Gene Expression and Isoflavone Concentrations in Soybeans Treated with Chitosan

Isoflavones in soybean seeds have putative health-beneficial effects. Previous studies demonstrated that foliar application of chitosan could increase soybean isoflavone concentrations. In this study we determined the impact of different chitosan solutions on gene expression and isoflavone concentrations of two soybean cultivars [AC Orford (low isoflavone cultivar) and AC Proteina (high isoflavone cultivar)]. QRT-PCR was used to quantify genes encoding enzymes at key points of the phenylpropanoid pathway, including phenylalanine ammonia lyase (PAL), chalcone synthase (CHS) and chalcone reductase (CHR), and at branch point enzymes in isoflavone biosynthesis [isoflavone synthase (IFS)]. Foliar applications of chitosan solutions [low (75-150 kDa) and high (>100 kDa) molecular weight] were done at early podding; untreated plants served as control. Plants were harvested 1 and 7 days after treatment and separated into leaf, stem, root, flower, pod, and seed parts; other plants were grown to maturity to sample mature seeds. Gene expression 1 day after treatment and isoflavone concentrations 7 days after treatment were not affected by chitosan in any plant part for both cultivars. Expression of genes was however consistently greater in AC Proteina than AC Orford, and was generally higher in roots than other plant parts. Differences in isoflavone concentrations between cultivars were observed in leaves only. Concentrations were greatest in roots and negligible in pods and seeds. Isoflavone concentrations in mature seeds were unaffected by treatments, but differed between cultivars being greater in AC Proteina. Media Summary Foliar applications of chitosan did not alter the expression of genes involved in isoflavone synthesis nor did it increase seed isoflavone concentrations.