Boron Alleviates Drought Stress by Enhancing Gene Expression and Antioxidant Enzyme Activity

Drought is one of the major abiotic stress factors for plants, especially in arid and semiarid areas, where plants are facing with boron (B) contamination problem as well. In these soils, plants deal up with two destructive phenomena: excessive B and water scarcity. The current study aims to understand the adaptation strategy of tomato plant against excess B and drought stresses. For this purpose, hydroponically grown tomato seedlings were subjected with excess B (+B), drought (+PEG), and excess B with drought (B+PEG) stresses. Antioxidant enzyme activities (superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR)); chlorophyll, soluble protein, and MDA contents; and the root histograms were analyzed. In addition, expression of stress-related genes (GR1, MT2, and Hsp90) was determined by qRT-PCR method. Compared to the non-treated (control) or B+ and PEG+ treated plants, the transcript abundance of the stress-related genes was significantly increased in plants grown under B+PEG condition. The highest relative increase was observed on GR1 gene (similar to 7-8-fold), indicating the activation of oxidative stress enzymes. At the same time, chlorophyll content analysis showed a significant increase; MDA level showed a reduction under B+PEG condition. SOD activity was limited, while APX and GR enzymes were found to be increased upon B+ PEG application. Activation of stress-related genes and antioxidant enzymes under B+PEG condition could help to protect plants against excess B and drought stresses. Inclusion of B can enhance the drought adaptation of plants by stimulating the early stress response mechanisms.