Affect Of Lead&Zinc Stress On Flowering Physiology Of Ricinus Communis L.

Ricinus communis L.has large biomass and strong stress resistance,and is highly resistant to heavy metal pollution.It's one of the important oil plants for ecological restoration of heavy metal-contaminated soil.In this study,the ramie 9 was used as the test material,and the Pb and Zn were used as stress factors to test the effects of single and combined Pb2+ and Zn2+ application on the initial flowering time of ramie and the differentiation of male and female flowers.The relationship between the changes of physiological and biochemical indexes such as soluble sugar,starch,nitrogen and IAA content and the flowering time and female flower differentiation of plants were studied under different concentrations of lead and zinc,and the differentially expressed genes related to major metabolic pathways were analyed.Exploring the adaptability and flowering mechanism of ramie under different lead and zinc stresses,can have significant application value for ramie industrialization and bioenergy application,and soil remediation for heavy metal contamination.The main findings are as follows:(1)The vegetative growth of plant varied with different stress concentrations of Pb2+ and Zn2+.At low concentration stress(Pb2+=0.50 mM·kg-1,Zn2+=1.50 mM·kg-1),stem base diameter,height and leaf area of castor plants increased slightly.With the increase of single and combined lead and zinc stress concentrations,the indicators of vegetative growth showed a significant downward trend(P<0.05),among which the effect on stem and internode length was the most serious,followed by plant height.(2)The initial flowering time,total inflorescence length and female inflorescence length varied with concentrations of Pb2+ and Zn2+.Low concentration of lead and zinc stress could promote the differentiation of female flowers,and the initial flowering stage was advanced;high concentration of Pb2+,Zn2+ single and compound stress inhibits the reproductive growth of plants and delayed flowering.(3)The uptake and transport of Pb2+,Zn2+ and nutrient N by plants differed under Pb2+ and Zn2+ single and combined stress.The accumulation of Pb2+ and Zn2+ in different organs of ramie was as follows:root>leaf.Under the same molar stress,the accumulation of Pb2+ and Zn2+ in ramie was Zn2+>Pb2+.Under the compound stress,the accumulation of Pb2+ and Zn2+ in plants was lower than that of single stress.Under single and combined Pb and Zn stress,the total N content in roots and leaves of plants increased first and then decreased with the increase of concentration.When the concentration of single Pb2+ was 1.00 mM·kg-1,the total N content of leaves and roots reached 15.25 mg·g-1,8.12 mg·g-1,and the concentration of single Zn2+ was 4.50 mM·kg-1,the total nitrogen content of the leaves was 18.77%higher than that of the control,while in the roots was significantly reduced by about 1.15%.When the compound stress was 1.00+3.00 mM·kg-1,the total nitrogen content in leaves and roots was 22.77%and 5.59%higher than that of the control group respectively.(4)The physiological and biochemical indexes in plants are different under different concentrations of Pb2+ and Zn2+ and combined stress.Both soluble sugar and starch content showed a phenomenon of "low promotion and high inhibition",and the C/N ratio increased first and then decreased.When treated with single lead,the content of proline in leaves increased first and then decreased with the increase of concentration.When combined with single Zn2+ and Pb2+Zn2+,the content of proline in leaves increased with the increase of concentration,and the ammonia concentration in each concentration was treated.The acid content was higher than the control group.Both IAA oxidase and POD oxidase showed a decrease in concentration with an increase in concentration.The content of IAA decreased first and then increased with the increase of lead and zinc single stress and compound stress.(5)Under Pb and Zn stress the carbon,nitrogen and IAA content in leaves had close relationship with initial flowering time,inflorescence length and female flower rate.There was a significant negative correlation between soluble sugar content and C/N ratio in leaves;N content and Zn2+concentration in plant had positive correlation;The total length of inflorescence was significantly positively correlated with soluble sugar content in leaves,and also positively correlated with C/N ratio.The relative length of female inflorescence was significantly positively correlated with soluble sugar and C/N ratio in leaves.The content of IAA in castor leaves was significantly negatively correlated with total inflorescence length and female inflorescence length;it was significantly positively correlated with the initial flowering stage.This indicates that low IAA content leads to early flowering of plants may be achieved by affecting POD and IAA oxidase activity.(6)Compared with the control,in the first 20 pathways with Pb2+concentration of 1.50 mM-kg-1,the significant carbon and nitrogen metabolic pathways were nitrogen,galactose and fructose,and mannose metabolism(P<0.05);The significant metabolic pathways for Zn2+concentration of 3.00 mM-kg-1 were starch and sucrose,glycolysis/gluconeogenesis,and fructose and mannose metabolism(P<0.05).And the overall expression of key enzyme genes involved in metabolism is down-regulated.