 5. FREEZING STRE
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10 K.V. Madhava Rao of these pathwa
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12 K.V. Madhava Rao Bray, E.A. (199
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14 K.V. Madhava Rao Rao, K.V. Madha
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16 A. Yokota, K. Takahara and K. Ak
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41 CHAPTER 3 SALT STRESS ZORA DAJIC
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Salt Stress 43 activities (mainly i
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Salt Stress 45 In summary, mechanis
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Salt Stress 47 tolerance research i
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Salt Stress 49 need to rely on sodi
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Salt Stress 51 (Echeverria, 2000).
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Salt Stress 53 Therefore, the capac
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Salt Stress 55 Reduced plant growth
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Salt Stress 57 Table 3. Salt tolera
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Salt Stress 59 6.2. Nitrogen Fixati
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Salt Stress 61 A significant number
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Salt Stress 63 macromolecules, irre
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Salt Stress 65 8.2. Ion Homeostasis
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Salt Stress 67 1997), is speculated
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Salt Stress 69 together with the At
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Salt Stress 71 important role in si
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Salt Stress 73 Figure 5. Determinan
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Salt Stress 75 9.1.Transgenic Plant
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Salt Stress 77 tolerance from halop
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Salt Stress 79 sponse and yield (Su
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Salt Stress 81 Table 5. Possible ut
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Salt Stress 83 monitored with fluor
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Salt Stress 85 Func. Plant Biol. 29
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Salt Stress 87 Dajic, Z., Stevanovi
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Salt Stress 89 Gouia, H., Ghorbal,
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Salt Stress 91 Larcher, W. (1995).
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Salt Stress 93 Munns, R. and James,
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Salt Stress 95 Rausell, A., Kanhono
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Salt Stress 97 durum wheat crops gr
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Salt Stress 99 Yoshida, K. (2002).
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102 T.D. Sharkey and S.M. Schrader
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Page 162 and 163: Freezing Stress 153 ellin acid on f
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214 K. Janardhan Reddy and Cobbett,
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216 K. Janardhan Reddy 143, 109-111
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219 CHAPTER 8 HEAVY METAL STRESS KS
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Heavy Metal Stress 221 porter) and
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Heavy Metal Stress 223 Figure 1. Su
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Heavy Metal Stress 225 is enzymatic
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Heavy Metal Stress 227 BjPCS1 was e
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Heavy Metal Stress 229 following: (
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Heavy Metal Stress 231 a precursor
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Heavy Metal Stress 233 notype. Incr
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Table 1. Proposed specificity and l
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Heavy Metal Stress 237 4.2. Chapero
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Heavy Metal Stress 239 of prokaryot
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Heavy Metal Stress 241 5. HYPERACCU
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Table 2. Genes introduced into plan
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Heavy Metal Stress 245 7. CONCLUSIO
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Heavy Metal Stress 247 controlled b
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Heavy Metal Stress 249 Kägi, J.H.R
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Heavy Metal Stress 251 Murphy, A.,
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Heavy Metal Stress 253 through xyle
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255 CHAPTER 9 METABOLIC ENGINEERING
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Metabolic Engineering for Stress To
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302 A.K. Tyagi, S. Vij and N. Saini
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Table 3. Continued... Source Resour
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336 Index Auxins, 146 Avena sativa
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338 Expressed sequence tags (ESTs),
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340 Index Magnesium, 195 Mairiena s
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342 Index Processes less sensitive
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344 Index Sunflecks, 104 Sunflower,
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