Top PDF POLLEN MORPHOLOGY OF CROCUS L.(IRIDACEAE) IN BULGARIA

POLLEN MORPHOLOGY OF CROCUS L.(IRIDACEAE) IN BULGARIA

POLLEN MORPHOLOGY OF CROCUS L.(IRIDACEAE) IN BULGARIA

morphological characteristics of the pollen of the wild Bulgarian Crocuses define it as a primitive one [6]. The Scanning Electron Microscope investigations, made by Beug [1], established two types of pollen morphology. The results of our investigation led to the conclusion that the same types are also presented in Bulgarian species: –

8 Ler mais

Pollen morphology of Menispermaceae in the state of Bahia, Brazil

Pollen morphology of Menispermaceae in the state of Bahia, Brazil

Braga, J.M.A. 2010. Menispermaceae. In: Forzza, R.C.; Leitman, P.M.; Costa, A.F.; Carvalho Jr., A.A.; Peixoto, A.L.; Walter, B.M.T.; Bicudo, C.; Zappi, D.; Costa, D.P.; Lleras, E.; Martinelli, G.; Lima, H.C.; Prado, J.; Stehmann, J.R.; Baumgratz, J.F.A.; Pirani, J.R.; Sylvestre, L.; Maia, L.C.; Lohmann, L.G.; Queiroz, L.P.; Silveira, M.; Coelho, M.N.; Mamede, M.C.; Bastos, M.N.C.; Morim, M.N.C.; Barbosa, M.R.; Menezes, M.; Hopkins, M.; Secco, R.; Cavalcanti, T.B. & Souza, V.C. (Orgs). Lista de Espécies da Flora do Brasil. http://floradobrasil.jbrj.gov.br/2010/ FB000163. Acesso em 22/09/2010.
Mostrar mais

9 Ler mais

Pollen morphology of selected species of Passiflora L. (Passifloraceae) from the Atlantic Forest

Pollen morphology of selected species of Passiflora L. (Passifloraceae) from the Atlantic Forest

Pollen grains from twelve species of the Passifloraceae family from the Brazilian Atlantic Forest were analyzed: Passiflora subg. Astrophea (1sp.), P. subg. Decaloba (1sp.) and P. subg. Passiflora (10spp.). The current study aims to acquire additional information and feature the pollen morphology of the herein studied species to help setting a more precise taxa delimitation. Acetolyzed pollen grains were measured, described and illustrated using light and scanning electron microscopy. The pollen grains were medium or large sized, oblate spheroidal, suboblate, prolate spheroidal and subprolate; 4-colpate (P. kermesina), 6-12-pantocolporate (P. mediterranea), 6-colpate (P. mucronata), 6-colporate (P. pentagona), 12-colporate (P. misera) or 6-syncolpate (in most species). The presence of reticulate sexine, pseudopercula, pontopercula and/or opercula was observed. The endoaperture was just found in P. pentagona and P. misera. It was concluded that pollen morphology is an important source of taxonomic features useful for distin- guishing species and characterizing the three subgenera. The current study provides additional information that, along with other previously published studies, will enable a better understanding of phylogenetic relations among these strains.
Mostrar mais

9 Ler mais

Viability, production and morphology of pollen grains for diff erent species in the genus Manihot (Euphorbiaceae)

Viability, production and morphology of pollen grains for diff erent species in the genus Manihot (Euphorbiaceae)

studies have been performed on in vitro germination of pollen grains of castor bean (Ricinus communis L.), a plant belonging to the cassava family. Vargas (2006) obtained a low percentage of in vitro castor bean germination in all of the treatments evaluated, with a variation ranging from 0.4 to 0.82% for germinating pollen grains. One potential hypothesis is that there may be a specifi c substance found in the stigma that induces pollen tube formation. Th e re- sults from that author did not diff er from those obtained by Orrego & Hershey (1984) who, when studying in vitro germination of Manihot esculenta Crantz pollen, also did not observe the growth of the pollen tube in any of the culture media assessed. On the other hand, Mbahe et al. (1994) found a variation from 0.4 to 0.57% for pollen germination in cultivated cassava.
Mostrar mais

7 Ler mais

Laboratório de Biologia Celular, Universidade Federal de Santa Catarina (UFSC), Campus Universitário Curitibanos, Rodovia Ullysses Gaboardi Km 3, Caixa Postal 101, 89520-000 Curitibanos, SC, Brasil

