Effects of Exposures of Seeds to Various Physical Agents. II. Physiological and Chemical Aspects of Heat Injury in the Red Kidney Bean Embryo. Contributions from the Hull Botanical Laboratory 640

Abstract

Investigations were made on physiological and chemical changes associated with heat injury (exposure to 100[degree]C. or 103[degree]C. for periods up to 45 min.) in the excised embryonic axis of Red Kidney bean. Heat injury was partially relieved by visible light; the relative stimulatory effect of light on elongation increased with increasing severity of treatment. It is noted that photostimulation as a concomitant of heat injury is not limited to this sp. Indole-3-acetic acid was found to alleviate heat injury (i. e., promote growth) at a concn. inhibitory to control plants. Injury was markedly reduced when embryos were heated under reduced O2 tension; application of cysteine to heat-injured embryos was also compensatory to a limited extent. Respiratory activity of heat-injured embryos was retarded but tended to approach the control rate as incubation progressed. Heat injury was not associated with reduction in amyloclastic and catalase activities, but peroxidase was reduced 21%. Distr. studies revealed the reduction in peroxidase to be localized in the root and the normal gradient of peroxidase activity to be disturbed. Changes in carbohydrate and N fractions during the incubation were essentially similar in control and heat-injured plants. Permeability in heat-injured embryos was markedly increased. It is suggested that: (a) oxidation is an important factor in heat injury, and in Red Kidney bean embryos its effects are largely irreversible; (b) parallels may be drawn between the reactivation by light of heat-injured embryos and the photoreactivation of ultraviolet-inactivated microorganisms; (c) of the metabolic features studied, only the localized reduction in root peroxidase can be correlated with loss of viability; (d) in many respects heat injury may operate as an accelerated aging process.