Research On The Mechanism Of Response To Different Light Qualities In Green Onion (Allium Fistulosum L.)

With the rapid development of facility agriculture,the cultivation pattern of green onion has undergone significant changes.To meet the needs of green onion factory production,this paper investigated the effects of different light quality on green onion growth,yield quality,secondary metabolism,photosynthetic capacity,and reactive oxygen metabolism,and screened key differential genes through transcriptome analysis,to elucidate the response mechanism of green onion to different light quality and provide theoretical basis for the regulation of light environment of green onion in facilities.The main findings were as follows:1.In LED conditions,the relative growth rate of white(W)treated green onion was significantly higher than other monochromatic light treatments,with blue(B),red(R),green(G)and yellow(Y)only 94.36%,89.30%,84.33% and 76.21% of W,respectively.Compared to B,R,G and Y,the net photosynthetic rate(Pn)of W increased by 11.39%,24.07%,39.23% and 59.62%,respectively.Significant differences were also found among different monochromatic light treatments,with B treatment being better,with significantly higher Pn,transpiration rate(E),stomatal conductance(Gs),apparent quantum efficiency(AQY),light saturation photosynthetic rate(Pmax),carboxylation efficiency(CE)and maximum regeneration rate of Ru BP than R,G and Y monochromatic light treatments.2.In LED conditions,the different forms of nitrogen and sugar contents,as well as nitrate reductase(NR),glutamine synthetase(GS),glutamate dehydrogenase(GDH),glutamate synthase(GOGAT),sucrose phosphate synthase(SPS)and sucrose synthase(SS)activities of green onion leaves in the W treatment were significantly higher than those in each monochromatic light treatment;the above indicators in the monochromatic light treatment were higher in B,lower in Y,and intermediate in R and G.The leaf structure and chloroplast ultrastructure were better developed in the W and B treatments.3.In the combined LED conditions,the leaf area,plant height,stem thickness,relative growth rate(RGR),pigment content,photosynthetic capacity,and photosynthetic electron transfer efficiency of green onion treated with white + blue(WB)were significantly higher than those of white(W),white + red(WR),white + green(WG),and white + yellow(WY).The WB promoted the growth of green onion,and its RGR was higher than those of W,WR,WG and WY by 3.43%,14.17%,21.54% and 33.35%,respectively.The chloroplast ultrastructure of the leaves of the WB was better developed,indicating that increasing the blue light ratio was beneficial to improve the light energy utilization efficiency of the green onion.4.Different light qualities had significant effects on the organ morphology and functional component substances of green onion.WB increased the contents of soluble sugars,soluble proteins,free amino acids,crude cellulose,and important sulfur compounds of green onion,while WY and WG inhibited the synthesis of pseudostem and root compounds of green onion,indicating that WB could increase the content of nutrients and improve the palatability and nutritional value of green onion.5.The growth of green onion was significantly affected by covering different photoselective net in the field,but blue(BN)performed better with 14.54% increase in yield compared with CK,and its leaf photosynthetic pigment content,Pn,E and Gs were higher,followed by white(WN),BN and WN were better than CK,while red(RN),green(GN)and yellow(YN)were inferior to WN.Fv/Fm,?PSII and q P were in descending order: BN > WN > CK > RN > GN > YN.The reactive oxygen content of BN-treated green onion leaves was significantly lower than the other treatments,and their key enzyme activities were significantly higher.BN also improved the absorption and transformation ability of elements in all organs of green onion,and significantly increased the content of soluble sugar,Vc and free amino acids in green onion with better overall quality,which could be promoted and applied in production as a special net for green onion facility cultivation.6.Combination of Illumina and single molecule real-time(SMRT)RNA sequencing was used to sequence the transcriptome of BW,W,and B green onion leaves.These results showed that 327 and 386 differentially expressed genes(DEGs)were identified under BW and B,respectively,compared to W.Analysis by KEGG pathway showed that DEGs under the three light conditions were closely associated with the pathways of photosynthesis,carbon metabolism,photosynthesis-antenna protein,glyoxylate and dicarboxylic acid metabolism,sulfur metabolism,porphyrin and chlorophyll metabolism,photo-transduction,amino acid biosynthesis,RNA transport,and carbon fixation by photosynthetic organisms.