Research On Signal Transfer In The Biosynthesis Of Phenols In Plants Induced By Arbuscular Mycorrhizal Fungi

Phenols are important secondary metabolites in plant tissues, providing wellprotection against the biotic or abiotic stresses in plants. In this experiment, clover(Trifolium repens L.) were employed to study the changes of phenolic content and thepreliminary examination on the possible signaling molecules of SA, H2O2, NO inclover roots inoculated with arbuscular mycorrhizal (AM) fungus, Glomus mosseae.The results indicate that:AM fungal inoculation significantly enhanced the contents of SA, H2O2, NO inclover roots in the pot experiment, suggesting the localized induction of signalingmolecule, SA, H2O2, NO, doe to AM fungal colonization. In the split-root experiment,AM fungal inoculation of half roots increased the contents of SA, H2O2, but not of NO,in the other half roots without inoculation, indicating the systmetical induction ofincrease in signaling molecules of SA, H2O2in clover roots by AM fungus. However,the role of NO in systemic induction needs further investigation.Inoculation with G. mosseae significantly enhanced the activities of SOD, POD,CAT, PAL, NOS in clover roots in the pot experiment, suggesting the localizedpromotion of defense-related enzymes by AM fungus. In the split-root experiment,inoculation of half roots with G. mosseae increased the activities of SOD, POD, PAL,in the other half roots without inoculation, indicating the systmetical induction of thesedefense-related enzymes by AM fungus. However, no induction of increase in NOSactivity was observed, in accordance with NO. This implied that NOS was the mainenzynme responsible for the NO synthesis in clover roots.The contents of cell wall-bound and free phenols in clover roots significantlychanged following the AM fungal inoculation, with the former increasing by25%~41%and the latter increasing by23%~36%, respectively, compared with the non-inoculatedcontrol. In the split-root experiment, inoculation of half roots increased the contents ofcell wall-bound and free phenols in the other non-inoculated half roots. This resultsuggests both localized and systematical increases in phenolic contents induced byAM fungus.Defense-related genes of pal, chs were locally induced due to the inoculation withAM fungus, with their expression2~3times higher than that of the non-inoculatedcontrol. In the split-root experiment, the expressions of pal, chs in the non-colonizedhalf roots were increased, indicating the systematical increase in the expression of defense-related genes due to AM fungal colonization.These results indicated that AM fungal colonization locally induced the increase inphenolic content, and SA, H2O2were the possible signaling molecules, furthertriggering the expression of pal, chs and the synthesis of the enzymes catalyzing theproduction of phenols. This casade process increased the phenolic content in thecolonized roots. Meanwhile, SA and H2O2were translocated to the non-colonized roots,inducing the expression of genes (e.g. pal and chs) related to the production of phenols,and the synthesis of SOD, POD, PAL, and finally increasing the phenolic content in thenon-colonized roots. Therefore, AM fungus contributed to the protection of the entireroots, not only of the colonized ones.