An ultrastructural survey of plastome mutants of Hosta (Liliaceae).

In an ultrastructural survey of 82 plastome mutants of Hosta two general groups of mutants were distinguished: yellow to yellow-green photostable mutants, and pale green to white mutants that 'photobleach' during development. The yellow to yellow-green mutants had reduced granal stacking compared to the wild type plastid, and thylakoids were frequently dilated. In the photobleaching group, thylakoids were aggregated into a tight mass, known as a magnograna. During development, the thylakoids vesiculated to a great extent, with a subsequent photo-oxidation of the photosynthetic pigments. Peripheral reticula, invaginations of the chloroplast inner membrane, were found consistently in the photobleaching strains. Osmiophilic globules were increased in both number and size in these two groups and occasionally more extensive electron dense areas were noted in the plastids of the photobleaching group.