Effect of Drought Stress on Anatomical Structure and Chloroplast Ultrastructure in Leaves of Sugarcane

In order to provide a reference for investigating the mechanism of drought resistance in sugarcane, variations of chlorophyll content and chloroplast ultrastructure in sugarcane leaves were analyzed. The present research was conducted using sugarcane cultivars, strongly drought-resistant F172 and weakly drought-resistant YL6, as plant materials in pot experiment under controlled greenhouse condition. At elongation stage, the plants were provided different degrees of drought stress: (1) mild drought with 65-70 % of the soil water capacity; (2) moderate drought with 45-65 % of the soil water content; (3) severe drought with 25-45 % of soil water capacity and; (4) control with 70 % of soil water capacity. Chlorophyll content in leaves was measured, and variations of green leaves number and chloroplast ultrastructure were observed. It was found that the green leaves of sugarcane and chlorophyll content were significantly reduced in the process of drought stress. Upper and lower cuticle thickness was getting thickened during drought stress, but the thickness of lower epidermal cuticle of YL6 variety was reduced under severe drought condition. Ultrastructure observation showed that, in most cases, the chloroplasts were close to the cell wall and well arranged, and the chloroplast thylakoids were orderly arranged in the chloroplasts. With the ongoing of drought stress, plasmosis occurred, the chloroplasts moved closer to the center of the cell, and turned gradually from long oval to nearly round, and starch grains increased. Under severe drought conditions, F172 still maintained integrity of the chloroplast structure while the chloroplast in YL6 were severely deformed and became blurred in shape.