Structural changes during the first divisions of embryos resulting from anther and free microspore culture inBrassica napus

Summary Ultrastructural and cytochemical features of embryo development during anther and free microspore culture inBrassica napus have been followed from the late uninucleate microspore stage through the first embryonic division. On transfer to culture, the microspore cytoplasm possesses a large vacuole, often containing electron opaque aggregates, and a peripheral nucleus. Mitochondria, endoplasmic reticulum and starch-free plastids are distributed throughout the cytoplasm. The conditions of culture induce a number of major changes in the cytoplasmic organisation of the microspore. First, the central vacuole becomes fragmented allowing the nucleus to assume a central position within the cell. Secondly, starch synthesis commences in the plastids which, in turn, are seen to occupy a domain investing the nucleus. Thirdly, the cell develops a thick fibrillar wall, situated immediately adjacent to the intine of the immature pollen wall. Finally, the microspores develop large cytoplasmic aggregates of globular material. The nature of this substance remains unknown, but it remains present until the young embryos have reached the 30 cell stage. The first division of cultured microspores destined to become embryos is generally symmetrical, in contrast to the asymmetric division seen in normal development in vivo. Consideration is given to the differences observed between embryos developing from anthers and free microspores in culture.     

The influence of paternal species on the origin of callus in anther culture of Solanum hybrids

Summary Stamen culture of several Solanum species and interspecific hybrids was performed and each stamen was scored for presence and origin of callus. Each species and hybrid has a characteristic callus growth pattern — either no growth (0), callus growth from the filament (F), or callus growth from the anther (A). Characteristic growth types of the interspecific hybrids indicate that callus growth takes precedence over no growth. Hybrids between F and A species exhibit mainly paternal passage of either characteristic callus type. Possible explanations for this pattern of inheritance are male plastome factors or imprinting of paternal genes. The latter explanation is presently preferred.Paper No. 2084 from the Laboratory of Genetics. Research supported by the College of Agricultural and Life Sciences, a gift from Frito-Lay, Inc., and grants from NIH (GM15422) and the International Potato Center.     

Mapping genes conditioning in vitro androgenesis in maize using RFLP analysis

Summary This research was designed to map the genes in maize which condition a high response to anther culture using RFLP analysis. A set of 98 S₁ families were developed from the cross of B73 × 139/39-05. In vitro-cultured anthers of 139/39-05 produce numerous embryolike structures while anthers cultured from B73 produce none. Plants from each of the families were grown in the greenhouse. Tassels were harvested from ten individual plants within each family and pretreated prior to culture. Up to three Petri dishes with 60 anthers each were cultured from each tassel. Response was measured as the number of embryo-like structures per 100 anthers cultured. In excess of 105 RFLP clones were screened to detect polymorphism among the parents. A subset of 75 widely distributed clones were scored in the 98 families. Based on the analysis of the resulting genetic data set, the high anther culture response observed in 139/39-05 is conditioned by two major recessive genes, which are epistatic, and two minor genes. One of the two major loci resides in the proximal region of the long arm of chromosome 3 near the indeterminate gametophyte (ig1) gene. The second major locus maps to the centromeric region of chromosome 9. The minor genes reside on chromosomes 1 and 10. Fifty seven percent of the variability among the 98 family means is explained by a genetic model which includes these four chromosomal regions. Moreover, segregation at these loci explains much of the variability observed within the families.     

Effects of temperature on the mode of pollen development in anther culture of Brassica campestris

In anther culture of Brassica campestris L., the yield of pollen-derived embryoids is greatly stimulated by a high-temperature (35°C) tratment for the first 1 to 3 days of the culture. We have inestigated the effects of the high-temperature treatment on the mode of pollen division in cultured anthers.
Anthers containing late uninucleate pollen were cultured on modified B5 medium. High-temperature treatment for the first 24 h inhibited the normal development of the pollen and induced abnormal symmetrical division. Which is the first step in androgenesis. This symmetrical division was rarely observed in pollen developed in vivo. In anthers cultured without high-temperature treatment, the mode of pollen development was similar to that in vivo. This suggests that the normal differentiation of the pollen is blocked by high temperatures, and sporophtic growth is induced. Sucrose (0.29 M) was essential for the induction of this symmetrical division, though neither plant growth regulator nor any other nurient was necessary. Pollen division could not be induced effectively if sucrose was replaced by either mannitol or sorbitol plus a lower concentration of sucrose. Therefore, it seems that sucrose actively influences the embryogenic division of pollen, and does not have only an osmotic effect.     

