Photosynthesis Inhibition in the Arabidopsis Thaliana Photorespiration Mutants
Chastain, Chris J.
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https://hdl.handle.net/2142/77659
Description
Title
Photosynthesis Inhibition in the Arabidopsis Thaliana Photorespiration Mutants
Author(s)
Chastain, Chris J.
Issue Date
1985
Department of Study
Plant Biology
Discipline
Botany
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Plant Physiology
Language
eng
Abstract
The inhibition of photosynthesis occurring in the Arabidopsis photorespiration mutants during illumination under atmospheres which promote photorespiration is predominantly due to declining leaf RuBP concentrations resulting from the impairment of carbon recycling to the Calvin cycle.
Rubisco light activation level is inhibited during inhibition of photosynthesis in the stm, glyD, sat, gluS, and dct mutants (Table 3). Furthermore, the reduction in Rubisco activation in the stm mutant can be suppressed when the pcoA and stm lesions are genetically combined to form a double mutant. Thus, the inhibition of Rubisco is dependent on site specific blockage of the photorespiration pathway.
Rubisco inactivation contributes only minimally, if any, to the rapid reduction of photosynthesis in the photorespiration mutants. This is based on an analysis of photosynthesis in the Arabidopsis rca mutant, which is known to have a photosynthesis rate limited by Rubisco activation level. Comparisons of activation levels and photosynthesis in the rca mutant to those occurring in the photorespiration mutants suggest that the degree of inactivation occurring in the photorespiration mutants is not the major factor mediating photosynthesis inhibition.
The mechanism of Rubisco inactivation may be due to glyoxylate which is a potent inhibitor of Rubisco light activation in intact spinach chloroplasts. This hypothesis is supported by the discovery that under photorespiratory conditions, glyoxylate levels increase 2- and 4-fold in the photorespiration mutants which exhibit Rubisco inactivation. The calculated intracellular concentration of the elevated levels of glyoxylate exceed 100 (mu)M, a concentration which is physiologically significant since the Ki for intact chloroplasts is approximately 50 (mu)M. However, if glyoxylate mediates the inhibition of Rubisco activation level, its mode of action is unknown since the inactivation does not appear to involve stromal pH or Mg('2+) or direct inhibition of the enzyme.
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