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Abstract: Abscisic acid (ABA) is an important plant hormone and may be involved in drought resistance in crops. The object of this study was to understand the effects of exogenous ABA on wheat (Triticum aestivum L.) plant under drought stress. After drought stress simulated with polyethylene glycol (PEG) for 72 h at grain-filling stage, flag leaves of Yumai 949 and Shaanmai 5 showed significant increase in malondialdehyde (MDA) content and decreases in relative water content (RWC), chlorophyll content, and yield. Meanwhile, the transcription of psbA gene in photosystem II system was also depressed according to the analysis of reverse transcriptional PCR. Application of exogenous ABA had a significant effect on alleviation of these reactions from PEG stress. Compared to Yumai 949, Shaanmai 5 received smaller injury in plasma membranes and less reduces in RWC, chlorophyll content, yield, and psbA transcriptional level after PEG stress. Moreover, exogenous ABA treatment resulted in restoration of all parameters tested to the levels before stress in Shaanmai 5. This result indicated that the expression of psbA gene was closely related to drought stress resistance subject to wheat cultivar. The primary evidence of ABA regulation on psbA expression may enrich the mechanism of drought resistance and suggest the potential of exogenous ABA to enhance resistance to drought stress in wheat during grain filling period. [Copyright &y& Elsevier]