Departamento de Bioquímica e Biologia Molecular, Laboratório de Metabolismo de Plantas, Universidade Federal do Ceará, Av. Humberto Monte 2825, Campus do Pici, Bl. 907, CP 6020, Fortaleza, Ceará, CEP 60451-970, Brazil.
Photosynth Res. 2019 Jun;140(3):321-335. doi: 10.1007/s11120-019-00614-z. Epub 2019 Jan 29.
Mechanisms involving ammonium toxicity, excess light, and photosynthesis are scarcely known in plants. We tested the hypothesis that high NH supply in presence of high light decreases photosynthetic efficiency of rice plants, an allegedly tolerant species. Mature rice plants were previously supplied with 10 mM NH or 10 mM NO and subsequently exposed to 400 µmol m s (moderate light-ML) or 2000 µmol m s (high light-HL) for 8 h. HL greatly stimulated NH accumulation in roots and in a minor extent in leaves. These plants displayed significant delay in D1 protein recovery in the dark, compared to nitrate-supplied plants. These responses were related to reduction of both PSII and PSI quantum efficiencies and induction of non-photochemical quenching. These changes were also associated with higher limitation in the donor side and lower restriction in the acceptor side of PSI. This later response was closely related to prominent decrease in stomatal conductance and net CO assimilation that could have strongly affected the energy balance in chloroplast, favoring ATP accumulation and NPQ induction. In parallel, NH induced a strong increase in the electron flux to photorespiration and, inversely, it decreased the flux to Rubisco carboxylation. Overall, ammonium supply negatively interacts with excess light, possibly by enhancing ammonium transport towards leaves, causing negative effects on some photosynthetic steps. We propose that high ammonium supply to rice combined with excess light is capable to induce strong delay in D1 protein turnover and restriction in stomatal conductance, which might have contributed to generalized disturbances on photosynthetic efficiency.
在植物中，涉及铵毒性、过量光照和光合作用的机制鲜为人知。我们测试了一个假设，即在高光下高 NH 供应会降低据称具有耐受性的水稻植物的光合作用效率。成熟的水稻植株之前用 10 mM NH 或 10 mM NO 供应，并随后暴露于 400 µmol m s（中度光-ML）或 2000 µmol m s（高光-HL）8 小时。HL 极大地刺激了根部和叶片中 NH 的积累。与供应硝酸盐的植物相比，这些植物在黑暗中 D1 蛋白恢复明显延迟。这些反应与 PSII 和 PSI 量子效率的降低以及非光化学猝灭的诱导有关。这些变化还与供体侧的限制和 PSI 受体侧的限制降低有关。后一种反应与气孔导度的明显下降密切相关，净 CO 同化率降低，这可能强烈影响叶绿体中的能量平衡，有利于 ATP 积累和 NPQ 诱导。同时，NH 诱导向光呼吸的电子流大量增加，相反，它减少了向 Rubisco 羧化的流。总的来说，铵的供应与过量光照相互作用，可能通过增强向叶片的铵转运，对一些光合作用步骤产生负面影响。我们提出，水稻中高铵供应与过量光照相结合，能够强烈延迟 D1 蛋白周转并限制气孔导度，这可能导致光合作用效率普遍受到干扰。
