Effects Of Mineral Element Deficiency On Secondary Metabolism,Physiology And Biochemistry Of Houttuynia Cordata

Mineral elements play an important role in plant growth and functional traits.In this study,Houttuynia cordata Thunb.as research object,and mineral-elements deficiency as the guidance,and the secondary metabolites(oxalic acid,phenolics and volatiles)as starting point,the effects of mineral-element(phosphorus(P),calcium(Ca),magnesium(Mg),potassium(K),iron(Fe))deficiency on H.cordata oxalic acid metabolism and physiological characteristics and accumulation of secondary metabolites were explored.The relationship between P deficiency and H.cordata oxalic acid metabolism,and the effects of lacking mineral elements on the morphology,growth metabolism,oxidative stress and secondary metabolism of H.cordata were revealed.The results are following:1.After 30 days of culture deficiency of P,Ca,Mg,K and Fe,accumulation and distribution of oxalic acid in H.cordata showed:(1)leaves>petiole>roots;(2)Water-soluble oxalic acid>acid-soluble crystalline oxalic acid;(3)There is the most significant effect of P on accumulation of oxalic acid in H.cordata.Absence culture of mineral elements was beneficial to the accumulation of oxalic acid in leaves of H.cordata,and the total oxalic acid in leaves,petioles and roots increased by 56.84%(P deficiency,P>0.05,the same below),24.45%(P deficiency),25.35%(Mg deficiency).Compared with water-soluble oxalic acid,the accumulation of acid-soluble crystallized oxalic acid was more significant.The amount of acid-soluble crystallized oxalic acid in leaves and stalks increased by 384.91%(P deficiency)and95.21%(P deficiency),respectively.However,water-soluble oxalic acid was still the main component,which was more than 50%of the total oxalic acid content.2.By setting the P concentration gradient,the change trend of different types of oxalic acid in different organs of H.cordata with the P concentration was learned,and the optimal P concentration level was determined to explore the relationship between mineral elements and oxalic acid metabolism.The total oxalic acid and water-soluble oxalic acid in different organs of H.cordata were decreased with the concentration of P,and the acid-soluble crystalline oxalic acid was the lowest in low P culture and the highest in CK.The total oxalic acid content in leaves was 2.26 mg·g^-1(the highest,P deficiency),and the acid soluble crystalline oxalic acid content in leaves was 0.05mg·g^-1(the lowest,low P).The content of available P in H.cordata leaves first increased and decreased with the increase of P concentration.The results were different in different parts of H.cordata with different element deletion treatments,which may be related to oxalic acid synthesis,transport routes and nutrient requirements of plants.Oxalic acid forms different types of acids by combining with cations of different elements.Mineral elements may be involved in the accumulation and distribution of oxalic acid by combining with organic acids after entering plant tissues.3.Long-term P deficiency culture,the acid phosphatase activity in H.cordata tissue was higher,especially in petiole and old leaves,which increased by 101.20 and74.80%,respectively.The activity of glycolate oxidase and ascorbate peroxidase decreased by 53.13 and 0.61%,respectively.With the increase of time,the content of PO₄^-dissolved by oxalic acid,oxalic acid and deionized water increased,and the solubility of Ca₃(PO₄)₂from high to low was oxalic acid>root secretes oxalic acid>deionized water.At 0?5 min,oxalic acid,root oxalic acid and deionized water increased significantly and dissolved at 37.08,21.78 and 19.83 mg·kg^-1·min^-1,respectively.At 5?60 min,the solubility of oxalic acid,root oxalic acid and deionized water on Ca₃(PO₄)₂tended to be gentle.At 60?20 min,the solubility of deionized water on Ca₃(PO₄)₂increased significantly,and the solubility of Ca₃(PO₄)₂was 3.36 mg·kg^-1·min^-1.4.From the aspects of morphology,physiology and biochemistry,secondary metabolism and antioxidant stress,the adaptive response of H.cordata to the absence of mineral elements was discussed.After 30 days of culture with P,Ca,Mg,K and Fe deficiency,the leaves in the treatment group were thin,prematurely aged(P and Ca deficiency),yellow(K deficiency)and less new roots(Fe deficiency).In antioxidant stress,MDA content,SOD and POD activities increased in different degrees.The results showed that the balance of free radical production and scavenging in H.cordata tissue was broken in the absence of element culture to a certain extent,and the free radical accumulated in the body greatly,and the membrane lipid peroxidation intensified,causing certain damage to the plant body.On physiological and biochemical,deficiency training for nitrate(K,Ca,Mg and Fe deficiency),available potassium(P,Ca,Mg and Fe deficiency)content significantly increased,but the effective phosphorus(P,Ca,Mg and Fe deficiency),content of chlorophyll(Mg,Fe and P deficiency)is reduced,leaf photosynthetic performance,reduce photosynthesis,chlorophyll,reducing;Secondary metabolic components,P,Ca,Mg,K deficiency treatment,chlorogenic acid,rutin,Alfred bean glycosides,quercetin were significantly increased,Fe deficiency under cultivation,reduce;Cis-3-hexene-ethyl ester,trans-2-hexene-1-ol,decanal aldehyde and borneol(except K deficiency)increased,while camalene and?-laurene decreased,but 3-tetradecanosterone did not change significantly.