Role Of NO In The Alleviation Of Cadmium Toxicity By Exogenous SO₂ Derivatives In Foxtail Millet Seedlings

Cadmium?Cd?is a toxic heavy metal.Excessive Cd exerts adverse effects on a series of physiological processes such as photosynthesis,respiration,and nutrient metabolism,leading to growth and development inhibition,and eventually plant death.Sulfur dioxide?SO₂?has traditionally been considered to be an air pollutant.Recently,it was discovered that SO₂ exhibits beneficial roles during a variety of physiological processes and disease responses in animals,such as inducing vasodilation,lowering blood pressure and protecting against myocardium injury.Studies on plants revealed that exogenous SO₂ could regulate plant responses to adversity stress.SO₂ enters plants mainly through the stomata.In the aqueous phase of cytoplasm,SO₂ dissociates into its sulfite derivatives?sulfite ions/bisulfite ions,3:1 M/M?.To date,the regulatory mechanisms of SO₂ in crop adaptation to Cd stress are still unclear.Nitric oxide?NO?is an important signalling molecule that has been reported to play vital roles in plant responses to Cd stress.Foxtail millet?Setaria italica L.Beauv?is an important food crop in northern China.In this paper,using foxtail millet seedlings as materials,taking derivative solution Na2SO3/Na HSO3?M:M=3:1?as SO₂ donor,we investigated the effect of exogenous SO₂ derivatives on the Cd-induced toxicity of foxtail millets,as well as the regulatory roles and mechanisms of NO in the alleviation of Cd toxicity triggered by SO₂ derivatives.The main results are as follows:?1?Treatment with 100 ?M Cd Cl2 could inhibit the growth of foxtail millet seedlings,and cause obvious oxidative damage to the roots and leaves.Exogenous SO₂ derivatives?0.5 m M?could significantly reduce the O₂^- production rate,MDA and H₂O₂ content within seedlings under Cd stress,and thus effectively alleviate the growth inhibition induced by Cd stress.?2?100 ?M Cd could induce the accumulation of NO in the leaf and root tissues of foxtail millet seedlings.In addition,the endogenous NO content increased gradually with the increase of Cd concentration and treatment time.?3?Exogenous SO₂ derivatives?0.5 m M?could reduce the activity of NR and NOS,thereby inhibiting NO accumulation in the leaf and root tissues of foxtail millet seedlings.?4?Exogenous SO₂ derivatives could alleviate Cd-induced oxidative damage and root growth inhibition through reducing NO content in leaf and root tissues of foxtail millet seedlings.In addition,SO₂ derivatives decreased the expression level of genes involved in Cd uptake and transport?Si ZIP4 and Si HMA2?by reducing NO level in foxtail millet roots.The purpose of this thesis is to reveal the roles of NO in the alleviation of Cd toxicity induced by exogenous SO₂ derivatives,and to thoroughly explore the mechanisms of SO₂ derivatives in regulating Cd stress responses of foxtail millets.This study may provide theoretical basis for improving Cd tolerance of millet plants.