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

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 (g s ), transpiration (E), and quantum yield of electron flow through photosystem II (PSII) in vivo (Φ F ). In addition, L-DOPA and aqueous extracts increased the internal CO 2 concentration (Ci) and the leaf wax and trichome density on the leaf surface, while the maximum quantum yield of PSII (F v /F m ) 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 Φ F . 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.