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Title: EFFECT OF THE TWO FORMS OF RUBISCO ACTIVASE ON THE HIGH TEMPERATURE INHIBITION OF PHOTOSYNTHESIS IN ARABIDOPSIS PLANTS

Author
item KELLY, WALTER - PLANT BIOLOGY UOFI URBANA
item WHITMARSH, CLIFFORD
item PORTIS JR, ARCHIE

Submitted to: Plant Physiology Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 7/1/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: The activation state of Rubisco is one of the most thermolabile aspects of photosynthesis; Rubisco activase loses activity in vitro in the same temperature range at which many plants undergo reversible inhibition. In numerous species, activase is present as two distinct isoforms. It has recently been shown that the higher MW form of spinach activase is much more thermostable in vitro than the lower MW form, and a mixture of the two forms exhibit the stability of the high MW form (1). Here, we address the proposal that a physiological function of having two distinct isoforms in planta is that the higher MW form confers greater thermal stability on the heteromultimeric activase protein than would otherwise be the case. The reversible inhibition of photosynthesis by elevated temperature was studied in Arabidopsis plants: a transgenic line expressing only 42 kD activase, and the wild type with both 42 kD and 46 kD forms. Fluorescence vs. Leaf temperature curves were recorded as leaves were slowly heated to determine the critical temperature (Tc) in light and darkness. Tc was about 6 deg C higher in the light than in the dark, but in both conditions Tc for the 42 kD-only plant was about 2 deg C higher than for the wild type. Fluorescence quenching analysis showed a reduction in photochemical yield starting 6-8 deg C below Tc, with other parameters consistent with energized thylakoids (favorable for activase activity), but the temperature for which yield was reduced 50 percent was greater-than 3 deg C higher for the 42 kD-only plant than for the wild type. Thus, the higher MW form does not appear to confer higher temperature stability to activase in Arabidopsis plants. (1) Crafts-Brandner et al. (1997) Plant Phys. 114:439-444.