Date of Award

Fall 1995

Project Type

Dissertation

Program or Major

Plant Biology

Degree Name

Doctor of Philosophy

First Advisor

Leland Jahnke

Abstract

Light absorbed by photosynthetic pigments must be distributed either for chemical work, reemitted as fluorescence or safely dissipated as heat. Adverse environmental conditions reduce the dissipation capacity of plants and the excess energy leads to damage to the photosynthetic mechanism, termed photoinhibition. Low, non-freezing temperatures cause such photoinhibition, especially in tropical plants grown in the temperate zone. This damage occurs in the photosystem II and is triggered by highly reactive radicals or reactive forms of dioxygen. Numerous studies point to the involvement of oxygen and antioxidant enzymes and substrates in amelioration of these damages. In C$\sb3$ plants, dioxygen is thought to offer some protection against photoinhibition by functioning as energy sink in the process of photorespiration and Mehler reaction. In C$\sb4$ plants this has not been previously investigated.

The goal of this research was to investigate the role of oxygen and antioxidants in low temperature photoinhibition by comparing two C$\sb4$ plants: one chilling sensitive corn (Zea mays) and the other its chilling-tolerant relative Z. diploperennis. Attached leaves of these plants were exposed to chilling (5$\sp\circ$C) and ambient (25$\sp\circ$C) temperatures at different concentrations of oxygen and either darkness or varying light intensities, and the extent of photoinhibition and concentration of antioxidants were then measured. The rates of recovery under non-stressful conditions were also monitored.

Our results show that oxygen imparted a significant protection to corn, but not Z. diploperennis, at low temperature. Nevertheless, Z. diploperennis sustained less photoinhibitory damage than corn. Photoinhibition in corn was accompanied by lower antioxidant concentrations. Both photosynthesis and antioxidants recovered by 2 days, suggesting that slow recycling of the latter induced photoinhibition at low temperature and retarded recovery. Maximum oxidation of the antioxidants took place in the presence of high light and low temperature. Chilling induced photoinhibition also required the presence of light.

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