The Formation of Pollen Dimorphism in Paris axialis in Vivo

It is obsreved that the dimorphic populations of pollen are producedin Paris axialis H. Li In vivo. The normal pollen grains and abnormal pollen grainsare 77.1% and 22.9% respectively; more than 70% of abnormal pollen grains conformto the equal nucleus type. The abnormal pollen grains show no delayed development,and thay are stained as dark as the normal ones. During the first mitotic division of microspore, most of the spindles are anticlinal(perpendicular to the intine), the cytokinesis is generally asymmetric, and a completewall is formed. However, a few mitotic spindles of mitotic microspores are periclinal,and the cytokinesis are symmetric. Sometimes a partial wall is observed between twodaughter nuclei, which are produced by the abnormal pollen grains. We believe thatthese phenomena are related to differentiation of the dimorphic pollen.     

Variation in pollen formation and its cytological mechanism in an allotriploid white poplar

Variation in pollen formation and its cytological mechanism in an allotriploid white poplar were investigated by the squashed technique and indirect immunofluorescence. Besides 0.5% stuck pollen grains, this allotriploid produced regularly spherical pollen grains. It was estimated that 90.3% of pollen grains were viable. Diameters of the viable spherical pollen grains ranged from 23.2 to 72.9 μm, with a bimodal frequency distribution. Numerous meiotic abnormalities were found, including highly irregular chromosome pairing, lagging chromosomes and chromosome bridges, micronuclei, and multiple spindles, which indicate highly genetic imbalance of this allotriploid. Some micronuclei triggered minispindle formation in metaphase II and participated in cytokinesis to form microcytes in sporads. Abnormal orientation of metaphase II spindles contributed to production of dyads and triads, which produced unreduced microspores. However, parallel orientation of spindles was not necessary for dyad formation, because an organelle band positioned in the equatorial region prevented the spindles from coalescing. Some microsporocytes exhibited a complete or partial absence of cytokinesis, which resulted in the formation of monads and the increased frequency of dyads and triads. The perspective of this triploid in the polyploid breeding program of white poplar is discussed.     

Calamagrostis hakonensis (Poaceae): Distribution and differentiation of cytotypes

Chromosome counts were made for a total of 540 collections ofCalamagrostis hakonensis from 66 localities ranging from Kyushu to Hokkaido. Distribution and habitat preferences of the cytotypes involved are described. Sympatric occurrence of tetraploids (=semidiploids, 2n=28) and higher polyploids, as well as that of septaploids and plants at hexaploid and/or octoploid levels, was confirmed in several localities, and mixtures of hexaploids and octoploids within a population were frequently observed. Plants at hexaploid and octoploid levels were the most abundant and widespread. An examination of pollen of the voucher specimens showed that tetraploids (amphimictic) had good pollen, while higher polyploids (apomictic) were generally devoid of pollen and very rarely produced moderately good pollen, the grains of higher polyploids being larger than those of tetraploids. Distributions of tetraploids and higher polyploids were more precisely delineated through an examination of pollen of many herbarium specimens. In relation to the processes by which the complicated internal structure ofC. hakonensis has been established, the following subjects are discussed: infraspecific hybridization between ecotypically differentiated populations, enrichment of variability through occasional sexual reproduction expected in plants with more than 2n=42, persistence of the variants by apomictic reproduction, and probable roles of some extinct taxa.     

In vitro protein synthesis in isolated microspores of Zea mays at several stages of development

Summary A new procedure has been used providing large and homogenous populations of pollen from maize at different stages of their development. In order to label proteins synthesized during the course of microsporogenesis, a method has been developed that allows an efficient uptake of amino acids in the microspores. Results are presented showing that during pollen development three specific steps are involved: an early period active in protein synthesis, followed by a rest period when starch is accumulated, and a third period preceding the sorting out of mature pollen grains and during which protein synthesis starts again at a relatively low level. New polypeptides, some of which are very basic, appear at the time of starch deposition and accumulate up to the mature stage.     

