The effect of humic acid on some physiological parameters and gene expressions against drought stress in tomato

The aim of this study, in which the plant material is tomato (Kayra F1) seedlings, is to determine the effects of drought stress, as well as the effects of humic acid application (3 ml/l) under drought stress. In this study, the examined stress parameters were shoot/root wet-dry weights, shoot-root lenghts, proline, chlorophyll, MDA, ion leakage and relative water contents in addition to CAT, SOD, GR and APX antioxidative enzyme gene expressions. The results of the study showed that drought stress reduced shoot and root wet/dry weights, shoot and root lenghts, chlorophyll and relative water content levels, although the humic acid application under drought stress increased all of these parameters in significant levels. However, drought+humic acid application reduced ion leakage, MDA and proline levels. Results of the study also showed that humic acid application mitigated the negative effects caused by drought stress. Investigation of the tomato plants under drought stress showed that humic acid application did not significantly affected SOD and APX gene expression levels, however, it increased CAT gene expression and decreased GR gene expression levels. Overall results of the study revealed the interaction of the humic acid application and stress releated antioxidative enzyme gene expressions. The results of the study showed that the application of humic acid under drought stress could possibly have a mitigating effect on drought stress in tomato plants.