Root Endophytic Fungi Regulate Changes in Sugar and Medicinal Compositions of Polygonum cuspidatum

Abstract

<i>Polygonum cuspidatum</i> Sieb. et Zucc is an important industrial crop because it contains a large amount of medicinal secondary metabolites (such as polydatin, resveratrol, chrysophanol, and emodin). However, it is unclear whether root endophytic fungi increase the content of secondary metabolites in the plant. This study aimed to analyze the effects of <i>Funneliformis mosseae</i> (<i>Fm</i>) and <i>Piriformospora indica</i> (<i>Pi</i>) alone or in combination on plant growth, root morphology, thirteen sugars concentrations, and six secondary metabolites (physcion, chrysophanol, emodin, aloe-emodin, polydatin, and resveratrol) concentrations of <i>P</i>. <i>cuspidatum</i>. After 11 weeks of the fungal inoculation, the roots could be colonized by <i>Fm</i> and <i>Pi</i> single or in combination, along with the higher root colonization frequency of <i>Fm</i> > <i>Pi</i> > <i>Fm</i> + <i>Pi</i> in the descending order. In addition, <i>Fm</i> and <i>Pi</i> improved plant growth performance (plant height, stem diameter, leaf number, and shoot and root biomass) and root morphology (average diameter, maximum diameter, total length, area, and volume) to varying degrees, depending on fungal inoculations, in which <i>Pi</i> displayed a relatively better effect on plant growth. Single <i>Fm</i> and <i>Pi</i> inoculation significantly increased three disaccharides (sucrose, maltose, and trehalose) accumulation, while dual inoculum (<i>Fm</i> + <i>Pi</i>) only elevated sucrose concentrations. Most monosaccharides concentrations, such as D-arabinose, D-galactose, D-sorbitol, D-fructose, glucose, and L-rhamnose were not altered or inhibited by the endophytic fungi, except the increase in L-fucose and inositol. All fungal treatments significantly increased root chrysophanol and resveratrol concentrations, while decreased aloe-emodin concentrations. In addition, single <i>Pi</i> and dual <i>Fm</i> + <i>Pi</i> increased emodin concentrations, and single <i>Fm</i> and dual <i>Fm</i> + <i>Pi</i> elevated physcion and polydatin concentrations. It was concluded that <i>Fm</i> and <i>Pi</i> promoted the growth of <i>P</i>. <i>cuspidatum</i>, and the combination of <i>Fm</i> and <i>Pi</i> was more conducive to the production of some secondary metabolites than single inoculation.