The systematics of autopolyploidy in Epilobium latifolium (Onagraceae)

Diploid (2n = 36) plants ofEpilobium latifolium L. have been found in Alaska and the western Cordillera of North America, and tetraploids in Iceland, western Greenland, and southeastern Quebec. Study of the morphology of these chromosome races revealed a character, the number of pores in the pollen grains, by which they could be distinguished with an average probability of 75%. Tetraploids ofE. latifolium tend to have high percentages of 4-pored pollen, while the diploids usually have only 3-pored pollen. On this basis, the ranges of the races were extrapolated from herbarium material. Detailed comparisons of eight other features of the presumptive diploids and tetraploids showed no significant difference between them. The races appear to form worldwide, allopatric, ecogeographic phases. A high level (57.4%) of quadrivalent formation observed during tetraploid meiosis, and other considerations, indicate that the tetraploids arose by autopolyploidy. The recommendation is made that the races not be given formal taxonomic recognition.     

Studies on Chemically Induced Change in Expression of Gene(s) Controlling the Pollen Shapes in Pimpinella Monoica

Pollen variability in Pimpinella monoccia was artificially induced by treating seedlings with different chemicals. Positive results in the treated plants were obtained with acsculine, saponin, α-bromonapthalene and 8-hydroxy-quinolene. All these plants were 2n. Their meiosis was typified by multiple and multipolar spindles, laggards, strays, bridge-fragment configuration, spindle breakdown and unequal division of the chromosomes into many groups giving rise to variable number of spores at the sporad stage. Besides polyads the variable grains were asymmetric and nonfixiform while the controls had all radiosymmetric grains. One of the interesting facts was that similar pollen shapes were induced by all these diverse chemicals. The development of variable grains has been traced with the help of a scheme. The causes of pollen variability are discussed.     

Discovery of a synaptic mutant in potato haploids and its usefulness for potato breeding

Summary A synaptic mutant was found in haploids (2n=2x=24) extracted from the Mexican potato variety Atzimba (2n=4x=48). The mutant is inherited as a simple Mendelian recessive, designated sy4. Meiotic abnormalities of the mutant during microsporogenesis include: poor synapsis at pachytene; high frequency of univalents at diakinesis; elongated and curved spindles and univalents being scattered over the spindles at metaphase I and anaphase I; abnormal chromosome distribution at anaphase I; and production of sterile pollen, presumably due to unbalanced chromosome complement. The expression of sy4 in megasporogenesis was also detected. The sy4 mutant is very useful for potato breeding when combined with another meiotic mutant, parallel spindles (ps), because haploids homozygous for sy4 and ps produce fertile 2n pollen which transmit almost intact genotypes of the parents to the progenies. Thus, the meiotic mutants provide a powerful breeding method for maximizing heterozygosity and epistasis. They can also provide a very efficient method of transferring diploid germplasm, which has desired characteristics efficiently combined at the 2x level, to tetraploids. Many haploids have been identified with 2n pollen production by ps alone or by sy4 and ps, vigorous growth and good flowering, and a high level of resistance to late blight. The importance of a further search for meiotic mutants and their use for breeding is discussed.     

Instability of the ploidy level in autotetraploid sorghum plants from a line with variable male fertility

It was found that, in some of the plants in generations C1-C5 of induced tetraploids in the semisterile sorghum line AS-1-30, more than 30% of pollen grains (PGs) have sizes typical of haploid PGs. Pollen of these plants was used to pollinate different lines of sorghum with cytoplasmic male sterility (CMS). Diploid hybrids were obtained, which confirms the presence of haploid PGs in the tetraploids studied. When tetraploid plants with an increased frequency of haploid PGs were pollinated with pollen of plants from fertile diploid lines, diploid hybrids were also obtained. This demonstrates that the tetraploids studied had haploid ovicells. In generation C4, a chimeric plant was found; one of its shoots was diploid (judging from morphological characters) and produced as many as 99% of haploid PGs. It is assumed that haploid gametes in autotetraploids are formed through somatic reduction of chromosomes at different ontogenetic stages.     

Radial spindle and the phenotype of the maize meiotic mutant, dv

The morphological phenotype of the maize meiotic mutant dv (divergent spindle) has been further analysed by visualization of the division spindle and examination of its fine structure in mother cells of pollen. Previous research showed that dv blocks convergence of spindle fibres at the poles. New observations reveal abnormalities caused by this mutation, with dv showing disturbances in nuclear envelope breakdown during vesiculation, preventing the spindle fibres from adopting a bipolar orientation (with convergence on the poles). The anomalies result in radial spindles which are similar to monoastral spindles in animal cells.     

