The Mechanism Of Culm Lodging Resistance Difference In Wheat Varieties And Its Regulation Effects Of Nitrogen And Density

In field conditions,increasing nitrogen and density are major technical measures for improving yield.However,these measures led to increase the contradiction of population and individual and decrease the quality of stem,then decrease the mechanical strength and tend to lodging which would significantly decrease the grain yield.Du to the difference of varieties heredictary character,the quality of culm has various grade among varieties.Clarifying the genotype differences of wheat stem lodging resistance has an important theoretical guiding significancefor varieties improvement andreleasing the varieties potential.Cultivation measures have regulation effects on lodging resistance of wheat culm.Lignin endows the stiffness structure on culm and significantly affects the mechanical strength of culm.Therefore,Clarifying the effect of nitrogen and density on the lignin metabolism and the relationship with lodging resistance is the necessary fundamental research and is a guide for practical production.The study was performed at Shandong Agricultural University experimental station in 2014-2016.Two experiments were designed in this study.One is the genotypes difference on lodging resistance,8 varieties(weimai8,linmai4,shannong11,shannong23,laizhou95021,jiamai22,shannong16,zhoumai22)which have difference on lodging resistance were chosen.The second is the regulation effects of nitrogen and density.SN16 and SN23 which have significantly difference on lodging resistance were chosen as the experimental material.Three nitrogen levels,120(N1),240(N2),360(N3)and three density levels,75(D1),225(D2),375(D3)were designed.Combined phsiology,anatomy and molecular biology to clarify the mechanism of lodging resistance among different lodging degree varieties and regulation mechanism on lignin metabolism by nitrogen and density.Aiming to supply theoretical basis for excavating the lodging potential and cultivation measure.The main results were as follows: 1 The physiological mechanism of different lodging degree among varietiesThe lodging resistance of the basal second internode of 8 varieties was measured by culm strength tester at anthesis stage(DC,65),milking stage(DC,75)and dough stage(DC,85).From anthesis stage,the lodging resistance was gradually reduced.The 8 varieties were artifically divided into two groups which have significantly difference on lodging resistance.The two groups were defined as lodging resistance group and lodging sensitive group.The morphological characteristics including the plant height,the center of gravity height,the percentage of gravity account for plant height,culm diameter,culm filling degree were measured between the two groups at dough stage.The results indicated that the plant height of lodging resistance group were higher than that of lodging sensitive group.The center of gravity height of the two groups shows no significantly differences.However,the center of gravity height account for plant heigh at lodging resistance group was higher than that at lodging sensitive group.The culm diameter and filling degree of lodging resistance group were higher than that of lodging sensitive group.These results indicated that culm diameter,filling degree and the percentage of gravity height account for plant height can be as the reference characters.For further analysis the difference of lodging resistance between the two groups,anatomical structures were observed.The basal second internodes were fixed in FAA at ten days after anthesis.Making paraffin section using the fixed tissues and staining the tissue using sarranine and fast green.The lignified tissue was stained in red,unlignified tissue in green.The results showed that the degree and area of lignified tissue in lodging resistance group were remarkably higher than that of lodging sensitive group.SN11 which has the highest lodging resistance has the strongest lignified degree and area,and SN16 which has the lowest lodging resistance has the weakest lignified degree.The number and are of the big and small vasculars were quantified using the CaseViewer scanning paraffin software.The results indicated that the area of small vascular and the number of big vascular in lodging resistance group were significantly more than that of lodging sensitive group.Based on the difference of lignified degree,lignin content of the two groups varieties were measured through acetyl bromide method.The result showed that the lignin content of lodging resistance group was significantly higher than that of lodging sensitive group.SN11 which has the highest lodging resistance has the highest lignin contents,SN16 which has the lowest lodging resistance has the lowest lodging resistance.The correlation analysis showed that the lodging resistance has the significantly positive relationship with lignin content,culm diameter and culm filling degree.Increasing the lignin content,culm diameter