Effects Of Shading On Growth And Accumulation Of Active Constituents Of Taraxacum Mongolicum Hand

Taraxacum mongolicum Hand.-Mazz is a perennial herb in the Asteraceae family and contains a variety of active ingredients.Light is an important environmental regulator in plant growth,but its effect on the growth and accumulation of the main active ingredients of Taraxacum mongolicum are still infancy.Therefore,in this study,biennial Taraxacum mongolicum was selected as the experimental subject and four shade treatments:20%(T1)、40%(T2)、60%(T3)、80%(T4))and a control group with natural light(CK)were set up,one for sampling without harvesting(15,30,45,60,75 and 90d after shade)and the other for harvesting(the first crop was harvestedd on 20June,followed by one crop every 20d for five consecutive harvests,with relevant indicators measured at the same time).The effect of different shading rates on the growth and accumulation of the main active ingredients of Taraxacum mongolicum was studied to clarify the relationship between primary metabolism,secondary metabolism,photosynthetic properties and the main active ingredients of Taraxacum mongolicum,to provide a reference for Taraxacum mongolicum production and a theoretical basis for the analysis of the accumulation pattern of the effective active ingredients of Taraxacum mongolicum.The following results were obtained from the experiments:(1)Shade significantly changes the morphology of Taraxacum mongolicum leaves.20%-40%shade increases the growth of Taraxacum mongolicum leaves and above-ground biomass accumulation and photosynthetic efficiency,but shade is detrimental to the accumulation of below-ground biomass in Taraxacum mongolicum.The control(CK)Taraxacum mongolicum leaves without shading showed narrower and deeper leaf fractures,which became shallower with increasing shade.The number of Taraxacum mongolicum leaves,leaf area,above-ground biomass,root to crown ratio,net photosynthetic rate(Pn),and maximum photochemical efficiency of PSII(Fv/Fm)tended to increase and then decrease with increasing shade,and reaching a maximum at20%(T1)or 40%shade(T2);shade was detrimental to the growth of Taraxacum mongolicum roots,and its dry weight of the under ground tended to decrease significantly with increasing shade.(2)Shade was not favourable for the accumulation of total triterpenes in Taraxacum mongolicum,while 20%shade was favourable for the accumulation of total flavonoids,total choline,luteolin,rutin,quercetin,chlorogenic acid,caffeic acid and chicory acid in Taraxacum mongolicum,and 40%shade was more favourable for the accumulation of total phenols in the leaves.The content of each active ingredient in the leaves was significantly higher than that in the roots.For the unharvestedd Taraxacum mongolicum,the content of total flavonoids,total phenols,total choline,luteolin,rutin,quercetin,chlorogenic acid,caffeic acid and chicory acid firstly increased and then decreased with increasing shade from 15 d to 75 d.The content of total phenols in the 40%shade treatment was highest among all shade treatment,and other ingredients content in the 20%shade treatment has a highest level.While,the content of total flavonoids,rutin and chlorogenic acid in the leaves was slightly lower than that of CK at 90 d.The content of quercetin,lignan,total choline and total flavonoids in the roots was also slightly lower than that of CK.For harvestedd Taraxacum mongolicum,the content of all active ingredients firstly increased and then decreased with increase of shading rate in the first four harvests,and reaching a maximum content at T1 or T2.The content of each active ingredient showed a first increase and then decrease trend with the number of harvests increased,and the higher value at the second or third harvests.(3)Shading was beneficial in improving the antioxidant activity of Taraxacum mongolicum in vitro.DPPH,ABTS~+and OH~-radical scavenging capacity were positively correlated with the contents of total flavonoids,total phenols,chlorogenic acid,caffeic acid and chicory acid.The scavenging capacity of DPPH,ABTS~+and OH~-radicals tended to increase and then decrease with increasing shading.T1 significantly increased the free radical scavenging capacity of DPPH and ABTS~+;T2 significantly increased the OH~-radical scavenging capacity of leaves.Correlation analysis showed that the OH~-radical scavenging capacity was highly significantly and positively correlated with the content of total flavonoids,total phenols,chlorogenic acid,caffeic acid and chicory acid.ABTS~+radical scavenging capacity was highly significantly and positively correlated with the content of total phenols,and the DPPH radical scavenging capacity was also positively correlated with each active ingredient.(4)Photosynthetic efficiency was positively correlated with the accumulation of each active ingredient in Taraxacum mongolicum.In the leaves,total choline content showed a highly significant positive correlation with net photosynthetic rate.Total flavonoids,rutin,chlorogenic acid,and Fv/Fm showed a highly significant positive correlation;total flavonoids,total phenols,rutin,luteolin,quercetin,chlorogenic acid,caffeic acid,and chicory acid content showed a highly significant positive correlation with photochemical burst coefficient(q P),and total phenol content showed a highly significant negative correlation with non-photochemical burst coefficient(NPQ).Total flavonoids in the roots showed a significant positive correlation with Pn,Fv/Fm,and the actual photochemical efficiency of PSII(ΦPSII).(5)The accumulation of active ingredients in Taraxacum mongolicum was influenced by primary and secondary metabolic related enzyme activities.The higher content of soluble sugars,sucrose,soluble protein and total amino acids in leaves facilitated the accumulation of total phenols,caffeic acid,chlorogenic acid and chicory acid.High levels of phenylalanine demineralase(PAL),cinnamic acid hydroxylase(C4H),4-coumaric acid-Co A ligase(4CL),and chalcone synthase(CHS)activities favoured the accumulation of total flavonoids,rutin,and chlorogenic acid,all of which reached highly significant positive correlations.Total flavonoids,total phenols,luteolin,quercetin,chlorogenic acid,caffeic acid and chicory acid content in the roots showed highly significant positive correlations with GS(glutamate synthase),NR(nitrate reductase),PAL,C4H,4CL enzyme activities and C4H gene expression.