SCREENING OF PLANT GROWTH REGULATORS FROM INTERMEDIATES OF PLANT PIGMENT BIOSYNTHESIS

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Chlorophylls and carotenoids biosynthetic pathways are peculiar to plants. Recently, it was reported that chlorophyll precursor such as protoporphyrin IX showed phytotoxic activity by its photodynamic action. This study aimed to screen new plant growth regulators available for herbicidal use from intermediates of the pigments biosynthetic pathways and modulators of the biosynthesis. The results of the study are summarized as follows.1.Effect of chlorophyll precursors, intermediates, and modulators of chlorophyll pathway on growth of several plant species were surveyed. Among the natural compounds tested, d-aminolevulinic acid (ALA), precursors of all the terapyrrole intermediates of the chlorophyll are most herbicidal when they were exogenously applied to the plants. ALA solution sprayd at 10^<-4> to 10^<-3> M caused bleaching and killed many plant species. Levulinate, dioxoheptanoic acid and gabaculine also showed phytotoxic activity such as chlorosis at higher concentrations.2.From the mode of action study of ALA,huge accumulation of chlorophyll intermediates was identified. Protoporphyrin IX was the prevalent porphyrin accumulating. This known to photosensitizer generating singlet oxygen under light. Therefore, chemicals that accumulate this intermediate may become effective growth regulator.3.To stimulate ALA synthesis in plants, regulation of ALA synthesis in plants was investigated. It was shown that ALA synthesis was regulated by light and feedback inhibition of the products of the pathway.4.Bioassay system of plant growth regulators using hydroponically grown barnyardgrass seedlings, most troublesome annual weed in rice paddy, was established