Photosynthesis across African cassava germplasm is limited by Rubisco and mesophyll conductance at steady state, but by stomatal conductance in fluctuating light
Photosynthesis across African cassava germplasm is limited by Rubisco and mesophyll conductance at steady state, but by stomatal conductance in fluctuating light
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DOI：
10.1111/nph.16142
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发表时间：
2019-10-01
期刊：
影响因子：
9.4
通讯作者：
Long, Stephen P.
中科院分区：
文献类型：
--
作者：
De Souza, Amanda P.;Wang, Yu;Long, Stephen P.
预计到2035年，撒哈拉以南非洲的粮食需求将增长55%，木薯是那里种植最广泛的作物，也是主要的卡路里来源。然而，13年来，该地区的木薯产量并没有显著增加。遗传产量潜力的提高是第一次绿色革命的基础，可以通过提高光合作用效率来实现。首先，必须了解限制光合作用的因素及其在现有种质中的遗传变异性。分析了13个偏爱农场和高产的非洲品种在稳态和波动光下叶片光合作用CO2吸收的生化和扩散限制。开发了一个木薯叶片代谢模型，以量化克服叶片光合作用限制的价值。在稳态时，活体Rubisco活性和叶肉电导占极限的84%。在阴阳过渡的非稳态条件下，气孔导度是主要的限制因素，导致一天中CO2吸收和水分利用效率分别损失13%和5%。磷酸三糖的利用虽然足以支持观察到的速率，但除非自身得到改善，否则将把叶片光合作用的改善限制在33%以内。木薯品种间碳同化在非稳态条件下的差异是稳态条件下的3倍，为提高木薯的光合作用效率指明了被忽视的重要育种目标。
Sub-Saharan Africa is projected to see a 55% increase in food demand by 2035, where cassava (Manihot esculenta) is the most widely planted crop and a major calorie source. Yet, cassava yield in this region has not increased significantly for 13 yr. Improvement of genetic yield potential, the basis of the first Green Revolution, could be realized by improving photosynthetic efficiency. First, the factors limiting photosynthesis and their genetic variability within extant germplasm must be understood. Biochemical and diffusive limitations to leaf photosynthetic CO2 uptake under steady state and fluctuating light in 13 farm-preferred and high-yielding African cultivars were analyzed. A cassava leaf metabolic model was developed to quantify the value of overcoming limitations to leaf photosynthesis. At steady state, in vivo Rubisco activity and mesophyll conductance accounted for 84% of the limitation. Under nonsteady-state conditions of shade to sun transition, stomatal conductance was the major limitation, resulting in an estimated 13% and 5% losses in CO2 uptake and water use efficiency, across a diurnal period. Triose phosphate utilization, although sufficient to support observed rates, would limit improvement in leaf photosynthesis to 33%, unless improved itself. The variation of carbon assimilation among cultivars was three times greater under nonsteady state compared to steady state, pinpointing important overlooked breeding targets for improved photosynthetic efficiency in cassava.