ARS | Publication request: Effect of Activase Level and Isoform on the Thermotolerance of Photosynthesis in Arabidopsis

Submitted to: American Society of Plant Biologists Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: July 26, 2006
Publication Date: July 26, 2006
Citation: Salvucci, M.E., Deridder, B.P., Portis, A.R. 2006. Effect of Activase Level and Isoform on the Thermotolerance of Photosynthesis in Arabidopsis. American Society of Plant Biologists Annual Meeting, P 14010.

Technical Abstract: The activation state of Rubisco decreases under moderate heat stress. This decrease is caused by an impairment of activase function, which is exacerbated by faster rates of Rubisco deactivation at elevated temperatures. To determine if stromal oxidation causes the inhibition of activase, we examined transgenic Arabidopsis plants expressing similar, but suboptimal amounts of either the redox-regulated 46 kD '- or non-redox regulated 43 kD '-isoform of Arabidopsis activase. Net photosynthesis of the '- and '-isoform expressing plants was about 68 and 58% of wild type, respectively, while Rubisco activation was 68 and 69%. Photosynthesis, as measured by gas-exchange and chlorophyll fluorescence, and Rubisco activation were inhibited to a much greater extent by moderately high temperatures in the two transgenic lines expressing suboptimal levels of the individual isoforms of activase compared with wild type plants or transgenic plants expressing wild-type levels of the '-isoform. The results demonstrate that photosynthesis is equally sensitive to inhibition by moderately high temperature in plants expressing the two different isoforms of activase. Thus, impairment of activase function under heat stress is not caused by oxidation of the redox-sensitive sulfhydryls of the '-isoform of activase. Instead, the results are consistent with thermal denaturation of activase being the main cause of reduced Rubisco activation under moderate heat stress, an effect that would be enhanced when activase levels are suboptimal for photosynthesis.