Sterile Pollen Grains Research Articles

Elimination of micronuclei from microspores in a Brazilian oat (Avena sativa L.) variety

Chromosome elimination in interspecific hybrids is a powerful tool in breeding programs. Of 12 Brazilian oat varieties recommended for cultivation in southern Brazil, one variety, UFRGS 15, presented a new type of chromosome elimination never described in any other species. Chromosomes that produced micronuclei during meiosis were eliminated from microspores as microcytes. The micronucleus reached the microspore wall and formed a kind of bud, separated from the microspore. The eliminated microcytes gave origin to small and sterile pollen grains. The possible applications of this finding for oat breeding are discussed.

Meiotic Behavior in Several Brazilian Oat Cultivars(Avena sativa L.).

Considering that the production of grains is a characteristic closely related to meiotic behavior, the purpose of the present study was to evaluate some oat cultivars recommended for the southern region of Brazil in order to verify if tose which currently do not display a good performance present meiotic irregularities that might be impairing the production of viable gametes. The most common meiotic abnormalities were those related to the irregular segregation of chromosomes, characterized by the presence of precocious chromosome migration to the poles or laggard chromosomes and of non-oriented bivalents at the equatorial plate. In general, these chromosomes gave rise to micronuclei during telophase that remained until the tetrad stage. Another very common meiotic abnormality in all varieties was the occurrence of multiple bridges in anaphase I and II. Other less common meiotic abnormalities, such as cytomixis, mixoploidy and chromosome stickiness were observed in some varieties. Although meiotic abnormalities can cause pollen sterility, there was no correlation between these abnormalities and sterility. The percentage of sterile pollen grains was much lower than expected. The grains produced by the 12 cultivars ranged from 820 to 2601 kg/ha, showing no correlation with the rate of meiotic abnormalities or pollen fertility. Thus, the results obtained by cytological analysis suggest that the meiotic abnormalities were not the sole factors responsible for the decrease of productivity in the varieties analyzed.

Transfer of wild abortive cytoplasmic male sterility through protoplast fusion in rice

Wild abortive cytoplasmic male sterility has been extensively used in hybrid seed production in the tropics. Using protoplast fusion between cytoplasmic male sterile and fertile maintainer lines; we report here, transfer of wild abortive cytoplasmic male sterility to the nuclear background of RCPL1-2C, an advance breeding line which also served as maintainer of this cytoplasm. In total, 27 putative cybrids between V20A and RCPL1-2C and 23 lines between V20A and V20B were recovered and all of them were sterile. DNA blots prepared from the mitochondrial DNA of the cybrid lines from both the sets were probed with orf155 that is known to exhibit polymorphism between the mitochondrial DNA of the male-sterile and fertile maintainer lines. Hybridization of orf155 to 1.3 kb HindIII-digested mitochondrial DNA fragment of the cybrids showed transfer of mitochondrial DNA from wild abortive cytoplasmic male-sterile line to the maintainers, viz. RCPL 1-2C and V20B. Expression of male sterility was confirmed by the presence of sterile pollen grains and the lack of seed setting due to selfing in all the cybrid lines. These cybrids, on crossing with respective fertile maintainers set seeds that in turn, produced sterile BC1 plants. DNA blots from HindIII-digested mitochondrial DNA of these BC1 plants when probed with orf155 again exhibited localization of orf155 in wild abortive cytoplasm-specific 1.3 kb HindIII-digested mitochondrial DNA fragments. This demonstrated that the cytoplasmic male sterility transferred through protoplast fusion retained intact female fertility and was inherited and expressed in BC1 plants. Fusion-derived CMS lines, on pollination with pollen grains from restorer, showed restoration of fertility in all the lines. The results demonstrate that protoplasts fusion can be used for transferring maternally inherited traits like cytoplasmic male sterility to the desired nuclear background which can, in turn, be used in hybrid seed production programme of rice in the tropical world.

Hybridization and evolution inCardamine (Brassicaceae) at Urnerboden, Central Switzerland: Biosystematic and molecular evidence

Hybridization between two diploid (2n = 2x = 16) species ofBrassicaceae, Cardamine rivularis andC. amara, at Urnerboden, Central Switzerland, resulted in the rather unusual triploid hybridC. insueta (2n = 3x = 24), and later on in the amphiploidC. schulzii (2n = 6x = 48). The hybrid and the neopolyploid species colonized successfully some man-made biotopes. Plants ofC. insueta are mostly functional females with non-dehiscent anthers, but true hermaphrodite individuals with partly sterile pollen grains also occur within the population. Analyses of cpDNA and nuclear DNA permitted to establish the parentage of the hybrid: the maternal parent which contributed unreduced egg cells proved to beC. rivularis whereas the normally reduced pollen originated fromC. amara. The pronounced genetic variability inC. insueta revealed by isozyme and RAPD analyses, at variance with the polarized segregation, heterogamy and strong vegetative reproduction of the hybrid, is possibly influenced by recurrent formation ofC. insueta which party results from backcrosses betweenC. insueta andC. rivularis but may also proceed by other pathways. The amphiploidCardamine schulzii has normally developed anthers but its pollen is sometimes highly sterile. The surprisingly uniform genetic make-up of the new amphiploid species might be related to its possible monotopic origin and/or young phylogenetic age but should be further assessed. Site management seems to be very important to a further development of hybridogenous populations and their parent species. In conclusion, the evolution at Urnerboden is discussed in the context of the traditional concept of multiple plant origins.

