RESPONSE OF MELON PLANTS TO SALT .1. GROWTH, MORPHOLOGY AND ROOT MEMBRANE-PROPERTIES

An excess of NaCl in the growth medium of melon (Cucumis melo L.) seedlings affected growth rate, morphology, and contents of dry weight, chlorophyll, potassium, sodium and chloride in the root and leaf tissues. In roots of seedlings grown in NaCl the electrolyte leakage to iso-osmotic medium was more rapid. Fluorescence polarization measurements revealed that root membranes isolated from these seedlings were significantly less fluid. Chemical analysis disclosed a lower lipid to protein weight ratio in these membranes. The relative contents of phospholipids and free sterols were only slightly affected by excess NaCl. Accordingly, the fluidity of liposomes prepared from lipid extracts of membranes isolated from control and from salt-grown seedlings was similar. The extent of partitioning of the root microsomal membranes between the two phases of aqueous polymer mixtures revealed differences in the surface properties of the root plasma membrane of control and salt-grown seedlings. Possible relationships between the changes in membrane properties and the response to excess salt are discussed.