Nitric Oxide Ameliorates Plant Metal Toxicity by Increasing Antioxidant Capacity and Reducing Pb and Cd Translocation

Abstract

Recently, nitric oxide (NO) has been reported to increase plant resistance to heavy metal stress. In this regard, an in vitro tissue culture experiment was conducted to evaluate the role of the NO donor sodium nitroprusside (SNP) in the alleviation of heavy metal toxicity in a bamboo species (Arundinaria pygmaea) under lead (Pb) and cadmium (Cd) toxicity. The treatment included 200 µmol of heavy metals (Pb and Cd) alone and in combination with 200 µM SNP: NO donor, 0.1% Hb, bovine hemoglobin (NO scavenger), and 50 µM L-NAME, N(G)-nitro-L-arginine methyl ester (NO synthase inhibitor) in four replications in comparison to controls. The results demonstrated that the addition of L-NAME and Hb as an NO synthase inhibitor and NO scavenger significantly increased oxidative stress and injured the cell membrane of the bamboo species. The addition of sodium nitroprusside (SNP) for NO synthesis increased antioxidant activity, protein content, photosynthetic properties, plant biomass, and plant growth under heavy metal (Pb and Cd) toxicity. It was concluded that NO can increase plant tolerance for metal toxicity with some key mechanisms, such as increasing antioxidant activities, limiting metal translocation from roots to shoots, and diminishing metal accumulation in the roots, shoots, and stems of bamboo species under heavy metal toxicity (Pb and Cd).

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

“…Plants activate a plethora of adaptive responses to withstand abiotic stresses, including a high accumulation of proteins [ 48 ]. The current study showed that the significant reduction in protein content due to Pb-induced damages is significantly mitigated by exogenous application of SNP, as shown in Figure 2 C. This result is in accordance with the previous reported result [ 47 ].…”

“…SNP significantly ameliorated Pb-induced negative impacts on chlorophyll a and b contents, as shown in Figure 2 A,B. Similarly, under heavy-metal (Pb and Cd) stress, adding SNP increases chlorophyll and carotenoid concentrations in bamboo plants [ 47 ].…”

Silicon and Nitric Oxide-Mediated Regulation of Growth Attributes, Metabolites and Antioxidant Defense System of Radish ( L.) under Arsenic Stress

“…Biomass production can be improved through the application of Si in the form of soluble silicic acid Si(OH) 4 , which ultimately stimulates biochemical and molecular processes [67]. Shoot length and dry weight were observed to be increased by the addition of NO under Pb and Cd stress in Arundinaria pygmaea [12]. Similar findings were observed by Singh et al [68] in terms of an increase in root length, shoot length, and biomass under As stress in Oryza sativa plants.…”

“…Plant leaves were used for further analysis. The experiment included 16 treatments: (1) control, (2) As I (0.3 mM), (3) As II (0.5 mM), (4) As III (0.7 mM), (5) Si, (6) Si + As I, (7) Si + As II, (8) Si + As III, (9) NO, (10) NO + As I, (11) NO + As II, (12) NO + As III, (13) Si + NO, (14) Si + NO + As I, (15) Si + NO + As II and (16) Si + NO + As III.…”

“…At the same time, at larger amounts, it causes nitroso-oxidative stress and acts as a stress molecule [10]. Nitric oxide is also considered to reduce metal toxicity due to its signaling role and stimulates the plant's antioxidant defense system to decline oxidative stress by decomposing H 2 O 2 to molecular oxygen and triggering H 2 O 2 -suppressing enzymes [11][12][13]. An increase in the activities of catalase (CAT), superoxide dismutase (SOD), and ascorbate peroxidase (APX) enzymes showed a positive role of NO in the activation of stress-responsive enzymes [14].…”