Polyploid gametophytes of Gracilaria tikvahiae (Gigartinales, Rhodophyta)

Abstract

Polyploid gametophytes up to the 4n level were obtained by cross- and self-fertilization of bisexual mutants of Gracilaria tikvahiae. Haploid and diploid gametophytes were morphologically normal, sexually fertile, bisexual plants. Triploids were stunted, having irregular, twisted growth at the apices, and their cystocarps released no viable carpospores after self-fertilization. Tetraploid plants were very abnormal, severely stunted, and did not become reproductive. Attempts to obtain pentaploid and hexaploid gametophytes were unsuccessful. Haploid and diploid plants had similar apical tip elongation rates, but at higher ploidy levels the growth rate of tips was reduced. Cortical cell size increased progressively from haploid to tetraploid gametophytes, even though the size of the plants decreased. Some of the tetraploid plants were phenotypically unstable during somatic growth; fronds occasionally reverted to a more nearly normal, although not completely normal, phenotype. A variable number of fertile bisexual revertants with completely normal morphology were present among the abnormal tetraploid plants obtained from self- or cross-fertilization of diploid plants. Both types of reversion appear to involve chromosome loss from the polyploids.