Laboratório de Biologia Celular, Universidade Federal de Santa Catarina (UFSC), Campus Universitário Curitibanos, Rodovia Ullysses Gaboardi Km 3, Caixa Postal 101, 89520-000 Curitibanos, SC, Brasil

The pollen morphology and exine structure of 17 species of Lippia L. were investigated in this work using light and scanning electron microscopy. Among the species studied, 14 showed tricolporate pollen grains, two had tri- and tetracolporate pollen grains and a single species exhibited, only tetracolporate pollen. The amb ranged from triangular to square, and the shape varied from oblate-spheroidal to prolate-spheroidal. Three different types of exine ornamentation were observed: psilate, scabrate and perforate. In addition to morphological data, we found positive association between the chromosome numbers and size of pollen grains, and also between the length and width of the colpi. The results indicate that the characteristics of pollen grains in Lippia may be used as an additional taxonomic character of the genus.
Mostrar mais

11 Ler mais

Morfologia, viabilidade polínica e índice meiótico de Byrsonima crassifolia (L.) Kunth / Morphology, pollen viability and meiotic index of Byrsonima crassifolia (L.) Kunth

Morfologia, viabilidade polínica e índice meiótico de Byrsonima crassifolia (L.) Kunth / Morphology, pollen viability and meiotic index of Byrsonima crassifolia (L.) Kunth

Braz. J. of Develop., Curitiba, v. 6, n.6, p.37514-37536 jun. 2020. ISSN 2525-8761 acetic carmine dye and orcein. B.crassifolia is a species with few meiotic irregularities, with pollens considered large, 3-collporate and with reticulate exine. Pollen viability was estimated with Sudan IV, Alexander Reactive, 1% Lugol and 1% Carmine Acetic dyes. The dye that showed the highest average percentage of pollen viability for the species was sudan IV (98.8%). The tests with dyes show a significant difference and reveal that the species has high pollen viability and high meiotic regularity. The information collected from Byrsonima crassifólia helps in the understanding of reproductive aspects and can be used in the implantation of commercial crops, as well as programs of improvement and conservation of the species.
Mostrar mais

23 Ler mais

Pollen morphology of Rubiaceae Juss. species occurring in an area of caatinga (dryland) vegetation in Bahia State, Brazil

Pollen morphology of Rubiaceae Juss. species occurring in an area of caatinga (dryland) vegetation in Bahia State, Brazil

The pollen grains of the species analyzed ranged from small to large, with the smallest grains belonging to Psyllocarpus asparagoides (ED=13.6 μm) and the larg- est belonging to Richardia grandiflora (PED=92 μm), and were isopolar in most species, with the exception of Palicourea rigida (apolar); suboblate to subprolate; and amb circular, sub-circular (Coccocypselum hirsu- tum, Declieuxia fruticosa and Leptoscela ruellioides), or triangular to quadrangular (Cordiera rigida). In terms of the aperture type, the grains were inaperturate (P. rigida), zonoaperturate, colpate (Diodella apiculata, D. teres, Mitracarpus baturitensis, M. villosus, and Richardia grandiflora), or colporate in the remaining species; the number of apertures varied from 3 to more than 20 (R. grandiflora), while the lengths of the ectoapertures varied from short to long, with the smallest being observed in Diodella teres (PAI= 1.6) and the largest in R. grandi- flora (PAI= 0.1). In relation the exine ornamentation, the analysis under light microscopy (LM) revealed that the pollen grains were microreticulate in most species, reticulate (C. hirsutum, C. rigida and P. rigida), echinate- granulate (R. grandiflora), echinate-granulate-perforated (Diodella apiculata and D. teres), or psilate (P. asparagoi- des). Pollen grains were observed under an SEM that were microreticulate (L. ruelioides), bireticulate (D. fruticosa), and microechinate-perforated (Coutarea hexandra). The sexine was thicker than the nexine in most species, although the sexine of Coutarea hexandra was thinner than the nexine; the sexine and nexine were indistinct in Diodella teres and Palicourea rigida.
Mostrar mais

12 Ler mais

Morphology and viability of pollen grains from passion fruit species (Passiflora spp.)

Morphology and viability of pollen grains from passion fruit species (Passiflora spp.)

