When Defense Pathways Collide. The Response of Arabidopsis to a Combination of Drought and Heat Stress  

Abstract

Within their natural habitat, plants are subjected to a combination of abiotic conditions that include stresses such as drought and heat. Drought and heat stress have been extensively studied; however, little is known about how their combination impacts plants. The response of Arabidopsis plants to a combination of drought and heat stress was found to be distinct from that of plants subjected to drought or heat stress. Transcriptome analysis of Arabidopsis plants subjected to a combination of drought and heat stress revealed a new pattern of defense response in plants that includes a partial combination of two multigene defense pathways (i.e. drought and heat stress), as well as 454 transcripts that are specifically expressed in plants during a combination of drought and heat stress. Metabolic profiling of plants subjected to drought, heat stress, or a combination of drought and heat stress revealed that plants subject to a combination of drought and heat stress accumulated sucrose and other sugars such as maltose and gulose. In contrast, Pro that accumulated in plants subjected to drought did not accumulate in plants during a combination of drought and heat stress. Heat stress was found to ameliorate the toxicity of Pro to cells, suggesting that during a combination of drought and heat stress sucrose replaces Pro in plants as the major osmoprotectant. Our results highlight the plasticity of the plant genome and demonstrate its ability to respond to complex environmental conditions that occur in the field.The study of abiotic stress in plants has advanced considerably in recent years. However, the majority of experiments testing the response of plants to changes in environmental conditions have focused on a single stress treatment applied to plants under controlled conditions. In contrast, in the field, a number of different stresses can occur simultaneously. These may include conditions such as high irradiance, low water availability, extreme temperature, or high salinity and may alter plant metabolism in a novel manner that may be different from that caused by each of the different stresses applied individually. The response of plants to abiotic stresses in the field may therefore be very different from that tested in the laboratory (Cushman and Bohnert, 2000;Mittler et al., 2001;Zhu, 2002). Drought and heat stress represent an excellent example of two different abiotic stresses that occur in the field simultaneously, especially in semi-arid or drought-stricken areas (Mittler et al., 2001;Moffat, 2002;Rizhsky et al., 2002). Although drought and heat stress have been extensively studied (Vierling, 1991;Ingram and Bartels, 1996; Shinozaki and YamaguchiShinozaki, 1996;Miernyk, 1999;Queitsch et al., 2000), relatively little is known about how their combination impacts plants. A number of studies examined the effect of a combination of drought and heat stress on the growth and productivity of maize, barley, sorghum, and different grasses. It was found that a combination of drought and heat stress had a significantl...

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