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Higher temperature and elevated carbon dioxide (CO2) concentration are expected to cause changes in global precipitation patterns and thus increased water stress events in soils. Few studies have reported the interaction between plants and the main three components of climate change (high temperature, elevated CO2, water stress). In the present study the abscise acid (ABA)-insensitive mutant (abi1-1) and its associated wild-type (WT) of Arabidopsis thaliana (Arabidopsis) were used to determine the effects of these three factors on Arabidopsis during vegetative and reproductive stages. Arabidopsis plants were grown under two temperature regimes (22/18˚C and 28/24˚C, 16 h light/8 h dark), two CO2 concentrations (400 and 700 μmol mol-1), and two watering regimes (well-watered - watering to field capacity; and water-stressed - watering at wilting point). I found that the negative effects of higher temperatures and water stress on Arabidopsis plants during their vegetative stage were mitigated by elevated CO2 by increasing antioxidant activity and plant water status. Also, the WT plants had better performance than the abi1-1 plants under our experimental conditions, and even under the optimal conditions for plants (lower temperatures, elevated CO2, and well-watered), suggesting the role of ABA in mitigating the negative effects of stress factors by elevated CO2 especially in the abi1-1 genotype. Higher temperatures inhibited the ability of wild-type plants to produce ABA in response to drought. Elevated CO2 decreased the expression of the two ABA-responsive genes, RD22 and RD29B, without affecting ABA. Higher temperatures and water stress, individually and together, led to decreased growth, yield, and seed quality. Elevated CO2, in general, did not compensate for the negative effects of higher temperatures and water stress on the measured parameters, such as sound-seed number and seed mass. Elevated CO2 seems to have more positive effects on the biomass of the reproductive structures (siliques) than on the seed production or biomass. Amino acid contents of Arabidopsis seeds were positively affected by higher temperatures, elevated CO2 or water stress; with highest effects of higher temperatures. This could compensate for the negative effects of higher temperatures and water stress and no effects of elevated CO2, respectively, on seed mass, and consequently, on seed quality. Seeds that matured under higher temperatures could have less dormancy and exhibit more germ iniability than those that matured under lower temperatures. This study showed that the climate-change related factors would have an effect on the fate of seeds after dispersal. Climate change seems likely to have little effects on the germ inability of WT seeds, but can decrease germ iniability of abi1-1 seeds through changing their phenolic and other such compounds. Therefore, this study indicates that there are factors other than ABA that are involved in controlling seed germination in response to climatic factor. Based on these findings, rising CO2 will have more positive effects on plants at the vegetative stage than at the reproductive stage. In addition, ABA is important to help plants survive under stressful growth conditions, but it seems that under climate change other factors would also affect the plant survival through, for example, changing seed germ ability.
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