Abstract: Meiotic protoplasts of Ulmusamericana (American elm) are potentially valuable for producing interspecific elm hybrids through protoplast fusion. Meiotic cells (pollen mother cells, tetrads, and microspores) were incubated in either a cellulase, hemicellulase, and pectinase enzyme solution or a β-1,3-glucanase (laminarinase) solution. Respective protoplast isolation frequencies for the three meiotic cell types were 100, 50, and 10%. Exclusion staining with 0.2% Evans blue and 0.1% methyl blue suggested protoplast viability. Some of the microspore protoplasts were vacuolated, which is an important condition for cell division. Although attempts to regenerate cell walls and induce cell division were unsuccessful, these two problems may be superceded by protoplast fusion with more regenerative protoplasts. To our knowledge this is the first report of protoplast isolation from meiotic cells of a tree species.

Abstract: Parallel spindles occur during microsporogenesis in the cultivar Sebago (2n=4x =48) and are the basis of 2n pollen production in this clone. The relations between the frequencies of parallel spindles, 2n microspores, and 2n pollen are striking. The predicted frequency of 2n pollen based on the percentage of microsporocytes with parallel spindles is highly correlated with the frequency of 2n pollen observed. The percentage of 2n microspores at the sporad stage also corresponds very closely with the observed percentage of 2n pollen. Sebago is thus nulliplex (psp sp sps) for the meiotic mutant which governs spindle orientation at the second meiotic division in microsporocytes. This finding agrees with the prediction that if parallel spindles were involved in the origin of cultivated tetraploid potatoes, the genesps should be present in some 4x cultivars. It adds further support to the concept that 2n gametes have been a creative factor in the origin and evolution of cultivated tetraploids.

Abstract: Microspore mother cells of dihaploid Solanum tuberosum plants were mutagenically treated during the stage of meiosis. Mutagenesis was performed either by irradiation with x- or γ-rays or by the application of nitrosomethylurethane or methylnitronitrosoguanidine. Then, by use of the anther culture technique, 913 functional plants and 442 untreated control plants were regenerated. From the exposed plants seven distinct mutants could be isolated, predominantly chlorophyll deficient lines, while from the controls no clear-cut mutants arose. One mutant turned out to be photomorphogenetic in addition to having a chlorophyll defect. In addition to the production of mutants the treatments significantly increased the frequency of multicellular structure formation from microspores.

Abstract: SUMMARY Cytochemistry and transmission electron microscopy reveal that the mature megaspores of Azolla filiculoides contain protein bodies, lipid globules, polysaccharide vacuoles and amylo-plasts whereas the microspores are packed with saturated lipid. The megaspore indusium is lignified but the flotation apparatus, capture mechanism, massulae and glochidia are heavily impregnated with sporopollenin. Ultrastructurally the walls of the massular pseudocells are closely similar to those of the flotation collar, from which filaments, identical to those in fossil taxa, extend. The microspore glochidia usually become attached to this region of the megaspore and the capture mechanism around the latter's blunt end is a misnomer. New details of distinctive internal surfaces of the sporocarps are demonstrated from fractured resin embedded specimens, a technique which may permit more accurate diagnosis of fragmentary fossil remains. The unsculptured exine around the megaspore is overlain by a two layered perine. The inner stratum, or endoperine, has a granular texture and expands to make up the bulk of the notation collar and the excrescences (tubercles) of the capture mechanism, whereas the outer, or exoperine forms a thick continuous layer between the tubercles and an anastomosing network above them. Since the filaments around the flotation apparatus have a similar homogeneous texture these are also assigned to the exoperine.

Abstract: During pollen development loading of pollen grains of rye with allergen(s) takes place in the anther. Young microspores after meiosis have no allergenic activity. Under greenhouse conditions rye pollen becomes allergenically active about 6 days before release of pollen grains from the anther.

Abstract: Forty-six callus cultures of rice (Oryza sativa L., 2n = 24), each presumably originating from a single microspore, were established and maintained on a medium containing 2,4-D. At the end of the first transfer 24% of the cultures were nonhaploid consisting of only diploid or polyploid cells, or of cells of two ploidy levels. Nuclear fusion and endomitosis occurring during the initial stages of in vitro microspore development were postulated to account for the formation of nonhaploid callus. Seventeen cultures were studied cytologically through 19 transfers. Only in one tetraploid and one hexaploid callus did the ploidy levels of cells remain unchanged during culture. Chromosome numbers in 13 cultures fell into a geometric series. Since no diplo- and quadruplochromosomes were observed, it was inferred that endomitosis rather than endoreduplication was responsible for the changes. In spite of the tendency for chromosome doubling, the proportions of cells of different ploidy levels were fixed in the 13 cult...