Investigation of the effects of certain antioxidants in tomatoes on alleviating drought stress

Drought stress is one of the most significant abiotic stresses that limits plant growth, development, and productivity. Nitric oxide and glycine betaine antioxidants are known to enhance plants' defense against abiotic stress. In this study, the mitigating effects of two different antioxidant applications, namely 10 mM glycine betaine and 200 µM nitric oxide donor sodium nitroprusside (SNP), on drought stress were investigated in tomato (Solanum lycopersicum L.) cultivation. Four different genotypes, including drought-tolerant (D2 and D15) and drought-sensitive (D1 and D14) varieties, were used. Drought stress adversely affected plant growth parameters, morphological, physiological and biochemical parameters. It was determined that the glycine betaine and nitric oxide antioxidants applied to tomato plants reduced the harmful effects of drought stress on physiological parameters, such as leaf relative water content, leaf water potential, stomatal conductance, and membrane damage index. Compared to plants under drought stress, the leaf relative water content increased by % 5.91 with GB application, while stomatal conductivity increased by % 68.28 with SNP application. Drought stress led to water loss in tomato plants, causing stomatal closure and a reduction in CO₂ uptake. Antioxidant applications developed a defense mechanism against stress, resulting in increased photosynthesis rate and transpiration. These antioxidant applications inhibited lipid peroxidation, reducing MDA production and increasing proline content. The increase in proline content helped maintain osmotic balance in the plant. The glycine betaine and nitric oxide applications made tomato plants more resistant to oxidative stress by enhancing antioxidant enzyme activities. This situation is supported by the increases of % 28.18 and % 45.23 in ascorbate peroxidase (APX) and glutathione reductase (GR) activities, respectively, with GB application compared to drought-stressed plants, and an % 18.28 increase in superoxide dismutase (SOD) activity with SNP application compared to drought-stressed plants. It was determined that the glycine betaine and nitric oxide antioxidant applications used in tomato cultivation reduced the effects of drought stress on plant growth parameters, morphological, physiological and biochemical parameters.