Effects Of Shading On Physiological Characteristics And Lignin Biosynthesis Mechanism Of Asparagus Shoots

Asparagus is belonging to the Liliaceae family and has important economic and pharmacological value.The asparagus variety Fengdao 2 was used in this study.Four different shading treatments(0% shading,35% shading,55 shading and 75% shading)were used to study the effects of shading on physiological of asparagus shoots and explore the biosynthetic mechanism of lignin accumulation in asparagus shoots under shading treatment.The results are as follows:(1)Chlorophyll a,chlorophyll b and total chlorophyll decreased with the increase of shading rate,which limits the ability of asparagus to photosynthesize.Chlorophyll a/b value decreased at 35% shading and 55% shading,and increased at 75% shading,indicating that asparagus had strong negative tolerance when shading rate was less than 55%.(2)Soluble sugar increased with the increase of shading rate,but soluble protein showed the opposite trend.Compared with full light,SOD activity of asparagus shoots was significantly increased under shading treatment.MDA content,CAT and POD enzyme activities were significantly decreased under 35% shading treatment,and increased under55% shading treatment.These results indicated that there was no damage to the membrane of asparagus shoots under 35% shading,the damage to the cell membrane of asparagus shoots was alleviated under 55% shading treatment.(3)With the increase of shading rate,the stem diameter of asparagus shoots decreased significantly.The microstructure observation showed that the number of vascular bundles and xylem area were decreased under shading treatment,and lignin was reduced,which reduced the lignification of asparagus shoots.(4)Transcriptional and metabolic analysis revealed the changes of regulatory genes and metabolites in lignin synthesis pathway of asparagus shoots under shading treatment.Transcriptome analysis showed that a total of 37 differentially expressed genes related to lignin were identified,involving PAL,C4 H,4CL,CAD,CCR,POD,CCo AOMT and F5 H related enzyme activity regulatory genes.POD and CCo AOMT genes were significantly down-regulated,and the expression of CCR homologous genes were significantly decreased under different shading treatments.Metabolic analysis showed that intermediate metabolites such as cinnamic acid,caffeic acid,ferulic acid and sinapyl alcohol were significantly downregulated after shading,and the expression level decreased significantly under 55% shade and 75% shading treatment.It can be inferred that,under shading treatment,the decliner expression levels of POD,CCo AOMT and CCR genes decreased the activity of corresponding enzymes,and the expression levels of cinnamic acid,caffeic acid and ferulic acid in the upstream and sinapyl alcohol in the downstream also decreased significantly,which reduced the catalytic substrates of CCo AOMT enzyme,CCR enzyme and POD enzyme.In the end,the lignin content of asparagus shoots decreased.