Normal Pollen Grains Research Articles

In vitro flowering in cassava (Manihot esculenta Crantz)

Meristem-derived plantlets of cassava (Manihot esculenta Crantz) were induced to flower in vitro. Five genotypes out of 13 consistently responded to our culture conditions giving rise to male or female flowers. Male flowers contained anthers in which meiosis occurred and apparently normal pollen grains were formed.

Cytotaxonomical studies in Tribulus terrestris and T. alatus (Zygophyllaceae)

The chromosome numbers and meiotic behaviour of twenty morphologically variable populations of 7. terrestris and four of T. alatus were studied and compared. All populations of /. terrestris were hexaploid (2n = 36). They fall in one of the three morphological–eytological groups: I) robust with normal meiosis and pollen grains, II) less–robust with abnormal meiosis and high frequency of smaller pollen grains, and III) mixture of type II and dwarf plants. Seed set was high in all but the dwarfs. It appears that group I reproduces sexually while the other two groups have a certain degree of apomixis, and that the dwarf plants probably resulted from the fusion of cytologically unbalanced gametes. Tribulus alatus populations were tetraploid (2n = 24). Bud material adequate for meiotic studies were unavailable, but the wide range in size of pollen grains indirectly signifies meiotic abnormalities. So far, only the tetraploid race has been examined, while other chromosome races may exist.

Maize pollen test systems to detect nondisjunction.

Three pollen test systems to detect the induction of nondisjunction in maize are actively being explored. (1) Each member of a tetrad of haploid microspores produced by meiosis contains a single chromosome 6 which carries the only nucleolar organizing region in the maize genome. Thus, each member of a normal tetrad contains one nucleolus. If nondisjunction took place at the first or second meiotic division, 2:2:0:0 or 2:1:1:0 tetrads would be produced respectively. (2) If a male parent carrying a dominant endosperm marker is crossed by a female carrying a recessive allele of this gene, all normal kernels would be heterozygous and would express the dominant phenotype in their endosperm. If nondisjunction of the chromosome carrying this gene took place at the second microspore division and the nullisomic and disomic sperm fertilized the polar nuclei and egg of a given embryo sac respectively, an exceptional kernel is produced which would express the recessive endosperm phenotype and contain a trisomic embryo. (3) Complementing null mutations of genes expressed in individual pollen grains can be utilized to detect nondisjunction. Normal haploid pollen grains from plants heterozygous for two complementing null alleles of a locus would each express the recessive phenotype. If nondisjunction took place during either meiotic division, disomic pollen grains containing both alleles could be produced expressing the dominant phenotype due to complementation. We are exploring this test system utilizing appropriate alcohol dehydrogenase mutants.

Maize Pollen Test Systems to Detect Nondisjunction

Three pollen test systems to detect the induction of nondisjunction in maize are actively being explored. (1) Each member of a tetrad of haploid microspores produced by meiosis contains a single chromosome 6 which carries the only nucleolar organizing region in the maize genome. Thus, each member of a normal tetrad contains one nucleolus. If nondisjunction took place at the first or second meiotic division, 2:2:0:0 or 2:1:1:0 tetrads would be produced respectively. (2) If a male parent carrying a dominant endosperm marker is crossed by a female carrying a recessive allele of this gene, all normal kernels would be heterozygous and would express the dominant phenotype in their endosperm. If nondisjunction of the chromosome carrying this gene took place at the second microspore division and the nullisomic and disomic sperm fertilized the polar nuclei and egg of a given embryo sac respectively, an exceptional kernel is produced which would express the recessive endosperm phenotype and contain a trisomic embryo. (3) Complementing null mutations of genes expressed in individual pollen grains can be utilized to detect nondisjunction. Normal haploid pollen grains from plants heterozygous for two complementing null alleles of a locus would each express the recessive phenotype. If nondisjunction took place during either meiotic division, disomic pollen grains containing both alleles could be produced expressing the dominant phenotype due to complementation. We are exploring this test system utilizing appropriate alcohol dehydrogenase mutants.

Chromosomal Differentiation Among Ecotypes of Phalaris aquatica L.

