Expression of cycloheximide resistance in carrot somatic hybrids and their segregants.

Cycloheximide resistance (CH(r)) was shown to be a function expressed in differentiated plant tissues, but not in unorganized callus tissues. A variant, WCH105, expressing CH(r) in the callus, as well as in regenerated plantlets, was isolated from a cell line derived from a wild carrot plant. The plantlets regenerated from WCH105 are green, but do not produce normal, dissected leaves. Protoplasts of WCH105 were fused with that of a cycloheximidesensitive (CH(s)) cell line derived from an albino, domesticated carrot. Hybrid selection was based on (1) irreversible growth inhibition of WCH105 protoplasts by iodacetamide, and (2) restoration of green plants producing dissected leaves.--Analysis of the CH(r) trait as an unselected marker in the callus cells of the somatic hybrids indicated that it behaved as a recessive. The combined recessive and resistant phenotype of this trait allowed the recovery of CH(r) segregants from CH(s) hybrids at a frequency of 10(-4), 1000 times higher than the spontaneous frequency of CH(r). The recovery of CH(r) somatic segregants confirmed the recessiveness of the CH(r) trait.