29 research outputs found
Effects of individual and population parameters on reproductive success in three sexually deceptive orchid species
Reproductive success (RS) in orchids in general, and in non-rewarding species
specifically, is extremely low. RS is pollinator and pollination limited in
food deceptive orchids, but this has rarely been studied in sexually deceptive
orchid species. Here, we tested the effects of several individual (plant height,
inflorescence size, nearest neighbour distance and flower position) and
population (patch geometry, population density and size) parameters on RS
in three sexually deceptive Ophrys (Orchidaceae) species. Inter-specific differences
were observed in RS of flowers situated in the upper versus the
lower part of the inflorescence, likely due to species-specific pollinator
behaviour. For all three species examined, RS increased with increasing
plant height, inflorescence size and nearest neighbour distance. RS generally
increased with decreasing population density and increasing patch elongation.
Given these results, we postulate that pollinator availability, rather
than pollinator learning, is the most limiting factor in successful reproduction
for sexually deceptive orchids. Our results also suggest that olfactory
‘display’ (i.e. versus optical display), in terms of inflorescence size (and covarying
plant height), plays a key role in individual RS of sexually deceptive
orchids. In this regard, several hypotheses are suggested and discusse
Distribution patterns of phosphorylated Thr 3 and Thr 32 of histone H3 in plant mitosis and meiosis
Cell cycle dependent phosphorylation of conserved
N-terminal tail residues of histone H3 has been described
in both animal and plant cells. Through cytogenetic
approaches using different plant species we show a detailed
description of distribution patterns of phosphorylated histone
H3 at either threonine 3 or threonine 32 in mitosis and
meiosis. In meristematic cells of the large genome species
Secale cereale, Vicia faba and Hordeum vulgare we have
found that phosphorylation of both threonine residues begins
in prophase, and dephosphorylation occurs in late anaphase.
However, in the small genome species Arabidopsis
thaliana dephosphorylation occurs at anaphase. In the first
division of meiosis of species with large genomes phosphorylation of histone H3 at either threonine 3 or threonine 32
is seen first in diakinesis and extends to anaphase I, whereas
in the second division these post-translational modifications
are visible at metaphase II through anaphase II. While
in A. thaliana dephosphorylation takes place at anaphase I
and II. In all species analysed phosphorylated H3 at either
threonine 3 or threonine 32 are distributed along the entire
length of chromosomes during mitotic metaphase and
metaphase I. In the second meiotic division threonine 3
phosphorylation is restricted to the pericentromeric domain,
while phosphorylation of threonine 32 is widespread
along chromosome arms of all species analysed.Research in the W.V. laboratory was supported by Fundação para a Ciência
e Tecnologia, Portugal grant SFRH/BPD/26442 to A.D.C. and SFRH/
BPD/27219/2006 to M.D., respectively. D.D., R.K. and A.H. were supported
by the Deutsche Forschungsgemeinschaft and by the Land Sachsen Anhal
Interplay of ribosomal DNA Loci in nucleolar dominance: dominant NORs are up-regulated by chromatin dynamics in the wheat-rye system
Background: Chromatin organizational and topological plasticity, and its functions in gene expression regulation, have
been strongly revealed by the analysis of nucleolar dominance in hybrids and polyploids where one parental set of
ribosomal RNA (rDNA) genes that are clustered in nucleolar organizing regions (NORs), is rendered silent by epigenetic
pathways and heterochromatization. However, information on the behaviour of dominant NORs is very sparse and needed
for an integrative knowledge of differential gene transcription levels and chromatin specific domain interactions.
Methodology/Principal Findings: Using molecular and cytological approaches in a wheat-rye addition line (wheat genome
plus the rye nucleolar chromosome pair 1R), we investigated transcriptional activity and chromatin topology of the wheat
dominant NORs in a nucleolar dominance situation. Herein we report dominant NORs up-regulation in the addition line
through quantitative real-time PCR and silver-staining technique. Accompanying this modification in wheat rDNA
trascription level, we also disclose that perinucleolar knobs of ribosomal chromatin are almost transcriptionally silent due to
the residual detection of BrUTP incorporation in these domains, contrary to the marked labelling of intranucleolar
condensed rDNA. Further, by comparative confocal analysis of nuclei probed to wheat and rye NORs, we found that in the
wheat-rye addition line there is a significant decrease in the number of wheat-origin perinucleolar rDNA knobs,
corresponding to a diminution of the rDNA heterochromatic fraction of the dominant (wheat) NORs.
Conclusions/Significance: We demonstrate that inter-specific interactions leading to wheat-origin NOR dominance results not
only on the silencing of rye origin NOR loci, but dominant NORs are alsomodified in their transcriptional activity and interphase
organization. The results show a cross-talk between wheat and rye NORs, mediated by ribosomal chromatin dynamics,
revealing a conceptual shift from differential amphiplasty to ‘mutual amphiplasty’ in the nucleolar dominance process.This work was supported by the Fundação para a Ciência e Tecnologia (projects POCI/BIA-BDE/57575/2004 to M.S. and POCI/BIA-BCM/59389/2004 to N.N.
