LAUSR

C4 plants supply concentrated CO2 to bundle sheath (BS) cells, improving the photosynthetic efficiency by suppressing photorespiration. Mesophyll chloroplasts in C4 plants redistribute toward the side of the BS cells (aggregative movement) in response to environmental stresses under light. Although this chloroplast movement occurs commonly in C4 plants, the significance and mechanisms underlying the aggregative movement remain unknown. Under environmental stresses such as drought and salt, CO2 uptake from the atmosphere is suppressed by closing stomata to prevent water loss. We hypothesized that CO2 limitation may induce the aggregative movement. In this study, the mesophyll chloroplast arrangement in the leaf of finger millet, an NAD-malic enzyme-type C4 plant, was examined under different CO2 concentrations and light conditions. CO2 limitation around the leaves promoted the aggregative movement, but the aggregative movement was not suppressed even at the higher CO2 concentration than the atmosphere, under high intensity blue light. In addition, mesophyll chloroplast did not change their arrangement under dark or red light. From these results, it can be concluded that CO2 limitation is not a direct inducer of the aggregative movement but would be a promoting factor of the movement under high intensity blue light.