Low photosynthetic rate under low light stress inhibited sucrose distribution and transportation to grain

Abstract Under the condition of low light, the yield of summer maize decreased significantly, but the decrease of yield under low light stress was not only caused by the lack of photosynthetic assimilates in leaves, but also the transportation and utilization of assimilates by stems and grains. In this study, we investigated the effects of low light stress on leaves, stems and grains of summer maize and the relationship between them. The results showed that the synthesis ability of sucrose and export sucrose to grains ability in leaves decreased under low light. Due to dry matter transfer, the number and area of small vascular bundles in spike node and shank decreased, which restricted the translocation of photoassimilates to grains at filling stage. The activities of SUS and AGPase was decreased in grains under low light stress, which limited the availability of sucrose. The process of leaf synthesis, sucrose loading and sucrose utilization in grains was affected under low light, resulting in relatively higher sucrose concentration in grains than in leaves, forming a “leaf low” - “grain high” sugar concentration gradient, resulting in the opposite hydrostatic pressure, and then feedback inhibition of sucrose output in leaves, reducing sucrose loading and transportation rate. Hightlight The key factor of low light stress reducing summer maize yield was the decrease of leaf photosynthetic rate, resulting in insufficient grain dry matter supply. The sugar concentration gradient between leaves and grains further restricted the sucrose transport from leaves to grains.