MEASUREMENT OF CELL-MEMBRANE STABILITY EVALUATED BY ELECTROLYTE LEAKAGE AS A DROUGHT AND HEAT TOLERANCE-TEST IN RICE (ORYZA-SATIVA L)

To explore possibilities of adaptation of cell membrane stability meas urement as a evaluation of drought and heat tolerance (or injury) in r ice (Oryza sativa L.), we have measured electrolyte leakage (EL) from leaf discs exposed to desiccation and temperature stresses. In desicca tion test with polyethylene glycol (PEG), EL increased from 10% to 80% with increasing from 20% to 60% of PEG concentration [PEG]. We have u sed 30% of [PEG] at which 25% of EL was occured. EL was increased with the time of PEG treatment; accordingly, 24 hours as a period of subme rged leaf were selected. We have investigated an optimal temperature a nd treatment period, and around 42 degrees C is likely to be suitable for testing membrane thermostability. EL was increased almost linearly with the time of leaf tissues submerged in test temperature (42 degre es C) solution; we selected 24 hours for the following experiments. EL of PEG test was greater in senescing leaf (the 4th leaf from the youn gest fully expanded leaf) than leaf in which senescence is less advanc ed (the youngest fully expanded leaf). EL of leaf tissue was also incr eased with water deficit, indicating physiological status of plant its elf can be reflected by the technique. Therefore, this technique is co nsidered to be useful to assess injury, presumably at the membrane lev el, resulting from an environmental stress in rice.