[Responses of stomata and Kranz anatomy of maize leaves to soil water shortages].

Seedlings of the popular maize cultivar "Zhengdan-958" growing in pots individually were exposed to suitable soil water conditions as control, light water shortage, moderate water shortage, and severe water shortage, corresponding to soil water contents between 75%-85%, 65%-75%, 55%-65%, and 45%-55% of field water capacity, respectively. Responses of stomatal aperture, Kranz anatomy, and vascular bundle structure to different water contents of maize leaves were investigated. Results showed that under increased water shortages, the levels of H2O2 in both guard cells and subsidiary cells were enhanced, also the fluorescence intensity of H2O2 labeled with fluorescent dye increased, while stomatal aperture and conductance decreased gradually. Moreover, Kranz cells were messily arranged and the cell size became smaller and smaller, and the structure of bundle sheath cells went irregular; and the sectional area of the big bundle and xylem, the cell number of phloem, and the thickness of whole leaf and of upper and lower epidermis reduced. In addition, the number of chloroplasts in mesophyll cells and vascular bundle sheath cells decreased, particularly under the moderate water deficit, chloroplasts in Kranz cells which located in the inside of cytoplasmic membrane and cling on the cell wall spread to the direction of cell center. It demonstrated that stomatal closing of maize could be regulated by H2O2 in guard cells and subsidiary cells together, and H2O2 in subsidiary cells maybe played a cooperative role. In conclusion, under increased soil water shortages, drought-induced H2O2 accumulations in both guard cells and subsidiary cells of maize leaves participated in the regulation of stomatal closing. And, the size of Kranz cells and bundle sheath cells, the cell number of phloem, and the area of the xylem and phloem re- duced, thereby, reducing water shortage-induced damage.

[Effects of water deficit at seedling stage on maize root development and anatomical structure].

A pot experiment was conducted to study the effects of water deficit at seedling stage on the root development and anatomical structure of maize. Four treatments were installed, i.e., 75%-85% of field capacity (control), 65%-75% of field capacity (light deficit), 55%-65% of field capacity (moderate deficit), and 45%-55% of field capacity (heavy deficit). Drought stress inhibited the plant growth. With increasing drought stress, the root length, diameter, and total biomass reduced, while the root vigor, root/shoot ratio, and root apex polysaccharide content increased. Under moderate water deficit, the branch root hair length, root hair density, and total length of root hair reached to the maximum. Anatomical observation showed that the decrease of root diameter was mainly due to the decrease of root central cylinder area and of root vessel diameter. No significant difference was observed in the root vessel number among the treatments, but the root vessel wall became irregular under water deficit. The increase of root apex polysaccharide content mainly occurred in the epidermal cells and pileorhiza cells. In epidermis cells, the polysaccharide was mainly in dissociation, while in pileorhiza cells, polysaccharide was mainly as starch grains. In sum, under water deficit, maize root could alter its vessel structure, increase the polysaccharide content in epidermal cells and pileorhiza cells, and expand the total surface area of root hair to enhance the water-absorbing ability of hair root, and to strengthen the drought resistance of maize. However, with the increase of water deficit, root hair didn't have unrestrictive growth, while in adverse, its growth was inhibited or damaged under severe drought.