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Carol C. Baskin - One of the best experts on this subject based on the ideXlab platform.

  • PART OF A HIGHLIGHT SECTION ON SEEDS Identification and characterization of the water gap in physically dormant seeds of Geraniaceae, with special reference to Geranium carolinianum
    2020
    Co-Authors: N. S. Gama-arachchige, Jerry M. Baskin, Robert L. Geneve, Carol C. Baskin
    Abstract:

    †Background and Aims Physical dormancy in seeds of species of Geraniaceae is caused by a water-impermeable palisade layer in the outer integument of the seed coat and a closed chalaza. The chalazal cleft has been reported to be the water gap (i.e. location of initial water entry) in innately permeable seeds of Geraniaceae. The primary aim of this study was to re-evaluate the location of the water gap and to characterize its morphology and anatomy in physically dormant seeds of Geraniaceae, with particular reference to G. carolinianum. †Methods Length, width, mass, anatomy and germination of two seed types (light brown and dark brown) of G. carolinianum were compared. Location, anatomy and morphology of the water gap were characterized using free-hand and microtome tissue sectioning, light microscopy, scanning electron microscopy, dye tracking, blocking and seed-burial experiments. †Key Results Treatment with dry heat caused a colour change in the palisade cells adjacent to the micropyle. When placed in water, the ‘hinged valve’ (blister) erupted at the site of the colour change, exposing the water gap. The morphology and anatomy in the water-gap region differs from those of the rest of the seed coat. The morphology of the seed coat of the water-gap region is similar in G. carolinianum, G. columbinum, G. molle and G. pusillum and differs from that of the closely related species Erodium cicutarium. †Conclusions Dislodgment of swollen ‘hinged valve’ palisade cells adjacent to the micropyle caused the water gap to open in physically dormant seeds of G. carolinianum, and it was clear that initial water uptake takes place through this gap and not via the chalazal opening as previously reported. This water gap (‘hinged valve gap’) differs from water gaps previously described for other families in morphology, anatomy and location in the seed coat.

  • the autumn effect timing of physical dormancy break in seeds of two winter annual species of Geraniaceae by a stepwise process
    Annals of Botany, 2012
    Co-Authors: N S Gamaarachchige, Jerry M. Baskin, Robert L. Geneve, Carol C. Baskin
    Abstract:

    †Background and Aims The involvement of two steps in the physical dormancy (PY)-breaking process previously has been demonstrated in seeds of Fabaceae and Convolvulaceae. Even though there is a claim for a moisturecontrolled stepwise PY-breaking in some species of Geraniaceae, no study has evaluated the role of temperature in the PY-breaking process in this family. The aim of this study was to determine whether a temperature-controlled stepwise PY-breaking process occurs in seeds of the winter annuals Geranium carolinianum and G. dissectum. †Methods Seeds of G. carolinianum and G. dissectum were stored under different temperature regimes to test the effect of storage temperature on PY-break. The role of temperature and moisture regimes in regulating PY-break was investigated by treatments simulating natural conditions. Greenhouse (non-heated) experiments on seed germination and burial experiments (outdoors) were carried out to determine the PY-breaking behaviour in the natural habitat. †Key Results Irrespective of moisture conditions, sensitivity to the PY-breaking step in seeds of G. carolinianum was induced at temperatures ≥20 8C, and exposure to temperatures ≤20 8C made the sensitive seeds permeable. Sensitivity of seeds increased with time. In G. dissectum, PY-break occurred at temperatures ≥20 8C in a single step under constant wet or dry conditions and in two steps under alternate wet–dry conditions if seeds were initially kept wet. †Conclusions Timing of seed germination with the onset of autumn can be explained by PY-breaking processes involving (a) two temperature-dependent steps in G. carolinianum and (b) one or two moisture-dependent step(s) along with the inability to germinate under high temperatures in G. dissectum. Geraniaceae is the third of 18 families with PY in which a two-step PY-breaking process has been demonstrated.

