Stomatal density affects rice mesophyll cell size and shape and modulates a conserved pattern of cells through the leaf

The structure of the mesophyll influences how light, CO2 and water travels inside a leaf, affecting the rates of both photosynthesis and transpiration. Recent studies in wheat and Arabidopsis have shown that the structure of the mesophyll is influenced by the density and activity of stomata, consistent with the hypothesis that gas flow via stomata can modulate internal cell growth and separation to co-ordinate leaf structure and function. To investigate whether this also occurs in rice, a staple food crop for a large fraction of the worlds population, we examined mesophyll structure in rice mutants with altered stomatal density. Our data show that stomatal function modulates mesophyll structure in rice. Variation in the degree of mesophyll lobing made a major contribution to altered mesophyll structure, suggesting that modified leaf gas flux through stomata influences an aspect of cell shape directly linked to gas exchange capacity in rice. In addition, our analysis revealed a previously unreported underlying pattern in cell size, shape and axiality across layers of the rice mesophyll, which further investigation revealed is present in a range of rice species and cultivars. The potential origin and significance of this mesophyll patterning are discussed. HIGHLIGHTWe describe a previously unreported cellular pattern in rice leaves and show that it is modulated by stomata. These results shed new light on leaf structure and function.