Idiosyncratic chromosome behaviour during meiosis was found in pollen mother cells of Cuscuta babylonica Choisy, a thread-like holoparasitic herb. Its main features are among the following: (i) telomeric association between homologues through most stages of the process, which leads to persisting chromatid bivalents (= "demibivalents"); (ii) uncommon chromosome segregation in first and second anaphase; and (iii) prolonged intensified heterochromatinization. Although "regular" in its own way, this process leads to the formation of unviable products. Its further investigation might contribute to our understanding of the role of the spindle and chromosome movement in the ordinary process of meiosis. Key words: meiosis (abnormal), persisting demibivalents, Cuscuta babylonica.
Seedlings at different stages of development were treated with colchicine. Successive selections on the aspect of the seedlings soon after treatment, on size of the guard cells at the time of repotting, and finally, after overwintering, on counts of the chromosomes in the pollen mother cells yielded a few hundred plants with tetraploid crowns. These plants bore fewer, broader leaves and fewer, bigger inflorescences with larger achenes than did selected large-celled diploids given the same treatment, but in general the plants were no bigger. A few of the tetraploids were self-fertile (if not apomictic) early in the spring, but later all tested plants proved self-sterile.
In two diploid specimens of Haworthia subfasciata (2n = 14) several kinds of chromatid and subchromatid aberrations occurred. In some pollen mother cells E-type and U-type bridges were present. In other cells bridges and fragments were formed due to asymmetrical reunion of nonsister chromatids following breakage. A translocation involving the satellites of two L pair chromosomes was observed in one plant.
Nonreduction of pollen mother ceils was observed in a wild tetraploid morning-g&y related to the sweetpotato (Ipomoea batatas L. Lam.). Techniques for identifying and determining the frequency of expression of the trait are straightforward. Previous strategies for transfer of germplasm from tetraploid (2n = 4x = 60) species to the hexaploid (2n = 6x = 90) sweetpotato involved crosses with diploids (2n = 2x = 30) to obtain triploids that then were doubled to 6x. Nonreduction of pollen mother cells probably represents the natural mechanism for raising 4x to 6x since pollination of 2x ovules with unreduced pollen (4x) should give rise to 6x progeny without need for somatic doubling. Plants carrying this trait should be useful as bridging types for introgressing genes from wild 4x species into sweetpotato. A wide range in nonreduction (up to, 74%) was recovered In progeny of controlled crosses among selected plants, but data were not sufficient to estimate gene action.
Cytochemical electron microscopic studies on the kinetochore of pollen mother cells in tradescantia reflexa.