Abstract: A dimorphism is observed in barley (Hordeum vulgare L, cv Akka) pollen when stained with acetocarmine from the mid-binucleate stage onwards The majority of grains have staining cytoplasms, while the remainder have cytoplasms which take up little or no stain (NS grains) The staining dimorphism cannot be detected at the late-uninucleate microspore stage when anthers are normally cultured, but the evidence suggests that the microspores have already diverged at this time and it is the cells destined to become NS grains in vivo that respond in culture to become pollen calluses Evidence comes from a comparison of the frequencies of NS grains and pollen calluses and from their distribution between and within anthers

Abstract: Production of callus from anthers of D. purpurea was obtained on several basal media supplemented with various amounts of auxins. Chromosome counts showed that the callus produced was haploid when the anthers 1) were of a dark-brown to black color, and 2) were cultured in the late tetrad stage of microspore development. Subsequent differentiation to plants at high frequencies was possible only 1) when the anthers had been cultured on the medium of Nitsch and Nitsch (Science 163, 85–87; 1969) supplemented with 5 mg/l 2,4-dichlorophenoxyacetic acid (2,4-D), 2) when the callus was transferred to the same medium but without 2,4-D, and 3) when it was cultured under continuous light from fluorescent lamps. Proliferation of the callus and regeneration of plants did not diminish through as many as 20 subcultures. The high frequency of regenerates permits the propagation of a distinct geno-type to a virtually unlimited number of plants. Diploid plants were obtained when the anthers had been cultured in the dark. Tetraploid plants were regenerated by callus from anthers which had been cultured in light. When the time of 2,4-D treatment was shortened a few haploid plants were produced which however did not survive transfer to soil. Cytological observations demonstrated that regeneration started from haploid callus, leading to intermediate degrees of ploidy and finally to diploid plants. Most of the regenerated plants were euploid and flowered and fruited normally under greenhouse and field conditions. If the anther-derived callus was cultured on the medium of Nitsch and Nitsch supplemented with 2.2 mg/l kinetin, plants regenerated only under photoperiodic conditions of 16 h light at 28° and 8 h dark at 20° but the survival was lowered to one third. These plants had a different leaf and flower morphology as compared to the control without kinetin and to the starting material, but their progeny was again essentially normal.

Abstract: A technique is described to isolate rye microspores from anthers precultured on agar and from intact spikes. Highly purified fractions consisting predominantly of viable late uninucleate or early binucleate microspores are obtained by filtration and centrifugation techniques. The preparations form an excellent starting material to attempt to increase the frequency of microspore plantlet formation above that normally obtained by anther culture. Microspores isolated from anthers precultured for five or six days on agar, develop after three weeks culture in a liquid medium into multicellular structures, the largest of which burst through the microspore wall.

Abstract: Anthers of Hyoscyamus niger L. were cultured by two different methods. In the first method anthers were cultured in the dark in the late tetrad stage of microspore development on the basal medium of Nitsch and Nitsch (Science 163, 85–87; 1969) supplemented with 5 or 10 mg/l 2,4-dichlorophenoxyacetic acid. The callus which developed was able to produce a large number of plants under photoperiodic conditions of 16 h light from fluorescent tubes at 28° and 20° during the dark cycle. Cytological analysis revealed that about 50% of these plants were haploid. A further imporvement to raise the level of haploids by the use of p-fluorophenylalanine was not achieved. In the second method anthers were cultured in the early mononucleate stage of microspore development on the basal medium of Nitsch and Nitsch which was little modified under various conditions. The largest number of plants which developed directly by embryoids was observed on the medium of Nitsch without indolylacetic acid under photoperiodic conditions of 16 h fluorescent light at 28° and 8 h dark at 20°. Cytological examination determined that approximately 70% of the plants were diploid. A genetic marker was used to ensure homozygoty of the diploid regenerates. 98% of the regenerates which developed via callus as well as by direct formation of embryoids were found to be homozygous and originated therefore from generative cells.

