95 research outputs found
The orchid flora of Portugal - Addendum n.2 - Chorological and systematic remarks on Dactylorhiza maculata (L.) Soó s.l. and Epipactis helleborine (L.) Crantz - First report of E. phyllanthes G.E.Sm.
Close examination of Dactylorhiza maculata s.l. populations in the Serra da Estrela
lead to the proposal that all of them are referable to D. caramulensis and that D.
ericetorum is probably absent from this area, although it is well represented in
the north of the country. New hypotheses are formulated towards a possible
hybrid origin of D. caramulensis between D. ericetorum and D. elata. Three
localities with truly typical representatives of Epipactis helleborine are
reported, two from the Bragança district and one from the Serra da Estrela. A
single individual of E. phyllanthes was discovered close to Bragança; this is the
first mention of an autogamous Epipactis in Portugal. Trend towards autogamy
was also detected on one plant from the Serra da Estrela. A discussion is
initiated on the need to further develop understanding on chromosome structure
and mating systems in orchid species, especially in complex genera such as
Dactylorhiza and Epipactis, to adequately fulfil conservation purposes
Effects of high temperature on mitotic index, microtubule and chromatin organization in rye (Secale cereale L.) root-tip cells
Stressful high temperatures on plants can limit whole-plant function and
decrease crop productivity. However, little is known regarding heat stress effects on
microtubule cytoskeleton and chromatin in roots from intact plants. Here we studied
high temperature effects on cell division, microtubule and chromatin organization patterns
in rye root tips from intact plants subjected to 40ºC for 4 h and after different
recovery periods (0RT, 7RT, 24 RT). We showed that heat stress induced changes in
nuclear morphology as detected by the unusual presence of interphase cells with irregularly
shaped nuclei, probably associated with changes in chromosome segregation at
anaphase, leading to micronuclei formation as well as changes in the mitotic index.
These alterations were associated to differential effects in microtubules organization in
both heat-stressed interphase and mitotic cells at 0RT and 7RT. Although no changes
in the distribution of H3 phosphorylation of Ser 10 residues on chromatin were found
in cells from heat-stressed plants, marked alterations in chromatin DNA methylation
patterns were detected. These effects included higher agglutination of 5-methylcytosine
domains in both interphase and metaphase cells compared to controls. Taken together
these results seem to suggest that alterations in microtubule conformation upon heat
stress influences nuclear chromatin organization and cell cycle progression. However,
when seedlings recovered from stress (24RT), root tip cells presented microtubule configurations
and chromatin organization patterns similar to controls. We conclude that
in spite of heat stress markedly altered cell cycle progression and distribution of epigenetic
marks, these responses are transient to cope with such stress conditions in the
rootsinfo:eu-repo/semantics/publishedVersio
Conservation of a critically endangered endemic halophyte of West Portugal: a microcosm assay to assess the potential of soil technology for species reintroduction
Original ResearchThe soil system has been frequently overlooked during plant reintroduction planning
and practice since working with soils and plant roots can be difficult, particularly in
saline environments. Coastal saline environments are major contributors to regional
and global biodiversity and an important source of endemic species. However, various
species are in decline or considered threatened, particularly halophytes (salt tolerant)
due to negative anthropic impacts. The Lusitanian endemic halophyte Limonium daveaui
formerly had a large distribution range along the west coast of Portugal but currently
it shows a restricted distribution in the Tagus estuary. Field surveys revealed that this
critically endangered species forms few local populations with small size invaded by
exotic species. In this study, we investigated the potential utilization of Technosols, an
innovative sustainable, ecological engineering method combined with brackish water
irrigation for potential L. daveaui reintroduction in native habitats. Seed germination
percentages were evaluated in different environmental conditions. Through a microcosm
assay, a Technosol was constructed using a saline Fluvisol with a mixture of low
value inorganic and organic wastes, which were chemically characterized. Plants were
cultivated in the Fluvisol and Technosol and irrigated with brackish water collected in
the nearby area. To assess plant growth, morphometric parameters and the plants’
physiological status were assessed and the fresh and dry biomass determined. Results
showed that seed germination was higher on moist filter paper with distilled water
than in Fluvisol or Technosol. Plants grown in Technosol had a greater development,
with higher values of photosynthetic indexes and biomass production than in Fluvisol.
