Research On Cell Wall Degradation And Related Enzymes Localization In The Developing Aerenchyma Of Wheat Seminals Roots

Aerenchyma formation has been an important mophorlogical adaption to flooding. Wheat is an upland crop, which develops aerenchyma under waterlogging conditions. Aerenchyma formed from the cell wall degradation and cortical cells selectively autolyzed. At present, it has rarely been reported that cell walls changed during the development of aerenchyma. The aim of this study is to show characterize of cortical aerenchyma formation and changes of cell wall during waterlogging in wheat roots (Triticum aestivum L. cv. Huamai8, with high flooding tolerance). The characterize of aerenchyma formation was systemically observed at micro-level; Fluorescence microscopy was used to detect the accumulation of Ca2+in wheat roots; The changes of cell wall was detected and dynamic changes of cellulose, pectinase and polysaccharides were studied at subcellular localization in wheat roots; Cell wall modification-related genes regulating were studied by q-PCR method. The results were as follows:1. The process of aerenchyma formation showed it has been formed by waterlogging in cortical cells. In this process.We also obtained that at the position4showed the highest elongation incidence, besides cells elongation position3and5were also detected. Transmission electron microscopy (TEM) indicated that radial elongation cortical cells are characteristic of PCD, including plasma membrane invagination, double-membrane-bound bodies, degrading vacuole and chromatin condensation to the nuclear periphery. These feactures proved cortical cells were radial elongation with cortical cells PCD.2. The results show that waterlogging6～12h the gap of cortical cells expanded and adjacent cortical cells occurred schizogenous separation, but it’s no change in cell wall. In this process, the cortical wall has been deformed, intercellular layer disappears, the cell wall transparency and began to form breaking local sites. After waterlogging24h, the whole segment of selective degradation of cell wall transparent. Finally (flooded by48h) cell walls degraded and others aggregated together, which resulted in gas spaces formation in a radial direction.3. The cellulase and pectinase activity was stronger at early flooding phase and some places where the cellulase got together become to cell wall degradation sites. After aerenchymal formation (flooded by48h), the activity of cellulase and pectinase was significantly reduced. Cellulase and pectinase directly involved in cell wall degradation. There was an obvious correlation between tissue distribution of cell wall degradation products-polysaccharide and aerenchymal formation. The early stage of waterlogging, lots of polysaccharides deposits were detected and were even-distributed in the cell walls. with the continuing of waterlogging treatment, lots of polysaccharides deposits were still detected but were uneven-distributed in the cell walls. After waterlogging48h, faint polysaccharides deposits were detected in the cell walls but some polysaccharides deposits in the cytoplasm.4. Besides, gene expression analysis showed that the expression level of genes controlling the modification of cell wall were up-regulated during waterlogging. When waterlogging12h, showing the highest up-regulated level and then decreased at24-48h. Cell wall modification-related gene and enzymes change in the synchronization. These results indicated that cell wall modification-related gene might lead to aerenchyma formation.5. In-situ detection of Ca2+showed that Ca2+was an important regulator of cell wall degradation and aerenchymal formation. At the early stage, Ca2+was observed in the cell wall of endodermis, stele and epidermis. With the continuing of waterlogging treatment, at the later stage, Ca2+was accumulated in the cell wall of exodermis and further spread to almost the entire central region of the cortex cells which be exist as the support of aerenchyma. By waterlogging24h, cell walls have begun to degrade and aerenchyma has started to form, Ca2+fluorence accumulation was gradually decreased, only some cells and tissue which as ventilation aerenchyma was detected.These results suggest that the aerenchyma development in wheat roots is also elongated by radial cortical cell. Cell wall modification-related enzymes (cellulase and pectinase) and Cell wall modification-related gene (XET, CEL) study found that the relevant events in the flooded cell wall degrading treatment early (6h) has occurred, while the cell wall degradation in flooded post-treatment (24h) began. The uneven-distribution of cellulase and pectinase in the degradation of the cell wall led to uneven-distribution of polysaccharide content, which may result in the selective degradation of cell wall and aerenchyma formation.