Identification and inheritance of male sterility in groundnut (Arachis hypogaea L.)

Some plants without pods but with gynophores were observed in two F4 progenies of two crosses of goundnut (Arachis hypogaea L.). The flowers on these plants had translucent white anthers with no or a few sterile pollen grains. Three such plants in the succeeding generation were hand pollinated with pollen from a short-duration Indian cv. JL 24. The resulting F1 hybrid plants (male sterile x ‘JL 24’) were normal. Chi-square tests for segregation for male fertile and male sterile plants in F2 and F3 generations indicated that the male sterility in these crosses of groundnut is governed by two recessive genes. We designate these genes as ms1 and ms2 with ms1ms1ms2ms2 being a male sterile genotype.

The Induction of Tetraploid in Crotalaria linifolia Linn..

The production of tetraploid plants in Crotalaria linifolia Linn. was attempted with a view to produce more robust plant for fodder. Seed and seedling treatment with different concentrations of colchicine was tried. Seedling treatment proved to be effective.Size of leaves, flowers, stomata and pollen grains of the tetraploid plants showed enchancement over the diploids. Plant height, raceme length, number of flower per raceme, number of pods, size of pods, seeds per pod were however, lower in tetraploid plants. Pollen fertility in diploid and tetraploid plants was 99.82% and 28.57% respectively.Meiotic observations showed abnormalities such as, univalents, and trivalents at metaphase I, unequal distribution of various combination, laggards at analphase I, II micronuclei at telophase I, II and at tetrad. These irregularities were the major factors for high sterility of pollen grains in induced tetraploid plant of C. linifolia.In having larger leaves and bigger seeds, the tetraploids possesses promising economical features. The lower production of pods and seeds in these plants may be eliminated by selection in later generations of the autotetraploids.

Pollen morphology ofcrossandrasalisbury andcrossandrellac. b. clarke (acanthaceae: acantheae)

Abstract The pollen of 30 species, five subspecies and one possible hybrid of Crossandra Salisbury, together with that of one species of Crossandrella C. B. Clarke, was examined with light microscopy, scanning electron microscopy and selectively with transmission electron microscopy. A remarkable range of exine stratification was discovered and this was used as the basis for the delimitation of six pollen types. Pollen Types I-V are found in Crossandra and Pollen Type VI in Crossandrella. The relationships between these Pollen Types and the sectional classification of Crossandra are discussed. The pollen of one species, Crossandra flava, was found to be highly variable, with both ridged and unridged pollen, and some abnormally shaped sterile pollen grains. Three evolutionary trends are recognised in the pollen morphology of Crossandra and Crossandrella and these are discussed, together with functional aspects.

Colchiploidy in Lindernia crustacea (L.) F. Muell.

Autotetraploid has been raised in Lindernia crustacea, a medicinal weed, by treating the seedlings with 0.2 percent of aqueous solution of colchicine for 20 hours. Morphological and cytological characters of colchiploid and diploid were studied in detail. Cytology of colchiploid was highly non-synchronized and one interesting phenomenon was observed that the frequency of multivalents were very low whereas the sterility of pollen grains was very high. Other anomalies like clumping of chromosome at various stages, precocious separation of chromosomes, formation of univalents and unequal distribution of chromosomes at anaphase I and II were also observed and discussed. Pollen grains were variable in size.

Pollen irradiation and gene transfer in Capsicum

The aim of the experiment was to study the possibility of facilitating the gene transfer and reducing the number of required backcrosses through pollen irradiation and subsequent selection of F1M1 plants containing a very high proportion of sterile pollen as male parent for backcrossing. Anthers of a donor line, C-3-1, were irradiated with 1,500 rad γ-rays and the pollen used for pollination of a recipient genotype W-8 which posseses a number of recessive marker genes. Five F1M2 plants containing more than 80% sterile pollen grains and one semi-sterile plant were selected and used for backcross to W-8. The segregation pattern of four characters expressed in the first backcross generation [W-8×(W-8×C-3-1)] was assessed and compared with the non-irradiated control. A changed segregation pattern was observed (in some cases even non-transfer of a paternal allele) as well as a shift towards more plants possessing the investigated maternal alleles. A scheme for backcross procedure in combination with pollen irradiation is discussed.

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.

Cyto-taxonomical studies in the genus Euphorbia L.

