Bisexual Plants Research Articles

Polyploid gametophytes of Gracilaria tikvahiae (Gigartinales, Rhodophyta)

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.

POLYMORPHISMS FOR PURELY CYTOPLASMICALLY INHERITED TRAITS IN BISEXUAL PLANTS

It is shown that cytoplasm polymorphisms transmitted only by the ovules can be maintained without gene-cytoplasmic interactions. The necessary prerequisites are asymmetry of the plasmotypes in production of ovules and pollen (sexual asymmetry), incomplete and frequency-dependent fertilization efficiency and differential selfing rates. These factors can generate the negative frequency dependence of cytoplasmic fitnesses required for a stable polymorphism. The model considered allows also for facultative fixation of either of two plasmotypes and, thus, may produce all of the dynamical characteristics known for nuclear selection with two alleles at one locus.Strong sexual asymmetry, which probably occurs frequently in bisexual plants, may facilitate stable cytoplasmic polymorphisms. However, these polymorphisms may also endanger survival of the whole population in the absence of nuclear interactions. Gene-cytoplasmic interactions avoid this risk and, at the same time, utilize the advantages of sexual asymmetry in maintaining genetic polymorphisms.

GENETICS OF GRACILARIA TIKVAHIAE (RHODOPHYCEAE). X. STUDIES ON A BISEXUAL CLONE12

ABSTRACTA male done of the red alga Gracilaria tikvahiae McLachlan spontaneously produced a bisexual frond which remained bisexual in subsequent subcultures. Both male and female components of bisexual fronds were functional; however, some unusual results were obtained in crosses. When bisexual fronds were crossed with a normal haploid male, the resulting carpospores all developed into diploid male gametophytes. When bisexual plants were self fertilized, all the carpospores yielded diploid bisexual gametophytes. Only when bisexual plants were crossed to normal haploid females, did carpospores develop into diploid tetrasporophytes as they normally do. The F1 gametophyte generation obtained from these tetrasporophytes, however, included not only females and males but also bisexual plants, in a 2:1:1 ratio. These results are consistent with the interpretation that bisexual plants have a recessive mutation of a gene other than the primary sex determining locus, and that this mutation is expressed only in male plants. It is suggested that the altered gene may ordinarily have a regulatory function in the maintenance of the dioecious condition.

Paratylenchus labiosus n.sp. (Nematoda: Paratylenchidae) from Canada

Paratylenchus labiosus n.sp., a bisexual plant parasitic nematode from Prince Edward Island, is described and illustrated. Females have short stylets 15 to 17 μm long and concave–conoid heads with large, rounded submedian dorsal and ventral lips which readily separate this species from most paratylenchids. The spermatheca is well developed and usually filled with sperm. Males were present in a ratio of 1:2 females. They lacked a stylet and their distinctively conoid heads and delineated lips are the main diagnostic characters that identify the males of this species. A bisexual species from Saskatchewan and Alberta is compared and judged to be identical with P. labiosus n.sp.

Sex expression and determination in spinach. : III. Inheritance and breeding of intersexuality (continued).

In the previous paper, the authors (1960) divided 'the sexual characters in spinach into two categories, and sexual habit , and announced that some differences in the growth habit make it possible to classify sexuality into three patterns, two are males with XY chromosomes, called the the bracted :male (B ♂ ) with XYB and the leafy male (L ♂ ) with XYL, and the third pattern is female (♀) with XX. It was also reported that the bisexual plant with both male and female flowers occurs in the two patterns, other than B♂ A bisexual intersex from L♂ is named andromonoeclous and another int-ersex from♀ named gynomonoecious .