Unreduced Pollen Grains Research Articles

Morphological Characterization and Molecular Verification of a Fertile Haploid Pummelo (Citrus grandis Osbeck)

The morphological characteristics and reproductive potential of a haploid plant obtained from the cross between `Banpeiyu' pummelo (Citrus grandis) and `Ruby Red' grapefruit (C. paradisi Macf.) were investigated. The haploid was confirmed to be derived from female gamete of `Banpeiyu' pummelo by isozyme and random amplified polymorphic DNA (RAPD) analysis. Flow cytometry analysis revealed that the haploidy was maintained in several tissues and organs of this plant. It also had the typical morphology of a haploid, such as small leaves and flowers, and had slightly fertile pollen grains. Furthermore, diploid progenies were obtained from the cross between `Kiyomi' tangor and the haploid. The hybridity of these seedlings was confirmed by assessment of the leaf characteristics and RAPD analysis. These results suggest that this haploid produced fertile unreduced pollen grains (n = 9).

Cytogenetic study of some rapeseed (Brassica napusL.) cultivars and their hybrids

Abstract Meiotic study was performed in 22 Brassica napus cultivars considering chiasma frequency and distribution as well as chromosome pairing. All cultivars possessed n = 19 chromosome number (4x) and showed a deviant course of prophase-I meiosis with synezetic knot and post pachytene diffuse stage. Chromosome stickiness occurred in most of the cultivars from early prophase to late telophase-II leading to the formation of laggard chromosomes and micronuclei. The cultivars studied differed significantly in chiasma frequency and distribution as well as bivalent formation indicating their genomic differences. Cluster analysis and ordination based on principal components analysis grouped those cultivars showing meiotic similarities. Some of the cultivars showed the occurrence of unreduced meiocytes and pollen grains.

Microsporogenesis in the endangered species Cupressus dupreziana A. Camus: evidence for meiotic defects yielding unreduced and abortive pollen.

To understand the reproductive biology of Cupressus dupreziana A. Camus (Cupressaceae), a highly endangered Mediterranean conifer, the processes of microsporogenesis and pollen differentiation were investigated cytologically. Pre-meiotic development proved to be similar to the coniferous pattern: the microsporangia differentiated sporogenous tissue in which microsporocytes separated and underwent meiosis. As the meiotic steps proceeded, unexpected irregularities were observed concerning chromosomal and nuclear behaviour. This mainly included: abnormal chromosome segregation and cytokinesis, and nuclear fusion of the meiotic products. The result was the formation, in the same microsporangium, of heterogeneous microspore populations arranged in monads, dyads, triads, tetrads, and polyads, and cytoplasts giving rise to pollen grains of different sizes. This indicates that in C. dupreziana both abortive and unreduced pollen grains are generated. The significance of the finding is discussed in relation to reproductive biology and vulnerability to extinction.

A statistical mixture model for estimating the proportion of unreduced pollen grains in perennial ryegrass (Lolium perenne L.) via the size of pollen grains

The size of pollen grains is commonly used to indicate the ploidy level of pollen grains. In this paper observations of the diameter of pollen grains are evaluated from one diploid accession of perennial ryegrass (Lolium perenne L.), which was expected to produce diploid (unreduced) pollen grains in addition to haploid pollen grains. The considerable overlap of the diameter distributions of haploid and diploid pollen grains severely hampers the accurate estimation of the proportion of diploid pollen grains. To overcome this problem we develop in this paper a statistical normal mixture model and we describe a method to test for the production of diploid pollen grains from a diploid parent, and to estimate the proportion of diploid pollen grains.

Occurrence of unreduced pollen in diploid blueberry species, Vaccinium sect. Cyanococcus

A total of 1475 individuals belonging to 43 natural populations of seven diploid (2x) blueberry species (Vaccinium section Cyanococcus) and two natural interspecific 2x hybrid populations were evaluated for unreduced pollen production. Significant differences were found in the frequency of unreduced pollen producers between species and within and between populations of the same species. Individuals with 1% or more unreduced pollen were considered unreduced pollen producers. The average frequency of unreduced pollen producers in these diploid species was 13.5%, ranging from 7.4% (V. corymbosum) to 18.4% (V. darrowii). The frequency of unreduced pollen grains in individual clones varied from <-1% to 28.6%. The production of unreduced pollen was not associated with male fertility. The widespread occurrence of unreduced pollen in the diploid species should allow the introgression of this germ plasm to the tetraploid level via unilateral sexual polyploidization.