Studies in Montia L. and Claytonia L. and Allied Genera

The pollen morphology of several genera in Portulacaceae is described. Particular attention has been paid to the genera of the subfamily Montioideae, as a stage of continued monographical studies. Among genera especially dealt with are Claytonia, Montia, Crunocallis, Naiocrene, Neopaxia, Mona, Maxia, Limnalsine, and Montiastrum. In the taxonomical treatment of these genera the pollen morphology has proved to afford many important additional characters.

The pollen grains of Claytonia are distinguished from those of the remainder in being 3-colpate. The grains of the Claytonia-type have many similarities with those of Lewisia, a genus of the subfamily Portulacoideae. The other genera of Montioideae have pantocolpate pollen grains. Among these genera several different pollen types are distinguished, chiefly with regard to the sexine structures and the aperture membranes. The Montiastrum-type is especially interesting, with tholate grains, a particular pollen type not met with in any other genus in the family. The pollen morphology of some genera in the Portulacoideae is also treated. In some species in Calandrina and Talinum pantotreme pollen grains are observed with apertures transitional between pori and colpi. The apertures of the pantotreme grains are arranged in characteristic patterns.

Particular attention has been given to the variation of the pollen morphological characters. This variation has been examined with regard to the differences between different populations of the same species as well as between different species. The greatest variation has been observed in the shape and size of the grains. The structure and sculpture and thickness of the sexine and the aperture membranes are less variable. Some polyploid taxa are connected with the occurrence of pollen grains with divergent and varying aperture numbers.

In a survey of the genera the taxonomical results of the investigation are presented with particular regard to the pollen morphology. The new genus, Maxia Ö. Nilss., is described. One new species, Montia clara Ö. Nilss., is described and some new combinations are made.

Pollen morphological diagnoses are given for 46 different taxa. The aperture conditions for 96 different species are presented.     

Effects of X-rays and Colchicine on Pollen of Trichosanthes anguina L. (Cucurbitaceae)

Pollen grains of M, and C, generation plants of Trichosanthes anguina L. were studied after treatment of seeds with X-rays and colchicine respectively. Pollen sterility increased with increase in X-ray dose and colchicine concentration. The polar axis of X-irradiated populations was shorter than that of controls. But colchicine treatment resulted in larger pollen grains than the controls, although the exine did not increase as much. Ex-perimentally-produced tetraploids had larger pollen grains than diploids and triploids. The triploids were characterised by changes in pore morphology. Of 293 treated plants examined, 11 aberrant plants were isolated in the M, and C, generations. These plants had large and small fertile pollen grains, and also showed treatment effects in external morphology and chromosomal aberration during meiosis. The changes in polar diameter were not associated with variation in chromosomal material.     

Unusual cytological patterns in microsporogenesis in a cultivar of Fuchsia

Summary Multiple and multipolar spindles are a generalized feature of microsporogenesis in a cultivar of Fuchsia. Only the first meiotic division occurs and gives rise to sporads with nine microspores. Variation in chromosomal complements of the microspores is illustrated by pollen polymorphism. Since some of these pollen grains are able to germinate, the possible breeding value of this super-reductional type of division is questionable. Hypotheses concerning this phenomenon found in the literature are discussed in the light of our results.     

Instability of the Ploidy Level in Autotetraploid Sorghum Plants from a Line with Variable Male Fertility

It was found that, in some of the plants in generations C₁–C₅ of induced tetraploids in the semisterile sorghum line AS-1-30, more than 30% of pollen grains (PGs) have sizes typical of haploid PGs. Pollen of these plants was used to pollinate different lines of sorghum with cytoplasmic male sterility (CMS). Diploid hybrids were obtained, which confirms the presence of haploid PGs in the tetraploids studied. When tetraploid plants with an increased frequency of haploid PGs were pollinated with pollen of plants from fertile diploid lines, diploid hybrids were also obtained. This demonstrates that the tetraploids studied had haploid egg cells. In generation C₄, a chimeric plant was found; one of its shoots was diploid (judging from morphological characters) and produced as many as 99% of haploid PGs. It is assumed that haploid gametes in autotetraploids are formed through somatic reduction of chromosomes at different ontogenetic stages.     

