Abscisic acid normally inhibits growth and male sexual differentiation (antheridia formation) in gametophytes of the fern Ceratopteris. Abscisic acid resistant mutants show increased growth and sexual differentiation in comparison with the wild type when cultured in the presence of abscisic acid. Two different mutants that confer resistance to the effects of abscisic acid have been fully characterized. One shows moderate resistance and the other strong resistance. The mutations involve separate but linked loci. Recombination between the loci yields double mutant (cis) recombinants that exhibit additive effects and show exceptional levels of abscisic acid resistance.
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Leslie G. Hickok (1985) studied this question.
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