Alleviation of Hg-, Cr-, Cu-, and Zn-Induced Heavy Metals Stress by Exogenous Sodium Nitroprusside in Rice Plants.

The cultivation of rice is widespread worldwide, but its growth and productivity are hampered by heavy metals stress. However, sodium nitroprusside (SNP), a nitric oxide donor, has been found to be effective for imparting heavy metals stress tolerance to plants. Therefore, the current study evaluated the role of exogenously applied SNP in improving plant growth and development under Hg, Cr, Cu, and Zn stress. For this purpose, heavy metals stress was induced via the application of 1 mM mercury (Hg), chromium (Cr), copper (Cu), and zinc (Zn). To reverse the toxic effects of heavy metals stress, 0.1 mM SNP was administrated via the root zone. The results revealed that the said heavy metals significantly reduced the chlorophyll contents (SPAD), chlorophyll a and b, and protein contents. However, SNP treatment significantly reduced the toxic effects of the said heavy metals on chlorophyll (SPAD), chlorophyll a and b, and protein contents. In addition, the results also revealed that heavy metals significantly increased the production of superoxide anion (SOA), hydrogen peroxide (H 2 O 2 ), malondialdehyde (MDA), and electrolyte leakage (EL). However, SNP administration significantly reduced the production of SOA, H 2 O 2 , MDA, and EL in response to the said heavy metals. Furthermore, to cope with the said heavy metals stress, SNP administration significantly enhanced the activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and polyphenol peroxidase (PPO). Furthermore, in response to the said heavy metals, SNP application also upregulated the transcript accumulation of OsPCS1 , OsPCS2 , OsMTP1 , OsMTP5 , OsMT-I-1a , and OsMT-I-1b . Therefore, SNP can be used as a regulator to improve the heavy metals tolerance of rice in heavy-metals-affected areas.