Mechanism of selective phytotoxicity of L-3,4-dihydroxyphenylalanine (l-dopa) in barnyardgrass and lettuce.
L-3,4-dihydroxyphenylalanine (L-dopa) is one of the few allelochemicals in which the phytotoxic action mechanism has been studied. Excess exogenous L-dopa suppresses root elongation in some plant species, and the inhibitory action is species-selective. The main factor of phytotoxicity of L-dopa is considered to be oxidative damage by reactive oxygen species (ROS) and/or free radical species (FRS). This study was performed to elucidate the mechanism of species-selective phytotoxicity. The involvement of ROS/FRS and polyphenol oxidase (PPO) in species-selective phytotoxicity was examined with barnyardgrass (Echinochloa crus-galli L.) and lettuce (Lactuca sativa L.), tolerant and susceptible species, respectively. Lipid peroxidation and melanin accumulation correlated with growth inhibition by L-dopa. Antioxidants, ascorbic acid and alpha-tocopherol, decreased lipid peroxidation and melanin accumulation and rescued lettuce root from growth inhibition. The oxidation of L-dopa by PPO was much greater in lettuce than in barnyardgrass. From these results, the phytotoxicity of L-dopa is considered due to the oxidative damage caused by ROS/FRS generated from the melanin synthesis pathway. PPO activity might be involved in the mechanism of species-selective phytotoxicity between barnyardgrass and lettuce.
Hachinohe
Mayumi
M
Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba 305-8572, Ibaraki, Japan.
Matsumoto
Hiroshi
H
D004156:Catechol Oxidase / Q000378:metabolism; D006540:Herbicides / Q000494:pharmacology*; D018545:Lactuca / Q000187:drug effects* / Q000254:growth & development; D007980:Levodopa / Q000494:pharmacology*; D008543:Melanins / Q000096:biosynthesis; D010777:Photochemistry; D018517:Plant Roots / Q000201:enzymology; D006109:Poaceae / Q000187:drug effects* / Q000254:growth & development; D013997:Time Factors
D006540:Herbicides; D008543:Melanins; D007980:Levodopa; D004156:Catechol Oxidase