PORPHYRIN INTERMEDIATE INVOLVED IN HERBICIDAL ACTION OF DELTA-AMINOLEVULINIC-ACID ON DUCKWEED (LEMNA-PAUCICOSTATA HEGELM)

Using an aquatic higher plant duckweed (Lemna paucicostata Hegelm.), which was highly susceptible to exogenously applied delta-aminolevulinic acid, the relationship between phytotoxic activity and its induced accumulation of porphyrin intermediates was investigated. When the plants were floated on 0.5 or 1 mM of delta-aminolevulinic acid solution for 12 hr in darkness and then exposed to light, rapid electrolyte leakage and bleaching from the plants occurred. The herbicidal action in the light was much greater after the 12-hr treatment than that after the 2-hr treatment. In darkness, large amounts of protochlorophyllide and protoporphyrin IX were accumulated with the incubation time. However, the ratio of accumulation of protoporphyrin IX was the greatest among the tested tetrapyrroles. It reached more than 8.6- and 101-fold of control after 2 and 12 hr, respectively. The ratios of other porphyrins were small and changed little between the incubation periods. It is considered that phytotoxic action of delta-aminolevulinic acid to duckweed is caused by the photodynamic action of accumulated protoporphyrin IX. (C) 1994 Academic Press, Inc.