Research On The Morphological Characteristics Related To The Development Process And The Function Of Short Cells In Epidermis Of Maize

Short cells are specialized epidermal cells, such grass as maize (Zea mays L.), including cork cells and silica cells. Mature cork cells are living cells with suberized cell wall, while silica cells are dead cells filled with siliceous bodies. In the different plants or different parts of the same plants, the two cells are different on the generation time, the morphological change, distribution and the count. So far, it is not refer to the systematic reports about the morphological characteristics of short cells in epidermis of maize, and for cork cells with large nucleus and a variety of abundant organelles, in addition to as the sisters of silica cells only make it reported about the development process and characteristics, the function report of cork cells is almost blank. In this study, a popular maize cultivar "Zhengdan 958" was used as material, grown in fields and pot, leaves epidermis of maize were torn, fixed, stained via combining the simple staining, counterstaining, fluorescence and other cytological chromogenic methods, and observed through optical microscopy, fluorescence microscopy, scanning electron microscopy and transmission electron microscopy. The generation time, developmental process, distribution, morphological structure and ultrastructure characteristics of short cells in epidermis of maize, the relationship of K+ and H2O2 distribution change of cork cells with those in other epidermal cells and the stomatal switch in light/dark and different water stress [soil water content was 75%～85% of field capacity, (CK); 65%～75% of field capacity, (LS); 55%～65% of field capacity, (MS); 45%～55% of field capacity, (SS)], and the effects of the short cells on photosynthetic characteristics of maize leaves were investigated. The results and the conclusion showed that:(1) The generation time:short cells appeared when new epidermal tissue in the multi-leaf positions of maize formed, and the generation occurred in all plants from the seventh new leaf, the base of the sixth leaf of most plants and the fifth leaf of few plants, and appeared in all later grown leaves. Short cells density of different parts of leaf increased with leaf position elevating. No short cells were found in the four initial leaves of all plants (because of no further growth).(2) The developmental process:the initial leaf epidermal cells divided asymmetrically to produce alternating long and short epidermal cells. Some short epidermal cells divided horizontally (vertical to leaf vein) and formed cork and silica cells pairs. The cork cells base were adjacent to the mesophyll cells while the silica cells were embedded top between cork cells and epidermal cells, two cells were not in the same plane.(3) The morphological structure and ultrastructure characteristics:the leaves with short cells, macrocosmically, the back of leaves was bright and covered with waxy layer, and the staining character of epidermal cells changed from a microcosmic perspective. The mature cork cells were bread-shaped columnar cells while the silica cells were dumbbell flat cells. Ultrastructure level, the cork cells had abundant mitochondria, rough endoplasmic reticulum, ribosome, and the nucleus was bigger, as the living cells; and the silica cells of height fibrosis and lignification, were without the nucleus and other organelles, as the dead cells.(4) The relationship between K+ and H2O2 accumulation of short cells (cork cells) and the stomatal switch:in light, the stomat opened, no K+ or H2O2 was in cork cells; while in dark, the stomat closed, a large amount of K+ and H2O2 accumulation can be found in cork cells; along with the increase of water stress, the stomata aperture decreased significantly, and the accumulation of K+ and H2O2 in cork cells increased gradually. Under different treatment, the K+ and H2O2 accumulation in cork cells changed periodically along with the stomatal switch, and was consistent with those in subsidiary cells, while no K+ or H2O2 accumulation in silica cells and long cells.(5) The effects of the short cells on photosynthetic characteristics of maize leaves:the effects of the short cells on the increasing photosynthetic function of leaves. Compared to the same parts of the different leaves, and the different leaves of the same leaf positions, the leaves with short cells were increased on net photosynthetic rate, stomatal conductance and transpiration rate, but the intercellular CO2 concentration decreased compared to those without short cells, the leaves photosynthetic capacity in 12:00 was higher than 15:00.The conclusion:The generation time of short cells in epidermis of maize was identified, the morphological variation characteristics of developmental process was showed, and the accumulation of K+ and H2O2 in cork cells changed periodically along with the stomatal switch was found, moreover, it was consistent with those in subsidiary cells, and the effects of the short cells on the increasing photosynthetic function of leaves were also found in the study.