Benefits of a Combination of Hexanal and Pantoea agglomerans KSC03 on Plant Growth and Accumulations of Bioactive Isoflavone Glycosides in Astragalus membranaceus var. mongholicus

Abstract

Hexanal belongs to green leaf volatiles that function as signal molecules in plants. However, it remains elusive whether and how hexanal functions in herbal medicines besides imparting unique flavor. In this study, the effects of hexanal and Pantoea agglomerans KSC03 on plant growth and secondary metabolism were investigated in medicinal plant Astragalus membranaceus var. mongholicus by treating the seedlings with hexanal, KSC03, and their combination. Biomass yield and the contents of chlorophyll a and b in mature leaves were used as indexes as well as the contents of bioactive isoflavones in the roots. Meanwhile, lipoxygenase (LOX) inhibitor phenidone was applied 48 h before hexanal treatment to obtain the LOXlow seedlings to understand signal roles of LOX pathway in the accumulations of bioactive isoflavones in the roots under hexanal and KSC03 treatments. The results revealed that hexanal alone and its combination with KSC03 significantly increased the shoot and root yields, and hexanal + KSC03 showed stronger promotion on the shoot yield, which coincided with significantly enhanced accumulations of ononin and calycosin-7-O-β-d-glycoside in hexanal + KSC03 treatment. Hexanal + KSC03 also alleviated the detrimental chlorophylls cycle compared with hexanal alone. Except for the combined treatment, phenidone pretreatment greatly enhanced the concentrations of ononin and calycosin-7-O-β-d-glycoside in the roots of the control and the application of hexanal and KSC03 alone. In conclusion, hexanal + KSC03 treatment was more beneficial on plant growth and accumulations of bioactive isoflavones in the roots of A. membranaceus var. mongholicus, partially due to the attenuated inhibition of LOX signaling.