Seventy-two hybrids of P. aquatica were made among 13 diverse Mediterranean ecotypes and cv. Australian, and five indicators of hybrid abnormality were measured in the first two generations. The proportions of stainable, apparently normal pollen grains formed by F, hybrids varied between 5 and 98% and their spikelet fertility ranged from 19 to 77%. Of the 43 hybrids that were derived from pairs of self-incompatible parents, 13 were highly self-compatible. Crosses between lines from different groups of parents produced F2 progeny containing up to 17% of lethal seedlings and up to 39% of male sterile plants. In the cross between cv. Australian and the Moroccan ecotype, CPI 19331: the frequency ofzebra-striped lethal seedlings was as high as 33% in F2 progenies, but only 0 or 1% in back-crosses to either parent. Hence the zebra-striped phenotype was not caused by a mutation existing in the parents but rather by deletions or duplications generated during meiosis in the F1 hybrids. Many meiotic irregularities were observed in the pollen mother cells of the F1 and F2 hybrids between cv. Australian and CPI 19331. These included small loops, acentric fragments, univalents and multivalents at diakinesis, and bridges at anaphase I, indicating that the genomes of these two lines differed by several inversions and interchanges. These structural differences would lead to a range of duplications and deficiencies in the gametes. and hence could account for each of the five kinds of hybrid abnormality observed in the F1 and F2 generations. One aneuploid F2 plant with 25 chromosomes was found. A dihaploid plant in cv. Australian had an average of 4.3 bivalents per pollen mother cell, whereas virtually all chromosomes in the tetraploid parental lines paired as bivalents. Thus, P. aquatica is a segmental allotetraploid with a system which prevents homoeologous pairing in tetraploids but not in dihaploids. The partial barriers to hybridization between P. aquatica lines are not closely related to their geographic origins or varietal classifications. These barriers may hinder but have not prevented the recombination of parental traits during the development of improved cultivars.

Analyses of a Dominant Male‐Sterile Character in Upland Cotton. I. Cytological Studies1

Cytological observations of microsporogenesis breakdown were used to differentiate a new dominant malesterile character in Upland cotton, Gossypium hirsutum L., from the two known dominant male steriles, Ms4 and Ms7. Unlike the Ms4 genotype where breakdown is either premeiotic or occurs during early stages of meiosis, and unlike the Ms7 genotype where the latest reported breakdown in microsporogenesis occurs at the onset of pollen wall formation, the pollen in the new male sterile aborted only after the entire pollen wall, both intine and exine, had been fully developed. Thus, breakdown was consistently postmeiotic although a few sporogenous cells may first degenerate. Compared to normal fertile pollen grains, the sterile grains had a significantly thicker and more intenscly staining intine. They also possessed plugs at germ‐pore regions that failed to stain with toluidine blue. Histochemistry revealed these plugs were composed of hemicellulose or some complex polysaccharide. Histochemical studies also disclosed a unique layer of insoluble carbohydrate located between the intine and exine walls in the sterile microspores. Cytoplasm disintegrated progressively during pollen development resulting in sterile pollen grains that were conspicuously shriveled and vacuolate at maturity.

Development of the Anther and Ovule in Capsicum L

The structure of the anther and ovule and the development of the male and female gametophytes have been studied in seven cultivated varieties of Capsicum-C. annuum L. var. acuminatum Fingerh. (long red cayenne), C. annuum L. cv. Floral Gem, C. annuum L, var. grossum (L.) Sendt. (giant bell), C. annuum var. longum (DC.) Sendt. (long sweet yellow), C. baccatum L. var. pendulum (Willd.) Eshbaugh, C. frutescens L, var. baccatum (L.) Irish and C. frutescens L, cv. Tabasco. Marked differences in the development were observed between flower buds formed in summer and in winter. In the anthers of winter flower buds of C. annuum var, acuminatum the pollen grains show nuclear multiplication and pollens with all nuclear numbers between two and eight are represented. However, 'pollen embryo sacs' as such are not formed. The normal viable pollen grains are binucleate. The pollen fertility in summer is 93.6% while in winter, on the same plants, it is only 31.3 %. In the development of the ovule there are no marked differences amongst the varieties except in size. Coexistence of mono-, bi- and tetrasporic embryo sac developments has been found in C. annuum var. acuminatum in which monospory is dominant in summer but bispory in winter. Monosporic and bisporic embryo sacs coexist in C. baccatum var. pendulum and C. frutescens var. baccatum. The other varieties show only monosporic development.

