Photosynthetic response of soybean to L-DOPA and aqueous extracts of velvet bean

Abstract

L-3,4-Dihydroxyphenylalanine (L-DOPA) is an allelochemical released by roots of velvet bean (Mucuna pruriens) that affects the growth of several plant species. However, its mechanism of action is inconclusive. In this work, we compared the effects of L-DOPA (0.01–1.0 mmol L−1) and of aqueous extracts (300, 1200, and 3000 mg L−1) of velvet bean on growth and photosynthesis (gas exchange and chlorophyll a fluorescence) of soybean (Glycine max). Overall, the results showed that both L-DOPA and aqueous extracts of velvet bean reduced the growth, leaf area, photosynthetic rate (A), stomatal conductance (gs), transpiration (E), and quantum yield of electron flow through photosystem II (PSII) in vivo (ΦF). In addition, L-DOPA and aqueous extracts increased the internal CO2 concentration (Ci) and the leaf wax and trichome density on the leaf surface, while the maximum quantum yield of PSII (Fv/Fm) was not changed. These results suggest that the reduction of A should not be related exclusively to the stomatal closure, but also to limitations of the carbon metabolism, as indicated by the increase of Ci and decrease of ΦF. Briefly, we concluded that soybean growth inhibition by L-DOPA and aqueous extracts of velvet bean is due to the combination of damage in the root meristem and reduction in A.