Effects of sodium nitroprusside applications on antioxidant defense system and oxidative stress in leaf and berry tissues of the ‘Horoz Karası’ grapevine (Vitis vinifera L.)

Nitric oxide (NO) has been widely recognized as a multifunctional signaling molecule in plants, participating in the regulation of growth, developmental transitions, and stress adaptation processes. Its involvement in modulating cellular redox homeostasis is considered one of the key mechanisms underlying these effects. In experimental studies, sodium nitroprusside (SNP) is widely used as an exogenous NO donor, and several studies have reported a potential role of SNP in modulating antioxidant systems in different plant species. However, information regarding the temporal effects of repeated SNP applications under vineyard conditions and their integrated effect on leaf and grape berry antioxidant responses in grapevines remains limited. Foliar SNP applications significantly modulated antioxidant enzyme activities and oxidative stress indicators in the Horoz Karası grape variety. Among the tested concentrations, a 300 ppm SNP consistently resulted in the highest activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), and glutathione reductase (GR), while effectively suppressing malondialdehyde (MDA) and hydrogen peroxide (H 2 O 2 ) accumulation in leaf tissues. The effects of SNP were more pronounced during the veraison and harvest periods than in the pre-veraison stage, indicating a stronger regulatory role under elevated metabolic activity. In grape berry tissues, SNP applications, particularly at 300 ppm, reduced MDA levels and promoted higher antioxidant enzyme activities, demonstrating a possible systemic leaf - grape berry interaction mediated by NO signaling. Repeated foliar application of SNP effectively enhances the antioxidant defense capacity and limits oxidative damage in Horoz Karası grapevines in a dose- and time-dependent manner. The 300 ppm can be considered an effective dose for maintaining redox homeostasis in both leaf and grape berry tissues. These findings highlight the potential of NO-based applications as an environmentally friendly strategy to improve oxidative stress management and quality preservation in sustainable viticulture practices.