Solute Leakage in Soybean Seedlings under Various Heat Shock Regimes

The leakage of solute from intact seedlings during incubationunder various heat shock (HS) regimes was studied. ContinuousHS at 40?C did not induce leakage of amino acids, soluble sugarsand electrolytes into the incubation medium, when compared withcontrol incubation at 28?C. Continuous HS at 45?C (lethal treatment)caused leakage to increase continuously and linearly duringa 5-h treatment period. However, brief HS at 47.5?C, (lethaltreatment), unlike continuous HS at 45?C, induced leakage ata slower rate which reached a plateau within 2 to 3 h at 28?C.Preincubation for 2 h at 40?C completely prevented the leakagecaused by the brief HS at 47.5?C, but not that caused by continuous45?C HS. The amount of leakage during 2 h of incubation at 45?Cwas reduced to half by 30 min preincubation at 40?C and wasreduced to a minimal level by 1-h preincubation. Greater reductionof leakage at 45?C HS was observed when an additional 4 h ofincubation at 28?C immediately followed the 40?C preincubation.These results and previous findings (Lin et al. 1984) indicatethat the synthesis and accumulation of HS proteins (HSPs) areimportant for preventing HS-induced leakage from the cells.One of the HSPs, 15 kD in size appeared to be associated withthe plasma membrane. (Received February 12, 1985; Accepted August 30, 1985)