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 measurement as a evaluation of drought and heat tolerance (or injury) in rice (Oryza sativa L.), we have measured electrolyte leakage (EL) from leaf discs exposed to desiccation and temperature stresses. In desiccation test with polyethylene glycol (PEG), EL increased from 10% to 80% with increasing from 20% to 60% of PEG concentration [PEG]. We have used 30% of [PEG] at which 25% of EL was occurred. EL was increased with the time of PEG treatment; accordingly, 24 hours as a period of submerged leaf were selected. We have investigated an optimal temperature and 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 degrees C) solution; we selected 24 hours for the following experiments. EL of PEG test was greater in senescing leaf (the forth leaf from the youngest fully expanded leaf) than leaf in which senescence is less advanced (the youngest fully expanded leaf). EL of leaf tissue was also increased with water deficit, indicating physiological status of plant itself can be reflected by the technique. Therefore, this technique is considered to be useful to assess injury, presumably at the membrane level, resulting from an environmental stress in rice