Research Of Water Stress In Relation To New Root And Mesophyll Tissue Cells' Microstructure Of Prunus ArmniacaL

In this research we take the Prunus ArmniacaL as the test materials. The experiments take place in a big shed, and the materials were planted in the 50cm width plastic flowerpots for the water stress. The degree of water stress was graded into three levels: 1) unstressed plots, which marked as control, 2) moderately stressed plots, and 3) severely stressed plots. Water stress resulted in an acceleration of nucleus degradation and a decrease in starch accumulation in the mesophyll parenchyma and in the apical meristem of the root tip areas. Also the water tress resulted in the cell wall ingrowth, an unusual secondary cell wall thickening, in two layers of cortical tissue-adjacent to the endodermis. The cell wall thickened inwardly, but unevenly until it had appearance of an oblong ball. These cells exhibiting the ingrowth formed a single layer ring adjacent to the endodermis of new roots. Cell wall ingrowth subsequently occurred in two layers of the cortex as the roots aged. Using fluorescent microscopy, the casparian strip in the endodermis became much more visible during the second layer of the cell wall ingrowth formed. The anatomical changes, relating to cortical cell ingrowth and the formation of casparian strip in the endodermis may play an important role in protecting Prunus Armniacal roots from water and solute loss. The main conclusions of the observation as follows:(1) Among the different treatments, the degrees of endodermis` cell wall ingrowth are different. Samples marked with severely water stressed are easy to get the observation of the endodermis cell wall ingrowth in the new roots from the root tip to 5mm areas, which meanings the changes appeared very early; also the samples marked with moderately water stress are easy to get the observation of the endodermis cell wall ingrowth, but the change appeared a little later, beyond the areas from the root tip to 1cm; and also we can observe this phenomena in the control experiments, beyond the areas from the root tip to 1.5cm,.which appeared latest.(2) With the increasing time and the degree of water stress, the content of starch accumulation in the mesophyll parenchyma and in the apical meristem of the root tip areas is decreased. Samples marked with control have the most content of starch accumulation; after 15days, the samples marked with severely water stressed have little content of starch accumulation both in the mesophyll parenchyma and in the apical meristem of the root tip areas; the samples marked with moderately have a little content of starch accumulation. (3) Among the different treatment experiments, the degrees of nucleus` activity in the mesophyll parenchyma and in the apical meristem of the root tip areas are different. After 15 days, the control samples` degree of nucleus activity is the highest, which the nucleus are bright and easy to be observed after stained by DAPI and using the fluorescent microscopy; samples, marked with moderately, which the degree of nucleus activity is not so high as the control samples, the content of bright nucleus is not too many; the samples marked with severely water stressed, which the degree of nucleus activity is very low, the nucleus both in the mesophyll parenchyma and the apical meristem of the root tip areas are difficult to be observed.(4)With the increasing time and the degree of water stress, the microstructure of mesophyll tissue had changed some. Palisade tissue cells became much more longer, the tissue present much more thicker, and the cells ranged for 3 to 4 layers, while spongy tissue become thinner, also the intercellular space become smaller. To the vein of the leaves` ambiside, the size of cells presented much smaller. This phenomenon of the cells` size change may play an important role in protecting Prunus Armniacal leaves from water and solute loss.