Avocado fruit protoplasts: a cellular model system for ripening studies.

Mesocarp protoplasts were isolated from mature avocado fruits (Persea americana cv. Hass) at varying stages of propylene-induced ripening. Qualitative changes in the pattern of radiolabel incorporation into polypeptides were observed in cells derived from fruit at the different stages. Many of these differences correlate with those observed during radiolabeling of polypeptides from fresh tissue slices prepared from unripe and ripe fruit. Protoplasts isolated from fruit treated with propylene for one day or more were shown to synthesize cellulase (endo-ß-1,4-glucanase) antigen, similar to the intact propylene-treated fruit. These results suggest that the isolated protoplasts retain at least some biochemical characteristics of the parent tissue. The cells may also be used in transient gene expression assays. Protoplasts isolated from preclimacteric and climacteric fruit were equally competent in expressing a chimeric test gene, composed of the CaMV 35S RNA promoter fused to the bacterial chloramphenicol acetyltransferase gene, which was introduced by electroporation.