Poster: Photosynthesis
Abs #
373: Rubisco deactivation caused by altered activase activity drives the early inhibition of photosynthesis at moderately high temperature
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Presenter: |
Kim, Kangmin , kkim1@uiuc.edu |
Authors | Kim, Kangmin (A) Portis, Archie (A) | | Affiliations: |
(A): Photosynthesis Research Unit, USDA-ARS
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Net photosynthesis (Pn) is reversibly inhibited at moderately high temperature. To investigate this further, we examined the effects of heat stress on Arabidopsis in which Rubisco activase or thylakoid membrane fluidity has been modified. Upon heating leaves from 25 to 40 °C under low CO2 and 1% O2, the wild type (WT), rwt 43 (expressing small isoform of activase only) and fad7fad8 double mutant (49% decrease in polyunsaturation of thylakoid lipids) showed similar inhibition profiles in Pn rate. Regardless of better membrane integrity than WT, the fad7fad8 double mutant failed to maintain greater Pn at < 40 °C. The antisense activase Arabidopsis line, R100 (accumulating activase 60% less than WT) also exhibited a similar T50 but slightly higher onset temperature than other lines. The rwt 46 (expressing large isoform of activase only) plants showed the greatest inhibition and even lower onset temperature. The activation states of Rubisco extracted from leaves were well correlated with Pn rate measured by gas exchange. After recovery at 25 °C, whereas most of lines showed >90% recovered Pn, rwt 46 recovered only to 59%. Within the temperature range examined, there was slight decrease in photochemical quenching (qP) with all plants. From the results, we conclude that increased thermal stability of thylakoid membranes caused no apparent changes on heat inhibition of Pn below 40 °C. Rubisco deactivation potentially caused by reduced activase activity accounts for the early stages of inhibition. The results with the rwt46 plants suggest that increased stromal oxidation and/or increased ADP/ATP ratios at higher temperature may contribute to the observed reduction in photosynthesis rate.
-Supported in part by DOE grant 97ER20268
