The association between chloroplasts of Codium fragile and the mollusc Elysia viridis I. Characteristics of isolated Codium chloroplasts

Abstract

Chloroplasts of Codium fragile fix carbon photosynthetically at rates comparable to or higher than those of the intact plant for several hours after isolation. When stored in the dark at 5°C in a simple mineral medium containing mannitol as an osmoticum and no added cofactors, the chloroplasts continued to fix carbon photosynthetically for at least 5 days after isolation, although at a progressively declining rate; they retained the ‘halo’ characteristic of an intact outer envelope for the entire period. Patterns of 14 C fixation by isolated chloroplasts and intact Codium were generally similar, except that no incorporation of 14 C into sucrose could be detected in isolated chloroplasts, and incorporation into glycolic acid was higher. Only 2% of the photosynthetically fixed 14 C was released to the medium by isolated chloroplasts. Their Hill reaction was relatively weak, but this may have been due to the impermeability of the outer envelope which could not be ruptured even by the severe osmotic shock of transfer from the suspension medium (osmotic pressure greater than 14 atm) to distilled water. It is suggested that the ‘robustness’ of chloroplasts from siphonaceous algae may be an important factor in their ability to enter and continue functioning inside animal cells.