Abstract: Anther ontogeny of a genic male-sterile mutant (ms 10/ms 10) and a related fertile cultivar of Zea was studied from the primordial stage through to tassel maturity. From material glutaraldehyde–formalin fixed, OsO4 postfixed, and plastic embedded, light microscopy of 0.7-μm sections revealed no developmental differences between the two until the young microspore stage. Vacuolation or cytoplasmic disintegration of tapetal cells was detected in male-sterile anthers at this stage. Disintegration of microspores was not detected until the intermediate microspore stage. By the young pollen stage, tapetal cells were highly disorganized and degeneration of the middle layer and endothecium was apparent. No endothecial wall thickenings developed in male-sterile anthers.In normal anther development in Zea, endothecial thickenings are found only at the anterior and posterior ends of the anther. A highly ridged anther cuticle, which is essentially absent in male-sterile anthers, is a common feature of fertile flowers....

Abstract: After conventional fixation procedures and embedding in low-viscosity resin, anthers were studied using light and electron microscopy. Wall development is dicotyledonous. Sporogenous tissue undergoes one mitosis before meiosis. Entry of pollen mother cells (PMCs) into meiosis is indicated by formation of a prominent polar nucleolar cap. Cytomictic channels form between PMCs in early prophase I. In Pisum sativum the middle lamella breaks down between meiocytes. The quartets are surrounded by an extensive callose wall within which primexine starts to form. Callose dissolution is centripetal. Once microspores are released from the callose wall tectate exine development continues and the pollen cytoplasm vacuolates. Mature cytoplasm of the pollen exhibits zonation. No plastids were observed in the generative cell. Endothecial cells develop extensive thickenings. In Pisum the thickenings are primarily cellulosic whereas in Lens culinare besides cellulose some lignin may be present. Various developmental stages...

Abstract: In microspores of angiosperm plants, the period from the end of meiosis in microsporocytes unitl the first cell division may be considered as one cell cycle, and the division is polarized, resulting in the formation of two functionally different nuclei. InLilium longiflorum, the duration of the cell cycle was measured in some detail. Identification of individual stages was based on the correlation between bud length and developmental stage. The results showed that the process begins at a bud length of 24 mm and is completed about 15 days later, at a bud length of 58 mm. By autoradiography of cells cultured in the presence of3H-thymidine, approximate durations of the G1, S, and G2 plus M phases were estimated to be about 12, 2, and 1 days, respectively. A detailed cytological analysis of the transitions between the various microspore stages has revealed some convenient parameters which point to ghe progression of change during the interval.

Abstract: RNA synthesis during pollen embryogenesis in cultured anther segments of Hyoscyamus niger (henbane) has been followed by autoradiography of 3H-uridine incorporation Embryogenic divisions were initiated in binucleate pollen grains in which the generative nucleus or both generative and vegetative nuclei synthesized RNA When the first haploid mitosis in culture resulted in pollen grains with two nearly identical nuclei, those in which both nuclei synthesized RNA became embryogenic Binucleate pollen grains in which 3H-uridine incorporation was confined exclusively to the vegetative nucleus gradually became starch-filled and nonembryogenic Based on the degree of involvement of the vegetative nucleus in embryoid formation, some differences were noted between the counts of autoradiographic silver grains over cells cut off by the generative and vegetative nuclei during progressive embryogenesis The possible significance of RNA synthesis in the nuclei of binucleate pollen grains in determining the pathway of embryogenic divisions is discussed IN ANGIOSPERMS, formation of microspores following meiosis in the microspore mother cell is the beginning of a short-lived male gametophytic generation The microspore matures into the pollen grain which undergoes two successive mitotic divisions The first division (first haploid mitosis) is characteristically asymmetric and results in the formation of a small generative cell and a large vegetative cell Next, the generative cell divides producing two male gametes The pollen tube is formed from the vegetative cell whose nucleus eventually disintegrates or remains as a

Abstract: Several different expressions of male sterility were observed in the plants sampled for the study of pollen and anther development in the third substitution backcross generation to intermediate wheatgrass. These included (1) pollen abortion following engorgement with starch, (2) abortion of microspores with exine abnormalities (found most often in plants with a high degree of meiotic irregularities), (3) abortion of microspores with normal exines, (4) release at anther dehiscence of normal-appearing late vacuolate microspores, (5) enlargement of one of the parietal layers of the anther, and (6) tapetal abnormalities, including orbicular wall malformations. Anthers from plants which were male sterile or partially male sterile and meiotically irregular were shorter than anthers from fertile or partially male-sterile, meiotically regular plants.Definite statements about specific causes of the male sterility could not be made. Meiotic irregularities may be involved in some of the male sterility, and exine mal...

