Nowadays, the threat of drought to crop production is increasing due to ongoing climate change and a growing world population, which poses a challenge to food security. To solve the problem of plant susceptibility to drought, one potential solution is to study new varieties that are more resistant and investigate key regulators of plant responses to unfavorable environmental conditions. In our research, we examined the effect of exogenous abscisic acid (ABA) treatment, a plant hormone crucial for the response to drought, on barley mutants carrying mutations in the genes encoding the CBC complex, an important component of ABA-related signaling pathways, as well as on the parental cultivar Sebastian. Using the TILLING technique, we created mutants in the genes (hvcbp20.ab and hvcbp80.b) encoding both subunits of the CBC complex and we also generated a double mutant (hvcbp20.ab/hvcbp80) carrying mutations in both genes simultaneously. We subjected these mutants and the parent variety to drought stress, ABA-only treatment, and ABA pretreatment followed by drought stress. Our studies showed that these mutations significantly affected photosynthetic parameters, especially after ABA treatment. Additionally, transcriptome sequencing enabled the observation of changes in biological processes within the analyzed genotypes and the identification of key genes that may cause the observed changes. In conclusion, we have shown that mutations in the genes encoding the CBC complex can increase plant resistance to drought conditions, providing valuable information for improving crop sustainability in the face of climate challenges.