There is evidence that the staining method overestimates pollen germination percentages, whereas the in vitro test underestimates them (Galletta 1983). According to Scorza & Sherman (1995), reactions to staining materials may not correlate well with in vitro pollen germination or with fertilisation abilities. The results obtained in the present study are in agreement with that statement, given that our pollen germination data indicated a significantly lower rate than that observed when using staining materials. Simi- larly, when analysing pollen viability for guava genotypes (Psidium guajava), in which estimations had been made for in vitro pollen germination and staining method ger- mination (Lugol’s solution and acetic orcein), Coser et al. (2012) observed that the results obtained through the use of staining materials were better than those when using in vitro methods. These authors state that the use of staining materials, while extremely attractive due to their simplicity and ease of use, overestimate guava pollen viability when compared with results obtained in vitro. However, a num- ber of authors acknowledge that histochemical analysis with the use of staining materials for certain species could produce false-positive results when compared with in vitro germination testing (Stone et al. 1995; Dafni et al. 2005). For example, Parfitt & Ganeshan (1989) reported that the- re was no significant correlation between in vitro pollen germination and that of the TTC staining test, in relation to Prunus species. Munhoz et al. (2008), compared five types of staining materials during pollen viability testing of Carica papaya L. and noted that only the TTC method correlated positively with the percent pollen germination for that particular species. However, when comparing five staining materials, Abdelgadir et al. (2012) noted that only the TTC method was capable of differentiating between viable and non-viable pollen grains, concluding that TTC staining was the most efficient method for assessing the viability of the pollen studied, which was that of Jatropha curcas L. (Euphorbiaceae).
Mostrar mais

9 Ler mais

Morfologia polínica de espécies de Euphorbiaceae s.l. arbóreas ocorrentes no Estado de Santa Catarina, Brasil.

Morfologia polínica de espécies de Euphorbiaceae s.l. arbóreas ocorrentes no Estado de Santa Catarina, Brasil.

ABSTRACT - (Pollen morphology of arboreal species of Euphorbiaceae s.l. at Santa Catarina State, Brazil). The pollen morphology of seven species of Euphorbiaceae occurring in the State of Santa Catarina, were examined: Actinostemon concolor, Hieronima alchorneoides, Maprounea brasiliensis, Pachystroma longifolium, Pausandra morisiana, Sapium glandulosum and Sebastiania argutidens. Except for Pausandra morisiana, all species have pollen grains in monads, isopolar, small to medium, radial symmetry, 3-colporate, oblate-spheroidal to prolate, and with a microreticulate ornamentation. Pollen grains of Pausandra morisiana follow the Croton–pattern. The morphometric data showed that Hieronima alchorneiodes pollen grains present the equatorial axis shorter than the other specimens studied. Pachystroma longifolium is the only species that shows a nexine thicker than the sexine, which characterizes pollen grains more resistant to the fossilization processes. Key words: Euphorbiaceae, Palynotaxonomy, pollen grains
Mostrar mais

6 Ler mais

Morphology and viability of castor bean genotypes pollen grains

Morphology and viability of castor bean genotypes pollen grains

ABSTRACT. The objective of this work was to characterize the morphology and viability of the pollen of 15 genotypes of castor bean (Ricinus communis L.) and to generate information that can assist in the selection of highly promising male parents for future use in genetic improvement programs aimed at producing seeds for oil extraction. Acetolysis and scanning electron microscopy was used to characterize the morphology of the pollen. The viability of the pollen grains was estimated by in vitro germination and colorimetric analysis (acetocarmine 2% and 2, 3, 5-triphenyltetrazolium chloride 1%). For the in vitro germination, pollen grains were grown in 10 types of solidified culture medium consisting of different concentrations of sucrose, boric acid, calcium nitrate, magnesium sulfate and potassium nitrate. The pollen grains had the following characteristics: medium size, isopolar and subspheroidal shape, radial symmetry, circular ambit, 3-colporate, elongated endoapertures, tectate exine and granulated sexine. The acetocarmine dye overestimated pollen viability. The media M5 and M8 were the most efficient at promoting the germination of pollen grains. The studied genotypes had high levels of viability and can therefore be used as male parents in genetic improvement programs.
Mostrar mais

7 Ler mais

Pollen morphology and study of the visitors (Hymenoptera, Apidae) of Solanum stramoniifolium Jacq. (Solanaceae) in Central Amazon

Pollen morphology and study of the visitors (Hymenoptera, Apidae) of Solanum stramoniifolium Jacq. (Solanaceae) in Central Amazon