Abstract: Anthers of the diploid (2n=77) and the colchi-tetraploid (2n=154) Pelargonium roseum were cultured in vitro. In both ploidy level anthers containing uninucleate or binucleate microspores were incubated on a modified White's medium. Calli formed were then subcultured on Murashige and Skoog's medium for organoid differentiation. Plants developed from organoids were transferred to filter paper bridges and after that transplanted into pots. Plants derived from anthers of the tetraploid had diploid chromosome number. Wide variation of their essential oil components suggested their genetic heterogeneity. Further, high correlations between different seasons in the rate of essential oil components showed that the wide variation was due to genetic differences. Therefore, these plants probably originated from pollen grains. On the other hand, plants derived from anthers of the diploid had diploid chromosome number. Small variation and low correlations between different seasons in essential oil components indicated their genetic homogeneity. Their origin was ascribable to the somatic tissues of the mother plant. It is concluded that in plant species in which usual sexual reproduction is difficult, anther culture of chromosome-doubled plants will give a useful method for obtaining genetic variation.

Abstract: Various methods for obtaining microgametophytes, megagametophytes, and sporelings of Selaginella have been described. Slagg (1932), in a study of microgametophyte development in S. kraussiana (Kunze) A. Br., germinated microspores on plaster of Paris blocks. A similar method for germinating both microspores and megaspores was described by Bold (1967). Bierhorst (1964) described methods for obtaining reproductive stages of Selaginella for classroom use. Webster (1967) described the induction of sporelings under greenhouse and field conditions. Wetmore and Morel (1951) germinated megaspores of S. pallescens (Presl) Spring in Mart. and S. flabellata (L.) Spring on nutrient agar under sterile conditions. Through the use of a medium supplemented with various growth factors, they were able to grow gametophytic tissue for several months. Despite the above procedures for germinating spores and obtaining sexual material of Selaginella, there is but one report of artificial crosses in the genus. Burgeff and Filippi (1957) made crosses between S. martensii Spring var. martensii and S. martensii var. variegata Hort. They sowed surface-sterilized megaspores and microspores together on nutrient agar in culture tubes and, after gametophytes had formed, flooded the cultures with water to achieve fertilization. After 30-40 days, sporelings appeared. Using this method, they studied the inheritance of variegation in S. martensii var. variegata. In this paper, a crossing technique differing in several respects from the one used by Burgeff and Filippi (1957) is described. Although it has been used successfully to repeat the crosses by Burgeff and Filippi, the technique was developed for making crosses with S. kraussiana and its varieties, and the following description is based on work with these taxa. Application of this technique to a study of inheritance of pigmentation in S. kraussiana var. aurea W. Bull will be the subject of a later report.

Abstract: In most plant breeding programs, the possibility of having haploids would allow for more rapid progress. Several procedures for obtaining haploid and homozygous diploid (named “homodiploid”) plants have been described in the literature (Nitzsche and Wenzel, 1977). The use of the in vitro culture technique has proved to be very advantageous in several respects: (1) The number of haploid plants obtained may be essentially unlimited when the technique is properly adapted to the species.Thus it allows maximum combination possibilities of the genomes. (2) In vitro culture is a means to rescue tissues that for various reasons would not grow in nature, therefore making available genotypic combinations which have never been or will never be obtained by normal sexual crosses. For example, when reduction at the meiotic cell level produces a nonviable pollen grain, such pollen grains may be rescued by in vitro culture and may eventually grow into plants showing characters normally unseen in nature. In this regard, it may be noted that “spontaneous mutations” have been observed in plants originating from pollen cultures in a larger number than normally. Therefore, new characters are made available which breeders may judiciously use in their breeding programs. (3) Starting from pollen alone, that is to say the male gametophyte, gives the possibility of studying in a simple system the cytoplasmic effect on a cross. This method can be contrasted with the somatic hybridization technique (Vasil, see Chapter 5), where the new plant has an enriched cytoplasm resulting from the fusion of cytoplasm from the two parents (Gleba, 1978). The pollen plant has the cytoplasmic inheritance reduced to a minimum, less than in a regular cross since the plant obtained originated from only one cell, namely the vegetative pollen cell, with a small cytoplasm rather than one resulting from the fusion of the sperm nucleus with the female zygotic cell. It also allows a new approach for studying the maternal effect. Starting from a plant with cytoplasmic inheritance reduced to a minimum allows the breeder to follow any single effect of cytoplasmic inheritance. (4) Another main advantage of the in vitro culture technique is that it allows the scientist to follow the growth and development of the plant in conditions where it is possible, at any time, to observe, modify, or stop its development. For fundamental research in morphology and biochemistry, this is indeed a very important point, especially since it pertains to the entire period from uninucleate cell level (i.e., from the microspore) to the complete plant. (5) The last but a still very important point is that this tissue culture method is probably the fastest way to obtain homodiploid plants, although not necessarily the cheapest. To date, in all successful cases less than six months have been needed to achieve the goal of obtaining haploid or homodiploid plants starting from a hybrid.

