These observations indicate that stomatal movement has a strong relationship to ozone sensitivity, likely because stomata regulate the first step of ozone absorption into plant cells. In addition, the Arabidopsis ecotype Cvi-0, which has higher stomatal conductance than other ecotypes, also exhibits hypersensitivity to ozone compared with other ecotypes ( 9, 10). To study the mechanisms of ozone damage in plants, researchers have isolated Arabidopsis thaliana mutants that exhibit hypersensitivity to ozone exposure ( 4), including several mutants with higher stomatal conductance than wild type (WT), such as radical-induced cell death1 ( rcd1), rcd2, and ozone sensitive1/slow anion channel-associated1 ( ozs1/ slac1) ( 5– 8). High concentrations of ozone induce oxidative stress, which activates programmed cell death and significantly inhibits plant growth, causing crop losses estimated to be in the billions of dollars ( 2, 3). Tropospheric ozone (O 3) is a major photochemical oxidant and one of the most phytotoxic air pollutants ( 1). Because the chimeric GLK1-SRDX repressor driven by a guard cell-specific promoter induced a closed-stomata phenotype without affecting chloroplast development in mesophyll cells, modulating GLK1/2 activity may provide an effective tool to control stomatal movements and thus to confer resistance to air pollutants. Our results indicate that GLK1/2 positively regulate the expression of genes for K + in channels and promote stomatal opening. Abscisic acid treatment did not affect the stomatal phenotype of 35S:GLK1/2-SRDX plants or the transcriptional activity for K + in channel gene, indicating that GLK1/2 act independently of abscisic acid signaling. The plants expressing GLK1-SRDX had reduced expression of the genes for inwardly rectifying K + (K + in) channels and reduced K + in channel activity. By contrast, plants that overexpress GLK1/2 exhibited an open-stomata phenotype and higher sensitivity to ozone. thaliana) plants expressing the chimeric repressors for GLK1 and -2 (GLK1/2-SRDX) exhibited a closed-stomata phenotype and strong tolerance to ozone. Here, we show that Arabidopsis thaliana ( A. The GARP family transcription factors GOLDEN 2-LIKE1 (GLK1) and GLK2 have known functions in chloroplast development. Stomatal movements regulate gas exchange, thus directly affecting the efficiency of photosynthesis and the sensitivity of plants to air pollutants such as ozone.
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