近日，華中農(nóng)業(yè)大學(xué)資源與環(huán)境學(xué)院作物養(yǎng)分管理團(tuán)隊(duì)在The Plant Journal上發(fā)表了題為“Photosynthetic plasticity aggravates the susceptibility of magnesium-deficient leaf to high light in rapeseed plants: the importance of Rubisco and mesophyll conductance”的研究論文，揭示了充足的鎂營(yíng)養(yǎng)緩解葉片光氧化損傷的光合生理機(jī)制。
我國(guó)農(nóng)田土壤有效鎂缺乏面積占比超過(guò)60%，鎂營(yíng)養(yǎng)缺乏逐漸成為繼氮磷鉀缺乏后限制作物產(chǎn)量和品質(zhì)的重要因子。缺鎂植株吸收的光能超過(guò)自身光合所需時(shí)會(huì)造成葉片光氧化，表現(xiàn)出“脈間失綠”的典型癥狀，且光照越強(qiáng)，損傷越嚴(yán)重。這主要是由于缺鎂導(dǎo)致葉片光能吸收與利用的不匹配，致使較多的電子與氧氣結(jié)合生成氧自由基，進(jìn)而引發(fā)葉綠體降解造成的，但目前對(duì)鎂營(yíng)養(yǎng)如何調(diào)控光能吸收與利用的平衡缺乏系統(tǒng)的認(rèn)識(shí)。
本研究分析了不同光強(qiáng)下油菜植株對(duì)缺鎂脅迫的響應(yīng)及其光氧化調(diào)控過(guò)程。結(jié)果顯示，缺鎂導(dǎo)致葉片能量過(guò)剩并誘發(fā)光氧化損傷，高光加劇了植株能量吸收與利用的不平衡，使缺鎂癥狀更明顯。葉片光能利用率的降低是導(dǎo)致能量失衡的主要原因，其中，Rubisco酶失活和底物CO2供給減少對(duì)光能利用率降低的貢獻(xiàn)達(dá)60%~70%。在高光環(huán)境下，葉片Rubisco酶含量及活性和葉肉導(dǎo)度（CO2從氣孔下腔傳輸至葉綠體羧化位點(diǎn)的效率）顯著增加，因此需要更多的鎂以維持Rubisco酶的高活化率和較高的葉綠體CO2吸收表面積，從而最大限度地利用吸收的光能。綜上所述，植物對(duì)高光強(qiáng)的適應(yīng)性變化有助于葉片光能吸收與利用的平衡，但同時(shí)也增加了對(duì)營(yíng)養(yǎng)元素的生理需求，若鎂營(yíng)養(yǎng)缺乏，葉片能量失衡將加劇，光氧化損傷癥狀也會(huì)更明顯。
資源與環(huán)境學(xué)院博士研究生葉曉磊為論文第一作者，陸志峰副教授為通訊作者。土耳其薩班哲大學(xué)Ismail Cakmak教授，華中農(nóng)業(yè)大學(xué)魯劍巍教授、任濤教授、李小坤教授和叢日環(huán)副教授參與了研究工作。該研究得到了國(guó)家自然科學(xué)基金、中央高校基本科研業(yè)務(wù)費(fèi)、國(guó)際鎂營(yíng)養(yǎng)研究所和國(guó)家農(nóng)業(yè)綠色發(fā)展研究院鎂素營(yíng)養(yǎng)研究中心的資助。
【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.
論文鏈接：http://doi.org/10.1111/tpj.16504
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