Nitric oxide regulates water status, antioxidant enzymes, nutritional balance, and growth of gazania (Gazania rigens) under drought stress.

Nitric oxide (NO) is a bioactive molecule that plays a crucial role in modifying the metabolic systems of plants and activating plant defence systems against environmental stresses such as drought. In this study, we investigated the impacts of exogenously supplemented sodium nitroprusside (SNP), a NO donor, on drought tolerance and physio-biochemical mechanisms mediated by NO that influence nutrient contents and growth of gazania (Gazania rigens ). In a lath house, plants at the four-leaf stage were treated with a foliar spray of SNP (100μM) under two watering conditions: (1) 50% field capacity (drought stress);and (2) 100% field capacity (normal-watering). Results revealed that water deficiency significantly reduced gaseous exchange, chlorophyll pigments, water relations, NO, and proline contents. However, supplementation with NO increased proline levels and antioxidant enzyme activities, leading to improved photosynthesis, water relations, and drought tolerance by reducing lipid peroxidation and hydrogen peroxide levels. Furthermore, enhanced NO levels from SNP treatment promoted the accumulation of essential nutrients resulting in improved growth and biomass in gazania plants. Our results indicated that SNP supplementation increased gaseous exchange (21-53%), chlorophyll pigments (30-70%), water status (12-31%), antioxidant enzyme activities (19-52%), nutrient uptake (22-36%), and flower yield (49%), potentially mitigating the negative effects of water deficiency in gazanias under drought stress. These findings suggest that foliar application of NO donors like SNP could be a practical and eco-friendly strategy to improve drought resilience and productivity of ornamental plants, especially in water-limited urban landscaping and nursery production systems.