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Chow, Wah Soon,Fan, Da-Yong,Oguchi, Riichi,Jia, Husen,Losciale, Pasquale,Park, Youn-Il,He, Jie,Oquist, Gunnar,Shen, Yun-Gang,Anderson, Jan M W. Junk ; Kluwer Academic Publishers 2012 Photosynthesis research Vol.113 No.1
<P>Given its unique function in light-induced water oxidation and its susceptibility to photoinactivation during photosynthesis, photosystem II (PS II) is often the focus of studies of photosynthetic structure and function, particularly in environmental stress conditions. Here we review four approaches for quantifying or monitoring PS II functionality or the stoichiometry of the two photosystems in leaf segments, scrutinizing the approximations in each approach. (1) Chlorophyll fluorescence parameters are convenient to derive, but the information-rich signal suffers from the localized nature of its detection in leaf tissue. (2) The gross O(2) yield per single-turnover flash in CO(2)-enriched air is a more direct measurement of the functional content, assuming that each functional PS II evolves one O(2) molecule after four flashes. However, the gross O(2) yield per single-turnover flash (multiplied by four) could over-estimate the content of functional PS II if mitochondrial respiration is lower in flash illumination than in darkness. (3) The cumulative delivery of electrons from PS II to P700(+) (oxidized primary donor in PS I) after a flash is added to steady background far-red light is a whole-tissue measurement, such that a single linear correlation with functional PS II applies to leaves of all plant species investigated so far. However, the magnitude obtained in a simple analysis (with the signal normalized to the maximum photo-oxidizable P700 signal), which should equal the ratio of PS II to PS I centers, was too small to match the independently-obtained photosystem stoichiometry. Further, an under-estimation of functional PS II content could occur if some electrons were intercepted before reaching PS I. (4) The electrochromic signal from leaf segments appears to reliably quantify the photosystem stoichiometry, either by progressively photoinactivating PS II or suppressing PS I via photo-oxidation of a known fraction of the P700 with steady far-red light. Together, these approaches have the potential for quantitatively probing PS II in vivo in leaf segments, with prospects for application of the latter two approaches in the field.</P>
The Photoinactivation of Photosystem II in Leaves: A Personal Perspective
Chow, Wah-Soon Korean Society of Photoscience 2001 Journal of Photosciences Vol.8 No.2
a, a parameter that describes how effectively photoinactivated PS II units protect their functional neighbours; car, carotenoids; ΔpH, transthylakoid pH difference; D1 protein, psbA gene product in the PS II reaction centre; f, functional fraction of PS II: F$\_$v//F$\_$m/, the ratio of variable to maximum chlorophyll a fluorescence; k$\_$d/, rate coefficient for degradation of D1 protein; k$\_$i/ and k$\_$r/, rate coefficient for photoinactivation and repair of PS II, respectively; NADP+, oxidized nicontinamide adenine dinucleotide phosphate; P680, the primary electron donor in the PSII reaction centre; Ph, pheophytin; PS, photosystem; Q$\_$A/, first quinone acceptor of an electron in PS II; R$\_$s/, the gross rate of D1 protein synthesis.
Ryu, Jee-Youn,Song, Ji-Young,Chung, Young-Ho,Park, Young-Mok,Chow, Wah-Soon,Park, Youn-Il The Korean Society of Plant Biotechnology 2010 Plant biotechnology reports Vol.4 No.2
Expression of the genes for carotenoid bio-synthesis (crt) is dependent on light, but little is known about the underlying mechanism of light sensing and signalling in the cyanobacterium Synechocystis sp. PCC 6803 (hereafter, Synechocystis). In the present study, we investigated the light-induced increase in the transcript levels of Synechocystis crt genes, including phytoene synthase (crtB), phytoene desaturase (crtP), ${\zeta}$-carotene desaturase (crtQ), and ${\beta}$-carotene hydroxylase (crtR), during a darkto-light transition period. During the dark-to-light shift, the increase in the crt transcript levels was not affected by mutations in cyanobacterial photoreceptors, such as phytochromes (cph1, cph2 and cph3) and a cryptochrome-type photoreceptor (ccry), or respiratory electron transport components NDH and Cyd/CtaI. However, treatment with photosynthetic electron transport inhibitors significantly diminished the accumulation of crt gene transcripts. Therefore, the light induction of the Synechocystis crt gene expression is most likely mediated by photosynthetic electron transport rather than by cyanobacterial photoreceptors during the dark-to-light transition.
