Silicon and nitric oxide modulate growth attributes, antioxidant defense system and osmolytes accumulation in radish (Raphanus sativus L.) under arsenic toxicity

Plants adjust their developmental processes for their survival against changing environments. Plant development is adversely affected by arsenic (As) contamination. In order to mitigate As toxicity, the effect of silicon (Si) (as silicic acid) and nitric oxide (NO) (as sodium nitroprusside; SNP) was observed on 7 days old radish (Raphanus sativus L.) seedlings under 0.3, 0.5 and 0.7 mM As concentrations. Plant growth traits, oxidative stress, carbohydrates, protein, antioxidants and osmolytes were measured. Arsenic stress inhibited the growth parameters and caused oxidative damage by elevating the level of oxidative stress markers and by causing membrane and nuclear damage, as shown by histochemical studies. Activities of antioxidative enzymes, content of non-enzymatic antioxidants, and levels of osmolytes were also decreased by As stress. However, Si and NO supplementation enhanced the As tolerance by improving the plant growth parameters. Moreover, Si and NO application improved carbohydrates and protein contents and stimulated plant antioxidant defense systems by decreasing the level of malondialdehyde and hydrogen peroxide and by diminishing the membrane and nuclear damage caused by As. An increase in the osmolytes levels were observed by the application of Si and NO. Fourier transform infrared (FTIR) analysis showed that Si and NO exerted various peaks in different lipids, proteins, carbohydrates and cell wall component regions. This study suggests that Si and NO can help mitigating As-induced toxicity in R. sativus seedlings and augment growth.