Cytological studies were carried out on 18 species of the genus Euphorbia, of which chromosome counts for five species are reported for the first time. The chromosome numbers in four other species of this genus are found to be at variance with the earlier reports. Of the 18 investigated species, 12 were found to be at different levels of ploidy, while 6 are at the diploid level. Abnormal meiotic behaviour (multivalents and univalents at diakinesis, laggards at A-I, sterility of pollen grains and formation of micropollen) is recorded in the two morphotypes of E. neriifolia collected from Chandigarh and Ahmedabad. Both of these exhibited the chromosome number 2n=90 but in the Chandigarh population 90 bivalents were observed in an occasional spore mother cell too at M-I. It is suggested that this taxon has probably arisen through hybridisation between E. royleana (n=60) and E. nivulia (n=30). On the basis of available data x=10 is suggested as the primary base number for the genus. It has been observed that sections Anisophyllum and Tithymallus are greatly diversified in regard to the basic chromosome number, while the section Euphorbium seems to be uniform in this respect. The role of polyploidy and aneuploidy in speciation and evolution of the genus has been stressed.

The plasmon-genic basis of pollen lobedness and tetrad sterility in Solanum verrucosum hybrids and duplicate linkage groups

In interspecific crosses in Solanum using certain introductions of Solanum verrucosum as female partners, a certain type of male sterility is observed referred to as tetrad sterility. This type is characterized by clumping of the sterile pollen grains in tetrads. In the same F1 hybrids, the pollen grains show a three-lobed appearance. Both tetrad sterility and lobed appearance of pollen grains are inherited through the interaction of dominant genes (Tr and Ld respectively) with the corresponding sensitive [Trs] and [Lds] plasmons, both plasmons occurring in S. verrucosum. The study of one of the interspecific hybrids led to the detection of duplicate linkage groups including the loci Tr and Ld with a recombination percentage for these loci of 13.7%. The possibility of a basic chromosome number less than 12 in Solanum is discussed in connexion with the occurrence of duplicate loci.

A contribution to the life history of Angophora floribunda (Sm.) Sweet (Myrtaceae)

The flower buds of Angophora floribunda appear in the last week of November and anthesis occurs in the middle of January the following year. There is no prolonged resting phase at any stage during embryology and the seeds are shed during late February to early March. In floral development, the petals are the last structures to be formed. Early anther development precedes corresponding stages in the ovules of the same flower, but events in the ovules proceed more rapidly and meiosis occurs simultaneously in the spore mother cells of both organs. The mature two-celled pollen grains are shed when the ovules contain four-or eight-nucleate embryo sacs. Many flowers bear anthers containing only sterile pollen grains, which occur either singly or as tetrads. Various abnormalities in the development of the pollen are reported, and the anthers containing sterile pollen neither develop fibrous bands in the endothecium nor do they dehisce. The ovules are bitegminal, crassinucellar, and hemianatropous. Occasional bifurcation of the inner integument was observed and a hypostase differentiates at the four-nucleate stage of the embryo sac. The embryo sac follows the Polygonum type of development and is five-nucleate and four-celled when mature. The endosperm is Nuclear in origin, and in about half the seeds examined a granular unidentified substance accumulates in the embryo sac. The development of the embryo is irregular and the seedlings bear a collar-like structure at the junction of the hypocotyl and the radicle. The mature embryos are usually dicotyledonous but rarely tricotyledonous. The seed coat is formed exclusively by the outer integument; in the ripe seed it consists of an outer epidermis of large, palisade-like, thin-walled, tanniniferous cells and an inner crystalliferous layer.

The critical period of degeneration of tapetum and pollen grains in Satsuma orange (Citrus unshiu MARC.)

In order to study the mechanism of male-sterility in Satsuma orange, the critical period of the degeneration of pollen grains and anther tapetum was determined. The results obtained were summarized as follows:1. The microspores at the vacuole stage were variable in size, and their sizes at the stages of vacuole appearance and vacuole disappearance were about 20.88 and 27.08μ, respectively.2. The great majority of sterile pollen grains investigated at the stage of pollen maturity could be included in the medium-sized group (from 22.5 to 27.5μ in diameter).3. The degeneration of pollen grains might take place at the vacuole enlarging stage, thereafter, they showed little or no increase in their own size and became empty medium-sized pollen grains.4. During the stage of vacuole disappearance, a few microspores with starch granules and a large number of microspores without starch granules were observed. The latter became sterile throughout thecourse of pollen grain development.5. The tapetum remained cellular and the tapetal cells became to be polynucleated at the pollen-tetrads stage. Breakdown and disappearance of the tapetum occurred at the vacuole enlarging stage and after the pollen mitosis stage, respectively.6. It may be concluded that the critical period of the degeneration of tapetal cells and pollen grains of Satsuma orange is the vacuole enlarging stage of microspores.

Nucleoli and cytoplasmic male sterility

The paper describes the relation of cytoplasmic male sterility and the differentiation of nucleoli. Defects in the formation of nucleoli of pollen grains of maize with cytoplasmic male sterility were observed whereas the nuclei of control, i.e. fertile maize contained always only a single nucleole. In the nuclei of sterile pollen grains nucleoli of various sizes and numbers are formed.