Variation for 2n pollen production in clones of Solanum phureja Juz. and Buk.

Frequency of unreduced pollen grains was estimated for five genotypes of Solanum phureja (2n=24) growing in three environments; (E1) cool (7.2-13.3°C) and (E2) warm (12.2-17.2°C) growth chambers and (E3) field conditions. Highly variable frequencies were found, with genotype, environment, and genotype x environment interaction as significant components of variance. The frequency of unreduced gametes for two additional genotypes was studied over time in two growth chamber environments (cool and warm). One genotype, characterized by mostly fused spindles at the second meiotic division, expressed a high frequency of big pollen (BP) in both environments, whereas the second, characterized by fused, parallel and tripolar second division spindless was found to increase in BP frequency over time in the cool chamber, but remained consistently low in the warm chamber. The identification of specific environmental components with general effect on the expression of un-reduced gametes is not possible because of the large genotype x environment interaction component of variance. A genetic hypothesis based on incomplete penetrance and variable expressivity of a dominant gene is presented as an alternative to the currently accepted theory of control of parallel spindles by a single recessive gene.

A Survey of Pollen Characteristics in Certain Vaccinium Species1

Abstract Pollen stainability, frequency of unreduced pollen grains, and pollen diameter were examined in 13 species and 4 interspecific hybrids of Vaccinium comprising 3 ploidy levels. Pollen in the tetraploid species was potentially more fertile (as judged by stainability) than in the diploid species. Pollen stainability in the hexaploids was not different from the diploids or tetraploids. Four pollen viability classes (good, fair, poor, and very poor) were established among species. Practically all of the species studied produced unreduced pollen grains. Mean pollen diameter was 11% larger in the tetraploids than in the diploids and 11% larger in the hexaploids than in the tetraploids. The normal pollen diameter ranges for the 3 ploidy levels of Vaccinium were calculated and presented as a possible taxonomic tool. Genetic, rather than seasonal or environmental differences, appeared to account for the major portion of the interclonal and interspecific variation observed in pollen stainability and in the frequency of unreduced pollen grains. Frequent irregularities observed were empty pollen grains and granular, unstained pollen, which were assumed to represent early postmeiotic abortions. Meiosis was studied in a representative species of each ploidy level. Pairing and segregation were essentially normal, but a few multivalents or pseudo-multivalents (bivalents secondarily associated) were observed in the hexaploid species.

Potential Fertility Levels in Four Diploid Vaccinium Species1

Abstract As a first step in determining the phylogeny of the rabbiteye blueberry (Vaccinium ashei Reade), the potential fertility levels among its purported diploid ancestral species. Vaccinium atrococcum (Gray) Heller, Vaccinium caesariense MacKenzie, Vaccinium darrowi Camp, and Vaccinium tenellum Ait., were determined. Differences existed among species in female fertility as determined by total number of seeds and number of potentially viable seeds. The number of seeds per berry was lower than that reported for highbush and rabbiteye blueberry cultivars. No differences were found among species in potential male fertility as indicated by percent stainable pollen. Pollen diameter was not a good criterion for distinguishing species or ploidy levels. Comparison of fertility of diploid species with that of purported polyploid derivatives is suggested as a possible aid in determining phylogeny in Vaccinium. Unreduced pollen grains were detected in only 2 of the 4 species in this study. The average return from heterploid (4n × 2n) crosses was 3 seedlings per 1000 pollinations.

HYBRIDS BETWEEN LOLIUM PERENNE AND FESTUCA PRATENSIS

SUMMARYMeiosis and fertility have been studied in natural and artificial hybrids between Lolium perenne and Festuca pratensis. In diploids, meiosis was normal except for a few desynaptic hybrids, but pollen fertility was very low, probably because of genie or chromosomal unbalance. In triploids the extent of homoeologous pairing varied, as did fertility.Several categories of synthetic hybrids were compared with their natural equivalents, and it is considered most likely that all the natural hybrids studied were F1 plants, although there were some discrepancies. Those that were triploid were probably produced by unreduced pollen grains.

