engleski

Gamma-ray-induced changes in the chloroplasts of Hamatocactus setispinus

The majority of chloroplasts of higher plants are similar in their shape and size. In some cases massive γ-irradiation induces the formation of giant chloroplasts. The outer green cell layers of untreated Hamatocactus setispinus represent one of the rare tissues normally containing giant chloroplasts. Here we elaborate the changes in the structure of these choroplasts in plants grown from γ-irradiated seeds. Material and methods: Electron microscopic and morphometric studies of chloroplast structures of plants grown from unirradiated and γ-irradiated seeds were performed. The final dose of irradiation was 64 Gy. Nucleoids were visualized by DAPI staining and by fluorescence microscopy. Results: The chloroplasts of control plants are typically lens-shaped. Their volume is significantly larger than that of average chloroplasts. Their diameter is approximately 15 μm, and thickness about 4-7 μm. The chloroplasts of plants developed from irradiated seeds are oval, with an average length of 10 μm and a width of 5-7 μm. Thylakoids are partially curved. Plastoglobules are numerous and big. Treated plants developed normally for about one year, but died shortly thereafter. Control plants grew continually through several years. Conclusion: Morphometric ultrastructural investigations of control plants indicate that the amount of all chloroplast structures is unusually large. In contrast, the decrease in size of chloroplasts in treated plants is the result of roughly equal reduction of all chloroplast structures. It is possible that this reduction is a consequence of senescence, i.e. the secondary effect of severe damage of the root system induced by the massive γ-irradiation

hamatocactus setispinum ; giant chloroplasts ; gamma-irradiation ; ultrastructure ; image analysis

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