RESUMO – (Morfologia polínica e estudo dos visitantes (Hymenoptera, Apidae) de Solanum stramoniifolium Jacq. (Solanaceae) na Amazônia Central). A família Solanaceae tem ampla distribuição, principalmente nas áreas tropicais e subtropicais da América do Sul. Solanum L. é um dos mais importantes gêneros desta família com aproximadamente 1.200 espécies. O objetivo deste trabalho foi o de estudar a biologia floral com enfoque na morfologia polínica e no registro de algumas abelhas visitantes de S. stramoniifolium. Dados preliminares indicam a presença de uma espécie de abelha com ferrão e quatro espécies sem ferrão como visitantes de S. stramoniifolium. O pólen de S. stramoniifolium é tricolporado e psilado, ou seja, sem ornamentação. Conclui-se, após o estudo da biologia floral, que S. stramoniifolium constitui fonte potencial de pólen para diferentes espécies de abelhas com e sem ferrão, representando interessante campo para estudos de germinação, interações inseto-planta e biologia floral.
Mostrar mais

5 Ler mais

Pollen morphology of the genus Eremanthus Less. (Vernonieae, Asteraceae)

Pollen morphology of the genus Eremanthus Less. (Vernonieae, Asteraceae)

Barroso and E. veadeiroensis H. Rob.—without specifi c morphological investigations. Th e narrower concept of Eremanthus, i.e., including Vanillosmopsis but not Paralych- nophora (MacLeish 1987, Hind 2000), is here followed (for a diff erent point of view, see Robinson 1997, 1999, 2006/2007). Pollen characters of Asteraceae have been shown to be particularly variable and form useful patterns in the context of phylogenies. Such patterns could be used to support hypotheses of relationships, or provide diagnostic characters for groups at diff erent levels (Wortley et al. 2007, Wortley et al. 2008, Blackmore et al. 2009). Blackmore et al. (2009) noticed that Vernonieae provides an example where a large number of pollen characters are congruent with the relationships presented in the Asteraceae supertree (Funk et al. 2005). Blackmore et al. (2009) provide puta- tive synapomorphies for groups, most of them concern- ing African clades. Vernonieae pollen grains are usually lophate or sublophate, tricolporate or triporate, with either a continuous or discontinuous punctate or micropunctate tectum, and are with or without spines (Keeley & Robinson 2009; for a detailed description see Blackmore et al. 2009). Th e large pollen diversity of the tribe has been used exten- sively in taxonomic delimitations at generic and subtribal levels (Jones 1979, 1981, Bolick & Keeley 1994; Keeley & Robinson 2009). Kingham (1976) created six pollen Types (I–VI) for the tribe, based on the study of 85 species (mostly African). Keeley and Jones (1977, 1979) also identifi ed six basic Types (A–F) to which additional variations have been added (Robinson 1999). Currently, ten pollen Types are recognised for the tribes (Dematteis & Pire 2008). Using mainly the classifi cation of Keeley and Jones, several authors have analysed and described pollen grains of Vernonieae, mostly of Vernonia s.l. (Keeley & Jones 1977, 1979; Jones 1979, 1981; Robinson 1987a,b,c, 1988a,b,c, 1990; Skvarla et al. 2005; Mendonça & Gonçalves-Esteves 2000; Mendonça et al. 2007a,b,c, 2009, 2010; Dematteis & Pire 2008; Angulo & Dematteis 2010).
Mostrar mais

12 Ler mais

Pollen morphology of some Fabaceae species from Patos de Minas, Minas Gerais State, Brazil

Pollen morphology of some Fabaceae species from Patos de Minas, Minas Gerais State, Brazil

ABSTRACT - (Pollen morphology of some Fabaceae species from Patos de Minas, Minas Gerais State, Brazil). This paper presents a palinologycal study of 16 Fabaceae species (Bauhinia variegata (L.), Caesalpinia echinata Lam., C. pulcherri- ma (L.) Sw., Calliandra surinamensis Benth., Cassia grandis L. f., Delonix regia (Bojer ex Hook.) Raf., Inga vera Willd., I. laurina (Sw.) Willd., Mimosa caesalpiniifolia Benth., M. pudica L., Myroxylon peruiferum L. f., Platypodium elegans Vogel, Poincianella pluviosa (DC.) L.P. Queiroz, Senna multijuga (Rich.) H.S. Irwin & Barneby, S. polyphylla (Jacq.) H.S. Irwin & Barneby and Senna trachypus (Mart. ex Benth.) H.S. Irwin & Barneby), which occur in the Centro Universitário de Patos de Minas Campus I- UNIPAM, and in the urban area of the city. The results showed that Fabaceae is euripalinous, displaying small, medium, large and very large sized pollen grains, dispersed in monads, tetrads and polyads, 3-colporate, 3-colpate, 4-(5)-(6)-24-porate, and with psilate, rugulate, reticulate-rugulate, retipilate to striate-reticulate sexine.
Mostrar mais

