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Arsenic (As) stress severely impairs plant growth and physiology, resulting in diminished crop quality and yield. Nitric oxide (NO) has been found to alleviate heavy metal toxicity effectively. This study aims to examine how NO donor sodium nitroprusside (50 µM) in conjunction with different arsenic levels (10 µM and 25 µM) affect the growth of diploid and autotetraploid rice. When exposed to As (25 µM), diploid rice showed reductions in root length (29.71%), shoot length (33.40%), fresh root weight (83.62%), and fresh shoot weight (79.06%), whereas tetraploid rice showed reductions by 18.58%, 18.46%, 60.00%, and 54.19% of the control, respectively. Notably, tetraploid rice absorbed less As than diploid rice. NO application mitigated As toxicity, particularly at As (10 µM), while showing weaker effects at As (25 µM). Chlorophyll contents, i.e., a, b, and carotenoids, decreased significantly under As stress, whereas NO application elevated chlorophyll levels. Due to toxicity, the levels of antioxidant enzymes (SOD, POD, and CAT) were lower in diploids than in tetraploid, while H2O2 and MDA levels increased, with tetraploid increasing by 0.77-fold and 0.96-fold, and diploid by 1.71-fold and 1.36-fold, respectively. The NO effect was more pronounced in tetraploid rice, particularly in non-enzymatic (GSH), and oxidative stress indicators (H2O2 and MDA). Gene expression analysis confirmed differences between rice types, including OsSOD, OsPOD, OsCAT, and GSH (OsGSTU5) genes, as well as higher expression of As transporters (OsHAC1, OsLsi2, and OsABCC1) in diploid rice. Semi-thin sectioning, confocal laser scanning, and transmission electron microscopy observations highlighted distinct structural variations under arsenic stress. In brief, tetraploid rice exhibited greater As tolerance than diploid rice, with NO proving effective in regulating physiological and biochemical processes and mitigating As toxicity.
Shahid et al. (Tue,) studied this question.