Exogenously Applied Sodium Nitroprusside Mitigates Lead Toxicity in Rice by Regulating Antioxidants and Metal Stress-Related Transcripts

Abstract

Sustainable agriculture is increasingly being put in danger by environmental contamination with dangerous heavy metals (HMs), especially lead (Pb). Plants have developed a sophisticated mechanism for nitric oxide (NO) production and signaling to regulate hazardous effects of abiotic factors, including HMs. In the current study, we investigated the role of exogenously applied sodium nitroprusside (SNP, a nitric oxide (NO) donor) in ameliorating the toxic effects of lead (Pb) on rice. For this purpose, plants were subjected to 1.2 mM Pb alone and in combination with 100 µM SNP. We found that under 1.2 mM Pb stress conditions, the accumulation of oxidative stress markers, including hydrogen peroxide (H2O2) (37%), superoxide anion (O2−) (28%), malondialdehyde (MDA) (33%), and electrolyte leakage (EL) (34%), was significantly reduced via the application of 100 µM SNP. On the other hand, under the said stress of Pb, the activity of the reactive oxygen species (ROS) scavengers such as polyphenol oxidase (PPO) (60%), peroxidase (POD) (28%), catalase (CAT) (26%), superoxide dismutase (SOD) (42%), and ascorbate peroxidase (APX) (58%) was significantly increased via the application of 100 µM SNP. In addition, the application of 100 µM SNP rescued agronomic traits such as plant height (24%), number of tillers per plant (40%), and visible green pigments (44%) when the plants were exposed to 1.2 mM Pb stress. Furthermore, after exposure to 1.2 mM Pb stress, the expression of the heavy-metal stress-related genes OsPCS1 (44%), OsPCS2 (74%), OsMTP1 (83%), OsMTP5 (53%), OsMT-I-1a (31%), and OsMT-I-1b (24%) was significantly enhanced via the application of 100 µM SNP. Overall, our research evaluates that exogenously applied 100 mM SNP protects rice plants from the oxidative damage brought on by 1.2 mM Pb stress by lowering oxidative stress markers, enhancing the antioxidant system and the transcript accumulation of HMs stress-related genes.

Mercury Content and Amelioration of Its Toxicity by Nitric Oxide in Lichens

“…SNP restored 10 µM Hg-induced depletion of AsA and thiols in wild-type Arabidopsis roots (which were directly in contact with the treatment solution), but not in leaves [ 22 ]. Cross-talk between SNP and heavy metal Cd led to an increase in AsA amount over single treatments in the green microalga [ 16 ], and cross-talk between SNP and Pb lowered oxidative stress markers and enhanced the antioxidant system in rice [ 23 ], indicating a similar positive effect of SNP in various plant lineages.…”

“…Nitric oxide (NO) is a unique simple gaseous molecule, but with considerable impact on plant physiology and metabolism, including adaptations to (heavy) metals [ 19 , 20 ]. It was observed—using NO modulators (donors or scavengers)—that NO often improves metal and Hg-induced negative changes in plants [ 16 , 21 , 22 , 23 ]. However, the role of NO in lichens is less known and only a few studies have reported the impact of NO scavenger under metal excess [ 24 , 25 ].…”

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

“…The typical symptoms of essential and nonessential heavy metals in plants include the reduction in root and shoot lengths, the number of tillers per plant, chlorophyll and protein contents, and an increase in the production of reactive oxygen species (ROS), malondialdehyde (MDA), electrolyte leakage (EL), water and nutrients imbalances, chlorosis, and senescence, ultimately resulting in plant death [ 1 , 5 , 6 ]. When a cell is exposed to heavy metals, some cell organelles are impacted, including the cell membrane, nucleus, endoplasmic reticulum, mitochondria, lysosome, enzymes, and metabolites involved in the healing process after injury [ 7 ].…”

“…Many plants have specialized systems for different metal ions, and they work to compartmentalize these ions to prevent exposure to cells’ most delicate parts [ 10 ]. Other detoxification mechanisms for these metals are now in place, chelating, transporting, sequestering, and detoxifying these metal ions in the plant’s vacuole, serving as a second line of defense [ 5 , 10 ]. Furthermore, in response to heavy metals stress, plants produce hormones, phytochelatins (PCs), metal tolerance proteins (MTPs), metallothionein (MTs) ROS, reactive nitrogen species (RNS), and antioxidants [ 5 ].…”

“…Different techniques are used by plant scientists to improve the defense system of the plants against heavy metal stress, including the application of plant-growth-promoting rhizobacteria (PGPR), exogenous phytohormones and fertilizers, melatonin (MT), and donors of nitric oxide (NO) [ 5 , 11 , 12 , 13 , 14 ]. As a signaling molecule, NO significantly contributes to regulate plant growth and development and defense responses against biotic and abiotic stress conditions [ 15 , 16 , 17 , 18 , 19 ].…”