Studies On DIMBOA And Flavonoid Compounds In Winter Wheat And Their Resistance To English Grain Aphid, Sitobion Avenue (Fabricius)

DIMBOA and flavonoid compounds are important secondary compoundsassociating with wheat resistance to aphids. Although being studied aboard sinceI 960s, the resistance of DIMBOA to English grain aphid hasn't been studied inChina, yet. Owing to the structures of flavonoid compounds in wheat beingunrecognized so far, it is difficult to study the resistance nature of thesecompounds to aphids. So,in this study, the following works were undertaken,attempted to make the conclusions in this area more clearly:(l)to extract, isolate,and identify the structure of DIMBOA and flavonoid compounds in the leaves ofwheat;(2) to determine the biological activity of the compounds to English grainaphids; (3) to measure their changes in different wheat growth stages and theirrelationship with the resistance levels of wheat to aphid.DIMBOA was isolated and purified from maize seedlings by the method ofWoodward(1978).Its structure was confirmed by paper chromatograph, UVspectrometry scan and nuclear magnetic resonance (NMR) techniques. The resultwas basicly in consistence with the literatures reported bofore.Flavonoids compounds were isolated and purified from wheat leaves atjointing stage by the Column Chromatograph method. The procedure was asfollows: the Leaf powder of wheat was extracted twice with differentmethanol-water solutions and condenced by circumratate evaporator.Afterdeesterified by petroleum ether,the residue extract was re-extracted with diethylether and ethyl acetate, respectively, and then divided into three parts:the ethylether extract, the ethyl acetate extract and the residual water solution. Twoflavonoid components were isolated and purified with Sephadex LH-20 columnfrom the EtOAC extract. Their structures were identified as isoorientin andisoorientin- 7-O-arabinosyl-glucoside by paper chromatograph, nuclear magneticresonance and UV spectrometer scan techniques. The same components wereisolated and purified from water solution after removed the sugar and otheranalogue substances by adding excessive dehydrated ethanol.The resistance abilities of the purified DIMBOA and flavonoid compoundsto English grain aphid were determined by adding them into the artificial diets ofEnglish grain aphids. DIMBOA and isoorientin showed strong antibioticresistance by significantly reducing the growth and reproductive rate of aphid.64While the resistance of isoorietin-7-O-arabinosyl-glusoside to aphids wasrelatively weaker.Using the isolated DIMBOA as the standard sample, the contents ofDIMBOA in wheat cultivars with different resistant levels in laboratory seedlingswere first studied by HPLC method. The contents of DIMBQA in wheatseedlings were O.232-0.389mg g' fresh weight.There was a weak negativerelationship between the content of DIMBOA and the resistant levels of wheatwith the correlation index at -0.57.According to the English grain aphid' s immigrating and out- breakingbehaviour in Northern China, the contents of DIMBQA in field-growth wheatcultivars from booting stage to early milky stage were analysed by HPLCmethod,too. The concentrations of DIMBOA in tested wheat stages were 0 - 0.09mg.g' fresh weight,which were much lower than that in seedlings grown in Lab.This result suggested that DIMBOA as a resistant factor in the later growth stagesof wheat may be negligible.The contents Flavonoid compounds in the later growth of wheat cultivarswere also measured by HPLC method. There were significant differences offalvonoid compounds among the different growth stages of wheat cultivars. Ingeneral, the leaves have the highest content of flavonoid compounds at jointingstage, then went down at booting stage, and increased at anthesis and early milkystage. The lowest content of flavonoid compounds in ears of wheat makes itpossible f...