Osmotic Adaptation in Panicum repens. Differences Between Organ, Cellular and Subcellular Levels

The process of osmotic adaptation was studied in leaves of Panicum repens. Two phases were observed: the first phase, which continued for 2–4 days, was mainly characterized by dehydration of leaves, a fast synthesis of organic acids and penetration of sodium into leaf cells. Chloride becomes dominant in the leaves only from the third day of exposure and onwards. The second phase of adaptation lasted for 4–6 days. During this phase, a decrease in organic acid content and an increase in leaf‐chloride content was observed. In spite of the fact that the osmotic potential of the leaves reached lower values than that of the external medium already after 2 days, the rate of growth of the plants was hampered. Such inhibition of growth disappeared 6–8 days after exposure to salinity. Ion content of the cell walls, chloroplasts and vacuoles of Panicum leaf cells was investigated during the various stages of osmotic adaptation. An increase in sodium and chloride content of the cell walls during the early period of adaptation probably prevented the full osmotic adaptation of the protoplasts. It is suggested that a locally unbalanced distribution of ions may be one of the reasons for the decrease in growth rate during the process of osmotic adaptation and frequently after that.