Pollen grains bind to lung alveolar type II cells (A549) via lung surfactant protein A (SP-A)

Lung surfactant protein A (SP-A) is the most abundant surfactant-associated protein present in the lung. A receptor for SP-A has been shown to be present on A549 alveolar type II cells and on other cell types, including alveolar macrophage. The SP-A receptor on A549 cells has been identified as the collectin receptor, or C1q receptor, which binds several structurally-related ligands. SP-A contains C-type lectin domains, but the role of carbohydrate binding by SP-A in physiological and pathological phenomena is not yet established. In this paper we report the binding of SP-A to pollen from Populus nigra italica (Lombardy Poplar), Poa pratensis (Kentucky blue grass),Secale cerale (cultivated rye) and Ambrosia elatior (short ragweed). Saturable and concentration dependent binding of SP-A to pollen grains was observed. Interaction of SP-A with pollen grains takes place through waterextractable components, in which the major species present, in Lombardy poplar pollen,are 57 kD and 7 kD (glyco)proteins. The binding of SP-A to pollen grains and their aqueous extracts was calcium ion dependent and was inhibited by mannose, and is therefore mediated by the lectin domain. Binding of SP-A to pollen grains was found to mediate adhesion of pollen grains to A549 cells. The results suggest that pollen grains or other carbohydrate-bearing particles (e. g. microorganisms) could potentially interact with different cell types via the collectin receptor (C1q Receptor) in the presence of SP-A.     

Variation Patterns and Systematics of the Widespread Species Epilobium angustifolium L.(Onagraceae) in China

Cytological, morphological, and geographical studies of Epilobium angustifolium in China reveal two partly distinct, partly overlapping entities that are best treated as subspecies. The diploid (n=18) subsp. angustifolium has smaller, triporate pollen grains, typically glabrous stems and leaves, and smaller leaves and flowers, and occurs in colder, more northern areas, and at higher elevations in overlap zones. The tetraploid (n=36) subsp. circumvagum has larger pollen with a mixture of quadriporate pollen grains, pubescent stems and leaves, and larger leaves and flowers, and occurs in warmer parts of southern China and at lower elevations. We report 11 chromosome counts, six diploid and five tetraploid, includingthe first reported tetraploids in Asia.     

Breeding system evolution in Tarasa (Malvaceae) and selection for reduced pollen grain size in the polyploid species

Polyploidy, primarily allopolyploidy, has played a major role throughout flowering plant evolution with an estimated 30-80% of all extant angiosperms carrying traces of ancient or recent polyploidy. One immediate and seemingly invariant phenotypic consequence of genome doubling is larger cell size in polyploids relative to their diploid progenitors. In plants, increases in pollen grain and guard cell sizes exemplify this rule and are often used as surrogate evidence for polyploidy. Tarasa (Malvaceae), a genus of 27 species primarily distributed in the high (>3000 m) Andes, has numerous independently generated tetraploid species, most of which have pollen grains smaller than their putative diploid parents. The tetraploids are also unusual because they are annual, rather than perennial, in habit. Data correlate these apparent anomalies to a change in the breeding system within the genus from xenogamy (outcrossing) in the diploid species to autogamy (inbreeding) in the tetraploids, leading to a convergence in reduced floral morphology. The harsh environment of the high-elevation Andean habitats in which all the tetraploid annuals are found is implicated as a critical factor in shaping the evolution of these unusual polyploids.     

Mating interactions between coexisting dipoloid, triploid and tetraploid cytotypes ofHieracium Echioides (Asteraceae)

