Abstract Cadmium (Cd) is an environmental pollutant that is highly toxic to animals and plants. Although sulfur dioxide (SO2) has recently been considered as a novel bio-regulator, whether and how SO2 regulates Cd-induced phytotoxicity in plant roots is largely unknown. In this study, SO2 derivatives (Na2SO3/NaHSO3, M/M = 3:1) were used to investigate the beneficial roles and detailed mechanisms of SO2 in the alleviation of Cd-induced root growth suppression in foxtail millet seedlings. Our results showed that exogenously applied SO2 derivatives (0.5 mM) reversed Cd inhibition of root elongation. Cd-induced endogenous nitric oxide (NO) production downregulated the enzyme activities of superoxide dismutase (SOD) and peroxidase (POD), as well as corresponding transcript levels, and increased the expression of genes involved in Cd uptake (SiNRAMP1, SiNRAMP6, SiIRT1, and SiIRT2) in foxtail millet roots. Upon Cd exposure, SO2 derivative application reduced NO generation by inhibiting nitrate reductase (NR) and nitric oxide synthase (NOS) activities, thus resulting in increased activities of SOD and POD and suppressed Cd uptake-related gene expression, which in turn reduced reactive oxygen species (ROS) accumulation and decreased Cd content in the roots. This study suggested a beneficial role of SO2 derivatives in protecting foxtail millet roots against Cd toxicity by decreasing endogenous NO; this might be applicable to enhancing crop tolerance to Cd pollutants.

中文翻译：

---

内源性一氧化氮的减少有助于二氧化硫衍生物减轻谷子根中的镉毒性

摘要 镉（Cd）是一种对动植物有剧毒的环境污染物。尽管二氧化硫 (SO2) 最近被认为是一种新型的生物调节剂，但 SO2 是否以及如何调节植物根系中 Cd 诱导的植物毒性在很大程度上是未知的。在本研究中，SO2 衍生物（Na2SO3/NaHSO3，M/M = 3:1）用于研究 SO2 在缓解 Cd 诱导的谷子幼苗根系生长抑制中的有益作用和详细机制。我们的结果表明，外源施用 SO2 衍生物 (0.5 mM) 可以逆转 Cd 对根伸长的抑制作用。Cd 诱导的内源性一氧化氮 (NO) 产生下调超氧化物歧化酶 (SOD) 和过氧化物酶 (POD) 的酶活性以及相应的转录水平，并增加参与 Cd 摄取的基因 (SiNRAMP1, SiNRAMP6、SiIRT1 和 SiIRT2) 在谷子根中。在镉暴露后，SO2衍生物的应用通过抑制硝酸还原酶（NR）和一氧化氮合酶（NOS）的活性来减少NO的产生，从而导致SOD和POD的活性增加并抑制与Cd摄取相关的基因表达，进而降低活性氧种 (ROS) 积累和根中 Cd 含量降低。该研究表明 SO2 衍生物在通过减少内源性 NO 来保护谷子根免受 Cd 毒性方面具有有益作用；这可能适用于提高作物对 Cd 污染物的耐受性。从而导致 SOD 和 POD 活性增加并抑制 Cd 吸收相关基因的表达，进而减少活性氧 (ROS) 积累并降低根中的 Cd 含量。该研究表明 SO2 衍生物在通过减少内源性 NO 来保护谷子根免受 Cd 毒性方面具有有益作用；这可能适用于提高作物对 Cd 污染物的耐受性。从而导致 SOD 和 POD 活性增加并抑制 Cd 吸收相关基因的表达，进而减少活性氧 (ROS) 积累并降低根中的 Cd 含量。该研究表明 SO2 衍生物在通过减少内源性 NO 来保护谷子根免受 Cd 毒性方面具有有益作用；这可能适用于提高作物对 Cd 污染物的耐受性。