  • the autumn effect timing of physical dormancy break in seeds of two winter annual species of Geraniaceae by a stepwise process
    Annals of Botany, 2012
    Co-Authors: N S Gamaarachchige, Jerry M. Baskin, Robert L. Geneve, Carol C. Baskin
    Abstract:

    BACKGROUND AND AIMS: The involvement of two steps in the physical dormancy (PY)-breaking process previously has been demonstrated in seeds of Fabaceae and Convolvulaceae. Even though there is a claim for a moisture-controlled stepwise PY-breaking in some species of Geraniaceae, no study has evaluated the role of temperature in the PY-breaking process in this family. The aim of this study was to determine whether a temperature-controlled stepwise PY-breaking process occurs in seeds of the winter annuals Geranium carolinianum and G. dissectum. METHODS: Seeds of G. carolinianum and G. dissectum were stored under different temperature regimes to test the effect of storage temperature on PY-break. The role of temperature and moisture regimes in regulating PY-break was investigated by treatments simulating natural conditions. Greenhouse (non-heated) experiments on seed germination and burial experiments (outdoors) were carried out to determine the PY-breaking behaviour in the natural habitat. KEY RESULTS: Irrespective of moisture conditions, sensitivity to the PY-breaking step in seeds of G. carolinianum was induced at temperatures ≥20 °C, and exposure to temperatures ≤20 °C made the sensitive seeds permeable. Sensitivity of seeds increased with time. In G. dissectum, PY-break occurred at temperatures ≥20 °C in a single step under constant wet or dry conditions and in two steps under alternate wet-dry conditions if seeds were initially kept wet. CONCLUSIONS: Timing of seed germination with the onset of autumn can be explained by PY-breaking processes involving (a) two temperature-dependent steps in G. carolinianum and (b) one or two moisture-dependent step(s) along with the inability to germinate under high temperatures in G. dissectum. Geraniaceae is the third of 18 families with PY in which a two-step PY-breaking process has been demonstrated.

  • acquisition of physical dormancy and ontogeny of the micropyle water gap complex in developing seeds of geranium carolinianum Geraniaceae
    Annals of Botany, 2011
    Co-Authors: N S Gamaarachchige, Jerry M. Baskin, Robert L. Geneve, Carol C. Baskin
    Abstract:

    †Background and Aims The ‘hinged valve gap’ has been previously identified as the initial site of water entry (i.e. water gap) in physically dormant (PY) seeds of Geranium carolinianum (Geraniaceae). However, neither the ontogeny of the hinged valve gap nor acquisition of PY by seeds of Geraniaceae has been studied previously. The aims of the present study were to investigate the physiological events related to acquisition of PY and the ontogeny of the hinged valve gap and seed coat of G. carolinianum. †Methods Seeds of G. carolinianum were studied from the ovule stage until dispersal. The developmental stages of acquisition of germinability, physiological maturity and PY were determined by seed measurement, germination and imbibition experiments using intact seeds and isolated embryos of both fresh and slow-dried seeds. Ontogeny of the seed coat and water gap was studied using light microscopy. †Key Results Developing seeds achieved germinability, physiological maturity and PY on days 9, 14 and 20 after pollination (DAP), respectively. The critical moisture content of seeds on acquisition of PY was 11 %. Slowdrying caused the stage of acquisition of PY to shift from 20 to 13 DAP. Greater extent of cell division and differentiation at the micropyle, water gap and chalaza than at the rest of the seed coat resulted in particular anatomical features. Palisade and subpalisade cells of varying forms developed in these sites. A clear demarcation between the water gap and micropyle is not evident due to their close proximity. †Conclusions Acquisition of PY in seeds of G. carolinianum occurs after physiological maturity and is triggered by maturation drying. The micropyle and water gap cannot be considered as two separate entities, and thus it is more appropriate to consider them together as a ‘micropyle–water-gap complex’.

  • Acquisition of physical dormancy and ontogeny of the micropyle–water-gap complex in developing seeds of Geranium carolinianum (Geraniaceae)
    Annals of Botany, 2011
    Co-Authors: N. S. Gama-arachchige, Jerry M. Baskin, Robert L. Geneve, Carol C. Baskin
    Abstract:

    †Background and Aims The ‘hinged valve gap’ has been previously identified as the initial site of water entry (i.e. water gap) in physically dormant (PY) seeds of Geranium carolinianum (Geraniaceae). However, neither the ontogeny of the hinged valve gap nor acquisition of PY by seeds of Geraniaceae has been studied previously. The aims of the present study were to investigate the physiological events related to acquisition of PY and the ontogeny of the hinged valve gap and seed coat of G. carolinianum. †Methods Seeds of G. carolinianum were studied from the ovule stage until dispersal. The developmental stages of acquisition of germinability, physiological maturity and PY were determined by seed measurement, germination and imbibition experiments using intact seeds and isolated embryos of both fresh and slow-dried seeds. Ontogeny of the seed coat and water gap was studied using light microscopy. †Key Results Developing seeds achieved germinability, physiological maturity and PY on days 9, 14 and 20 after pollination (DAP), respectively. The critical moisture content of seeds on acquisition of PY was 11 %. Slowdrying caused the stage of acquisition of PY to shift from 20 to 13 DAP. Greater extent of cell division and differentiation at the micropyle, water gap and chalaza than at the rest of the seed coat resulted in particular anatomical features. Palisade and subpalisade cells of varying forms developed in these sites. A clear demarcation between the water gap and micropyle is not evident due to their close proximity. †Conclusions Acquisition of PY in seeds of G. carolinianum occurs after physiological maturity and is triggered by maturation drying. The micropyle and water gap cannot be considered as two separate entities, and thus it is more appropriate to consider them together as a ‘micropyle–water-gap complex’.

