Physiological And Biochemical Changes During Flower Bud Development Of Male And Female Litsea Cubeba In Pb And Zn Contaminated Soils

Litsea cubeba(Litsea cubeba(Lour.)Pers.)is one of the important woody oil plants with the characteristics of fast-growing,large biomass and strong adaptability.It is also one of the important species for energy ecological restoration of heavy metal contaminated soil.Flowering is one of the important characters of higher plants,which is affected by the external environment and gene expression.Due to the different growth and energy distribution between sexes,there are differences in the response of male and female plants to the environment.In this study,three-year-old Litsea cubeba(Litsea cubeba(Lour.)Pers.)was used as experimental material to observe and analyze the morphological structure differentiation characteristics,soluble sugar,reducing sugar,starch,IAA content,C/N ratio,IAA related oxidase activity and other physiological and biochemical changes of male and female Litsea cubeba flower buds in the polluted soil environment of Chenzhou Manaoshan lead-zinc mining area.Based on the physicochemical characteristics and transcriptome sequencing,the gene differential expression of male and female flower buds of different treatment groups in budding stage and dormancy stage was analyzed to explore the gender differences in the regulation of gene expression of key enzymes in glucose metabolism pathway and auxin transduction pathway caused by heavy metal Pb-Zn pollution,and to preliminarily understand the adaptability of the development process of dioecious Litsea cubeba flower buds to heavy metal Pb-Zn pollution from the physiological,biochemical and molecular levels The results provide theoretical basis and technical guidance for revealing the differential response mechanism of dioecious plants to heavy metal stress,material selection and cultivation management of Litsea cubeba heavy metal contaminated soil.The main results are as follows:1.According to the observation results of Litsea cubeba phenology and flower bud morphology,the development process of male and female flower buds was roughly divided into five periods.The effect of male and female flower buds on the development of male and female flower buds was significantly earlier than that of the control(P<0.05).2.The results showed that Pb-Zn pollution level significantly increased the content of soluble sugar and starch,C/N ratio,but had no significant effect on reducing sugar content.Moreover,the synthesis and accumulation of IAA in male plants were more promoted than that in female plants.In the control group,ABA/IAA,ABA/Zr hormone content ratio increased and then decreased,Zr/IAA gradually decreased,and the decrease of female plants was faster;while in Pb/Zn heavy metal contaminated soil,ABA/IAA,Zr/IAA male plants continued to decline slowly,and the decrease of male plants was faster.The ratio of ABA/Zr in male flowers was significantly higher than that in female flowers.3.With the development of flower bud,IAA oxidase and pod oxidase increased first and then decreased in both control and stress groups.Pod content in male and female plants in stress group was significantly higher than that in control group.Except dormancy stage,IAA oxidase activity of the stress group was higher than that of the control group,that is,low concentration of lead and zinc stress increased IAA oxidase activity,and the effect on male plants was greater than that on female plants.4.Pb-Zn pollution affected the accumulation and relative content of carbon and nitrogen in male and female Litsea cubeba flower buds.The C/N ratio of starch and soluble sugar content in flower buds was significantly negatively correlated with the beginning of male and female flower buds.The content of reducing sugar was significantly positively correlated with the beginning of male and female flower buds.The activity of pod oxidase was positively correlated with the beginning of female and male flower buds Negative correlation,the impact on each index of Litsea cubeba male plant is slightly greater than that of its female plant.5.There are gender differences in the expression regulation of key genes involved in glucose metabolism and growth signal transduction pathway by Pb-Zn pollution.In the process of flower bud development,whether in the control or heavy metal contaminated soil,the differences in the expression patterns of key genes in the sugar metabolism pathway mainly occurred in the dormancy period of flower bud.Compared with the effects of heavy metal Pb-Zn pollution on the regulation of key enzyme genes in starch/sucrose metabolism,the key genes in glycolysis/gluconeogenesis pathway were more affected by Pb-Zn pollution,and the number of key genes regulated in dormancy stage was more than that in budding stage,and the number of genes regulated in female plant was more than that in male plant.At the same time,the expression patterns of IAA signal transduction key genes in different developmental stages were also different.The inhibition effect of Pb-Zn pollution on IAA signal transduction pathway key gene expression of female Litsea cubeba was greater than that of male Litsea cubeba.To a certain extent,the tolerance of male Litsea cubeba to Pb-Zn pollution was stronger than that of female Litsea cubeba.