Comparative study on the different responses of maize photosynthesis to systemic regulation under light heterogeneity.

Photosynthetic performance of a leaf is widely recognized to be systemically regulated by distal parts within the same plant. However, the effects of systemic regulation on different plant materials cannot be generalized. In this work, two cultivars of maize (Zea mays L.), 'Rongyu 1210' (RY) and 'Zhongdan 808' (ZD), were selected for a comparative study on the different responses of photosynthesis to light-dependent systemic regulation. After the growth of plants in heterogeneous light, the net photosynthetic rate of newly developed leaves increased in RY but decreased in ZD. A distinct capacity of CO2 fixation and assimilation between these two cultivars is also suggested. In ZD, the area of vascular bundles declined obviously, suggesting a restriction on carbohydrate export, which is also indicated by an increase in starch content. Resulting excessive accumulation of carbohydrates is proposed to inhibit the carbon assimilation, and eventually the photosynthesis. A decline in the area of bundle sheath cells also suggests a restriction on carbon assimilation. In contrast, these restrictions were unlikely to present in RY. This study reveals that the response of leaf photosynthetic performance to light heterogeneity is largely dependent on the systemic regulation of carbon assimilation, as well as carbohydrate export in maize.