Robert K Jansen - One of the best experts on this subject based on the ideXlab platform.

  • aberration or analogy the atypical plastomes of Geraniaceae
    2018
    Co-Authors: Tracey A Ruhlman, Robert K Jansen
    Abstract:

    Abstract A number of plant groups have been proposed as ideal systems to explore plastid inheritance, plastome evolution and plastome-nuclear genome coevolution. Quick generation times and a compact nuclear genome in Arabidopsis thaliana, the relative ease of plastid isolation from Spinacia oleracea and the tractability of plastid transformation in Nicotiana tabacum are all desirable attributes in a model system; however, these and most other groups all lack novelty in terms of plastome structure and nucleotide sequence evolution. Contemporary sequencing and assembly technologies have facilitated analyses of atypical plastomes and, as predicted by early investigations, Geraniaceae plastomes have experienced unprecedented rearrangements relative to the canonical structure and exhibit remarkably high rates of synonymous and nonsynonymous nucleotide substitutions. While not the only lineage with unusual plastome features, likely no other group represents the array of aberrant phenomena recorded for the family. In this chapter, Geraniaceae plastomes will be discussed and, where possible, compared with other taxa.

  • plastid nuclear interaction and accelerated coevolution in plastid ribosomal genes in Geraniaceae
    Genome Biology and Evolution, 2016
    Co-Authors: Robert K Jansen, Maolun Weng, Tracey A Ruhlman
    Abstract:

    Plastids and mitochondria have many protein complexes that include subunits encoded by organelle and nuclear genomes. In animal cells, compensatory evolution between mitochondrial and nuclear-encoded subunits was identified and the high mitochondrial mutation rates were hypothesized to drive compensatory evolution in nuclear genomes. In plant cells, compensatory evolution between plastid and nucleus has rarely been investigated in a phylogenetic framework. To investigate plastid-nuclear coevolution, we focused on plastid ribosomal protein genes that are encoded by plastid and nuclear genomes from 27 Geraniales species. Substitution rates were compared for five sets of genes representing plastid- and nuclear-encoded ribosomal subunit proteins targeted to the cytosol or the plastid as well as nonribosomal protein controls. We found that nonsynonymous substitution rates (dN) and the ratios of nonsynonymous to synonymous substitution rates (ω) were accelerated in both plastid- (CpRP) and nuclear-encoded subunits (NuCpRP) of the plastid ribosome relative to control sequences. Our analyses revealed strong signals of cytonuclear coevolution between plastid- and nuclear-encoded subunits, in which nonsynonymous substitutions in CpRP and NuCpRP tend to occur along the same branches in the Geraniaceae phylogeny. This coevolution pattern cannot be explained by physical interaction between amino acid residues. The forces driving accelerated coevolution varied with cellular compartment of the sequence. Increased ω in CpRP was mainly due to intensified positive selection whereas increased ω in NuCpRP was caused by relaxed purifying selection. In addition, the many indels identified in plastid rRNA genes in Geraniaceae may have contributed to changes in plastid subunits.

  • coordinated rates of evolution between interacting plastid and nuclear genes in Geraniaceae
    The Plant Cell, 2015
    Co-Authors: Jin Zhang, Robert K Jansen, Tracey A Ruhlman, Jamal S M Sabir, Chris J Blazier
    Abstract:

    Although gene coevolution has been widely observed within individuals and between different organisms, rarely has this phenomenon been investigated within a phylogenetic framework. The Geraniaceae is an attractive system in which to study plastid-nuclear genome coevolution due to the highly elevated evolutionary rates in plastid genomes. In plants, the plastid-encoded RNA polymerase (PEP) is a protein complex composed of subunits encoded by both plastid (rpoA, rpoB, rpoC1, and rpoC2) and nuclear genes (sig1-6). We used transcriptome and genomic data for 27 species of Geraniales in a systematic evaluation of coevolution between genes encoding subunits of the PEP holoenzyme. We detected strong correlations of dN (nonsynonymous substitutions) but not dS (synonymous substitutions) within rpoB/sig1 and rpoC2/sig2, but not for other plastid/nuclear gene pairs, and identified the correlation of dN/dS ratio between rpoB/C1/C2 and sig1/5/6, rpoC1/C2 and sig2, and rpoB/C2 and sig3 genes. Correlated rates between interacting plastid and nuclear sequences across the Geraniales could result from plastid-nuclear genome coevolution. Analyses of coevolved amino acid positions suggest that structurally mediated coevolution is not the major driver of plastid-nuclear coevolution. The detection of strong correlation of evolutionary rates between SIG and RNAP genes suggests a plausible explanation for plastome-genome incompatibility in Geraniaceae.