Pollen morphology and germination inNarcissus

Pollen grains of several species and varieties ofNarcissus were examined with a light microscope and a scanning electron microscope. Normal pollen grains were kidney- or spindle-shaped with a germination furrow and a reticulate structure similar to that of the pollen grains ofAmaryllis.

Pollen-Embryo Sacs inHeuchera MicranthaDougl.

SUMMARYIn Heuchera micrantha the anthers are tetrasporangiate and cytokinesis is of simultaneous type. In the majority of the tetrads microspores soon separate from one another but in a few they remain intact. Tetrads with two degenerating and two multinucleate microspores are often observed. In a few tetrads cell walls undergo lysis resulting in a large, spherical 4-nucleate structures. In some anthers, the behaviour of microspores deviates from normal course: (i) Instead of developing into normal pollen grains, the microspores enlarge, their cytoplasm becomes vacuolated and finally they degenerate, (ii) The microspore increases in size and the nucleus undergoes 3 successive divisions giving rise to an 8-nucleate structure. Three nuclei at each pole organize into cells while the remaining 2 lie in the centre. Such elongated microspores resemble organized Polygonum type of female gametophyte. (iii) Spherical, 4- and 8-nucleate microspores showing cruciate arrangement of nuclei are often met with. Disposition of nuclei is comparable to Penea and Plumbago type of female gametophyte. Cell wall formation is, however, not observed.Pollen-embryo sacs are generally seen in association with degenerated microspores. There is a positive correlation between the behaviour of tapetal cells and the developing microspores.

Intra‐Plant Variation for Pollen Production in Male‐sterile and Fertile Alfalfa1

In Medicago saliva L. intra‐plant variation in pollen production occurred in partially male‐sterile clones, but it was not associated with either flower position on the plant or sampling date. The variation occurred at random throughout the plant. Anthers within the same flower varied for both number of pollen grains and percentage of normal pollen grains.The average number of pollen grains per anther varied among clones from about 440 to 850. The free anther had only about two‐thirds as many pollen grains as each of the remaining nine anthers. The number of normal pollen grains correlated with visual estimates of the amount of dehisced pollen, r = .854**, 11 d.f. Pollen abortion in male‐sterile plants apparently reduced internal pressure sufficiently to prevent rupture of the anther wall and extrusion of pollen.

Embryological studies in the compositae. IV. Sporogenesis, gametogenesis, and embryogeny in Brachycome ciliaris (Labill.) Less

Material of two varieties of Brachycome ciliaris was obtained from several localities in southern Queensland and western New South Wales, and no embryological differences were found between populations in spite of considerable morphological variations. The plant was highly male-sterile, and although development of the anthers was normal up to the formation of microspore mother cells, presumed meiotic abnormalities resulted in failure to form microspore tetrads except in one instance. The formation of plasmodial microspore mother cells and unreduced pollen grains is described and the occurrence of normal pollen grains in two capitula is recorded. In the ovule, meiosis is suppressed and the megaspore mother cell becomes vacuolate and functions directly as the uninucleate embryo sac. Three nuclear divisions precede the formation of an eight-nucleate embryo sac in which the antipodal cells undergo secondary multiplication. There is circumstantial evidence that the polar nuclei divide simultaneously to form the fist four endosperm nuclei and do not first fuse to form a secondary nucleus. The egg cell develops parthenogenetically and cleavages follow the asterad type of development. The eariy stages of embryogeny are completed before the opening of the florets.

Cytogenetic and Cytoecological Studies on Some Japanese Species of <i>Rubus</i> II

1) This paper deals with the results of crosses among ten species of Rubus, and of observations of genetic characteristics and cytological phenomena of the six F1-hybrids.2) The crosses of R. trifidus (2n=14) as the mother with the other diploid species were more successful than the crosses among the other species. And all the crosses of R. hirsutus (2n=14) as the mother failed to give hybrids. All the crosses between the polyploids and the diploids give no hybrid. Hybrids are obtained regardless whether the parents belong to the same subgenera or not.3) The characteristics of the parental species are inherited to the F1-hybrids in several distinct behaviours, which may be classified into four types: a) dominant, b) recessive, c) intermediate betwecen the parents, and d) hybrid vigor.4) In the fertile hybrids, R. trifidus×palmatoides, ribisoideus×palmatoides, ribisoideus ×Fauriei and palmatoides×Fauriei, the most frequent configuration of chromosomes is 7II at IM. While in the sterile hybrids, R. trifidus×hirsutus and trifidus× ribisoideus, univalents are offen observed at IM. When the univalents appear at IM of the sterile hybrids, the frequencies of occurrence of 6II+2I and 5II+4I are higher than those of the other configurations. The fertile hybrids have a large amount of normal pollen grains, but the sterile hybrids have less normal grains. The phenomenon of the latter may be due to the irregularities of meiosis.

