Zakari Shamsu Ado, Zaidi Syed Hassan Raza, Sunusi Mustapha, Dauda Kabiru Dawaki
Institute of Crop Science, College of Agriculture and Biotechnology, Zhejiang University, Hangzhou, 310058, China.
Department of Crop Production, Audu Bako College of Agriculture, Dambatta, Kano, Nigeria.
J Genet Eng Biotechnol. 2021 Nov 23;19(1):177. doi: 10.1186/s43141-021-00275-3.
Leaf senescence occurs in an age-dependent manner, but the rate and timing of leaf senescence may be influenced by various biotic and abiotic factors. In the course of stress, the function, composition, and different components of photosynthetic apparatus occur to be synthesized homogeneously or degraded paradoxically due to different senescence-related processes. Nitrogen (N) deficiency is one of the critical environmental factors that induce leaf senescence, and its incidence may curtail leaf photosynthetic function and markedly alter the genetic information of plants that might result in low grain yield. However, the physiological and genetic mechanism underlying N deficiency regulates premature senescence, and flag leaf function, ROS homeostasis, and intercellular sugar concentration in rice during grain filling are not well understood. In this paper, Zhehui7954 an excellent indica restorer line (wildtype) and its corresponding mutant (psf) with the premature senescence of flag leaves were used to study the effect of different N supplies in the alteration of physiological and biochemical components of flag leaf organ and its functions during grain filling.
The results showed that the psf mutant appeared to be more susceptible to the varying N supply levels than WT. For instance, the psf mutant showed considerably lower Pn, Chl a, Chl b, and Car contents than its WT. N deficiency (LN) decreased leaves photosynthetic activities, N metabolites, but significantly burst O, HO, and relative conductivity (R1/R2) concentrations, which was consistent with the expression levels of senescence-associated genes. Sucrose, glucose, and C/N ratio concentrations increased with a decrease in N level, which was closely associated with N and non-structural carbohydrate translocation rates. Increases in POD activity were positively linked with the senescence-related enhancement of ROS generation under LN conditions, whereas, SOD, CAT, and APX activities showed opposite trends. High N (HN) supply significantly inhibits the transcripts of carbohydrate biosynthesis genes, while N assimilation gene transcripts gradually increased along with leaf senescence. The psf mutant had a relatively higher grain yield under HN treatment than LN, while WT had a higher grain yield under MN than HN and LN.
This work revealed that the C/N ratio and ROS undergo a gradual increase driven by interlinking positive feedback, providing a physiological framework connecting the participation of sugars and N assimilation in the regulation of leaf senescence. These results could be useful for achieving a higher yield of rice production by appropriate N supply and plant senescence regulation.
叶片衰老以年龄依赖的方式发生，但叶片衰老的速率和时间可能受多种生物和非生物因素影响。在胁迫过程中，由于不同的衰老相关过程，光合器官的功能、组成及不同成分会均匀合成或反常降解。氮（N）缺乏是诱导叶片衰老的关键环境因素之一，其发生可能会削弱叶片光合功能，并显著改变植物的遗传信息，进而导致低产量。然而，氮缺乏调控早衰的生理和遗传机制，以及水稻灌浆期旗叶功能、活性氧稳态和细胞间糖浓度尚不清楚。本文利用优良籼型恢复系（野生型）浙恢7954及其旗叶早衰的相应突变体（psf），研究不同供氮水平对灌浆期旗叶器官生理生化成分及其功能变化的影响。
结果表明，psf突变体比野生型对不同氮供应水平更敏感。例如，psf突变体的净光合速率（Pn）、叶绿素a、叶绿素b和类胡萝卜素（Car）含量明显低于野生型。缺氮（低氮，LN）降低了叶片光合活性、氮代谢产物，但显著增加了超氧阴离子（O₂⁻）、过氧化氢（H₂O₂）和相对电导率（R1/R2）浓度，这与衰老相关基因的表达水平一致。随着氮水平降低，蔗糖、葡萄糖和碳氮比浓度增加，这与氮和非结构性碳水化合物转运速率密切相关。在低氮条件下，过氧化物酶（POD）活性增加与衰老相关的活性氧生成增强呈正相关，而超氧化物歧化酶（SOD）、过氧化氢酶（CAT）和抗坏血酸过氧化物酶（APX）活性则呈相反趋势。高氮（HN）供应显著抑制碳水化合物生物合成基因的转录本，而氮同化基因转录本则随着叶片衰老逐渐增加。在高氮处理下，psf突变体的产量相对高于低氮处理，而野生型在中氮（MN）处理下的产量高于高氮和低氮处理。
本研究揭示了碳氮比和活性氧通过相互关联的正反馈逐渐增加，提供了一个连接糖和氮同化参与叶片衰老调控的生理框架。这些结果可能有助于通过适当的氮供应和植物衰老调控实现水稻高产。
