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Pollen Size (pollen + size)

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Life Sciences100%

Selected Abstracts

Direct and indirect responses to selection on pollen size in Brassica rapa L.

JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 3 2001
T. S. Sarkissian
Pollen size varies little within angiosperm species, but differs extensively between species, suggesting the action of strong selection. Nevertheless, the potential for genetic responses of pollen size to selection, as determined by additive genetic variance and genetic correlations with other floral traits, has received little attention. To assess this potential, we subjected Brassica rapa to artificial selection for large and small pollen during three generations. This selection caused significant divergence in pollen diameter, with additive genetic effects accounting for over 30% of the observed phenotypic variation in pollen size. Such heritable genetic variation suggests that natural selection could effect evolutionary change in this trait. Selection on pollen size also elicited correlated responses in pollen number (,), flower size (+), style length (+), and ovule number (+), suggesting that pollen size cannot evolve independently. The correlated responses of pollen number, flower size and ovule number probably reflect the genetically determined and physically constrained pattern of resource allocation in B. rapa. In contrast, the positive correlation between pollen size and style length may represent a widespread gametic-phase disequilibrium in angiosperms that arises from nonrandom fertilization success of large pollen in pistils with long styles. [source]

Karyotype morphology and cytogeography in Brunnera and Cynoglottis (Boraginaceae)

BOTANICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2001
MASSIMO BIGAZZI
A comparative study of karyotype morphology and heterochromatin patterns in Brunnera and Cynoglottis (Boraginaceae) was carried out with traditional methods and Giemsa C-banding. Two polymorphic species of Cynoglottis, each with two subspecies, and two of Brunnera were investigated using native population samples from the central-eastern Mediterranean and Middle East. Pollen size of these samples was measured to investigate relationships with ploidy level. C. barrelieri subsp. barrelieri and subsp. serpentinicola are characterized by In = 18 and smaller pollen grains in contrast to C. chetikiana subsp. chetikiana and subsp. paphlagonica, which are fundamentally tetraploid with 2n = 36. The occurrence of cytotypes with 2n ,/2 and 2n = 24 in both subspecies of C. chetikiana, however, would suggest x = 6 as the original haploid number and x = 9 as a derived one. Furthermore, the finding of a hypoploid cytotype with 2n = 16 in C. barrelieri ssp. barrelieri was consistent with previous reports and suggested relationships with Anchusa. Karyoevolutionary processes possibly associated with such a wide chromosome variation in Cynoglottis are discussed. Brunnera macrophylla and B. orientalis share a complement of 2n= 12 and an apparently identical karyotype, which differs from Cynoglottis in terms of asymmetry, chromosome size and morphology. A basic C-banding style was present in Brunnera and Cynoglottis, but heterochromatin content increased from the former to the latter. The parallel increase in chromosome number, heterochromatin content and size of the pollen from Brunnera to Cynoglottis may reflect an evolutionary progression, and is consistent with the supposed ancient origin of Brunnera. [source]

Direct and indirect responses to selection on pollen size in Brassica rapa L.

JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 3 2001
T. S. Sarkissian
Pollen size varies little within angiosperm species, but differs extensively between species, suggesting the action of strong selection. Nevertheless, the potential for genetic responses of pollen size to selection, as determined by additive genetic variance and genetic correlations with other floral traits, has received little attention. To assess this potential, we subjected Brassica rapa to artificial selection for large and small pollen during three generations. This selection caused significant divergence in pollen diameter, with additive genetic effects accounting for over 30% of the observed phenotypic variation in pollen size. Such heritable genetic variation suggests that natural selection could effect evolutionary change in this trait. Selection on pollen size also elicited correlated responses in pollen number (,), flower size (+), style length (+), and ovule number (+), suggesting that pollen size cannot evolve independently. The correlated responses of pollen number, flower size and ovule number probably reflect the genetically determined and physically constrained pattern of resource allocation in B. rapa. In contrast, the positive correlation between pollen size and style length may represent a widespread gametic-phase disequilibrium in angiosperms that arises from nonrandom fertilization success of large pollen in pistils with long styles. [source]

Pollen Morphology of Tundra Shrubs and Submarginal Plants from Barrow, Alaska

JOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 7 2006
Ling-Yu Tang
Abstract Investigation of plant morphological features, pollen, and habitat have been made for two shrub species from Barrow, Alaska, namely Dryas integrifolia M. Vahl and Salix rotundifolia Trautv., both of which are endemic to the Arctic floristic area. The former species has small lanceolate or plate leaves, whereas the latter has rounded leaves with distinct veins, rich in vitamin C. Both have dwarf and sprawling habits. Pollen studies showed that the pollen grains of the two species are spheroidal to sub-spheroidal or prolate. The type of aperture was tricolporate; pollen size 26.3,31.3 ,m; ornamentation finely reticulate under a light microscope (LM) and striate-reticulate under a scanning electron microscope (SEM) for D. integrafolia and finely reticulate under the LM and SEM for S. rotundifolia. Comparisons were made between the pollen from the same species from Arctic collections with those from China and Japan. Investigation of pollen morphology of tundra plants can provide significant data for comparative studies of fossil pollen and for the reconstruction of paleovegetation and paleoclimate in the Barrow area. (Managing editor: Ya-Qin Han) [source]

Palynotaxonomy of Brazilian species of Polygala subgenus Hebeclada

BOTANICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2008
ANA CRISTINA ANDRADE DE AGUIAR
This study used pollen morphology to address taxonomic controversies related to several species belonging to subgenus Hebeclada of the genus Polygala (Polygalaceae). According to the last traditionally accepted revision of this subgenus, it comprises 40 species. Nevertheless, a recent taxonomic treatment applying more comprehensive criteria reduced this number to only nine species. Our work focused on 15 traditionally accepted species that occur in Brazil, fourteen of which have been considered as only six species in this recent taxonomic study. Pollen grains from floral buds at pre-anthesis were collected from herbarium specimens and analysed using both visible light and scanning electron microscopy. Most of the traditionally accepted species were distinguished by different combinations of several pollen-related features, in particular colpi number (13 or 15), pollen size and shape, and endoaperture type (endocingulate or not) and arrangement (parallel or sinuous). The species accepted in the recent taxonomic treatment could not be discriminated by pollen characters. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 157, 609,619. [source]