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Heat-stress-induced Inhibition of The Activation State of Cotton Ribulose-1,5-bisphosphate Carboxylase/oxygenase (Rubisco) Is Mediated by Rubisco Activase

R. David Law and Steven J. Crafts-Brandner


Glandless upland cotton (Gossypium hirsutum L. cv. Coker 100A) plants were subjected to heat stress in a growth cabinet. Carbon exchange rate (CER), ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (rubisco) activation state, and RuBP and 3-phosphoglycerate (3-PGA) content were monitored. Air temperature increases from control (28°C) values were in 2.5°- to 5°-steps to 45°C, with a 1-h equilibration at each step with high ambient humidity (~75%) to allow leaf temperature to approach that of the air. Samples taken from young, fully-expanded leaves indicated that rubisco activation state (mediated by the presence of active, non-heat-denatured rubisco activase) began decreasing when leaf temperature was raised above 35°C and decreased to 25% of control values at 45°C. This was mirrored by decreases in net photosynthetic rate (CER) to 61% of control values at 42.5°C, and by a 50% decrease in the rubisco product 3-PGA, starting at 40°C and reaching a maximum at 45°C. Additionally, these changes in rubisco activity, activation state and 3-PGA content were reversible by subsequently lowering the temperature of the heat-stressed leaves. Fluorescence measurements indicated that increasing leaf temperature adversely affected flux through the photosynthetic electron transport chain. Cumulatively, these results complement a previous study (Feller et al. (1998) Plant Physiol 116, in press) demonstrating the importance of rubisco activase in the maintenance of maximal rubisco activity at relatively high temperatures.

Reprinted from Proceedings of the 1998 Beltwide Cotton Conferences pp. 1472 - 1475
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998