The Impact Of Dehydration Stress On The Apoplasts And The Micro-environment Of Cells In Plant Leaves

The life process of plants is often subjected to various environmental stresses. One of such stress is dehydration stress that results in the changes in the apoplasts or micro-environments of cells, leading to subsequent secondary changes in the physiological processes of plant cells. However, the issue has attracted little attention up to now, perhaps due to the lack of a convenient and reliable method. For this reason, we have made an approach to the development of a novel or modified method to investigate the changes in the concentration of apoplastic ions under dehydration stress. The principle of the method is a combination of apoplastic perfusion with bidistilled water and the press-out of the apoplastic solution mixed with the perfused water, with the application of a pressure chamber commonly used in the determination of plant water potential. In practice, the plant twigs being investigated were first sealed into the pressure chamber with the cut end in the chamber immersed in bidistilled water filled into the chamber in advance, with the leaves on the twig protruding to the atmosphere, then the chamber was pressurized to force water into all the leaves on the twig in the same way as the root pressure. Afterwards the twig was take out from the chamber and put upward down into the chamber again with the cut end of the twig protruding to the atmosphere, then the chamber was pressurized to press the the apoplastic solution mixed with the perfused water out of the cut end. The method has the advantages of both the methods of pressure squeeze and vacuum infiltration, but has eliminated the disadvantages of the injuries caused by over pressurization and anoxia. In this way the the impact of dehydration stress on the apoplasts and the micro-environment of cells in plant leaves in Forsythia suspense (Thunb.) Vahl and Euonymus japonicus Thunb. were studied and analysed. The results showed that the leakage of electrolytes from cells to apoplastic spaces increased with the increase in the intensity of dehydration stress. However, in contrast to the conventional view that dehydration stress will result in enhanced permeability of plasma membrane, our result showed that the rate of electrolyte leakage did not show significant change in the dehydration process, although the amount of sodium and potassium did increase with elevated dehydration levels. The stepwise analysis showed that the increase in apoplastic ions was due to the accumulation of ions in the efflux following the dehydration process rather than the enhanced permeability of plasma membrane. Although dehydration stress resulted in the increases in sodium and potassium concentrations both in the symplasts and apoplasts of both plants, the increases in the apoplasts were much faster, leading to the alteration of the ion gradient as well as the shift of membrane potential across the cell membrane. These changes may bring secondary physiological changes to plants under dehydration stress.