A Semi-asynaptic Plant of <i>Abelmoschus esculentus</i> (L.) Moench. (=<i>Hibiscus esculentus</i> L.)

1. A semi-asynaptic plant of Abelrnoschus esculentus (L.) Moens. has been reported and its morphology and cytology have been described. The plant showed luxuriant vegetative growth, produced a large number of flowers and fruits. It grew for a much longer time than normal plants. The normal looking fruits were, however, smaller than the fruits of normal ones and were completely empty.2. On cytological examinations pollen mother cells showed complete or partial failure of the pairing of chromosomes at meiosis. The univalents generally divided into two chromatids at first anaphase. Inspite of these meiotic irregularities some normal looking pollen grains were found and they germinated on the stigma forming small pollen tubes, which indicates that pollen grains can presumably to some extent survive the loss of some genes. Perhaps this is due to polyploid nature of this plant.3. Crossing experiments showed that no functional eggs were organised, hence the meiotic irregularities were presumably on the female side also. The formation of normal fruits was presumably due to the stimulus received from growth of pollen tubes through the style.

Polyploidy Studies in the Brassiceae, IV

1. Almost all of small seeds set on the tetraplold radish in the free pollination of 2x- and x-pollen grains were found cytologically to be triploid hybrids.2. The triploid hybrid showed a variation of chromosome configuration at meiosis from 9III to 3III+6II+6I, with 6III+3II+3I as the mode. The frequency of appearance of univalents is 25.7% at metaphase I of PMC-s. About half of lagging univalents at anaphase I divided longitudinally and their halves went to opposite daughter nuclei. The elimination of univalents at telophase II was found to be about 15.4% of the theoretical total number of univalents.3. It is especially noted that triploid plants have unexpectedly high percentage of good pollen grains and of set seeds, that is 72.3% of normal pollen grains and 1.87 seeds per capsule as compared with 98.0% of normal pollen grains and 3.50 seeds per capsule in the diploid variety.

On the F<SUB>1</SUB> hybrid, Vicia sativa x V. alegustifolia.

( 1 ) Crossing 22 flowers of Vicia sativa with pollen of V. angustifolia, 3 pods containing 14 seeds in total were obtained. The size of seeds obtained was somewhat smaller than those of the parents, and the numbers of days ne.cessary for germination were larger to some extent than those of the parents. ( 2 ) In F1, the type of branching, colour of stems and shape of leaflets in the main stem resembled the father plant, while the length of internodes, the shape and colour of stipules and petioles, the shape of leaflets in the lateral stems, the colour and hair of leaflets, the length and colour of tendrils and the colour of petals were inter mediate between the parents. ( 3 ) In F1 the plant heights were intermediate between the parents 'and the number of branches resembled the father Dlant in November. But in the next April the plant heights were similar and the number of branches more numerous compared with parents. The tirnes of blooming and the maturity of seeds were later by 12 and 6-10 days respectively than the parents. ( 4 ) In the parents and F1, the chromcsome numbers in root tips were 12, and at IM of PMC 6 bivalents were observed and the meiosis proceeds on normally. ( 5 ) The percentage of normal pollen grains were ca. 70-84% in the parents, but ca. 8-10 in F1 The size of pollen grains was similar to those of the parents but it was smaller in F1 ( 6 ) The percentage of the number of seeds to that of ovules per pod were ca. 73-79 in the parents and ca. 16-23 in F1 showing lower fertility.

