Mitigation Effect And Physiological And Ecological Regulation Mechanism Of Exogenous Hemin On Maize Seedling Under Cadmium Stress

Cadmium?Cd?is an important industrial and agricultural raw material.Due to the extensive use of fertilizers and pesticides in agriculture and the irrigation of cadmium-containing sewage,heavy metal poisoning has become one of the major abiotic stresses inhibiting the growth and development of maize.Maize C₄ plants,with short growth cycle and large biomass,are important crops widely used in heavy metal pollution research.With exogenous substances improvement on cadmium stresses of maize is one of the most fast and the most effective method at home and abroad in recent years,more and more researchers begin to pay close attention to chlorinated hemoglobin?Hemin?application in field crops,improve maize by exogenous substances currently to explore the mechanism of resistance to cadmium stress most test is carried out under the condition of a single,not very good for clear maize seed germination after Hemin fertilization under cadmium stress field,leaf growth,root system development as well as the conditions of the mechanism of physiological ecology.In this study,hydroponics,laboratory analysis and field validation were combined to analyze the response and mitigation mechanism of Hemin to maize under cadmium stress from the aspects of phenotype,physiology,molecule and ecology,and to provide experimental basis for the application of Hemin to field resist ance production.The main results are as follows:1.Hemin promoted the dry matter accumulation ability of seedlings under cadmium stress,enhanced the water use ability of plants,and regulated the morphogenesis.Under cadmium stress,maize seedling growth was short and slow,with yellow leaves and short roots.Hemin treatment under cadmium stress can increase the amount of new root generation,make the root system more robust,and the amount of root hair generation more white.Hemin+Cd treatment enhanced root absorption of water and nutrients by increasing root volume,expanding root surface area,increasing root activity,and improving root characteristic parameters and root tolerance index.2.Hemin regulated the cadmium content,distribution and transpo rt of seedlings under cadmium stress,and improved the resistance to cadmium stress.The TF decreased after Hemin+Cd treatment,which inhibited the cadmium transport and enrichment.Meanwhile,the chelation and detoxification of Cd by NPT and PCs were enha nced.In different subcells of the root system treated with Hemin+Cd,the cadmium content of soluble components and cell walls increased,while the cadmium content of organelles decreased,thus reducing the transport of Cd from underground to abovemention-site.The expression of HMA3gene in leaves and roots increased,and the amount of HMA3 gene in roots was higher than that in leaves.3.Hemin maintained the ultrastructural stability of leaf cells under cadmium stress,improved photosynthetic and chlorophyll fluorescence parameters,and increased the activity of photosynthase.Cadmium stress reduced Pn,gs,Tr,Fv/Fm,ETR and q P characteristics,and increased NPQ characteristics.Hemin treatment promoted the synthesis and transformation of Chla and Chlb,and the rise of photozymes RUBPCase and PEPCase comets,increased the size of jade total lutein cycle library?VAZ?,enhanced the desepoxidation of lutein cycle?DEPS?,and effectively alleviated the stomatal restriction and non-stomatal restriction of leaf photosynthesis caused by cadmium stress.4.Hemin mediates the increase of key enzyme activity of sucrose metabolism in leaves under cadmium stress.Hemin treatment can significantly enhance the activity of sucrose phosphoric acid synthase?SPS?and sucrose synthase?SS?under cadmium stress,and reduce the activity of soluble acid invertase?SAInv?and alkaline/neutral invertase?A/N-Inv?,indicating that Hemin promotes sucrose synthesis and inhibits sucrose decomposition,thus promoting sucrose accumulat ion in maize leaves.5.Hemin improves the metabolic capacity of reactive oxygen species and the balance of antioxidant system in leaves under cadmium stress.Hemin effectively reduces the membrane lipid peroxide?TBARS?content in leaves,increase the blade under cadmium stress Chinese super oxide dismutase?SOD?and catalase?CAT?activity,APX and GR activity,slows down MDHAR and DHAR activity decreased,at the same time increased the square one ascorbic acid?As A?and also types of glutathione GSH conte nt.The DHA and GSSG were decreased,and the As A/DHA and GSH/GSSG ratios were increased to maintain the integrity of cell membrane structure and function under cadmium stress.6.Hemin promotes the balance of osmotic regulatory substance content in leaves under cadmium stress.Hemin effectively increases the ability of maize to withstand cadmium stress,increases the accumulation of soluble sugar,soluble protein,free amino acid and proline,contributes to the stability of subcellular structure,improves the water state of cells,and thus alleviates the effects of cadmium stress on leaf tissues,which is conducive to maintaining photosynthesis and improving plant growth.7.Hemin mediates the improvement of nutrient elements and key enzymes in root damage flow and nitrogen metabolism in leaves under cadmium stress.Hemin treatment can increase the transfer rate of NO ₃^-in xylem of plants.Under cadmium stress,two varieties of maize seedling leaves and free amino acid content of NH₄⁺in were significantly increased,and the content of NO₃^-and nitrate reductase?NR?,glutamine synthetase?GS?,glutamate synthase?incorporated?,glutamate dehydrogenase?GDH?,aspertate aminotransferase?GOT?,cereal third transaminase?GPT?activities were reduced.Hemin can reduce the glutamate content by reducing the weakening of GS/GOGAT pathway,enhance the activity of GS/GOGAT and GDH as well as the activity of transaminases?GOT and GPT?,and alleviate the toxic effect of ammonia and the disorder of nitrogen metabolism.8.Hemin induced an adaptive balance of endogenous hormone content and hormone ratio in leaves and roots under cadmium stress.Hemin can increase the ratio of IAA/ABA,ZR/ABA and GA/ABA in maize seedlings under cadmium stress,increase the content of growth hormones in IAA,ZR