Fused lobed anther and hooked stigma affect pollination,fertilization and fruit set in mango: A scanning electron microscopy study

Mango malformation is the most threaten disease that limits mango production, worldwide. For a long time, due to its complex nature, the cause and causal agents were strongly disputed. Diverse Fusaria, including Fusarium mangiferae, are known to be associated with the disease. There are indications that augmented level of endogenous ethylene in response to various abiotic and biotic stresses alters the morphology of reproductive organs. Here, scanning electron microscopy (SEM) of healthy and malformed reproductive organs of mango cv. Baramasi was performed to compare the functional morphology. The SEM study revealed that anthers of hermaphrodite healthy flowers were bilobed with large number of turgid pollen grains whereas malformed flowers showed fused lobed anthers with scanty deformed pollen grains. Furthermore, the stigma of healthy flowers exhibited a broad landing pad as compared to malformed stigma which showed hooked and pointed tip. All these impaired morphology of male and female reproductive organs lead to failure of sexual reproduction. This is the first evidence to show fused lobed anther with impaired pollen grains and hooked stigma with poor stigmatic receptivity are mainly responsible for restricting the pollen germination and pollen tube growth. Here we suggest that abnormal development of anthers and pistils is due to endogenously produced stress ethylene. Further, added load of cyanide, a byproduct of ethylene biosynthesis, may also contribute to the development of necrosis which lead to desiccation of anther and pistil during hypersensitive response of plants.     

Identification of microspore-derived plants in anther culture of flax (Linum usitatissimum L.) using molecular markers

The microspore origin of anther-culture-derived plants of flax was determined using inter-simple sequence repeat (ISSR) and randomly amplified polymorphic DNA (RAPD) markers. Polymorphic fragments between the two parents of the F₁ donor plants were identified and their segregation patterns in anther-culture-derived plants were used to elucidate the origin of those plants and to determine the degree of independence of plants regenerated from the same callus. Using one ISSR primer (UBC 889) and two RAPD primers (UBC 556 and 561), 12 out of 16 plants were unequivocally identified as being derived from microspores. Plants derived from the same callus had identical PCR patterns at five polymorphic loci and thus were likely derived from the same microspore. Therefore, it is proposed that the number of calli forming shoots be used to describe the anther culture efficiency in flax. Received: 3 February 1998 / Revision received: 8 June 1998 / Accepted: 8 July 1998     

Promotive effect of polyvinylpolypyrrolidone on pollen embryogenesis in Datura innoxia

Pollen embryos of Datura innoxia Mill are produced in larger numbers from anthers on agar-gelled medium containing polyvinylpolypyrrolidone than on control. The best response is observed with 0.5% polyvinylpolypyrrolidone. The effect is possibly due to adsorption of substances (phenolics) emanating from cultured anthers and inhibiting the development of pollen grains into embryos.     

Chemical agents that inhibit pollen development: tools for research

Summary Several unrelated compounds are known to selectively inhibit the development of the male gametophyte. When applied at suitable dosages to plants at the appropriate stages of anther development, these substances block the formation of fertile pollen. The affected stage of pollen development is characteristic of the specific chemical structure of the compound, ranging from effects on microspore meiosis to the formation of pollen defective in the ability to germinate or fertilize. The range of effects mediated by these substances, and by known male-sterile mutants, indicates that microspore development has several critical phases that are particularly sensitive to fatal inhibition. We propose that chemical inhibitors of pollen development deserve attention as tools for elucidating the regulation of pollen development.