Iron And Zinc Absorption And Distribution Characteristics And Sterss Response Mechanism In Ceratoides Arborescens

Iron（Fe）and zinc（Zn）are essential mineral elements for plant growth and play a vital role in forage yield and quality.Deficiency of Fe and Zn can inhibit plant growth,while excess Fe and Zn can also lead to plant toxicity.To date,the research on plant Fe and Zn nutrition mainly focuses on crops with low Fe and Zn content,model crops and plants growing in southern acidic soil.Ceratoides arborescens is endemic to the arid and semi-arid regions in northern China,which is a high-quality forage for livestock and an excellent plant for ecological restoration.However,there are few studies on the mechanisms of Fe and Zn stress and their uptake and translocation by C.arborescens,which limit our understanding of the adaptive mechanism of iron and zinc in excellent grassland plants.In this thesis,the distribution of Fe and Zn in the plants of C.arborescens,the change of iron and zinc content to different mineral elements and organic acid treatments,and the plant morphology,physiology and biochemical indicators were obtained through field observation and indoor cultivation in response to different concentrations of iron and zinc solution treatments.By analyzing the m RNA data under low iron and excess zinc plants,the differential genes of Fe-and Zn-stressed plants were screened,and further,the Fe-and Zn-specific transporter protein genes were screened by yeast complementary function verification.The main findings were as follows.1.The Fe concentration of the above-ground parts of C.arborescens in different habitats ranged from 0.15～0.45μg?mg^-1（DW）and Zn concentration ranged from0.013～0.034μg?mg^-1（DW）,which were the higher levels in the same habitat and helped to supplement Fe and Zn nutrition for livestock due to its larger biomass.The roots of C.arborescens can be enriched with more Fe and Zn,with 93 and 71 times more Fe than its stems and leaves,and 5.4 and 6.2 times more Zn than its stems and leaves,respectively.The mature seeds of C.arborescens had higher Zn content(0.049μg?mg^-1（DW）),about 3times that of its bracts(0.016μg?mg^-1),but its bracts had higher Fe content(0.87μg?mg^-1（DW）),about 10 times that of its seeds(0.081μg?mg^-1（DW）).2.Different concentration of mineral elements had distinct effects on Fe and Zn uptake and transport in C.arborescens.The effect of nitrogen on iron and zinc absorption varies with different forms,the high-level concentration of ammonium nitrogen can promote the absorption of Fe and Zn,while the high-level concentration of nitrate nitrogen inhibits the absorption of Zn and has no significant effect on the absorption of Fe;low-level and high-level concentration of phosphorus both inhibit the absorption of Fe and Zn in C.arborescens;low-level concentration of calcium,potassium and magnesium promote the transport of Fe and inhibit the transport of Zn;high level concentrations of iron promote the transport of Fe but inhibit the transport of Zn;high-level concentration of manganese and zion inhibits the absorption of Fe and promote the absorption of Zn.3.Excess Zn inhibits Fe uptake and translocation in C.arborescens and reduces Fe content.Therefore,similar phenomena（i.e.leaf yellowing,reduced chlorophyll content,weakened photosynthesis,weak root system）and decreased biomass,occur in Fe-deficiency or Zn-excess environments.Fe deficiency or Zn excess decreased the biomass of C.arborescens by 47.25%and 64.27%,respectively.And the contents of POD,SOD,MDA,and SS in plants increased in response to the Fe and Zn stress.In addition,the toxic effects caused by excess Zn on C.arborescens can be alleviated when excess Fe was added and the plant leaves regained their green.Excess Fe had no effect on the phenotype of the aboveground parts of C.arborescens,but it reduced the 68.78%root biomass,which is one of the mechanisms that root can enrich Fe ions and reduce the toxic effect of high Fe concentration on the aboveground parts of the plant.Zn deficiency had no effect on seedling growth of C.arborescens,probably because the Zn stored in the seeds of C.arborescens itself is enough to support its seedling growth.4.The physiological response to Fe deficiency and Zn overexpression was mainly based on the expression of up-regulated genes.The number of differentially expressed genes in Fe-deficient treatment reached 18,943,and the number of up-regulated genes was about 5 times more than the number of down-regulated genes;the number of differentially expressed genes in Zn-over-treated C.arborescens reached 22,493,and the number of up-regulated genes was about 2 times more than the number of down-regulated genes.Iron deficiency induced up-regulated expression of MYB-related proteins involved in iron distribution and DPI in response to stress,and down-regulated expression of glutathione transferase and zinc transporter protein ZIP family involved in reactive oxygen species scavenging.Iron deficiency differential genes were mainly enriched to ribosomal pathway,phagocytic vesicles,lysosomal and m TOR signaling pathways.Excess zinc differential genes were mainly enriched to the ribosomal pathway,protein expression pathway,protein processing on the endoplasmic reticulum,oxidative phosphorylation,phagocytic vesicles,lysosomes,plant-pathogen interactions and glutathione metabolism pathways.5.After functional identification analysis,two zinc transporter genes unique to C.arborescens were identified.DN154722 and DN161460 both restored the growth phenotype of the high Zn-sensitive yeast mutant△zrc1/△cot1,which was localized in the endoplasmic reticulum,and it was speculated that DN154722 and DN161460 might be the transporter protein genes that mediated the uptake of cytoplasmic Zn²⁺into the endoplasmic reticulum unique to C.arborescens.DN163936,DN164529,DN172922,DN171650 may not have Zn²⁺or Fe²⁺transporter functions.In summary,C.arborescens has high iron and zinc content and can be used as iron and zinc nutritional supplement forage for livestock.Both Fe-deficiency and Zn-excess can affect the normal growth of C.arborescens,while Fe-excess can alleviate the toxic effects of Zn-excess on the plant performance.In our study,we identified two Zn transporter proteins specific to that mediated the transport of Zn²⁺from low to high concentrations,and these transporter proteins provide a theoretical basis for the mineral nutrient biofortification of C.arborescens.