In vitro culture of tobacco protoplasts: Survival of haploid and diploid protoplasts exposed to x-ray radiation at different times after isolation

Freshly isolated haploid and diploid tobacco mesophyll protoplasts were plated in agar medium and their survival, after irradiation with acute doses of X-rays, applied on the day of isolation or on any of three consecutive days was evaluated by scoring their ability to form cell colonies. Survival of diploid protoplasts irradiated on the day of isolation was reduced to about one half by 750 R. This dose-effect is similar to that of plant meristem cells and cultured mammalian cells and rather lower than that reported for plant calli and cell suspensions. The cells showed a relatively low radiosensitivity on the day of isolation which increased drastically in the two subsequent days. On the third day, when most of the cells completed their first karyokinesis, their sensitivity to irradiation was again reduced.