Date of Award:

5-1-1999

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Committee Chair(s)

Keith A. Mott

Committee

Keith A. Mott

Committee

Jon Y. Takemoto

Committee

Richard J. Mueller

Committee

Bruce Bugbee

Committee

Martyn Caldwell

Abstract

Rubisco's (ribulose 1,5-bisphosphate carboxylase/oxygenase) catalytic activity changes as light intensity changes. This study addresses factors that were expected to affect Rubisco deactivation during low light. First, effects of fluctuating light and constant sun or shade during plant growth on Rubisco deactivation and activation were evaluated for basil (Ocimum basilicum and impatiens (Impatiens wallerana). Rubisco activation rate and the degree of Rubisco deactivation were determined from gas-exchange measurements of photosynthesis following a step increase in light intensity. Rubisco activation state during low light was also determined from biochemical analyses of leaf extracts. There were no significant differences in Rubisco activation rate among the growth conditions or between the two species. However, the degree of Rubisco deactivation was less following a decrease in light, and activation states were higher prior to a subsequent increase in light for basil grown in sun or fluctuating light than in shade. Thus, the contribution of Rubisco activation to induction was less for basil grown under sun or fluctuating light than in shade. Impatiens deactivated Rubisco more than basil, but there was no substantial effect of the three growth-light conditions on the degree of Rubisco deactivation for impatiens. Second, effects of intercellular CO2 concentration on Rubisco deactivation during darkness or low light were examined for spinach (Spinacia oleracea). There were no significant differences in the apparent relaxation time for Rubisco deactivation among leaves exposed to high or low CO2 during periods of low light or darkness. However, following subsequent increases in light, leaves exposed to low CO2 and low light showed a lower contribution to induction by Rubisco activation than leaves exposed to the other three treatments. Third, effects of growth-light quantity and quality on Rubisco deactivation were examined. Spinach grown under low light and low red:far-red ratio showed a lower percent change in photosynthesis due to Rubisco activation than plants grown under high red:far-red ratio x low or high light. However, there were no significant differences among the growth-light treatments in the apparent maximum contribution of Rubisco activation to induction or in the apparent relaxation time for Rubisco deactivation during low light.

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