12 Ler mais

Pollen morphology of Waltheria L. (Malvaceae-Byttnerioideae) from Bahia, Brazil

Pollen morphology of Waltheria L. (Malvaceae-Byttnerioideae) from Bahia, Brazil

Th e nexine was thicker than the sexine in most cases; a thicker sexine was observed only in W. brachypetala, W. rotundifolia, and W. selloana. Th e supratectal elements are small and acute echinae, with a broad base, densely distributed throughout the surface of the pollen grain (Figs. 1C, 4H, L, N, 5C, F’, G, H, J, K’, N, 6A, B’, D). Th e form of the echinae distribution varied slightly among species: they were located more distant from each other in W. brachypetala (Fig. 4H-I) and W. excelsa (Fig. 5G-H), while interspinal distance was about 1 µm in W. rotundifolia, W. selloana, and W. vernonioides. Smaller echinae were observed in W. cinerascens (Fig. 4N) and the largest in W. macropoda (Fig. 5J-K’).
Mostrar mais

16 Ler mais

Pollen morphology of Centaurea L. (Asteraceae) in Iran

Pollen morphology of Centaurea L. (Asteraceae) in Iran

The genus Centaurea L. is one of the largest genera in the family Asteraceae. The number of taxa included in this genus ranges from 500 to 600 worldwide. Iran is one of the major centers of diversity for this genus. Pollen morphology has proved useful in the systematics of Asteraceae, as well as in that of some of its genera and species. The pollen morphology of 19 taxa of the genus Centaurea was investigated in detail by light and scanning electron microscopy. Examination under light microscopy showed pollen grains to be tricolporate, isopolar, radially symmetrical, oblate spheroidal, prolate spheroidal, subprolate, tectum perforate and scabrate. Based on the exine ornamentation observed under scanning electron microscopy, we identified two types of pollen grains, designated type I (dense acute spinules) and type II (sparse spinules). All of the taxa evaluated resemble Wagenitz’s Jacea type. We present micrographs of pollen grains, together with descriptions of the characteristics of their structure. We found that the pollen characters (shape, exine structure, sculpturing) were useful for classification.
Mostrar mais

11 Ler mais

Morphological characterization of pollens from three Apiaceae species and their ingestion by twelve-spotted lady beetle (Coleoptera: Coccinellidae)

Morphological characterization of pollens from three Apiaceae species and their ingestion by twelve-spotted lady beetle (Coleoptera: Coccinellidae)

There are few studies regarding the quantification in numerical terms of pollen grains ingested by predator lady beetles. In some studies on C. maculata, the results are presented in terms of weight, which renders further comparative discussions difficult. However, Lundgren et al. (2005) estimated that the consumption of corn pollen grains ( Z. mays) by fourth instar larvae of C. maculata was of 3.30 mg and the adults consumed 13.15 mg of pollen of this Poaceae during the period of anthesis in transgenic corn crops in Illinois, USA, without mentioning what this represents in terms of the number of ingested pollen grains. Dupuis et al. (1987) estimated that 2500 Z. mays pollen grains in one milligram, therefore, considering only the consumption of fourth instar larvae and of adults of C. maculata recorded by Lundgren et al. (2005), would give a total of 41125 pollen grains. Therefore, it gives a quantity relatively higher than the consumption of Apiaceae grains by these phases in the present study, reaching a peak of 14.94% greater than the dill grains. Although it is not possible to affirm, the lower ingestion of Apiaceae pollens might be due to the higher protein content. Roulston et al. (2000) recorded that the protein content of the Z. mays pollen is 23.9%, and 29.0% for the Anthriscus sylvestris (L.) (Apiacae). Nevertheless, data in the literature as to the protein content of Apiaceae pollens evaluated in the present study were not found. Furthermore, according to Patt et al. (1997a), the morphology of dill and coriander flowers, that present exposed stamens above the petals, is compatible with the morphology of the head of the C. maculata, facilitating prompt access to the pollen, as well as the floral nectar.
Mostrar mais

