Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av da República-EAN, 2780-157 Oeiras, Portugal.
J Exp Bot. 2011 Jan;62(3):869-82. doi: 10.1093/jxb/erq340. Epub 2010 Dec 14.
Photosynthesis is one of the key processes to be affected by water deficits, via decreased CO2 diffusion to the chloroplast and metabolic constraints. The relative impact of those limitations varies with the intensity of the stress, the occurrence (or not) of superimposed stresses, and the species we are dealing with. Total plant carbon uptake is further reduced due to the concomitant or even earlier inhibition of growth. Leaf carbohydrate status, altered directly by water deficits or indirectly (via decreased growth), acts as a metabolic signal although its role is not totally clear. Other relevant signals acting under water deficits comprise: abscisic acid (ABA), with an impact on stomatal aperture and the regulation at the transcription level of a large number of genes related to plant stress response; other hormones that act either concurrently (brassinosteroids, jasmonates, and salycilic acid) or antagonistically (auxin, cytokinin, or ethylene) with ABA; and redox control of the energy balance of photosynthetic cells deprived of CO2 by stomatal closure. In an attempt to systematize current knowledge on the complex network of interactions and regulation of photosynthesis in plants subjected to water deficits, a meta-analysis has been performed covering >450 papers published in the last 15 years. This analysis shows the interplay of sugars, reactive oxygen species (ROS), and hormones with photosynthetic responses to drought, involving many metabolic events. However, more significantly it highlights (i) how fragmented and often non-comparable the results are and (ii) how hard it is to relate molecular events to plant physiological status, namely photosynthetic activity, and to stress intensity. Indeed, the same data set usually does not integrate these different levels of analysis. Considering these limitations, it was hard to find a general trend, particularly concerning molecular responses to drought, with the exception of the genes ABI1 and ABI3. These genes, irrespective of the stress type (acute versus chronic) and intensity, show a similar response to water shortage in the two plant systems analysed (Arabidopsis and barley). Both are associated with ABA-mediated metabolic responses to stress and the regulation of stomatal aperture. Under drought, ABI1 transcription is up-regulated while ABI3 is usually down-regulated. Recently ABI3 has been hypothesized to be essential for successful drought recovery.
光合作用是受水分亏缺影响的关键过程之一，其途径是降低 CO2 向叶绿体的扩散和代谢限制。这些限制的相对影响因胁迫的强度、是否存在叠加胁迫以及我们所处理的物种而有所不同。由于生长的同时抑制甚至更早抑制，植物的总碳吸收进一步减少。叶片碳水化合物状态直接受水分亏缺影响，或间接（通过降低生长）影响，作为代谢信号，但其作用尚不完全清楚。水分亏缺下作用的其他相关信号包括：脱落酸（ABA），其对气孔开度有影响，并在转录水平上调节与植物应激反应相关的大量基因；其他激素，它们要么协同作用（油菜素内酯、茉莉酸和水杨酸），要么与 ABA 拮抗作用（生长素、细胞分裂素或乙烯）；以及由于气孔关闭而剥夺 CO2 的光合细胞的能量平衡的氧化还原控制。为了尝试系统地了解在水分亏缺下植物光合作用的复杂相互作用和调节网络的当前知识，对过去 15 年发表的超过 450 篇论文进行了元分析。该分析表明，糖、活性氧（ROS）和激素与干旱条件下光合作用的反应相互作用，涉及许多代谢事件。然而，更重要的是，它突出了（i）结果是多么零碎，而且往往不可比，以及（ii）将分子事件与植物生理状态（即光合作用活性）和胁迫强度联系起来是多么困难。事实上，同一数据集通常不整合这些不同的分析水平。考虑到这些限制，很难找到一个普遍趋势，特别是关于干旱条件下的分子反应，除了 ABI1 和 ABI3 基因。这些基因，无论胁迫类型（急性与慢性）和强度如何，在分析的两个植物系统（拟南芥和大麦）中对水分短缺表现出相似的反应。两者都与 ABA 介导的应激代谢反应和气孔开度的调节有关。在干旱条件下，ABI1 转录上调，而 ABI3 通常下调。最近，ABI3 被假设对成功的干旱恢复至关重要。
