Leaf Anatomical Structure, Physiological And Biochemical Changes In Different Sugarcane Cultivars Under Drought Stress

Sugarcane is a grassy crop grown in tropical and subtropical areas. Guangxi is the main sugarcane producer in China, and cane sugar industry is one of the most important economic pillars in Guangxi. Sugarcane growth duration is long, and the plants are tall and large, requiring large amount of water. Most of the sugarcane in Guangxi is grown in hilly, shallow tillage layer and rain-fed upland areas, therefore, sugarcane crop is seriously affected by drought that results in great economic losses.The present study employed strong drought resistant sugarcane cultivars F172and GT21and drought susceptible cultivars YT93-159and YL6as the plant materials, which were grown in pots. The plants were treated with varied degrees of drought stress:mild drought,65%-70%of the soil water capacity; moderate drought,45%-65%of the soil water content; severe drought,25%-45%of soil water capacity and; control,75%of soil water capacity. The changes of leaf stomata, anatomical structure and chloroplast ultrastructure of sugarcane in different drought stresses were analyzed using scanning electron microscopy, transmission electron microscopy and other techniques to investigate the cytological mechanism of drought resistance of sugarcane, and to provide the reference for screening drought resistant sugarcane cultivars. The main results were as follows.1. The results of leaf stomatal observation showed that the stomata were gradually closed, the length and width of stomatal apparatus were gradually getting smaller, and the stomatal density and stomatal closure percentage were increased under drought stresses. After rehydration, the stomata gradually opened, however, the drought resistant cultivars F172and GT21changed more but recovered faster after rehydration as compared with the drought susceptible cultivars. It is suggested that there are better morpho-physiological basis and self regulatory capacity in drought resistant cultivars than those of drought susceptible cultivars.2. The anatomical structure analyses indicated that the leaf thickness, areas of bulliform cells and adjacent parenchyma cells, length and width of chloroplasts showed a gradually downward trend under drought stress, but the changes were greater in F172and GT21than in TY93-159and YL6, and so was recovery after rehydration. The thickness of upper and lower stratum corneum in sugarcane leaves was getting thickened under drought stress, and returned to normal condition after rehydration. Under drought stress, the cell injury degree was lower in the drought resistant cultivars than in the drought susceptible cultivars which suggested that drought resistant cultivars have much better cytological basis than the drought susceptible cultivars.With time course of drought stress, direction of chloroplast arrangement in F172changed since the grana lamellae became loose and unclear though the chloroplasts kept intact in morphology. For YL6, however, the chloroplast showed looser, severely deformed and blurred. The ratio of width to length was much higher in YL6than in F172, indicating that F172is much more drought resistant than YL6.3. The water content in leaves, green leaves/plant, stomatal conductance, chlorophyll content and specific leaf weight showed varied degrees of decline under drought stress in the4cultivars. Under severe drought condition, these indexes showed higher in F172and GT21than in YL6and YT93-159, and the recovery was also faster in the former than in the latter cultivars after rehydration.