Humic Acid as a Biostimulant in Improving Drought Tolerance in Wheat: the Expression Patterns of Drought-Related Genes

Plants develop a series of physiological, biochemical, and molecular responses to survive in drought stress. Many drought-related genes with various functions which regulated by ABA-dependent and independent pathways have been identified in wheat. However, studies on the effect of biostimulants on drought-related genes are limited and unclear. As a biostimulant, humic acid (HA) has enormous roles on plant growth, yield, and protection of resistance in various abiotic stresses, but its relation to drought-related genes is unknown. Here, we aimed to determine the relationships between drought stress generated by - 6 bar and - 8 bar PEG6000 and ABA and HA treatments on total oxidant status (TOS) and total antioxidant status (TAS) and expression of miRNA target genes (AP2, GRF, LAC, CSD1/CSD2, and Plastocyanin) on tolerant (Aksel 2000 and Kirkpinar 79) and susceptible (Atli 2002 and Kirmizi Kilcik) bread wheat (Triticum aestivum L.) genotypes. According to the results, the expression of the genes varied depending on genotype and tissue and it was determined whether the genes used ABA-dependent or ABA-independent mechanisms to provide tolerance to stress in our promoter analysis. Also, the irregularities of the biochemical changes and expression of genes that were caused by PEG6000 could be improved by HA considering the positive effects on genes.