Nitric Oxide Signaling Is Involved In The Regulation Of Magnesium-Mediated Alleviation Of Aluminum And Cadminum Toxicity In Arabidopsis Thaliana And Panax Notoginseng

Nitric oxide?NO?is a signal molecule widely present in organisms,which not only regulates the growth and development of plants,but also participates in the response of various stresses.Aluminum(Al³⁺)and cadmium(Cd²⁺)are two toxic metal ions in the soil.In acidic soils?pH<5.5?,aluminum is a major factor limiting plant growth and crop yield,and the activity of heavy metal cadmium is also significantly increased with decreasing soil pH.Magnesium?Mg?is an essential nutrient for plant growth and plays an important role in plant growth and stress resistance.Magnesium deficiency is also an important factor limiting plant growth and crop yield in acidic soils due to problems such as easy leaching and aluminum toxicity.In this study,the model plant Arabidopsis thaliana and the medicinal plant Panax notoginseng?Burk?FH Chen were used to analyze magnesium to NO by means of plant physiology,biochemistry and molecular biology and genetics.Signal regulation is involved in the regulation of plant resistance to aluminum toxicity and reduction of heavy metal cadmium pollution.The research results provide new research ideas for improving the aluminum resistance of plants and reducing cadmium accumulation,and provide theoretical guidance for improving the quality and yield of medicinal plants P.notoginseng.The main findings are as follows:1.In Arabidopsis,Al toxicity and Mg deficiency-induced NO production contributed to inhibition of primary root growth and the root cell cycle progression.In contrast,Mg supply promoted root growth associated with decreasing NO production under Al stress and/or Mg deficiency conditions.The results of CYCB1;1::GUS and QC25::GUS transgenic materials indicate that Al-induced NO production inhibits cell division in the apical meristem and stem cell activity in the quiescent center,thereby inhibiting root growth.Magnesium decreased the activities and expression of the genes related to NO biosynthesis enzymes in wild type Col-0,but not in the Mg transporter mutant seedlings?mgt1?in the presence or absence of Al toxicity.Accordingly,the mgt1 mutant plants exhibited high Al accumulation,NO concentration and Al sensitivity in comparison with the Col-0 plants under Al stress.NO synthesis mutants noa1 and nia1nia2 all showed insensitivity to Al toxicity and Mg deficiency,further confirming reduction of NO production was involved in Mg-mediated root growth promotion under Al toxicity and/or Mg deficiency conditions.Taken together,our results suggested that Mg-mediated enhancement of root growth and Al tolerance is associated with altering NO production in Arabidopsis.2.In Panax notoginseng,Al toxicity and Cd stress-induced NO production led to a decrease in the absorption of Mg by roots.Cd increases the activity of NO-related synthetase NR,destroys cell membrane integrity,and increases Cd accumulation in roots.The use of NR and 14-3-3 protein interaction promoters?MgCl₂?significantly reduced Cd-induced NO production and Cd enrichment in roots.It is indicated that NR and 14-3-3 protein are the main factors affecting the accumulation of Cd in roots.In contrast,protein phosphorylation inhibitor?okadaic acid,OA?and NR and 14-3-3protein interaction inhibitors?5'-AMP?did not alter Cd accumulation in P.notoginseng.In addition,Western-Blot results showed that Cd significantly inhibited the expression of 14-3-3 protein and decreased the interaction with NR.MgCl₂ could effectively improve this condition.The results of this chapter indicate that magnesium can reduce cadmium-induced NR-dependent NO production in P.notoginseng and enhance the accumulation of Cd in roots by enhancing the interaction of 14-3-3protein with NR.3.In the field experiment,the foliar application of Mg increased the chlorophyll content of the leaves,the dry weight of the roots and leaves,and the total saponin content in the roots,and decreased the content of cadmium and aluminum while increasing the magnesium content in the roots.The results of soil magnesium application showed that although the use of Mg had no obvious effect on the dry weight of stems,it significantly increased the weight of roots and leaves.Compared with foliar application,the application of magnesium in the soil greatly increased the Mg content in the root while greatly reducing the enrichment of heavy metals Cd and Al in the root.The above experimental results show that the use of magnesium in the field planting process can effectively promote the growth of P.notoginseng,increase the yield of P.notoginseng,increase the content of medicinal components of P.notoginseng and reduce the content of heavy metals Cd and Al in the medicinal part of P.notoginseng.