The Influence Of Humic Acid On Flavonoids In Lemon Leaves And Its Mechanism

Humic acid-is a kind of natural organic matter extracted from lignite,which is widely used in agriculture and can significantly promote plant growth and development.Citrus limon(L.)Burm.F.is a plant belonging to the Rutaceae family.Because its branches,leaves,flowers and fruit contain a variety of active substances,the lemon has both edible and medicinal functions.Among them,flavonoids are the main active substances in lemon,and also one of the important indexes to reflect the quality of lemon.Ruili area in Dehong Prefecture,Yunnan Province is the second largest lemon planting base at present.In order to improve the quality of lemons,our research group carried out a series of experiments on the effect of humic acid on lemon quality.Based on these previous studies,the effect and mechanism of sodium humate and fulvic acid on the flavonoids in lemon leaves under different treatments in this work.The main researches and results are as follows:(1)The qualitative and quantitative analysis methods on 8 flavonoids in lemon leaves were established through HPLC analysis,which were vicenin 2,isoxoside,eriocitrin,vitexin,rutin,narcissoside,hesperidin and diosmin.(2)During 6 consecutive harvesting periods,compared with the control group,the contents of 8 flavonoids in lemon leaves were improved by applying fulvic acid and sodium humate.Among them,the effect of fulvic acid was than that of sodium humate,but the effect between spraying fulvic acid and sodium humate had great difference.(3)Based on the transcriptome sequencing results in our previous work,the activities of five flavonoid biosynthetases were determined by enzyme linked immunosorbent assay(ELISA),which are chalcone synthase(CHS),phenylalanine ammonlyase(PAL),4-coumarate-Co A ligase(4CL),flavonoid 3’-hydroxylase(F3’H)and flavonol synthase(FLS).The results showed that the activities of five flavonoid biosynthetases could be improved by irrigating sodium humate or fulvic acid,but their activities have some difference in spraying sodium humate or fulvic acid-treated groups.(4)The ELISA results were further verified by q RT-PCR.The results showed that the expressions of PAL,4CL,CHS,F3’H and FLS genes could be significantly upregulated by fulvic acid irrigation in five harvesting times except one.Irrigation with sodium humate could significantly up-regulate the gene expression of the above 5 enzymes.