Suk Weon Jeong,Sun Mi Choi,Dong Sook Lee,Sang Nag Ahn,Yoonkang Hur,Wah Soon Chow,박연일 한국분자세포생물학회 2002 Molecules and cells Vol.13 No.3
The primary target for light-chilling stress in chillingsensitive cucumber leaves is the chloroplast Cu,Zn- Superoxide dismutase, followed by subsequent inactivation of the photosystem (PS) I by reactive oxygen species (ROS). To test this hypothesis, two rice cultivars that were different in their ecological origins (a chilling-resistant Stejaree 45 and a chilling-sensitive Milyang 23) were evaluated with respect to photosynthetic properties, the ROS scavenging system, and expression of genes that are involved in sucrose synthesis and allocation upon the light-chilling stress. As expected, when the leaves were exposed to various low temperatures with illumination (150 μmol m−2s−1) for 6 h, the leaf photosynthesis of Milyang 23 decreased faster than that of Stejaree 45. The light-chilling induced differential photoinhibition of photosynthesis between the two cultivars was caused by the photoinactivation of PSII but not of PSI, since the potential quantum yield of PSII followed a similar trend to the changes in photosynthetic rates. The activities of the two chloroplastic antioxidant enzymes (superoxide dismutase and ascorbate peroxidase) that are known to be sensitive to oxidative stress were barely affected by the light-chilling treatments. Among various genes in sucrose metabolism (such as cytosolic FBPase, SPS, SUT, SuSy, and AGPase), the transcript levels of SuSy in Milyang 23 were significantly decreased by lightchilling stress compared to that of Stejaree 45. Based on these results, we propose that PSII, not PSI, is the sensitive site for light-chilling stress in chilling-sensitive rice. The extent of PSII photoinhibition depends on its capacity for the photochemical utilization of light.
Ya-Li Zhang,Hong-Zhi Zhang,Ming-Wei Du,Wei Li,Hong-Hai Luo,Wah-Soon Chow,Wang-Feng Zhang 한국식물학회 2010 Journal of Plant Biology Vol.53 No.1
Under severe water stress, leaf wilting is quite general in higher plants. This passive movement can reduce the energy load on a leaf. This paper reports an experimental test of the hypothesis that leaf wilting movement has a protective function that mitigates against photoinhibition of photosynthesis in the field. The experiments exposed cotton (Gossypium hirsutum L.) to two water regimes: waterstressed and well-watered. Leaf wilting movement occurred in water-stressed plants as the water potential decreased to −4.1 MPa, reducing light interception but maintaining comparable quantum yields of photosystem II (PS II; Yield for short) and the proportion of total PS II centers that were open (qP). Predrawn Fv/Fm (potential quantum yield of PS II) as an indicator of overnight recovery of PS II from photoinhibition was higher than or similar to that in wellwatered plants. Compared with water-stressed cotton leaves for which wilting movement was permitted, water-stressed cotton leaves restrained from such movement had significantly increased leaf temperature and instantaneous CO2assimilation rates in the short term, but reduced Yield, qP,and Fv/Fm. In the long term, predrawn Fv/Fm and CO2assimilation capacity were reduced in water-stressed leaves restrained from wilting movement. These results suggest that, under water stress, leaf wilting movement could reduce the incident light on leaves and their heat load, alleviate damage to the photosynthetic apparatus due to photoinhibition,and maintain considerable carbon assimilation capacity in the long term despite a partial loss of instantaneous carbon assimilation in the short term.