Zhou Yanhong, Lam Hon Ming, Zhang Jianhua
Department of Horticulture, Zhejiang University, Hangzhou, China.
J Exp Bot. 2007;58(5):1207-17. doi: 10.1093/jxb/erl291. Epub 2007 Feb 5.
Photoprotection mechanisms of rice plants were studied when its seedlings were subjected to the combined stress of water and high light. The imposition of water stress, induced by PEG 6000 which was applied to roots, resulted in substantial inhibition of stomatal conductance and net photosynthesis under all irradiance treatments. Under high light stress, the rapid decline of photosynthesis with the development of water stress was accompanied by decreases in the maximum velocity of RuBP carboxylation by Rubisco (V(cmax)), the capacity for ribulose-1,5-bisphosphate regeneration (J(max)), Rubisco and stromal FBPase activities, and the quantum efficiency of photosystem II, in the absence of any stomatal limitation of CO(2) supply. Water stress significantly reduced the energy flux via linear electron transport (J(PSII)), but increased light-dependent and DeltapH- and xanthophyll-mediated thermal dissipation (J(NPQ)). It is concluded that the drought-induced inhibition of photosynthesis under different irradiances in the rice was due to both diffusive and metabolic limitations. Metabolic limitation of photosynthesis may be related to the adverse effects of some metabolic processes and the oxidative damage to the chloroplast. Meanwhile, an enhanced thermal dissipation is an important process to minimize the adverse effects of drought and high irradiance when CO(2) assimilation is suppressed.
研究了水稻幼苗在水分和高光联合胁迫下的光保护机制。通过将PEG 6000施用于根部诱导水分胁迫，在所有光照处理下均导致气孔导度和净光合作用受到显著抑制。在高光胁迫下，随着水分胁迫的发展，光合作用迅速下降，同时在没有任何气孔对CO₂供应限制的情况下，Rubisco催化的RuBP羧化最大速度（V(cmax)）、1,5-二磷酸核酮糖再生能力（J(max)）、Rubisco和基质FBPase活性以及光系统II的量子效率均下降。水分胁迫显著降低了通过线性电子传递的能量通量（J(PSII)），但增加了光依赖的、ΔpH和叶黄素介导的热耗散（J(NPQ)）。得出结论，水稻在不同光照下干旱诱导的光合作用抑制是由于扩散限制和代谢限制。光合作用的代谢限制可能与某些代谢过程的不利影响以及叶绿体的氧化损伤有关。同时，当CO₂同化受到抑制时，增强的热耗散是将干旱和高光照的不利影响降至最低的重要过程。
