Dorsoventral regulation of photosynthetic functions related to morphological and anatomical structures in field-grown sorghum

The rapid dorsoventral regulation of photosynthesis is important because the light conditions around both surfaces of field-grown leaves vary considerably. The photosynthetic asymmetry has been intensively studied, but structure-related explanations for asymmetry were not exactly clarified. This study aimed to investigate the photosynthetic asymmetry in field-grown Sorghum bicolor L. and analyze the impacts of dorsoventral structures on photosynthesis. We found that the photosynthetic asymmetry changed with light conditions, and adaxial surfaces had higher primary photochemical activity owing to higher mesophyll density, while abaxial surfaces had higher CO2-diffusion capacity due to higher stomatal density, substomatal cavities, and contact areas between bundle sheath and mesophyll cells. Moreover, abaxial surfaces could mainly use self-transmitted light (residual light intercepted by adaxial surface) to drive photoreaction which could partly retain high photosynthetic rates in the field. This study can improve our understanding on the photosynthetic dorsoventral regulation.