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Title: TEMPERATURE DEPENDENCE OF PHOTOSYNTHESIS IN ARABIDOPSIS PLANTS WITH MODIFICATIONS IN RUBISCO ACTIVASE AND MEMBRANE FLUIDITY

Author
item Kim, Kangmin
item Portis Jr, Archie

Submitted to: Plant and Cell Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/6/2005
Publication Date: 3/1/2005
Citation: Kim, K., Portis Jr, A.R. 2005. Temperature dependence of photosynthesis in arabidopsis plants with modifications in rubisco activase and membrane fluidity. Plant And Cell Physiology. 46:522-530.

Interpretive Summary: The activity of Rubisco, the enzyme that captures carbon dioxide, often limits photosynthesis, the process by which plants use light energy from the sun to make carbohydrates for growth from carbon dioxide and water. Both photosynthesis and the activity of Rubisco decline as leaf temperature increases above the optimum. In this study we compared the temperature responses of plants expressing different forms of Rubisco activase, a protein that is required to maintain Rubisco's activity. The results indicated that while the presence of some activase is critical for the inhibition at moderately high temperature to be reversible, no improvement over the wild type response was observed with any of the modified plants we examined. This information will benefit scientists attempting to modify the properties of Rubisco or activase in ways beneficial for increased photosynthesis by crop plants at high temperatures.

Technical Abstract: Net photosynthesis (Pn) is reversibly inhibited at moderately high temperature. To investigate this further, we examined the effects of heat stress on Arabidopsis plants in which Rubisco activase or thylakoid membrane fluidity has been modified. During heating leaves from 25 to 40°C at 250 ppm CO2 and 1% O2, the wild type (WT), rwt43 (expressing 43KDa isoform only), and R100 (accumulating activase 40% of WT) plants exhibited similar inhibitions in Pn and Rubisco activation state. Despite better membrane integrity than WT, the fad7/8 double mutant (less polyunsaturation of thylakoid lipids) failed to maintain greater Pn than the WT. The rwt46 (expressing 46KDa isoform only) plants exhibited the most inhibition but the C411A plants (expressing a 46KDa isoform incapable of redox regulation) were similar to the WT. The rca lines (null mutant) exhibited a continuous decline in Pn. As measured by fluorescence, electron transport activity decreased concomitantly with Pn but PSII was not damaged. Following a quick recovery to 25 from 40°C, whereas most lines recovered 90% Pn, the rwt46 and rca lines recovered only to 59% and <10%, respectively. As measured by NADP-malate dehydrogenase activation, increased stromal oxidation accompanied the inhibition of photosynthesis. These results provide additional insight into the role of Rubisco activation and activase in the reversible heat inhibition of Pn.