近日，华中农业大学资源与环境学院作物养分管理团队在The Plant Journal上发表了题为“Photosynthetic plasticity aggravates the susceptibility of magnesium-deficient leaf to high light in rapeseed plants: the importance of Rubisco and mesophyll conductance”的研究论文，揭示了充足的镁营养缓解叶片光氧化损伤的光合生理机制。
我国农田土壤有效镁缺乏面积占比超过60%，镁营养缺乏逐渐成为继氮磷钾缺乏后限制作物产量和品质的重要因子。缺镁植株吸收的光能超过自身光合所需时会造成叶片光氧化，表现出“脉间失绿”的典型症状，且光照越强，损伤越严重。这主要是由于缺镁导致叶片光能吸收与利用的不匹配，致使较多的电子与氧气结合生成氧自由基，进而引发叶绿体降解造成的，但目前对镁营养如何调控光能吸收与利用的平衡缺乏系统的认识。
本研究分析了不同光强下油菜植株对缺镁胁迫的响应及其光氧化调控过程。结果显示，缺镁导致叶片能量过剩并诱发光氧化损伤，高光加剧了植株能量吸收与利用的不平衡，使缺镁症状更明显。叶片光能利用率的降低是导致能量失衡的主要原因，其中，Rubisco酶失活和底物CO2供给减少对光能利用率降低的贡献达60%~70%。在高光环境下，叶片Rubisco酶含量及活性和叶肉导度（CO2从气孔下腔传输至叶绿体羧化位点的效率）显著增加，因此需要更多的镁以维持Rubisco酶的高活化率和较高的叶绿体CO2吸收表面积，从而最大限度地利用吸收的光能。综上所述，植物对高光强的适应性变化有助于叶片光能吸收与利用的平衡，但同时也增加了对营养元素的生理需求，若镁营养缺乏，叶片能量失衡将加剧，光氧化损伤症状也会更明显。
资源与环境学院博士研究生叶晓磊为论文第一作者，陆志峰副教授为通讯作者。土耳其萨班哲大学Ismail Cakmak教授，华中农业大学鲁剑巍教授、任涛教授、李小坤教授和丛日环副教授参与了研究工作。该研究得到了国家自然科学基金、中央高校基本科研业务费、国际镁营养研究所和国家农业绿色发展研究院镁素营养研究中心的资助。
【英文摘要】
Plants grown under low magnesium （Mg） soils are highly susceptible to encountering light intensities that exceed the capacity of photosynthesis （A）， leading to a depression of photosynthetic efficiency and eventually to photooxidation （i.e., leaf chlorosis）。 Yet, it remains unclear which processes play key role in limiting the photosynthetic energy utilization of Mg-deficient leaves, and whether the plasticity of A in acclimation to high irradiance could have cross-talks with Mg nutrition, hence accelerating or mitigating the photodamage. We investigated the high-light acclimation responses of rapeseed plants （Brassica napus） grown under low and adequate Mg conditions. Magnesium deficiency considerably decreased rapeseed growth and leaf A, to a greater extent under high than under low light intensity, which is associated with higher level of superoxide anion radical and more severe leaf chlorosis. This difference was mainly attributable to a greater depression in dark reaction of photosynthesis under high light condition, with a higher Rubisco fallover and a more limited mesophyll conductance to CO2. Plants grown under high irradiance enhanced the content and activity of Rubisco and mesophyll conductance to optimally utilize more light energy absorbed. However, Mg deficiency could not fulfill the need to activate the higher level of Rubisco and Rubisco activase in leaves of high-light-grown plants, leading to lower Rubisco activation status and carboxylation rate. Additionally, Mg-deficient leaves under high light invested more carbon per leaf area to construct a compact leaf structure with smaller intercellular airspaces, lower surface area of chloroplast exposed to intercellular airspaces and CO2 diffusion conductance through cytosol. These caused a more severe decrease in within-leaf CO2 diffusion rate and substrate availability that is essential for Rubisco carboxylation. Taken together, plant plasticity helps to improve photosynthetic energy utilization under high light but aggravates the photooxidative damage once the Mg nutrition becomes insufficient.
论文链接：http://doi.org/10.1111/tpj.16504
日期：2023-11-07