Abstract: Alloplasmic plants of rye, Secale cereale L., with cytoplasm of Triticum durum Desf. are studied in order to investigate the causes of male sterility. Meiosis can be considered as normal because the alterations found had little entity. Abortion of pollen was progressive during microspore maturation; however, the variation among plants in percentage of aborted pollen was high (from 10%. to 98%.), being the average 29.3%. Histological observations showed that the only alteration in anther wall tissues was the non total disappearance of tapetum. So, the fusion of neighbouring loculi and the subsequent dehiscence of the anther was impeded. Therefore, the male sterility in this alloplasmic rye is a case of functional male sterility because the pollen being partially fertile cannot intervene in fertilization by the indehiscence of the anthers. The independence between pollen abortion and tapetum perdurability is discussed. Other events as pistilloidy are described.All studies were made simultaneously with the normal rye counterpart as control.

Abstract: Callusing by cultured anthers of Solanum mammosum is reported. Anthers contg. uninucleate microspores exhibited callusing. 2,4-D alone favored callusing by the anther, while in combination with kinetin pronounced callusing from the cut end of the filament was obsd. Incorporation of activated charcoal into the medium helped sustain growth of the callus in subcultures. Roots with abundant root hairs were produced in 2 light-grown cultures. [on SciFinder(R)]

Abstract: This chapter discusses pollination as spore dispersal. Although pollination exists only in higher plants, that is, those possessing pollen, it is, in fact, a specialized type of a phenomenon that occurs throughout a major part of the vegetable kingdom. As we see it in nature, the phanerogamic plant represents the diploid generation, the sporophyte. As the name implies, this generation produces spores, generally accompanied by chromosome reduction. These spores germinate into the haploid generation, the gametophytes, which are male or female, and produce sexual cells that fuse again at fertilization, thus, reconstituting the diploid number and producing a new sporophytic generation. Phanerogams also produce macro- and microspores, but the macrospore is included in the pistil and never becomes a discrete unit. Apart from the most primitive ones, plants have two sedentary stages, namely, sporophyte and gametophyte, and two mobile or motile ones, namely, spores and gametes. With gametes being confined to the original aquatic or at any rate moist conditions of primitive plants, spores are the stage adaptable to dispersal under dry conditions, and the existence of terrestrial plant life presupposes the existence of spores resistant to the adverse forces of land life. In higher plants, one of the primary ecological functions of the spore in lower plants, namely, dissemination, has been taken over by an entirely new dispersal unit, the seed, an arrested developmental stage of the new sporophyte.

Abstract: Diploid microspores were induced in Tradescantia paludosa by heat shocks; they occurred in anthers that also contained normal haploid microspores. Nuclear and cell volumes were determined from early G1 to late G2 for diploid and haploid microspores present in the same anther. Although the two cell types showed considerable overlap in cell and nuclear volumes, values from mixed samples did not yield a single straight line on a probit plot; there were always two straight lines articulated by an inflection point. The probit plots were used to distinguish between haploid and diploid microspores. Evidence is presented that demonstrates the degree to which this method is reliable. The two cell types developed at similar rates; they entered S and mitosis together and the time, in interphase, when increases in cell and nuclear volumes occurred was approximately the same for haploid and diploid microspores. However, increases in nuclear and cell volume occur at different rates during interphase and it appears that there is a poor correlation between nuclear DNA content and either cell or nuclear volume.

Abstract: The techniques of microspore and protoplast regeneration starting from dihaploid Solanum tuberosum plants has been improved to such an extent that the production of more than 2000 microspore derived A1 plant lines and of several hundred protoplast derived plantlets has become possible. Further, from the dihaploid Solanum species S. phureja the regeneration of microspores to plants, and from the species S. infundibuliforme, S. sparsipilum and S. tarijense the regeneration of protoplasts to calluses, has been achieved. The plants descending from the two single cell culture systems are compared with reference to phenotypic markers and economic qualities. Some principles characteristic for either microspore or protoplast derived plants are examined and their significance is discussed. The results are compiled into an extended analytical synthetic breeding scheme based on a stepwise reduction of the autotetraploid to the monohaploid level and a subsequent controlled combination to a new synthetic completely heterozygous tetraploid potato.