8 Ler mais

Roughness of surface of vacuum castings prepared in plaster moulds

Roughness of surface of vacuum castings prepared in plaster moulds

Experimental castings were prepared in moulds made of two types of plaster. Cast temperatures were 1120 and 1200°C for bronzes and 700 and 800°C for silumin. Temperatures of the mould were 500 and 600°C for bronzes and 200 and 300°C for aluminum alloy. The roughness measurements were carried out with use of Hommelwerke Tester T1000. The average arithmetic deviation of roughness profile Ra, the ten-point height of irregularities Rz and maximum peak to valley height Rm, were measured.

6 Ler mais

Pollen viability and quantification of pollen grains in species of Physalis

Pollen viability and quantification of pollen grains in species of Physalis

A adição de ácido bórico ao meio de cultura também aumentou significativamente a germinação dos grãos de pólen de fisális em estudo, mas os incrementos obtidos variaram entre as espécies. Na espécie Physalis angulata L., a adição de 626,58 mg de ácido bórico promoveu o incremento de 32% de germinação dos grãos de pólen (Figura 4A); para a espécie Physalis ixocarpa Brot., o incremento obtido foi de 12% com a adição de 481,13 mg de ácido bórico (Figura 4B); porém, para a espécie Physalis minima L., a adição de 228,57 mg promoveu aumento de apenas 1% em relação a não adição de ácido bórico ao meio de cultura (Figura 4C), o que não justifica o uso desse nutriente para essa espécie; por outro lado, a adição de 484,37 mg e
Mostrar mais

9 Ler mais

Assessment Of Some Acceleration Schemes In The Solution Of Systems Of Linear Equations.

Assessment Of Some Acceleration Schemes In The Solution Of Systems Of Linear Equations.

Abstract: In this paper, assessment of acceleration schemes in the solution of systems of linear equations has been studied. The iterative methods: Jacobi, Gauss-Seidel and SOR methods were incorporated into the acceleration scheme (Chebyshev extrapolation, Residual smoothing, Accelerated gradient and Richardson Extrapolation) to speed up their convergence. The Conjugate gradient methods of GMRES, BICGSTAB and QMR were also assessed. The research focused on Banded systems, Tridiagonal systems and Dense Symmetric positive definite systems of linear equations for numerical experiments. The experiments were based on the following performance criteria: convergence, number of iterations, speed of convergence and relative residual of each method. Matlab version 7.0.1 was used for the computation of the resulting algorithms. Assessment of the numerical results showed that the accelerated schemes improved the performance of Jacobi, Gauss-Seidel and SOR methods. The Chebyshev and Richardson acceleration methods converged faster than the conjugate gradient methods of GMRES, MINRES, QMR and BICGSTAB in general.
Mostrar mais

8 Ler mais

Epigenetic marks in the mature pollen of Quercus suber L. (Fagaceae)

Epigenetic marks in the mature pollen of Quercus suber L. (Fagaceae)

Chemical modifications of histones and DNA methylation patterns play an important role in regulating chromatin dynamics and transcription. The male germ cells of higher plants are initiated from haploid microspores following an asymmetric division. The nucleus of the microspore cell then migrates to one of the poles, where it undergoes a mitotic division, giving rise to two structurally and func- tionally different cells. The smaller and elongated cell closest to the pole, generative cell, has a reduced volume of cytoplasm containing relatively few organelles, and is pre- destined to divide and form the two male sperm nuclei. The larger and spherical cell vegetative cell contains higher amounts of stored molecules such as starch and lipids, and has an important role in pollen grain maturation and ger- mination, and also in pollen tube elongation. Once formed, the generative cell rapidly detaches from the pole and floats freely within the cytoplasm of the vegetative cell, resulting in a unique ‘‘cell-within-a-cell’’ structure in the pollen grain. Besides different sizes and composition, the generative and vegetative cells also present distinct nuclear configura- tions. Soon after the asymmetric division of the microspore, the generative nucleus enters the S phase, and then passes into G2 assuming a high chromatin condensation pattern. The vegetative nucleus is arrested at G1, and displays a diffuse chromatin appearance (Bino et al. 1990; Tanaka 1997).
Mostrar mais

7 Ler mais

Show all 10000 documents...

temas relacionados