Instituto de Fisiología Vegetal (INFIVE), Universidad Nacional de La Plata - Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), cc 327, 1900, La Plata, Argentina.
Instituto de Ciencias Polares, Ambiente y Recursos Naturales. Universidad Nacional de Tierra del Fuego, Argentina.
J Exp Bot. 2021 May 18;72(11):3956-3970. doi: 10.1093/jxb/erab125.
In C3 cereals such as wheat and barley, grain filling was traditionally explained as being sustained by assimilates from concurrent leaf photosynthesis and remobilization from the stem. In recent decades, a role for ear photosynthesis as a contributor to grain filling has emerged. This review analyzes several aspects of this topic: (i) methodological approaches for estimation of ear photosynthetic contribution to grain filling; (ii) the existence of genetic variability in the contribution of the ear, and evidence of genetic gains in the past; (iii) the controversy of the existence of C4 metabolism in the ear; (iv) the response of ear photosynthesis to water deficit; and (v) morphological and physiological traits possibly related to ear temperature and thermal balance of the ear. The main conclusions are: (i) there are a number of methodologies to quantify ear photosynthetic activity (e.g. gas exchange and chlorophyll fluorescence) and the contribution of the ear to grain filling (individual ear shading, ear emergence in shaded canopies, and isotope composition); (ii) the contribution of ear photosynthesis seems to have increased in modern wheat germplasm; (iii) the contribution of the ear to grain filling increases under resource-limitation (water deficit, defoliation, or pathogen infection); (iv) there is genetic variability in the contribution of the ear in wheat, opening up the possibility to use this trait to ameliorate grain yield; (v) current evidence supports the existence of C3 metabolism rather than C4 metabolism; (vi) the ear is a 'dehydration avoider organ' under drought; and (vii) thermal balance in the ear is a relevant issue to explore, and more research is needed to clarify the underlying morphological and physiological traits.
在 C3 谷类作物（如小麦和大麦）中，谷物灌浆传统上被解释为通过同时进行的叶片光合作用和从茎部再转移来维持。近几十年来，耳光合作用作为灌浆贡献者的作用已经出现。这篇综述分析了这个主题的几个方面：（i）估计耳光合作用对灌浆贡献的方法学方法；（ii）耳贡献的遗传变异的存在，以及过去遗传增益的证据；（iii）耳中存在 C4 代谢的争议；（iv）耳光合作用对水分亏缺的响应；以及（v）可能与耳温度和耳热平衡有关的形态和生理特征。主要结论是：（i）有许多方法可以量化耳光合作用活性（例如气体交换和叶绿素荧光）和耳对灌浆的贡献（单个耳遮光、遮光树冠中出现的耳、和同位素组成）；（ii）耳光合作用的贡献似乎在现代小麦种质中有所增加；（iii）在资源限制下（水分亏缺、刈割或病原体感染），耳对灌浆的贡献增加；（iv）小麦中耳对灌浆的贡献存在遗传变异，为利用这一特性来改善粒产量提供了可能性；（v）目前的证据支持 C3 代谢而不是 C4 代谢的存在；（vi）在干旱条件下，耳是一种“避免脱水的器官”；（vii）耳的热平衡是一个需要探索的相关问题，需要更多的研究来阐明潜在的形态和生理特征。
