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The ability of land plants to partially close their stomata in response to high vapor pressure deficit (VPD), called the limited transpiration trait, is a rare phenomenon in plants. The characteristic has been demonstrated in several crop species, including Sorghum bicolor. Genotypes within the sorghum species respond in different ways to high VPD, but the molecular basis and regulatory mechanisms of the responses are not clear. This study was conducted to determine the basis for the differences in stomatal responses to high VPD in sorghum genotypes (SC1345, SC35, and Macia). Gene expression patterns of genes involved in the abscisic acid pathway were investigated using quantitative-PCR after exposing plants to high VPD. The results showed marked differences in expression patterns for the genes across the three genotypes, coupled to differences in abscisic acid content. The results suggested natural variation in abscisic acid content within sorghum. Expression patterns in the genes BG1, ZEP, and SDR, in addition to the NCED3 gene, provide a basis for the variations in stomatal responses to high VPD in this crop species. [ABSTRACT FROM AUTHOR]