Investigation of the effect of para amino benzoic acid (PABA) applications on tomato (solanum lycopersicum l.)crops grown under salt stress

The main objective of this thesis is to investigate the protective effects of Para-aminobenzoic acid (PABA) on tomato plants under salt stress. PABA is a component of the vitamin B complex that plays a role in important metabolic processes in plants, such as folic acid synthesis. Tomato plants were subjected to seed priming with PABA and then exposed to salt stress using 150 mM NaCl. The study analyzed growth parameters (shoot length, leaf number, fresh and dry weight), physiological parameters (chlorophyll content, electrical conductivity - EC), and gene expression levels (WRKY33, WRKY70, PAL, TPK1b genes). A 1 mM PABA solution was prepared, and tomato (Solanum lycopersicum L.) seeds were used as the plant material. The results showed that PABA application supported plant growth under salt stress and positively affected the expression of some stress-related genes. In PABA-treated plants, the shoot length reached up to 10.506 cm, while in the salt-only treated groups, this value was measured at 5.717 cm. Additionally, it was found that PABA activated genes involved in antioxidant defense and ion transport mechanisms. The expression level of the WRKY33 gene showed approximately 6 times more expression in the PABA+WATER application compared to the PABA+SALT application, while the WRKY70 gene expression was upregulated by approximately 17 times in the PABA+SALT group compared to the PABA+WATER group. The increase in TPK1b gene expression in some stressed groups suggested a potential supportive effect on ion homeostasis. The lack of PAL gene expression in the PABA application group indicated that phenylpropanoid pathways are regulated differently in response to salt stress. These findings suggest that PABA may play a potential role in increasing plant tolerance to salt stress and could be used in agricultural applications. The study revealed that PABA has the potential to be used as a biostimulant against salt stress in tomato cultivation. However, further research is needed to investigate the effectiveness of PABA at different doses, under various conditions, and in different tomato cultivars. Future studies should be more comprehensive and application-oriented, focusing on determining the optimal dosage range and clarifying its molecular mechanisms.