Cold Resistance Identification At Germination Stage And Physiological Index Study Of Sweet Corn During Seedling Stage

Cold injury of low temperature in early spring occurs frequently in northeast China,which is one of the important factors restricting the maize production in this region.In this study,30 inbred lines of sweet corn were used as experimental materials to artificially simulate the conditions of low temperature stress,and the relative value and comprehensive D value of each evaluation index of cold resistance were measured and calculated.The cold resistance of the inbred lines of sweet corn at the budding stage was evaluated by cluster analysis.Two inbred lines,T12(cold-tolerant)and T27(cold-sensitive),were screened for cold injury stress at seedling stage.Photosynthetic indexes,chlorophyll fluorescence parameters and stress-related physiological and biochemical indexes were determined at seedling stage,and the ultrastructure of leaf mesophyll cells was observed after low-temperature treatment.The main research results are as follows:1.Clustering analysis results show that 30 sweet corn inbred lines can be divided into three groups: the first ? class contains 10 varieties,accounted for 33.33%,belong to the strong cold tolerance;First ? class contains nine species,accounting for 30%,belong to medium type cold tolerance;The first ? class contains 11 varieties,accounted for 36.67%,belong to the cold sensitive;Through the identification of the multi-index evaluation system established by the relative value,comprehensive D value and clustering analysis of each index in the bud stage of sweet corn,two materials T12(cold-resistant type)and T27(cold-sensitive type)were selected for the next study.2.Low temperature stress significantly inhibited the growth of T27 morphological indexes,and low temperature treatment at 6d had little effect on T12 morphological indexes compared with the control.As the temperature 15? after the extension of time,the T12 indicators quickly return to the control level.On the contrary,at R6 d,the differences in root fresh weight,leaf area and root surface area of T27 and the control group reached significant levels,and the differences in seedling fresh weight,seedling dry weight,root dry weight,plant height,total root length,root volume and average root diameter reached extremely significant levels,indicating that low temperature had a great impact on T27's plant morphology and development.3.After low temperature treatment,compared with the control,the chlorophyll a and chlorophyll b of T27,chlorophyll(a+b)declined significantly,with the lower net photosynthetic rate(Pn),stomatal conductance(GS)of T27 and the maximal photochemical efficiency(Fv/Fm),the actual photochemical efficiency(?PSII),acyclic photosynthetic electron transport(ETR)and light chemical efficiency(qp)was significantly lower than the control group,and transpiration rate(E),intercellular CO2 concentration(Ci)and the coefficient of photochemical quenching(NPQ)were higher than the contro,The variation range of chlorophyll content,photosynthetic index and chlorophyll fluorescence parameters of T27 at low temperature was significantly greater than T12,indicating that T27 reduced photosynthetic capacity and stress recovery capacity of plants due to stomatal factors.4.The analysis of physiological and biochemical indexes showed that the accumulation of reactive oxygen species induced by low temperature led to the increased activities of peroxidase(POD),catalase(CAT)and ascorbate inhibitor(APX)in the two materials at the initial stage of treatment.The increase of T12 is much larger than that of T27,indicating that the T12 ros scavenging system is more sensitive to stress than that of T27.Low temperature leads to the aggravation of lipid membrane oxidation,and the content of soluble sugar and malondialdehyde(MDA)in T12 and T27 increases.At 6d of low temperature,the content of soluble sugar in T12 increases compared with that in the control group,and the difference is extremely significant.5.Anatomic structure analysis showed that low temperature significantly damaged the cell structure of T27,with loose arrangement of mesophyll cells,intercellular hyphae and cell wall rupture.Chloroplast membrane dissolved,chloroplast lamellae vacuolated,the volume outward expansion;Mitochondrial structure dissolved and disappeared;Low temperature increased the number of plastids in the mesophyll cells of T12,but the cell structure was intact and the cell wall was clear.The chloroplast membrane was intact and the inner lamellae were clearly and orderly arranged.The outer membrane of mitochondria was intact and the inner ridge was clear.This indicated that the stability of T12 cells was higher than that of T27 cells under low temperature stress.