Allelochemical l-DOPA induces quinoprotein adducts and inhibits NADH dehydrogenase activity and root growth of cucumber

Allelochemical l-DOPA (l-3,4-dihydroxyphenylalanine) inhibits growth of several plant species. However, its mode of action is not well clarified in plants. The present studies were conducted to explore the action mechanism of l-DOPA in cucumber roots. The results revealed that l-DOPA suppressed the root growth of cucumber and induced quinoprotein and melanin formation in the roots. Moreover, l-DOPA not only decreased mitochondrial viability and NADH dehydrogenase (complex I) activity but also increased quinoprotein formation in vitro in isolated mitochondria from cucumber roots. Strong correlations were observed between quinoprotein formation and root growth inhibition, quinoprotein formation and NADH dehydrogenase activity, after l-DOPA treatment. The results suggest that quinoprotein formation and mitochondrial impairment might be involved in growth-inhibition mechanism of l-DOPA in cucumber roots.