To investigate the effect of exogenous brassinosteroid application on grain yield, catalase, chlorophyll
content, membrane mtability index and gene expression of some genes involving in brassinosteroid
signaling pathway (BES1 and BRI1) under drought stress, a split-split plot on randomized complete
block design with three replications was conducted at the experimental field of Seed and Plant
Improvement Institute, Karaj, Iran in 2019. The main factor was two irrigation treatments (normal
irrigation and water holding after 50% flowering stage), the subplots were four concentrations of
brassinosteroid (0, 0.25, 0.625 and 1 mg/l) and seven genotypes (Mehregan, Paris, 2858, 3505, 3737,
4228 and 4056) were considered as sub-sub plots. Samples were taken at 30 days after 50% flowering
stage (zadoks 89) from flag leaves. The results showed that drought stress significantly reduced grain
yield, chlorophyll content, membrane stability index and increased catalase in all genotypes. Genotype
4228 was identified as the most tolerant genotype among unknown wheat genotypes based on grian
yield, chlorophyll content, membrane stability index and catalase. Also, the result revealed that
applied epibrassinolide could reduce the destructive effects of drought stress on wheat thus grain yield
was enhanced under drought stress in all genotypes by increasing the aforementioned traits.
Forethermore, grain yield was increased by rising the epibrasinolide concentration. Gene expression
pattern of TaBES1 and TaBRI1 using real-time PCR showed that although brassinosteroid enhances
drought tolerance in wheat but its signaling pathway is different from the BRI1 signaling pathway.