Abstract: Cretaceous Salviniaceae, including numerous floats, an acrolamella, and a complex perispore. Microspores are borne singly, however, not in characteristic salviniaceous massulae. Microspores of Glomerisporites have a pseudovacuolate basal region and a single spore in an apical neck. Microspores of Ariadnaesporites are structurally like the megaspores but of smaller size. Ariadnaesporites varius occurs in the Cenomanian Stage (early late Cretaceous) and is the

Abstract: Important advance in genetic has been achieved as a result of the work with bacteria, unicellular haploid cells because of their short life cycle and low nutrient requirement. These advantageous in bacteria may now be expected in higher plants if one works with microspores: unicellular haploid cells.

Abstract: Considerations about our anther cultures of cultivated plants. – One of the main activities performed at the Casaccia Nuclear Centre, in the framework of a contract between CNEN and the European Communities, centers on the induction of haploid plants by anther culture and the subsequent chromosome doubling in order to obtain completely homozygous diploid plants. In tobacco, it is now possible to obtain haploid plants from any cultivar; we perform in vitro culture of internodes from which homozygous diploid plants are regenerated, taking advantage of natural phenomenon of endopolyploidy. In order to try to generalize this method of producing haploid plants in other plant species, we are studying the mechanism involved in haploid embryogenesis which occurs in vitro in the microspores. Datura, Nicotiana and Atropa are among the genera in which a direct embryogenesis from the microspore is observed; it is interesting to note that all three genera belong to the family Solanaceae and are very rich in a...

Abstract: During maturation, microspores pass through a series of morphologically distinguishable stages or compartments. A study has been made of the systematic fluctuations in the frequency of microspores in these compartments, when plants are grown under rigidly controlled conditions. A new approach to the construction of cumulative flux rate curves is described; these give the number of cells passing the compartment boundaries per unit time. The curves obtained indicate that simple models, which assume constant flux rates and compartment transit times, will not explain the observations. It is evident that not only do microspores mature at different rates, but that the maturation rate of individual microspores varies during the developmental sequence. The overall process may be controlled by the intimate relationship which exists between the microspores and the tapetal periplasmodium in the Tradescantiae.

Abstract: Megaspores of Marsilea, Pilularia, and Regnellidium possess an average viability of 50%,-75%0 when grown in the presence or absence of sporocarp contents. Approximately 96% of the viable megaspores in Regnellidium formed sporophytes uhen grown in the presence of microspores. In Marsilea and Pilularia in contrast sporophytes formed on 58% and 38CXo respectively of the viable megaspores. Factors influencing fertilization remain unknown but it was determined for Marsilea that archegonium receptivity to fertilization progressively decreased when archegonia were not fertilized within approximately 12-24 h and no fertilization occurred after 24 h. The appearance of sporophytes on nearly all isolated megagametophytes of Regnellidilem indicated the occurrence of parthenogenesis rather than apogamy. In contrast this phenomenon M as absent for isolated megaspores of Pilularia and for nearly all megaspores of Marsilea. Parthenogenesis appears to perform a major role in the reproduction of Regnellidium but not in Marsilea and Pillularia.

Abstract: Megaspores of Marsilea, Pilularia, and Regnellidium possess an average viability of 50%-75% when grown in the presence or absence of sporocarp contents. Approximately 96% of the viable megaspores in Regnellidium formed sporophytes when grown in the presence of microspores. In Marsilea and Pilularia, in contrast, sporophytes formed on 58% and 38%, respectively, of the viable megaspores. Factors influencing fertilization remain unknown, but it was determined for Marsilea that archegonium receptivity to fertilization progressively decreased when archegonia were not fertilized within approximately 12-24 h and no fertilization occurred after 24 h. The appearance of sporophytes on nearly all isolated megagametophytes of Regnellidium indicated the occurrence of parthenogenesis rather than apogamy. In contrast, this phenomenon was absent for isolated megaspores of Pilularia and for nearly all megaspores of Marsilea. Parthenogenesis appears to perform a major role in the reproduction of Regnellidium but not in Mar...