  • reconstruction of the ancestral plastid genome in Geraniaceae reveals a correlation between genome rearrangements repeats and nucleotide substitution rates
    Molecular Biology and Evolution, 2014
    Co-Authors: Maolun Weng, Robert K Jansen, John C Blazier, Madhumita Govindu
    Abstract:

    Geraniaceae plastid genomes are highly rearranged, and each of the four genera already sequenced in the family has a distinct genome organization. This study reports plastid genome sequences of six additional species, Francoa sonchifolia, Melianthus villosus, and Viviania marifolia from Geraniales, and Pelargonium alternans, California macrophylla, and Hypseocharis bilobata from Geraniaceae. These genome sequences, combined with previously published species, provide sufficient taxon sampling to reconstruct the ancestral plastid genome organization of Geraniaceae and the rearrangements unique to each genus. The ancestral plastid genome of Geraniaceae has a 4 kb inversion and a reduced, Pelargonium-like small single copy region. Our ancestral genome reconstruction suggests that a few minor rearrangements occurred in the stem branch of Geraniaceae followed by independent rearrangements in each genus. The genomic comparison demonstrates that a series of inverted repeat boundary shifts and inversions played a major role in shaping genome organization in the family. The distribution of repeats is strongly associated with breakpoints in the rearranged genomes, and the proportion and the number of large repeats (>20 bp and >60 bp) are significantly correlated with the degree of genome rearrangements. Increases in the degree of plastid genome rearrangements are correlated with the acceleration in nonsynonymous substitution rates (dN) but not with synonymous substitution rates (dS). Possible mechanisms that might contribute to this correlation, including DNA repair system and selection, are discussed.

  • comparative analyses of two Geraniaceae transcriptomes using next generation sequencing
    BMC Plant Biology, 2013
    Co-Authors: Jin Zhang, Robert K Jansen, Tracey A Ruhlman, Jeffrey P Mower
    Abstract:

    Background Organelle genomes of Geraniaceae exhibit several unusual evolutionary phenomena compared to other angiosperm families including accelerated nucleotide substitution rates, widespread gene loss, reduced RNA editing, and extensive genomic rearrangements. Since most organelle-encoded proteins function in multi-subunit complexes that also contain nuclear-encoded proteins, it is likely that the atypical organellar phenomena affect the evolution of nuclear genes encoding organellar proteins. To begin to unravel the complex co-evolutionary interplay between organellar and nuclear genomes in this family, we sequenced nuclear transcriptomes of two species, Geranium maderense and Pelargonium x hortorum.

Carlos Aedo - One of the best experts on this subject based on the ideXlab platform.

  • taxonomic revision of geranium sect ruberta and unguiculata Geraniaceae
    Annals of the Missouri Botanical Garden, 2017
    Co-Authors: Carlos Aedo
    Abstract:

    Abstract Geranium L. sect. Ruberta Dumort. and section Unguiculata (Boiss.) Reiche (Geraniaceae) consists of 10 and two species, respectively. The highest diversity of section Ruberta is located in Macaronesia with seven species, four of them endemic. Additionally, two species are endemic to Turkey, another is restricted to southern Spain and Morocco, and three are naturalized in many temperate regions of the world but are native to Europe and adjacent areas of Africa and western Asia. Section Unguiculata is mainly found on the Balkan Peninsula, although one species reaches eastward to the mountains of southern France. Geranium sect. Ruberta is characterized by its actinomorphic flowers (only G. palmatum Cav. has slightly zygomorphic flowers) and its petals with a bicarinate and well-developed claw. This broader concept of the section Ruberta, which includes section Lucida R. Knuth, permits the unequivocal inclusion of all species, unlike the previous proposal to separate these species into two sections. ...

