Plant Growth Regulation 43: 237–243, (2004).
L-DOPA (L-3, 4-ihydroxyphenylalanine) is one of the most highly active allelochemicals. L-DOPA is exuded from the roots of velvetbean (Mucuna pruriens (L.) DC. var. utilis) into soil, and causes growth inhibition of other species. In order to highly clarify the phytotoxic mechanism of L-DOPA, its effect on 32 species was surveyed, and absorption, translocation and metabolism in a tolerant species, barnyardgrass (Echinochloa crusgalli L.), and susceptible species, lettuce (Lactuca sativa L. cv. Great lakes 366), were examined at the germination stage. The species tested showed distinctly different responses to L-DOPA, with root elongation being more suppressed than that of shoots. Barnyardgrass was 77-fold more tolerant than lettuce based on the GR50 values determined 5 days after treatment. Absorption of L-DOPAin barnyardgrass and lettuce increased continuously during a 5 day exposure period, however, barnyardgrass absorbed a larger amount of L-DOPA than lettuce. The translocation of radioactivity derived from C14-L-DOPA to shoots was greater in lettuce than in barnyardgrass 3 and 5 days after treatment. Although the L-DOPA absorbed was metabolized in the roots of both species, the percentage of radioactive C14-L-DOPA increased in lettuce continuously but decreased in barnyardgrass over 5 days. In lettuce roots, a continuous increase of L-DOPA but not other metabolites was observed. However, the concentration of L-DOPA was higher in barnyardgrass roots compared with lettuce roots throughout the exposure period. These results suggest that L-DOPA itself is the active form, and the species.
