| Phosphorus is one of the essential micronutrients for plant growth.However,the concentration of available phosphorus in soil is far below the minimum requirement for phosphorus.Application of phosphate fertilizer is one of the main strategies to increase crop yield.A large amount of phosphate fertilizer will cause environmental problems such as eutrophication of water.Therefore,improving the efficiency of phosphorus absorption and utilization of crops has become a very urgent problem in agricultural production.In recent years,it has become one of the important means to study the response mechanism of low phosphorus stress to screen and identify varieties with low phosphorus tolerance and explore the potential of crop tolerance to low phosphorus stress.Foxtail millet is an ideal material to study the mechanism of low phosphorus stress because of its drought tolerance and infertility tolerance.In this study,we evaluated the low phosphorus tolerance of 165 millet germplasm resources,screened out low phosphorus tolerance and low phosphorus sensitive varieties,and explored the mechanism of foxtail millet response to low phosphorus stress from phenotypic and metabolic levels.The main results are as follows:1.Through a hydroponic experiment was carried out on the 165 foxtail millet seedling normal and low phosphorus processing,the method of membership grade function is used for seedling resistance to low phosphorus foxtail millet screening and evaluation,low phosphorus characteristics could be divided into five grades: 165 foxtail millet type low phosphorus tolerance,low phosphorus less resistant type,medium resistance to low phosphorus and low phosphorus sensitive type and low phosphorus sensitive type.Sixteen samples of low phosphorus tolerance and nine samples of low phosphorus sensitivity could be studied as extreme materials.2.In the above screening to low phosphorus sensitive cultivars B171 and B254 type varieties as materials,and low phosphorus tolerance again by hydroponic experiment on seedling agronomic traits and physiological character identification,found that the plant height,the ground fresh weight,root fresh weight and leaf SPAD value under low phosphorus stress have different degrees of lower,and B171 in 7 d and 14 d decline than the normal phosphorus under low phosphorus condition were greater than B254 decline.By analyzing the root phenotypic characteristics,it was found that the total root length,total projection area,total root surface area and total root volume of B171 decreased by 35.87%,32.10%,32.10% and 28.23%,respectively,after low P stress compared with the normal P level,while the total root length,total projection area and total root volume of B254 increased by 108.05%,86.38%,86.38% and 67.28%,respectively.The acid phosphatase activity of B171 and B254 at 7 d and 14 d was measured.Compared with the normal phosphorus level,the acid phosphatase activity of B171 and B254 at 7d and 14 d under low P stress increased by 42.30% and 43.02%,respectively,and that of B254 increased by 13.18% and 40.10%,respectively.3.Based on untargeted metabolic techniques,metabolites produced in leaves and roots of two different P tolerance types of foxtail millet were analyzed under normal P stress and low P stress(0,7 and 14 d).Detected 447 metabolites,including 68 amino acid and its derivatives,28 organic acids,21 nucleotides and its derivatives,9 indole derivatives,18 alkaloids,56 flavonoids,10 vitamins,6 sugar alcohols,36 lipids,5 plant hormones,44 terpenoids,6 aromatics,17 coumarins,6 pyridines,17 phenols,11 amines,6 esters,7 ketones and 73 other metabolites.4.Under low P stress,amino acids and their derivatives,lipids,sugar alcohols and secondary metabolites,such as asparagine,phenylalanine,siberogalanine A5 and diglycosides,were accumulated in foxtail millet,and the up-regulation ratio in B254 was greater than that in B171.Two common metabolites,L-phenylalanine and L-phenylalanine,were screened out from B171 leaves after 7 and 14 days of low P stress compared with those before and normal P stress.Three common metabolites,D-asparagine,α-linoleic acid ethanolamide and lysolecithin LPC(18:3),were screened from the leaves of B254.One common differential metabolite was screened out from the root system of B171,which was calcinolone.Two common differential metabolites,anisene and LPA(18:1),were screened out from the root system of B254.5.The different metabolites detected in the two cultivars of foxtail millet under low P stress were enriched and analyzed,and a total of 38 metabolic pathways were found.Among them,14 common metabolic pathways were found in the leaves of the two varieties,and 7 unique metabolic pathways were found in the leaves of B171,which were arginine and proline metabolism,arginine biosynthesis,β-alanine metabolism,histidine metabolism,phenylalanine metabolism,phenylalanine biosynthesis,tyrosine and tryptophan biosynthesis,and tryptophan metabolism.There are four metabolic pathways in leaves of B254,which are pentose and glucuronic acid conversion,phosphoinositol metabolism,ascorbic acid and alginate metabolism,and degradation of valine,leucine and isoleucine.There were 21 common metabolic pathways in the root system,and 6 specific metabolic pathways in the root system of B171,including arachidonic acid metabolism,butyric acid metabolism,D-glutamine and D-glutamic acid metabolism,nitrogen metabolism,steroid hormone synthesis,and porphyrin and chlorophyll metabolism.There were two distinct metabolic pathways in B171 root system,namely retinol metabolism and pantothenic acid and coenzyme A biosynthesis.This study preliminarily explored the mechanism of millet response to low phosphorus from the phenotype,physiology and metabolism levels of low phosphorus sensitive and low phosphorus tolerant millet,identified the metabolites and metabolic pathways of foxtail millet response to low phosphorus stress,and provided an important theoretical reference for the development of low phosphorus tolerant foxtail millet varieties. |
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