Department of Biology, University of the Balearic Islands, 07122, Palma, Illes Balears, Spain.
Centre of Excellence for Translational Photosynthesis, Research School of Biology, The Australian National University, Acton, ACT, 2601, Australia.
Plant J. 2022 Sep;111(5):1223-1237. doi: 10.1111/tpj.15915.
When C leaves are exposed to low light, the CO concentration in the bundle sheath (BS) cells decreases, causing an increase in photorespiration relative to assimilation, and a consequent reduction in biochemical efficiency. These effects can be mitigated by complex acclimation syndromes, which are of primary importance for crop productivity but are not well studied. We unveil an acclimation strategy involving the coordination of electron transport processes. First, we characterize the anatomy, gas exchange and electron transport of C Setaria viridis grown under low light. Through a purposely developed biochemical model, we resolve the photon fluxes and reaction rates to explain how the concerted acclimation strategies sustain photosynthetic efficiency. Our results show that a smaller BS in low-light-grown plants limited leakiness (the ratio of CO leak rate out of the BS over the rate of supply via C acid decarboxylation) but sacrificed light harvesting and ATP production. To counter ATP shortage and maintain high assimilation rates, plants facilitated light penetration through the mesophyll and upregulated cyclic electron flow in the BS. This shade tolerance mechanism, based on the optimization of light reactions, is possibly more efficient than the known mechanisms involving the rearrangement of carbon metabolism, and could potentially lead to innovative strategies for crop improvement.
当 C4 植物的叶片暴露在低光照下时，维管束鞘（BS）细胞中的 CO 浓度降低，导致光呼吸相对于同化作用增加，从而导致生化效率降低。这些影响可以通过复杂的适应综合征来缓解，这些适应综合征对作物生产力至关重要，但尚未得到充分研究。我们揭示了一种涉及电子传递过程协调的适应策略。首先，我们描述了在低光照下生长的 C4 柳枝稷的解剖结构、气体交换和电子传递。通过专门开发的生化模型，我们解析了光子通量和反应速率，以解释协同适应策略如何维持光合作用效率。我们的结果表明，在低光照下生长的植物中，较小的 BS 限制了漏泄（BS 中 CO 泄漏率与通过 C 酸脱羧供应的速率之比），但牺牲了光捕获和 ATP 产生。为了应对 ATP 短缺并维持高同化速率，植物通过质体增加了光的穿透并上调了 BS 中的循环电子流。这种基于优化光反应的耐荫机制可能比涉及碳代谢重排的已知机制更有效，并可能为作物改良带来创新策略。
