A possible role of glutathione as an electron source for flowering in Arabidopsis thaliana

We have recently found that glutathione (GSH) is associated with flowering in A. thaliana [Ogawa et al. (2001) Plant Cell Physiol. 42 (5): in press]. Since the first step of GSH biosynthesis is mediated by g -glutatmylcystein synthetase which is localized in plastids, we here investigated the relationship between the redox status associated with GSH and flowering in A. thaliana. In the present experiments, flowering time was defined as the number of rosette leaves for neglecting differences in growth rates among the mutants and the wild-type. Plants were grown under long-day conditions. An A. thaliana mutant, cad2-1, which has a defect in GSH biosynthesis, exhibited late flowering, compared to the wild-type plant. Treatment with L-buthionine sulfoximine (BSO), a specific inhibitor of GSH biosynthesis, tended to strengthen the late-flowering phenotype of this mutant, whereas treatment with GSH is tended to abolish it. These suggest that flowering is associated with GSH levels and/or the rate of GSH biosynthesis. Although strong light delayed flowering in the wild-type, it strengthened the late-flowering phenotype of the cad2-1 mutant. This is thought to reflect that flowering is delayed because GSH is consumed under photoinhibitory conditions. A chlorophyll-b-less mutant, ch1-1, also exhibited late flowering. Sucrose and GSH applied exogenously promoted flowering in the wild type and the mutants. These results may suggest that the rate of photosynthesis during the vegetative period determines flowering time through GSH level and/or the rate of GSH biosynthesis A. thaliana.