Abstract
Like other winter annual species, germination of Arabidopsis seeds is inhibited by high temperature (thermoinhibition). By using Arabidopsis (Columbia) seeds as a model, we have shown that bioactive GA4 production was repressed severely by high temperature, and their thermoinhibition was alleviated by exogenously applied GA3. To evaluate the contribution of negative regulators of GA signaling on thermoinhibition, we studied germination phenotype of their loss of function mutants. The seeds of spy showed high germination percentages at supraoptimal temperatures. The seeds of rgl2 also showed tolerance to thermoinhibition. Quantitative RT-PCR analyses with wild type seeds indicated that SPY and RGL2 increased their transcript levels by imbibition and maintained their levels even after 24h at 34 oC but decreased to the low levels after 12h at 22 oC. These results suggest that GA response is suppressed at supraoptimal temperatures by maintaining negative regulator levels in combination with the repression of GA synthesis.
