Institute of Plant and Environmental Sciences, Slovak University of Agriculture, Nitra, Slovak Republic.
Institute of Plant Physiology and Genetics, Bulgarian Academy of Sciences, Sofia, Bulgaria.
Photosynth Res. 2022 Dec;154(3):259-276. doi: 10.1007/s11120-022-00966-z. Epub 2022 Oct 1.
Nitrogen (N) deficiency represents an important limiting factor affecting photosynthetic productivity and the yields of crop plants. Significant reported differences in N use efficiency between the crop species and genotypes provide a good background for the studies of diversity of photosynthetic and photoprotective responses associated with nitrogen deficiency. Using distinct wheat (Triticum aestivum L.) genotypes with previously observed contrasting responses to nitrogen nutrition (cv. Enola and cv. Slomer), we performed advanced analyses of CO assimilation, PSII, and PSI photochemistry, also focusing on the heterogeneity of the stress responses in the different leaf levels. Our results confirmed the loss of photosynthetic capacity and enhanced more in lower positions. Non-stomatal limitation of photosynthesis was well reflected by the changes in PSII and PSI photochemistry, including the parameters derived from the fast-fluorescence kinetics. Low photosynthesis in N-deprived leaves, especially in lower positions, was associated with a significant decrease in the activity of alternative electron flows. The exception was the cyclic electron flow around PSI that was enhanced in most of the samples with a low photosynthetic rate. We observed significant genotype-specific responses. An old genotype Slomer with a lower CO assimilation rate demonstrated enhanced alternative electron flow and photorespiration capacity. In contrast, a modern, highly productive genotype Enola responded to decreased photosynthesis by a significant increase in nonphotochemical dissipation and cyclic electron flow. Our results illustrate the importance of alternative electron flows for eliminating the excitation pressure at the PSII acceptor side. The decrease in capacity of electron acceptors was balanced by the structural and functional changes of the components of the electron transport chain, leading to a decline of linear electron transport to prevent the overreduction of the PSI acceptor side and related photooxidative damage of photosynthetic structures in leaves exposed to nitrogen deficiency.
氮（N）缺乏是影响作物光合生产力和产量的一个重要限制因素。不同作物物种和基因型之间氮利用效率的显著差异为与氮缺乏相关的光合和光保护反应多样性的研究提供了良好的背景。我们使用先前观察到对氮营养反应不同的不同小麦（Triticum aestivum L.）基因型（Enola 和 Slomer），对 CO2 同化、PSII 和 PSI 光化学进行了深入分析，还重点研究了不同叶片层次胁迫反应的异质性。我们的研究结果证实了光合能力的丧失，且这种丧失在较低的叶片位置更为明显。通过 PSII 和 PSI 光化学的变化，包括从快速荧光动力学得出的参数，很好地反映了非气孔限制光合作用的情况。在氮剥夺叶片中，特别是在较低的叶片位置，光合作用较低与替代电子流活性的显著下降有关。例外的是在大多数具有低光合速率的样本中，PSI 周围的循环电子流增强。我们观察到了显著的基因型特异性反应。具有较低 CO2 同化率的老基因型 Slomer 表现出增强的替代电子流和光呼吸能力。相比之下，现代、高生产力的基因型 Enola 通过显著增加非光化学耗散和循环电子流来应对光合作用的下降。我们的研究结果表明替代电子流对于消除 PSII 受体侧的激发压力很重要。电子受体能力的下降通过电子传递链组件的结构和功能变化得到平衡，导致线性电子传递下降，以防止 PSI 受体侧的过度还原以及暴露在氮缺乏下的叶片中光合结构的相关光氧化损伤。
