| The involvement of heat shock in the induction of chilling tolerance was investigated on 36 h germinated cucumber (Cucumis sativus cv Ashley) seedling roots. Heat shock reduced the chilling-induced electrolyte leakage, and resulted in a greater total root growth after chilling compared to the control. Heat shocks of 40{dollar}spcirc{dollar}C for time periods ranging from 1 to 16 h resulted in increased chilling tolerance in a time dependent manner, reaching a peak with 12 h of heat shock. The heat shock induction of chilling tolerance was most effective when imposed immediately before chilling, and the effect persisted for up to 24 h after heat shock when seedlings were held at 25{dollar}spcirc{dollar}C before chilling.; Total protein analysed by SDS PAGE and two dimensional PAGE revealed the presence of four proteins, with relative molecular weights of 74, 67.4, 60.2, and 47.3 kD, which were enhanced by heat shock, and a new 19 kD protein. Among these proteins, the 74 and 19 kD proteins were correlated with heat shock induced chilling tolerance and its persistence. The role(s) of heat shock proteins in the induction of chilling tolerance is discussed.; A 96 h chilling at 2{dollar}spcirc{dollar}C significantly increased the malondialdehyde (MDA) level, suggesting increased peroxidative damage of membrane lipids. Chilling also promoted catalase (CAT) activity, but severely suppressed the activity of peroxidase (POD). Heat shock significantly reduced the MDA level and CAT activity, but increased POD activity. These effects of heat shock were observed both before and after chilling, and became greater with increased heat shock time up to 16 h. When seedlings were held at 25{dollar}spcirc{dollar}C after a 4 h heat shock, the heat shock effect on MDA and CAT disappeared at about 24 and 16 h respectively, while the POD activity was further increased. Heat shock may have a direct effect on induction of POD activity, whereas the level of CAT activity may simply reflect a low level of reactive oxygen species, particularly H{dollar}sb2{dollar}O{dollar}sb2.{dollar}... |