and culm filling degree can improve the lodging resistance in wheat.2 The regulation effects of nitrogen and density on lignin metabolism and relationships with lodging resistanceDifferent nitrogen and plant density treatments have a regulation effects on lodging resistance of the basal second internode.At the same nitrogen levels,the lodging resistance gradually reduced with the increasing plant densities.The effects of nitrogen on lodging resistance have difference under different plant densities.At D1 level,the lodging resistance showed the tendency of N2D1>N1D1>N3D1.At D2 and D3 levels,the lodging resistance reduced by increasing the nitrogen levels.The regulation effects were further analyzed through the morphological characteristics of different nitrogen and density treatments.The results showed that the fresh weight per plant decreased,the center of gravity height upper shift,the percentage of gravity height account for plant height increased,culm diameter slimed,and the culm filling degree decreased with increasing the plant density at the same nitrogen levels.Under low plant density(D1),the above characteristics were showed increase tendency with increasing the nitrogen levels.However,at D2 and D3 levels,the above traits decreased with increasing the nitrogen levels.Based on the above morphological traits difference,anatomical structures were further observed to clarify the regulation mechanism.The basal second internodes were fixed in FAA at ten days after anthesis.Making paraffin section using the fixed tissues and staining the tissue using sarranine and fast green.The lignified tissue was stained in red,unlignified tissue in green.The results showed that the epidermis,sclerenchyma,vascular bundle sheath,duct and tracheid cells were dyed in red.This showed that these tissues or cells occurred in lignification in wheat culm.Different nitrogen and density treatment have significantly affects on the lignified degree of the basal second internode.With the increasing the plant densities,the lignified degree showed a tendency of decreasing at the same nitrogen levels.The lignified degree showed no significant difference at D1 treatment with the changes of nitrogen levels.At D2 and D3 treatments,the lignified degree decreased with increasing the nitrogen levels.Through quantified the number and area of the big and small vasculars of the basal second internode,we found that there were no regular tendency under N1 and N2 nitrogen levels with increasing the plant densities.However,at N3D3 treatment,the number of small vascular was significantly lower than other treatments.Increasing nitrogen and plant density led to the decrease of the number of big vascular.The lignin autofluorescence at different stages were observed using laser confocal microscope.We found that lignin autofluorescence signal gradually strengthened during the developmental stages.Lignin is one of the important components in plant cell walls,which can endow stiffness structure for culm,increase the mechanical strength and lodging resistance.The results showed that the accumulation rate exist difference at different developmental stages.0-28 day after forming the second internode is the fast stages of lignin accumulation,after that,the accumulation of lignin still in,but the rate has lower than before.The lignin accumulation decreased with the increasing plant densities under the same nitrogen levels.At D1 treatment,the lignin accumulation exhibited the tendency of N2D1>N1D1>N3D1.At D2 and D3 treatments,the lignin accumulation decreased with the increasing the nitrogen levels.For further deeply clarifying the regulation mechanism by nitrogen and density,the enzyme activity and expression abundance of the key enzymes in lignin biosynthesis pathway.The results showed that the higher PAL,COMT,CCR,CAD activity and expression abundance were contributed to the lignin biosynthesis and accumulation.Through alkaline nitrobenzene oxidation method,the wheat culm lignin was degraded due to the chemical bond breakage.The lignin monomers were qualitative and quantitative analysis by high performance liquid chromatography mass spectrometer(UPLC-MS/MS).The results showed that H,G,S monomers are the main type of wheat culm lignin.G and S monomer have the higher percentage.Increasing the plant density,S monomer decreased,G monomer exhibited increased then decreased.Increasing applying nitrogen levels led to the relatively increase of H and G monomers,decreased the S monomer.It can be concluded that S monomer has the important role in the mechanical strength of wheat culm.Decreasing plant density and nitrogen can increase the lodging resistance in wheat.However,due to the not enough at ear number,the grain yield had decreased significantly.Therefore,we should comprehensive consideration the cultivation measures to maintain culm quality and acquire the relative high grain yield.In this study,N1D2 and D2D2 of SN16 and N2D2 and N3D2 of SN23 have the relative high culm quality and grain yield.