Pollen Production and Seed Development in the White Sapote

1. In the white sapote (Casimiroa edulis Llav. and Lex.) all the flowers observed were structurally hermaphroditic. 2. The anthers in the Dade and Blumenthal varieties differed markedly in appearance from those in the other varieties and seedlings studied and contained no normal pollen grains. 3. The other varieties and seedlings studied were found to produce an abundance of spheroidal pollen grains measuring 25-37 μ in diameter and containing three germ pores.

二倍種田山の体細胞染色体とその減数分裂における染色体行動

In the present study the idiogram in root-tips and the meiotic chromosome behaviour of pollen mother cells in the diploid potato species a n g ; Tayam e q u i v ; were investigated. The somatic chromosome number of this species is 24; among them 2 pairs of large chromosome have one satellite respectively; the members of one pair of chromosomes are unequal in size; and the other 9 pairs are small and nearly of the same size.Irregularities of chromosome behaviour in meiosis and in pollen grain formation have been described. Special attention was given to the preceding of one pair of chromosomes and, also to the appearance of both normal and abortive pollen grains corresponding to changes of temperature during sporogenesis. As a result of these investigations, the irregularity of meiosis and the formation of abortive pollen grains are ascribed to the hybrid nature of this species demonstrated in the idiogram and externally to high air temperature.The hypothetical two chromosome sets seem to have high affinity but it is, however, easily disturbed by daily high air temperature during sporogenesis as ascertained in the meiosis occuring in the month of July.

A spontaneous haploid of Nicotiana Tabacum

1. A spontaneous haploid (2n=24) was found in an F3 family of the crossNicotiana Tabacum (Amersfoorter)×N.Tabacum atropurpurea. 2. The plant was a typical dwarf and appeared to be completely sterile. 3. At diakinesis and first metaphase 0,1 or 2 bivalents occurred, the average number per cell being 0,63 at diakinesis and 0,43 at metaphase. 4. First metaphase shows the univalent chromosomes scattered all over the spindle. 5. During first anaphase most chromosomes pass to the poles without division; in many cells, however, a few chromosomes between the polar groups divide equationally. 6. Out of 436 interphase cells 6 (1,38%) showed a restitution nucleus. The very few normal pollen grains probably arise from such restitution nuclei. 7. The literature on haploidNicotiana Tabacum is discussed with respect to homologous and non-homologous pairing, bivalent formation, and the occurrence of first metaphase plates consisting of bivalents or univalents.

Cytological Study of Tobacco Mosaic, I

1. As previously reported (1935) “X-bodies” were often found in microsporogenous cells and tetrads. They were also found in the pollen mother cells in the resting stage, but not observed during reduction division. The process of reduction division showed no irregularities and normal tetrads were formed. Twenty four chromosomes were counted at the metaphase of both the first and second meiotic division.2. The diseased plant produced 88.91 per cent apparently normal pollen grains and 11.09 per cent degenerated ones. On the agar medium containing 5 per cent glucose the apparently normal pollen grains failed to germinate in 36.20 per cent. The healthy plant also produced 88.34 per cent apparently normal pollen grains and 11.66 per cent degenerated ones. In this case, among the apparently normal pollen grains 47.56 per cent could not germinateat all. The degeneration seemed to occur after tetrads were formed.3. The seeds obtained from the cross between diseased and healthy plants and from the self-pollination were abortive in high percentage. This fact is not due to the abnormality of pollen grains or ovules in diseased plants. Whether the female sterility as reported by KOSTOFF is concerned with it or not remained undecided. Most of the normal were ascertained to be germinable.4. The tobacco plant showed no symptoms of mosaic disease, to say nothing of “X-bodies” when inoculated with the expressed juice of diseased plants which boiled for about 15 minutes. Therefore the formation of “X-bodies” is due to the active virus and not to the stimulation of expressed juice which contains inactive virus. When the healthy plant was cultured with the TUKADA-NISIYAMA'S culture solution containing 0.05 per cent of ammonium molybdate it wilted after three days and many yellowish brown granules appeared in the cytoplasm of its cell. These granules gradually gathered into amorphous body which gave an appearance of “X-body”. In the culture solution containing 0.05 per cent of lactic acid it wilted after seven days and its cells showed coagulated cytoplasm. In the solution containing 0.005 per cent of ammonium molybdate or lactic acid the cells remained quite normally. Further, in the culture solution containing 0.001 per cent of potassium iodide or sodium iodide, they showed no changes in the cytoplasmic contents in about one month.