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

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160 A.R. Reddy and A.S. Raghavendra thesis, are also the potential sources of singlet oxygen ( 1 O 2 ) production. These reactive singlet oxygen molecules are generated by an input of energy by removing the spin restriction and therefore increasing the oxidizing ability of oxygen (Knox and Dodge, 1985; Niyogi, 1999). The half life time of 1 O 2 is about 200ns in plant cells (Gorman and Rodgers, 1992). 1 O 2 is known to react with DI protein, thus damaging PSII (Trebst et al., 2003). Keren et al. (2000) measured the degree of photoinactivation and loss of DI protein by using series of single turnover flashes. The highly reactive 1 O 2 is also reported to have a strongly deleterious effect on chloroplast pigment-protein complexes, as it is generated in the pigment bed (Slooten et al., 1998; Niyogi, 1999). However, the DI damage is also regarded as physiological defense mechanism as the damaged DI protein is efficiently replaced by newly synthesized DI (Prasil et al., 1992; Aro et al., 1993). Suh et al. (2000) showed the production of 1 O 2 in illuminated cytochrome b 6 f complex by using spin trapping techniques. However, the role of cytochrome b 6 f complex-generated 1 O 2 is still not completely understood. However, it is now known that chlorophyll sensitizers act as main source of reactive oxygen species and in case the chlorophyll is activated by energy transfer under high light conditions, 1 O 2 production is increased (Hippeli et al., 1999). 4.2. Photooxidation-Induced Free Radical Production in Plant Cells High irradiance produces fluxes of dioxygen and excess electrons leading to overreduction of electron transport chain (ETC), which might result increased formation of several free radicals, commonly referred as reactive oxygen species. Thus, high lightdriven photosynthetic processes are main contributors to chloroplastic-ROS production in plants. Highly active ETC in chloroplasts under excess growth light operate in an O 2 -rich environment and leakage of the excess electrons leads to the formation of ROS (Edreva, 2005a). Unlike the formation of 1 O 2 , chemical activation is the other mechanism to circumvent spin restriction through univalent reduction of dioxygen which results at least three intermediates namely superoxide (O 2?¯), hydrogen peroxide (H 2 O 2 ) and the hydroxyl radical (OH . ) (Figure 1). It is also known that these ROS colliding with an organic molecule may get an electron, rendering it a radical capable of propagating a chain reaction by forming peroxyl (ROO . ) and alkoxyl (RO . ) radicals (Perl-Treves and Peri, 2002). Excess electrons from ETC will be derived from ferridoxin to O 2 . In addition, leakage of electrons to O 2 may also occur from 2Fe-2s and 4Fe-4s clusters of PSI. It is now well established that Q A and Q B sites of PSII are also potential sources of O 2?¯ generation (Dat et al., 2000; Zhang et al., 2003). The addition of an electron to molecular oxygen by photosynthetic ETC produces O 2?¯ and this reaction is termed as Mehler reaction (Mehler, 1951). The electron transfer to oxygen will be more at the chloroplast under high light stress because of high O 2 levels occurring at that site, favouring markedly high levels of O 2?¯ and 1 O 2 . We will now concentrate on the fate of this
Photooxidative Stress 161 disproportionate production of oxygen free radicals in plant cells under excess growth light regimes. Superoxide is capable of both oxidation and reduction. It can also react to produce several other reactive species. An enzyme, superoxide dismutase (SOD), present in the chloroplast matrix and in the thylakoid membrane dismutates superoxide to H 2 O 2 , particularly at low pH. Figure 1. Formation of reactive oxygen species from dioxygen H 2 O 2 is not a free radical, but participates as an oxidant or reductant in several cellular metabolic processes. H 2 O 2 is also produced in peroxisomes during photorespiration. When both superoxide and H 2 O 2 are present at the same time a reaction catalyzed by transition metal ions, like iron and copper, favours the formation of toxic hydroxyl radical as shown in the following reaction known as Haber-Weiss reaction.
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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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210 K. Janardhan Reddy 18. MOLECULA
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212 K. Janardhan Reddy Bush, D.S.,
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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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