Histological And Transcriptomics Study Of Red Maple Cutting Rooting

Red maple(Acer rubrum L.)is a very valuable horticultural ornamental tree species.The introduction and cultivation of red maple faces the outstanding problem of large-scale and slow commercialization process,and the asexual propagation of improved varieties,especially the efficient cutting propagation technology,is an important way to solve this problem.However,there are still horticultural tree species that are difficult to survive.Therefore,it is necessary to use red maple as the material to analyze the mechanism in depth to provide theoretical guidance for the improvement and perfection of the rapid propagation technology of horticultural tree species.In this study,cutting experiments were carried out with the cuttings of the excellent horticultural variety of red maple’October Guanghui’.Based on the analysis of the key external factors affecting the survival of cuttings,the tissue and cell characteristics map was established for the key period of cutting rooting,and then the gene transcription regulation was carried out.Mechanism analysis,reveal key regulatory genes at the molecular level,and deeply understand the survival mechanism of red maple cuttings from the core physiological process.The main results are as follows:(1)The developmental state of cuttings,cutting time and exogenous hormone treatment are the main factors that affect the survival of red maple cuttings.The composite substrate is better than a single substrate on the cuttings of "October brilliance" of Acer red flower.Hesha: Perlite: Vermiculite(1:1:1)composite matrix has the highest rooting rate,number of roots,root length and rooting index.The best rooting rate is 69.44%,the average number of roots is 12.31,and the average root length is 5.40 cm,all were significantly(P<0.05)higher than other matrices.The growth regulator IBA+NAA treatment of hardwood and softwood cuttings can significantly promote the rooting effect.Hardwood cuttings are treated with IBA(500 mg/L)+ NAA(500 mg/L)soaked for 20 minutes,and the treatment is best;softwood cuttings are treated with IBA(200 mg/L)+ NAA(200 mg/L)soaked The best treatment is10 min after cutting.The rooting rate and adventitious rooting rate of softwood cuttings were higher than those of hardwood cuttings.Tender shoots have the best cutting effect in July.The highest rooting rate of cuttings is 80%,and it takes about 36 days to form adventitious roots;the highest rooting rate of hardwood cuttings is 76.67%,and the highest rooting rate of adventitious roots is about 45 days.(2)The histology of cutting rooting of red maple shows that the rooting process is divided into the induction period of root primordial cells,1d-30 d after cutting;the formation period of root primordium,30d-36 d after cutting;the expression period of adventitious roots,after cutting 36d-45d;the elongation period of adventitious roots.The anatomical characteristics of the hard branches of red maple are similar to those of the tender branches.The difference between the two is that the cross section of the hard branches occupies a large proportion of the xylem,and the outer side of the phloem has thick-walled tissue that is circular.There is no latent root primordium in the cuttings before cutting,and they are all induced after cutting.The adventitious roots originate from the intersection of vascular cambium and wood ray and the parenchyma of phloem.Therefore,Acer red flower belongs to the induced root primordium.Type of multiple locus occurrence.(3)Accurate sampling based on the critical period of cutting rooting determined by histology,and carry out corresponding transcription regulation analysis.Differential genes in the key period of cutting rooting were screened out: S2＿VS＿S1,9817;S3＿VS＿S2,2626;S4＿VS＿S3,402.Further cluster analysis of these differential genes revealed that 149 are related to hormone synthesis,metabolism and signal transfer.Genes,respectively related to ethylene(55),auxin(36),jasmonic acid(25),abscisic acid(13),brassinolide(6),gibberellin(6),zeatin nuclear Glycosides(6)and salicylic acid(2);41 genes related to root regeneration were found.(4)Based on the results of the differential gene expression network,the temporal and spatial distribution of endogenous hormones IAA,ABA and ZR and the dynamic changes of their ratios during the rooting process of red maple cuttings were studied.During the S1 period,IAA was mainly concentrated in the cambium area and around the ducts near the cambium,and a small part of it was distributed in the phloem parenchyma cells;ABA was spotted in the phloem,cambium and xylem rays;ZR was distributed in the cambium and cambium Nearby parenchyma cells;During S2,IAA and ABA were mainly distributed around the enlarged parenchyma cells and the newly formed root primitive cells,and ZR was scattered around the parenchyma cells;During S3,IAA was mainly concentrated in the cutting cambium In the area,ABA is located around the root primitive cells in a differentiated state,and ZR is mainly distributed near the adventitious root meristem;during S4,a small part of IAA is located in the peripheral parenchyma cells of the adventitious root,and ABA is mainly distributed in the adventitious root elongation zone and the original cambium of the cuttings.In the connected area,ZR gathers around the vascular tissue in a large amount,thus proposing the spatiotemporal distribution model of endogenous hormones in the cutting rooting process.