Plastid Damage in Photosynthetic Cells of Mizugayatsuri (Cyperus serotinus) Leaves Treated with a Pyrazole Herbicide

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The chloroplasts of mesophyll cells in Cyperus serotinus Rottb. (mizugayatsuri) leaves possessed well-developed stroma and granal thylakoids. In Kranz chloroplasts, many stroma thylakoids and a considerable amount of peripheral reticula were discernible. The interposed mestome cells had a thick cell wall and poor cytoplasm. The effect of DTP, the herbicidal entity of Pyrazolate, on the development of plastids in the photosynthetic cells of C. serotinus leaves was examined by TEM. Deformation of the plastids appeared under continuous light for 7 d in the plants treated with 1 mg L^>-1< DTP. However, even 50 mg L^>-1< DTP did not cause such damage either in the plants kept in darkness or in those exposed to light for less than 2 hr after darkness. The plastids deformed by DTP under prolonged exposure to light were very poor in the inner membrane system, but the envelopes were intact. DTP treatment in the dark allowed normal development of etioplasts, in which a central lattice was composed of numerous tubules about 40 nm in distance. Exposure to light after the dark treatment caused an extrusion of prothylakoids from a central crystalline structure of the etioplasts. The ultrastructure of nuclei and mitochondria in the DTP-treated leaves was not different from those in the untreated plants. From the above results, we draw a conclusion that DTP causes the collapse of thylakoid membranes only in light and not in darkness.
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