Exogenously Applied Sodium Nitroprusside Alleviated Cadmium Toxicity in Different Aromatic Rice Cultivars by Improving Nitric Oxide Accumulation and Modulating Oxidative Metabolism

Exogenous application of sodium nitroprusside (SNP) has previously been reported to trigger plant tolerance against a variety of environmental stresses. The present study was planned to investigate the possible role/s of exogenously applied SNP (50 or 100 μM) in alleviating cadmium (Cd)-induced effects on physio-biochemical processes, yield attributes, and grain quality traits of three fragrant rice cultivars, viz., Meixiangzhan-2 (MXZ), Guixiangzhan (GXZ), and Xiangyaxiangzhan (XYXZ) under 50 mg Cd kg−1 of soil. The results revealed that foliar spray of SNP (50 or 100 μM) on Cd-stressed rice plants reduced oxidative stress (lower hydrogen peroxide (H2O2), malondialdehyde (MDA), and electrolyte leakage (EL)) and improved the photosynthetic apparatus through higher chlorophyll contents, gas exchange attributes, and intact chloroplast configurations, and reduced Cd concentration in the leaves and grains of aromatic rice cultivars. The reduced levels of cellular ROS, MDA, and EL were related to the endogenous NO-mediated improvement in the activity of anti-oxidative enzymes and those involved during the ascorbate–glutathione cycle. However, among the different SNP levels, the foliar spraying of 50 μM of SNP was recorded to be the best treatment for fragrant rice growth, which increased grain yield by 42.06%, 46.03%, and 31.21%, and the quality trait of 2-acetyl-1-pyrroline (2-AP) content by 43.12%, 55.84%, and 35.72% in MXZ, GXZ, and XYXZ respectively, suggesting that GXZ is more responsive to SNP than MXZ and XYXZ fragrant rice cultivars. Collectively, our results deduced that cultivating the GXZ fragrant rice cultivar along with foliar application of 50 μM of SNP could sustain the grain yield and quality features of aromatic rice cultivation in heavy metal (especially Cd)-polluted soils.