| Lodging is an important abiotic stress factor that negatively affects oat production,limiting the quality and yield of oat crops.This study used 4 different lodging types of oat varieties as materials at the test base of Dingxi Academy of Agricultural Science during 2017 to 2019,systematically compared the morphological characteristics and anatomical structure,physical and chemical components,and enzyme activity and gene expression of lignin synthesis pathways.Revealed the influence of morphological,anatomical and physiological characteristics on the lodging resistance of oat stems,expected to provide theoretical support for the research on the lodging resistance mechanism of oats.The main research results are as follows:1.The morphological characteristics of the oat root,stem,and ear were related to lodging resistance.The internode below ear was the most sensitive to lodging stress,and its length was significantly correlated with the center of gravity height(P<0.05).The risk of lodging in the field increased significantly when the ratio was larger than30%.The stem base thickness,wall thickness,and fresh density were negatively correlated with the actual lodging rate(P<0.01).The stem density at the base of the internode and section configuration were the main factors affecting stem weight and quality.Lodging-resistant oat cultivars had large ear dry weights,short below the ear internodes,and base(1+2)internode to the ear height ratios of less than 20%.Additionally,lodging-resistant oat varieties had short and thick root necks,large root volumes,the base internode short,thick stems,thin stem walls,large stem fullness,and large stem type indices.Hence,the stem quality can be improved by optimizing the internode structure and composition ratio at the stem base,establishing an ideal plant type for lodging-resistant oat varieties.2.In lodging-resistant varieties,the thickness of the base internode was 4.74?m,the number and thickness of cell layers in mechanical tissues were 6 and 521.52?m,respectively,the number of vascular bundles was 8a,and the area of large vascular bundles was 7653.9?m~2.Additionally,the epidermis was hard,and the cell wall of the cortex was highly lignified and thickness;thick-walled cells were small and arranged tightly and regularly.However,in the lodging varieties,the thick-walled tissues were arranged loosely,the parenchyma cells and the medullary cavity were relatively large,and the number of large vascular bundles was small.The differences in the thickness of the mechanical tissue,number of large vascular bundles,and area of vascular bundles between lodging and lodging-resistant varieties were highly significant(P<0.01)and positively correlated with the stem puncture strength,bending resistance,and the actual lodging rate.In addition,lodging-resistant oat varieties had highly lignified epidermal cell walls,more developed mechanical tissues and cell layers,large numbers of vascular bundles and extensive adjacent areas,and small medullary cavity and cuticle volumes.3.The potassium,calcium,and silicon contents in the stem base internodes of lodging-resistant cultivars were respectively 1.36,1.49,and 1.20-fold higher than those of lodging cultivars.Furthermore,the soluble sugar,cellulose,lignin,and C/N contents were 16.82%,13.30%,11.72%,and 20.45%higher in lodging-resistant varieties.High root nitrogen and silicon contents could significantly increase the stem basal internode weight and degree of enrichment,reduce the stem gravity center.Mineral element contents in the basal internode were related to organizational structure and fullesss,and the soluble sugar,cellulose,lignin,and C/N contents determined stem weight and quality,affecting the ability of lodging-resistance oat stems.The contribution of the stem physical and chemical properties to the lodging index ranked as lignin>soluble sugar>potassium>silicon>cellulose>C/N>calcium>magnesium>nitrogen.Low nitrogen and high potassium,calcium,silicon,magnesium,soluble sugar,cellulose,and lignin contents in the stem base internode promoted root growth and enhanced the stem hardness on the ground.These outcomes were more conducive to maintaining the stem C/N balance and reducing the dry matter transport rate,which were characteristic physical-chemical properties of lodging-resistant oat varieties.4.The lignin content of the second internode of the stem base increased on average by 27.70%throughout growth in lodging varieties.The increase was higher for lodging-resistant varieties,reaching 38.38%from the filling to the dough stages.As growth progressed,the flexural resistance of the second internode at the base of the stem increased and then decreased,whereas the lodging index at the same internode decreased and then increased.In lodging varieties,the second internode at the stem base was resistant to flexure and had low lodging resistance;its strength drop rate and lodging index were significantly(P<0.05)higher than those of lodging-resistant varieties.The changes in breaking resistance in the second internode,lignin content,and lodging index of lodging-resistant varieties were obvious before and after the seed filling stage.PAL,TAL,CAD,and 4CL activities were related to the lignin content and stem breaking resistance.At the same growth stage,PAL,CAD,TAL,and 4CL activities in the basal internode were significantly(P<0.05)higher in lodging-resistant cultivars.PAL and CAD activities had the highest correlation with the lignin content(0.473 and 0.281,respectively);therefore,higher PAL and CAD activities were the main factors promoting lodging resistance in oat stems.5.Six lignin biosynthesis-related genes were expressed at the stem base internodes of oat cultivars with different lodging types.The expression levels of PAL,CAD,and CCR1 were relatively higher in lodging-resistant varieties at the filling stage.Conversely,the expression levels of 4CL,CAD,CCR1,and CCR2 were relatively higher in lodging-resistant varieties at the milking stage.CCR1 and CCR2were the most expressed genes,with an average of 1.563 at different growth stages.The expression levels of 4CL were the lowest registered,with an average of 0.823.The interaction between variety and growth stage had significant effects on PAL,4CL,and C4H expression levels.Furthermore,PAL,C4H,CAD,CCR1,and CCR2up-regulated lignin synthesis at the grain filling stage and down-regulated it at the physiological maturity stage.The expression levels of PAL,CCR1,and CAD had the strongest correlation with the lignin content,and the expression levels of PAL had the strongest correlation with the expression levels of C4H and CCR1.Additionally,the expression levels of CCR2 had the weakest correlation with the lignin content and the expression levels of the other enzyme-coding genes.Hence,we inferred that the relatively high expression of PAL,CAD,and CCR1 significantly regulates lignin synthesis in oat stems. |
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