Our findings provide a basis for future in situ conservation studies and support the
idea that eco-friendly soil technology approaches are beneficial to conserve rare
halophyte speciesinfo:eu-repo/semantics/publishedVersio
Relationships between transcription, silver staining and chromatin organization of nucleolar organizers in Secale cereale
Summary. The nucleolar organizer regions (NORs) are composed of
hundreds of rRNA genes, typically spanning several megabases. Cytologically,
NORs include regions that are highly condensed and regions
that are decondensed, the latter corresponding to regions at which associated
proteins stain intensively with silver (Ag-NORs) and where active
rRNA gene transcription is thought to occur. To test the relationship between
rRNA gene activity, NOR silver staining, and rDNA (genes
coding for rRNA) chromatin condensation, we used the DNA methyltransferase
inhibitor 5-azacytidine to evaluate the correlation between
the epigenetic regulation of rRNA genes and NOR silver staining in the
plant Secale cereale. Following 5-azacytidine treatment, we observed an
increase in rRNA gene transcription as well as a reduction in the number
of cells showing a significant difference in the size of the silver-stained
domains in the two NORs. These transcriptional changes occurred concomitantly
with an increase in nuclear and nucleolar size and were associated
with the reallocation of most of the rDNA from perinucleolar
heterochromatin into the nucleolus. Collectively, these results suggest
that rRNA gene transcription, silver staining, and NOR decondensation
are interrelated in S. cereale
Le statut et la protection des orchidées du Portugal
Fifty-six species and
subspecies are presently recognised as indigeneous in Portugal. About half of them are rare or very rare, or even
probably extinct for two of them. The causes of rarity and the factors responsible for the regression that still
affects many species are analysed. Besides the fact that a few species have only little Mediterranean or Atlantic
affinities, there are causes linked with habitat disappearance, mainly in humid and coastal zones. Regulations
applicable in Portugal are reviewed, but few of them are specifically concerned with orchids. Furthermore
orchids are never considered among priority options towards the establishment of nature reserves and parcs. We
propose a list of sites and habitats especially rich or favourable to the conservation of orchids, which should
receive a better attention on behalf of Portuguese officers responsible for nature protection. Moreover,
knowledge of demographic and genetic characteristics of orchid populations should absolutely be developed if
we wish to guarantee the effectiveness of conservation strategies
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
Genome restructuring in rye affects the expression, organization and disposition of homologous rDNA loci
Research ArticleThe standard rye cultivar ‘Imperial’ and a structural
variant carrying an intact 1R chromosome and two
telocentric 1R chromosomes (short and long arms) were
used to investigate expression patterns of homologous
rDNA loci, and the influence of chromosome structural
change on their interphase organisation and relative
disposition. Sequential silver staining and in situ
hybridization with the rDNA probe pTa71, established a
correspondence between the expression and organization
patterns of rDNA domains in metaphase and interphase
cells. In most cells of the cultivar Imperial, nucleolar
organizer region (NOR) silver staining on metaphase
chromosomes with equivalent numbers of rDNA genes
revealed a size heteromorphism between homologousrDNA loci, resulting from their differential expression.
NOR heteromorphism in the structural variant line was
significantly reduced. The preferential activity of one NOR
over its homologue was found to be random within cells and
independent of parental origin. Nucleotypic modifications
mediated by changes in the 1R chromosome structure
include increased proximity between homologous rDNA
loci in interphase, and an increase in the frequency of cells
with intra-nucleolar ribosomal condensed chromatin.
These results seem to indicate a ‘sequence recognition’
process for the regulation of homologous loci
Ribosomal DNA heterochromatin in plants
The aim of this review is to integrate earlier
results and recent findings to present the current state-of-the art
vision concerning the dynamic behavior of the ribosomal
DNA (rDNA) fraction in plants. The global organization and
behavioral features of rDNA make it a most useful system to
analyse the relationship between chromatin topology and gene expression patterns. Correlations between several heterochromatin
fractions and rDNA arrays demonstrate the heterochromatic
nature of the rDNA and reveal the importance of the
genomic environment and of developmental controls in modulating
its dynamicsFCT - Fundação para a Ciência e Tecnologi
Phosphorilation of histone H3 in plants - a dynamic affair
Histones are the main protein components of chromatin: they undergo extensive post-translational modifications, particularly acetylation,
methylation, phosphorylation, ubiquitination and ADP-ribosylation which modify the structural/functional properties of chromatin. Posttranslational
modifications of the N-terminal tails of the core histones within the nucleosome particle are thought to act as signals from the
chromatin to the cell, for various processes. Thus, in many ways histone tails can be viewed as complex protein–protein interaction surfaces that
are regulated by numerous post-translational modifications. Histone phosphorylation has been linked to chromosome condensation/segregation,
activation of transcription, apoptosis and DNA damage repair. In plants, the cell cycle dependent phosphorylation of histone H3 has been
described; it is hyperphosphorylated at serines 10/28 and at threonines 3/11 during both mitosis and meiosis in patterns that are specifically
coordinated in both space and time. Although this post-translational modification is highly conserved, data show that the chromosomal
distribution of individual modifications can differ between groups of eukaryotes. Initial results indicate that members of the plant Aurora kinase
family have the capacity to control cell cycle regulated histone H3 phosphorylation, and in addition we describe other potential H3 kinases and
discuss their functions
Rye Bs disclose ancestral sequences in cereal genomes with a potential role in gametophyte chromatid segregation
Research ArticleTwo sequence families, E3900 and D1100, are amplified on the subtelomeric domain of the long arm of rye B
chromosomes, the region that controls its drive mechanism. In this work, polymerase chain reaction (PCR) with
a number of primers spanning E3900 shows that the organization and nucleotide sequence of E3900-related portions are
present and highly conserved on rye A chromosomes as well as in other cereals. Quantitative Real-Time PCR estimates
two E3900 sequences to be represented in 100–150 copies on Bs and at least as single copies on As. A novel E3900-
related sequence, with a deletion that results in a frameshift and subsequently an open reading frame with putative DNA
binding motifs, is identified. Expression analysis of E3900 indicates identical transcription levels in leaves from plants
with and without Bs, showing that the expression of these sequences must be silenced on Bs and tightly regulated on As
in leaves. In contrast, E3900 transcription is upregulated during meiosis exclusively in plants with Bs, maintaining a high
level of transcription in the gametophyte. Interestingly, Bs not only influence their own chromatid segregation but also
that of the regular chromosome complement of both rye and wheat. There is a drastic increase in frequency of disrupted
metaphase and anaphase cells in the first mitosis of pollen grains carrying Bs, which appears to be due to anomalous
adherences between sister chromatids. Taken together, this work provides insight into how E3900 sequences are
potentially associated with important evolutionary mechanisms involved in basic cellular processes
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