Feller Urs
Institute of Plant Sciences and Oeschger Centre for Climate Change Research (OCCR), University of Bern, Altenbergrain 21, CH-3013 Bern, Switzerland.
J Plant Physiol. 2016 Sep 20;203:84-94. doi: 10.1016/j.jplph.2016.04.002. Epub 2016 Apr 7.
Global change is characterized by increased CO concentration in the atmosphere, increasing average temperature and more frequent extreme events including drought periods, heat waves and flooding. Especially the impacts of drought and of elevated temperature on carbon assimilation are considered in this review. Effects of extreme events on the subcellular level as well as on the whole plant level may be reversible, partially reversible or irreversible. The photosynthetically active biomass depends on the number and the size of mature leaves and the photosynthetic activity in this biomass during stress and subsequent recovery phases. The total area of active leaves is determined by leaf expansion and senescence, while net photosynthesis per leaf area is primarily influenced by stomatal opening (stomatal conductance), mesophyll conductance, activity of the photosynthetic apparatus (light absorption and electron transport, activity of the Calvin cycle) and CO release by decarboxylation reactions (photorespiration, dark respiration). Water status, stomatal opening and leaf temperature represent a "magic triangle" of three strongly interacting parameters. The response of stomata to altered environmental conditions is important for stomatal limitations. Rubisco protein is quite thermotolerant, but the enzyme becomes at elevated temperature more rapidly inactivated (decarbamylation, reversible effect) and must be reactivated by Rubisco activase (carbamylation of a lysine residue). Rubisco activase is present under two forms (encoded by separate genes or products of alternative splicing of the pre-mRNA from one gene) and is very thermosensitive. Rubisco activase was identified as a key protein for photosynthesis at elevated temperature (non-stomatal limitation). During a moderate heat stress Rubisco activase is reversibly inactivated, but during a more severe stress (higher temperature and/or longer exposure) the protein is irreversibly inactivated, insolubilized and finally degraded. On the level of the leaf, this loss of photosynthetic activity may still be reversible when new Rubisco activase is produced by protein synthesis. Rubisco activase as well as enzymes involved in the detoxification of reactive oxygen species or in osmoregulation are considered as important targets for breeding crop plants which are still productive under drought and/or at elevated leaf temperature in a changing climate.
全球变化的特征是大气中二氧化碳浓度增加、平均温度上升以及包括干旱期、热浪和洪水在内的极端事件更加频繁。本综述特别考虑了干旱和高温对碳同化的影响。极端事件对亚细胞水平以及整株植物水平的影响可能是可逆的、部分可逆的或不可逆的。光合活性生物量取决于成熟叶片的数量和大小以及胁迫和随后恢复阶段该生物量中的光合活性。活跃叶片的总面积由叶片扩展和衰老决定，而每叶面积的净光合作用主要受气孔开放（气孔导度）、叶肉导度、光合机构的活性（光吸收和电子传递、卡尔文循环的活性）以及脱羧反应释放的二氧化碳（光呼吸、暗呼吸）影响。水分状况、气孔开放和叶片温度代表了三个强烈相互作用参数的“神奇三角”。气孔对环境条件变化的响应对于气孔限制很重要。核酮糖-1,5-二磷酸羧化酶/加氧酶（Rubisco）蛋白具有相当的耐热性，但该酶在温度升高时会更快地失活（脱氨甲酰化，可逆效应），并且必须通过Rubisco活化酶重新激活（赖氨酸残基的氨甲酰化）。Rubisco活化酶以两种形式存在（由不同基因编码或来自一个基因的前体mRNA的可变剪接产物），并且对热非常敏感。Rubisco活化酶被确定为高温下光合作用的关键蛋白（非气孔限制）。在中度热胁迫期间，Rubisco活化酶可逆失活，但在更严重的胁迫（更高温度和/或更长暴露时间）下，该蛋白不可逆失活、不溶并最终降解。在叶片水平上，当通过蛋白质合成产生新的Rubisco活化酶时，这种光合活性的丧失可能仍然是可逆的。Rubisco活化酶以及参与活性氧解毒或渗透调节的酶被认为是培育在气候变化下干旱和/或叶片温度升高时仍能高产的作物品种的重要目标。