and GA,reduce the content of ABA inhibition growth hormones,and maintain the relative balance of endogenous hormones in maize seedlings.Hemin can effectively reduce the content of Me JA and SA in leaves under cadmium stress,which is conducive to maintaining the normal process of leaf aging and root function,and to reducing the adverse effects of cadmium stress on maize growth.9.Hemin stimulated the increase of secondary metabolites in leaves and roots and the increase of PAL enzyme activity under cadmium stress.Under cadmium stress,the indirect inducing effect of Hemin treatment on the aboveground part was not as strong as the direct inducing effect on the underground part.Compared with CK treatment,Hemin treatment increased the content of dingbu,total phenol and PAL activity in roots and leaves.Hemin treatment of the lower part of maize field can directly affect the chemical defense reaction of the treatment site?root system?,which is of great significance for the anti-stress characteristics of maize under cadmium stress.10.Hemin changed the polyamine PA content and enzyme metabolism physiology of leaves under cadmium stress,and enhanced the resistance of maize to cadmium stressHemin promoted the conversion of Put to Spd and Spm in cadmium-stressed plants,and the accumulation of binding and bound PAs.Hemin treatment increased the activity of ODC,SAMDC and DAO in maize seedling leaves under cadmium stress,decreased the activity of Hemin oxidase?PAO?,and had a more obvious effect on'fenghe 1'.Hemin can enhance the resistance of maize to cadmium stress by regulating the metabolism of endogenous PAs in maize seedlings.11.Hemin promoted seed germination under cadmium stress in simulated field and laid a population foundation for high yield of maize under stress.After Hemin+Cd treatment,germination rate,germination potential,vigor index and storage material transport rate increased,which improved the activity of alpha-amylase and beta-amylase,improved the conversion efficiency of endosperm starch,and improved the regularity of seed germination and germination.Hemin treatment can significantly improve the effect of Cd on the radicle and germ morphology of seedlings,which is beneficial to the emergence of apical soil in the germ sheath and the formation of root morphology.12.Hemin promoted the growth and development of maize leaves and roots under cadmium stress in field,and the yield and utilization efficiency of photothermal water resources were improved in coordination,providing experimental basis and technical approach for maize stress tolerance production.?1?Hemin enhanced photosynthesis of maize leaves under cadmium stress,delayed leaf senescence,and improved dry matter accumulation and distribution.Hemin treatment at an appropriate concentration can ensure that the net photosynthetic rate of maize after flower is maintained at a high level under cadmium stress,and the plant has a high chlorophyll content,thus maintaining a large green leaf area.A nalysis of leaf aging characteristics showed that Hemin treatment increased RGLAm,LAD and tmax values of stressed plants,decreased Vm and Vmax values,and prolonged the accumulation time of photosynthetic substances to ensure adequate carbohydrate supply for grain filling.?2?Hemin optimized the growth characteristic parameters of maize roots under cadmium stress in field,improved root activity and damage flow rate,and optimized the contents of mineral elements and amino acids in the damage flow of maize roots.Hemin can improve the absorption of water and nutrients by improving root activity and root damage flow.The contents of serine,glutamic acid,lysine,arginine and valine in root flow increased after Hemin+Cd treatment,which promoted the abilit y and level of maize root material circulation.Hemin+Cd treatment is beneficial to increase the content of mineral elements in the damaged flow of root system under cadmium stress,especially the flow of mineral elements in the transition period of vegetative growth and reproductive growth,which plays an important role in panicle differentiation and grain formation.?3?Hemin improved the starch characteristics of maize grain filling under cadmium stress in field,promoted the activity of key enzyme and gene expression of starch synthesis.The acceleration of Hemin+Cd treatment reduced the number of days(T _max)when the grains reached the maximum grouting rate,reached the maximum grouting rate faster,and increased the maximum grouting rate(V_max)and average grouting rate?V_m?,but had no significant effect on the grouting activity period?P?.The starch content of maize increased after Hemin treatment,and the effect of improving maize grain quality under cadmium stress was significant,among which amylose increased greatly.In the process of grain filling,AGPcase,SSS,GBSS and SBE all showed single peak curve changes.Cadmium stress treatment inhibited the activity of key enzyme of maize grain starch synthesis,while Hemin+Cd treatment increased the ac tivity of key enzyme of maize grain starch synthesis.Hemin treatment significantly increased the expression of zmsh1,zmsh2,zmwx1 and zmae1 genes in grains 30 days after anthesis.This indicated that under the cadmium stress,the appropriate concentration of Hemin had a direct regulatory effect on starch synthesis in the process of corn filling,which promoted the grain filling and the final grain weight increase.?4?Hemin increased maize yield under cadmium stress in field,improved the utilization efficiency of plants for photothermal water resources,and realized the coordinated improvement of maize yield and efficiency under cadmium stress.After Hemin+Cd treatment,the panicle number,1000-grain weight and panicle number of maize grains increased,in which the increase of 1000-grain weight was larger,the panicle length and panicle thickness increased,and the length of bald tip decreased.Hemin+Cd treatment significantly increased the light energy utilization efficiency?RUE?,heat utilization effici ency?HUE?and water use efficiency?WUE?of maize,and realized the coordinated improvement of maize yield and efficiency under cadmium stress.The study will provide a practical basis for the application of Hemin to the field resistance production of maize.