Further Studies on Natural Triploidy in Viviparous Onion

Triploid A. cepa var. viviparum has been earlier described as a genomic allotriploid with the genomic formula AAB. Studies conducted on the mode of chromosome pairing and used in conjecture with the nature of karyotype, however, favour segmental allotriploid status for the taxon with the genomic formula A A' A''. A. fistulosum and A. cepa are regarded as the progenitors of ‘Pran’ (3X A. cepa var. viviparum). The unreduced pollen grains of the F1 hybrid through backcrossing seem to have resulted in the formation of the triploid cultivar. Like many other polyploids, the latter has taken to vegetative mechanism of propagation to overcome the bottleneck of sterility.

Cytogeography of Achillea Millefolium in Western Oregon

A cytogeographic study was made of the tetraploid and hexaploid forms ofAchillea millefolium L. in western Oregon in order to clarify their distributions, to determine whether pentaploid hybrids are present at zones of contact between the two, and to correlate environmental conditions with the presence of the tetraploid in the coastal areas of Coos and Curry Counties, Oregon. The distributional pattern of the two chromosome forms was found to be more complex than previously reported, involving overlapping of ranges, the occurrence of mixed populations, and the presence of disjunct populations of one form in areas occupied by the other. A naturally occurring pentaploid hybrid with meiotic pairing of 18 II’s and 9 I’s was found, which could not be distinguished morphologically from the presumed parents. The coastal tetraploid form in southwestern Oregon is limited to the Siskiyou Mountains. Plants of this area, especially those at its geographical margins, were observed to be producing a large number of viable, unreduced pollen grains. It is suggested that the North American hexaploid form originated by autopolyploidy from earlier existing tetraploids.

Cytological relationships in theConvolvulus pluricaulis complex

InConvolvulus pluricaulis Chois. two forms (2n=18, 36) along with one colchicine-autotetraploid have been investigated morphologically and cytologically. The diploid regularly formed 9II although in the “off-season” plants certain irregularities were observed including formation of unreduced pollen grains. The natural tetraploid and the colchicine-autotetraploid had mean frequencies of configurations of 1.56IV+14.04II+1.48I and 2.95IV+0.56III+11,43II+0.8I, respectively. The mode of chromosome association in the two types of tetraploids was comparable. A comparison of the morphological characters of the two tetraploid types, further, suggested close similarity. In addition they were indistinguishable from the diploid from except being gigas. From these data it is inferred that the natural tetraploid presumably arose as a result of direct duplication of the diploid form, through the chance fusion of unreduced spores. The lower quadrivalent frequency of the natural polyploid is ascribed to a gradual shift towards bivalent association accompanying natural selection for fertility. The taxonomic status of the two forms (2x, 4x) is discussed and the varietal status accorded to the tetraploid form is supported.

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.

CYTOLOGY OF POPLAR SPECIES AND NATURAL HYBRIDS

Complete analyses of pollen-mother-cell nuclei at first metaphase, percentage good pollen, pollen diameter and pollen-size distribution were determired for the following poplar species and natural hybrids: Populus grandidentata Michx., P. tremuloides Michx., P. eugenei Simon Louis, P. alba L., P. canescens Sm., natural hybrids of P. alba × P. grandidentata and of P. alba × P. tremuloides.Both of the P. alba and two of the four P. canescens trees examined were triploids (2n = 57) while all other trees examined were diploids (2n = 38). Meiotic observations on the natural hybrids indicated a high degree of homology between the chromosomes of P. alba and the native aspens (P. grandidentata and P. tremuloides), since 17 to 19 bivalents were usually found at first metaphase. In collections from one triploid P. canescens and two diploid alba-grandidentata hybrid trees, failure of a high proportion of the chromosomes to pair was attributed to genetic factors limiting pairing, rather than to non-homology.Pollen characters such as percentage good pollen, pollen diameter, and pollen size distribution were, in most cases, not indicative of the chromosome number or pairing relations at first metaphase. Consequently, triploids could not be detected by pollen observations under the conditions of this experiment. In spite of the lack of correlation between first metaphase and pollen observations, abnormally large pollen grains were observed in collections from several of the trees, and these were considered to contain the diploid or unreduced chromosome complement. The tendency for the poplars to produce unreduced pollen grains probably accounts for the number of triploid trees discovered in Canada and Sweden.