Experimental crosses between diploids, triploids and tetraploids ofHieracium echioides were made to examine mating interactions. Specifically, cytotype diversity in progeny from experimental crosses, intercytotype pollen competition as a reproductive barrier between diploids and tetraploids, and differences in seed set between intra- and intercytotype crosses were studied. Only diploids were found in progeny from 2x × 2x crosses. The other types of crosses yielded more than one cytotype in progeny, but one cytotype predominated in each cross type: diploids (92%) in 2x × 3x crosses, tetraploids (88%) in 3x × 2x crosses, triploids (96%) in 2x × 4x crosses, triploids (90%) in 4x × 2x crosses, tetraploids (60%) in 3x × 3x crosses, pentaploids (56%) in 3x × 4x crosses, triploids (80%) in 4x × 3x crosses and tetraploids (88%) in 4x × 4x crosses. No aneuploids have been detected among karyologically analyzed plants. Unreduced egg cell production was detected in triploids and tetraploids, but formation of unreduced pollen was recorded only in two cases in triploids. Triploid plants produced x, 2x and 3x gametes: in male gametes x (92%) gametes predominated whereas in female gametes 3x (88%) gametes predominated. Cytotype diversity in progeny from crosses where diploids and tetraploids were pollinated by mixture of pollen from diploid and tetraploid plants suggested intercytotype pollen competition to serve as a prezygotic reproductive barrier. No statistically significant difference in seed set obtained from intra- and intercytotype crosses between diploids and tetraploids was observed, suggesting the absence of postzygotic reproductive barriers among cytotypes.     

Pollen Dimorphism--Origin and Significance in Pollen Plant Formation by Anther Culture

Pollen dimorphism during the ripening of Nicotiana tabacum antherstakes the form of differentiation at the binucleate pollen stageinto normal (N) grains, characterized by their high frequency,larger size, densely–staining cytoplasm and high starchcontent and into smaller (S) grains characterized by their variableand low frequency and weakly–staining cytoplasm. Mostof the S grains show distinctive vegetative and generative nuclei(A grains); a small number have two vegetative–type nuclei(B grains). Evidence is presented that when excised anthersare cultured, pollen plants arise only from S grains. It issuggested that the differentiation into N and S grains arisesby an abnormal second meiotic division in the pollen mothercells. Nicotiana tabacum, tobacco, pollen dimorphism, anther culture     

In vitro induction of tetraploid in pomegranate (Punica granatum)

Tetraploid plants were obtained in pomegranate (Punica granatum L. var. `Nana') by colchicine treatment of shoots propagated in vitro. Shoots cultured on MS medium supplemented with 10 mg l^–1 colchicine, 1.0 mg l^–1 BA and 0.1 mg l^–1 NAA for 30 days produced tetraploids at a high frequency of 20%. No tetraploids were detected by treating the shoots in 5000 mg l^–1 colchicine for 114 h. Shoots treated by 5000 mg l^–1 colchicine for 96 h produced three morphological mutants with narrow leaves, which were later confirmed as mixoploids that separated into diploids and tetraploids after further subculture. In vitro tetraploid plants had shorter roots, wider and shorter leaves than the diploid ones. Tetraploid pomegranate plants grew and flowered normally in pots, but possessed flowers with increased diameter and decreased length compared to diploids. The number of pollen grains per anther was higher in tetraploids, but the viability of pollen decreased significantly.     

Genome duplication and the evolution of conspecific pollen precedence

Conspecific pollen precedence can be a strong reproductive barrier between polyploid and diploid species, but the role of genome multiplication in the evolution of this barrier has not been investigated. Here, we examine the direct effect of genome duplication on the evolution of pollen siring success in tetraploid Chamerion angustifolium. To separate the effects of genome duplication from selection after duplication, we compared pollen siring success of synthesized tetraploids (neotetraploids) with that of naturally occurring tetraploids by applying 2x, 4x (neo or established) or 2x + 4x pollen to diploid and tetraploid flowers. Seed set increased in diploids and decreased in both types of tetraploids as the proportion of pollen from diploid plants increased. Based on offspring ploidy from mixed-ploidy pollinations, pollen of the maternal ploidy always sired the majority of offspring but was strongest in established tetraploids and weakest in neotetraploids. Pollen from established tetraploids had significantly higher siring rates than neotetraploids when deposited on diploid (4x(est) = 47.2%, 4x(neo) = 27.1%) and on tetraploid recipients (4x(est) = 91.9%, 4x(neo) = 56.0%). Siring success of established tetraploids exceeded that of neotetraploids despite having similar pollen production per anther and pollen diameter. Our results suggest that, while pollen precedence can arise in association with the duplication event, the strength of polyploid siring success evolves after the duplication event.