Preconditioning of Tobacco and Bean Leaves to Heat Shock by High Temperature or NaCl

The present paper examines whether leaves subjected to heat or salt pretreatment are better adapted to heat shock than untreated leaves. Such adaptation could result from either acquired thermo‐stability and/or better recovery. The rates of metabolic processes such as ¹⁴CO₂ fixation, ¹⁴C‐leucine incorporation into the TCA insoluble fraction, ³²P incorporation into phospholipids and ³⁶Cl efflux were used as indicators of adaptability. It was found that pretreatments (heat or salt) protect leaves only slightly against the short‐term effects of a heat treatment, but have a pronounced effect on recovery. Cytokinin level was reduced by heat shock, and as in the case of metabolic response, pretreatment had no effect on this reduction.