Secretory structures in plants: lessons from the Plumbaginaceae on their origin, evolution and roles in stress tolerance
Special IssueThe Plumbaginaceae (non-core Caryophyllales) is a family well known for species
adapted to a wide range of arid and saline habitats. Of its salt-tolerant species, at
least 45 are in the genus Limonium; two in each of Aegialitis, Limoniastrum and
Myriolimon, and one each in Psylliostachys, Armeria, Ceratostigma, Goniolimon and
Plumbago. All the halophytic members of the family have salt glands, which are also
common in the closely related Tamaricaceae and Frankeniaceae. The halophytic species
of the three families can secrete a range of ions (Na+, K+, Ca2+, Mg2+, Cl−,
HCO3
−, SO4
2-) and other elements (As, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn). Salt glands
are, however, absent in salt-tolerant members of the sister family Polygonaceae. We
describe the structure of the salt glands in the three families and consider whether
glands might have arisen as a means to avoid the toxicity of Na+ and/or Cl− or to regulate
Ca2+ concentrations within the leaves. We conclude that the establishment of
lineages with salt glands took place after the split between the Polygonaceae and its
sister group the Plumbaginaceaeinfo:eu-repo/semantics/publishedVersio
NOF1 Encodes an Arabidopsis Protein Involved in the Control of rRNA Expression
The control of ribosomal RNA biogenesis is essential for the regulation of protein synthesis in eukaryotic cells. Here, we report the characterization of NOF1 that encodes a putative nucleolar protein involved in the control of rRNA expression in Arabidopsis. The gene has been isolated by T-DNA tagging and its function verified by the characterization of a second allele and genetic complementation of the mutants. The nof1 mutants are affected in female gametogenesis and embryo development. This result is consistent with the detection of NOF1 mRNA in all tissues throughout plant life's cycle, and preferentially in differentiating cells. Interestingly, the closely related proteins from zebra fish and yeast are also necessary for cell division and differentiation. We showed that the nof1-1 mutant displays higher rRNA expression and hypomethylation of rRNA promoter. Taken together, the results presented here demonstrated that NOF1 is an Arabidopsis gene involved in the control of rRNA expression, and suggested that it encodes a putative nucleolar protein, the function of which may be conserved in eukaryotes
Colchicine-induced polyploidization depends on tubulin polymerization in c-metaphase cells
The microtubule cytoskeleton plays a crucial role in the
cell cycle and in mitosis. Colchicine is a microtubule-depolymerizing
agent that has long been used to induce chromosome individualization
in cells arrested at metaphase and also in the induction of polyploid
plants. Although attempts have been made to explain the processes
and mechanisms underlying polyploidy induction, the role of the cytoskeleton
still remains largely unknown. Through immunodetection
of alpha-tubulin, different concentrations (0.5 or 5 mM) of colchicine
were found to produce opposite effects in the organization of the cytoskeleton
in rye (Secale cereale L.). A low concentration (0.5 mM)
induced depolymerization of the microtubular cytoskeleton in all
phases of the cell cycle. In contrast, a high concentration (5 mM) was
found to induce the polymerization of new tubulin-containing structures
in c-metaphase cells. Furthermore, both treatments also showed
contrasting effects in the induction of polyploid cells. Flow cytometric
analysis and quantitative assessments of nucleolus-organizing regions
revealed that only the high-concentration colchicine treatment was effective
in the formation of polyploid cells. Our studies indicate that
spindle disruption alone is insufficient for the induction of polyploid
cells. The absence of any tubulin structures in plants treated with
colchicine at the low concentration induced cell anomalies, such as
the occurrence of nuclei with irregular shape and/or (additional) micronuclei,
12 h after recovery, pointing to a direct effect on cell viability.
In contrast, the almost insignificant level of cell anomalies in the
high-concentration treatment suggests that the presence of new tubulin-
containing structures allows the reconstitution of 4C nuclei and
their progression into the cell cycle
Different numbers of rye B chromosomes induce identical compaction changes in distinct A chromosome domains
In rye each B chromosome (B) represents 5.5% of
the diploid A genome. Rye Bs have several nuclear to whole
plant effects although they seem to bear no genes except for the
ones that lead to their maintenance within a population. In this
context, and considering that rye Bs are enriched in repetitive
non-coding regions that build up heterochromatin (het), we
investigated the influence of Bs on the organization of two
chromatin fractions, namely the ribosomal DNA (facultative
het) and satellite (non-het) domain of rye chromosome 1 by
silver staining on root tip metaphase cells. The results show that
rye Bs cause condensation both in the NOR and in the chromosome
1 satellite domain. Since the silver staining technique used is indicative of the transcriptional activity of the NORs,
the condensation observed at those loci demonstrates that the
rRNA gene arrays are down-regulated in the presence of Bs,
regardless of their number per individual. Furthermore, the
organizational changes of metaphase NORs find parallel with
the interphase organization of ribosomal chromatin, since the
frequency of cells with intranucleolar condensed rDNA regions
increases drastically and nuclear matrix attachment pattern is
altered in the presence of the Bs. Our results show an identical
effect of the Bs on the organization of two distinct chromosome
domains displaying a presence/absence dichotomyFCT - Fundação para a Ciência e Tecnologi
Distribution patterns of phosphorylated Thr 3 and Thr 32 of histone H3 in plant mitosis and meiosis
SIC PTCON00013 Ria Formosa e Castro Marim. Relatório Final. Cartografia de Habitats Naturais e Seminaturais e Flora dos Sítios Classificados no Âmbito da Diretiva Habitats – Cart-Pg Rn2000 (Operação Poseur-03-2215-Fc-000005)
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