Dynamic analysis of the evolution of a novel genetic system: the evolution of ciliate meiosis.

Many ciliates undergo a peculiar form of meiosis in which four haploid nuclei are produced, three are digested, and the single remaining nucleus undergoes mitosis. It is paradoxical that such a meiotic process occurs, since one could imagine several other less costly ways of producing two nuclei. Here we investigate a possible resolution of this paradox. It is shown that the spread of a selfish gene that kills the mate not containing it, provides the conditions for the spread of a costly modifier of the form of meiosis. We investigate the conditions under which the modifier can fixate.

Anther culture of maize and the visualization of embryogenic microspores by fluorescent microscopy.

Three maize genotypes previously shown in the literature to respond to anther culture were tested under various conditions. Studies indicated that embryogenic response ranged from 0 to 100 embryos per 1,000 anthers plated and was significantly lower without cold pretreatment of the anthers. Culture in liquid media tended to produce more embryos than in semi-solid as did the addition of activated charcoal to either liquid or solid culture media. Most results were confounded by plant-to-plant variation which tended to obscure significant differences. In one study, germination rate of androgenetic embryos averaged about 20%, but only 26% of those embryos that germinated completed their reproductive cycle and formed seed albeit through sibpollination since plants could not be selfed. Chromosome counts using root tip squashes indicated that regenerated plants were either haploid or diploid but plants scored as non-diploid yielded as much seed as scored diploids. This suggests that progeny can be recovered even from putative haploids, presumably as a result of "sectoring" in the developing ear. A DNA-specific fluorescent dye was used to visualize the presence of putative embryogenic microspores (PEMs) during the culture period. PEM counts were a function of time in culture and were apparently greater than the number of embryos obtained for a given treatment. The data indicate that, as previously reported for other species, both induction and survival phases also exist in maize anther culture.

Somatic embryogenesis from three commercially important inbreds of Zea mays.

Zea mays (maize) genotypes B73, Mo17 and LH38 were evaluated for their capacity to undergo somatic embryogenesis. Over 1500 immature embryos (ie's) of B73, 2900 ie's of LH38 and 400 ie's of Mo17 were excised 10-17 days after pollination and plated on six different media. Overall response, reported as a percentage of the ie's plated that developed embryogenic callus, was 2.1%, 1.6% and 26% for LH38, B73 and Mo17, respectively. Best response on a given medium for each of these genotypes was 9.2% (LH38), 4.4% (B73) and 100% (Mo17). Other parameters examined for their effects on production of embryogenic callus included self vs. sib pollination, ear ranking (1st, 2nd or 3rd ear), and temperature shock, all of which had no significant effect. Plantlets regenerated from selected treatments of B73 have been grown to maturity, selfed or sibbed and seed collected for field evaluation.