  • taxonomic revision of geranium sect polyantha Geraniaceae 1
    Annals of the Missouri Botanical Garden, 2016
    Co-Authors: Carlos Aedo
    Abstract:

    Abstract Geranium L. sect. Polyantha Reiche (Geraniaceae) consists of seven species. The highest diversity of the group is located in southwestern China with five endemic species. One species is found in the Himalaya, and another is located in the mountains of Burma. In contrast with some regional treatments, I have synonymized G. ascendens Z. M. Tan to G. moupinense Franch., and G. platylobum (Franch.) R. Knuth to G. hispidissimum (Franch.) R. Knuth. Micromorphological features of indumentum, pollen, and mericarps were investigated by SEM. The presence of pollen with Erodium L'Her.–type exine ornamentation is confirmed for all species of the section. A new key is provided, as well as new and detailed descriptions. Each species is illustrated and mapped, and three lectotypes are designated.

  • Taxonomic Revision of Geranium sect. Polyantha (Geraniaceae)
    Annals of the Missouri Botanical Garden, 2016
    Co-Authors: Carlos Aedo
    Abstract:

    Abstract Geranium L. sect. Polyantha Reiche (Geraniaceae) consists of seven species. The highest diversity of the group is located in southwestern China with five endemic species. One species is found in the Himalaya, and another is located in the mountains of Burma. In contrast with some regional treatments, I have synonymized G. ascendens Z. M. Tan to G. moupinense Franch., and G. platylobum (Franch.) R. Knuth to G. hispidissimum (Franch.) R. Knuth. Micromorphological features of indumentum, pollen, and mericarps were investigated by SEM. The presence of pollen with Erodium L'Her.–type exine ornamentation is confirmed for all species of the section. A new key is provided, as well as new and detailed descriptions. Each species is illustrated and mapped, and three lectotypes are designated.

  • taxonomic revision of geranium sect trilopha Geraniaceae
    Systematic Botany, 2016
    Co-Authors: Carlos Aedo, Patricia Barbera, Antoni Buira
    Abstract:

    Abstract Geranium sect. Trilopha (Geraniaceae) consists of seven species: G. biuncinatum, G. brevipes, G. favosum, G. mascatense, G. ocellatum, G. trilophum, and G. yemense. The highest diversity of the group is located in Iran, the Arabian Peninsula, and adjacent regions of northeast Africa with five endemic species. One species occurs in the Himalayas and another is widespread in the mountains of tropical Africa. In contrast with current literature, we consider G. yemense to be a separate species from G. trilophum, and G. brevipes also to be separate from G. ocellatum. Micromorphological features of indumentum, pollen, mericarps and seeds were investigated by SEM. Two features are present in all species of the section and give strong support to this group: a) pollen with Erodium-type exine ornamentation (first reported here), and b) fruit with twisted rostrum. A new key is provided, as well as new and detailed descriptions. Each species is illustrated and mapped and five lectotypes are designated.

  • The genus geranium L. (Geraniaceae) in North America II. Annual species (parte C)
    2015
    Co-Authors: Carlos Aedo
    Abstract:

    AEDO, C. (2001). El genero Geranium L. (Geraniaceae) en Norteam6rica. II. Especies anuales. Anales lard. Bot. Madrid 58(1): 3-65 (en ingles). Se revisan las especies anuales de Geranium de Norteameiica al norte de Mexico. Se aceptan once especies de las cuales seis pertenecen al subg. Geranium y cinco al subg. Robertium. Geranium bicknelli, G. carolinianum, y G. texanum son las linicas especies autoctonas, mientras que G. aequale, G. columbinum, G. dissectum, G. lucidum, G. molle, G. pusillum, G. robertianum y G. rotundifolium fueron introducidas desde el Viejo Mundo. Geranium sphaerospermum, a veces aceptado en la literatura reciente, es considerado como sinonimo de G. carolinianum. Se revisa la nomenclatura de todas las especies y se designan ocho lectotipos. Se incluyen descripciones completas, una clave, mapas de distribucion e ilustraciones.

N S Gamaarachchige - One of the best experts on this subject based on the ideXlab platform.

  • the autumn effect timing of physical dormancy break in seeds of two winter annual species of Geraniaceae by a stepwise process
    Annals of Botany, 2012
    Co-Authors: N S Gamaarachchige, Jerry M. Baskin, Robert L. Geneve, Carol C. Baskin
    Abstract:

    †Background and Aims The involvement of two steps in the physical dormancy (PY)-breaking process previously has been demonstrated in seeds of Fabaceae and Convolvulaceae. Even though there is a claim for a moisturecontrolled stepwise PY-breaking in some species of Geraniaceae, no study has evaluated the role of temperature in the PY-breaking process in this family. The aim of this study was to determine whether a temperature-controlled stepwise PY-breaking process occurs in seeds of the winter annuals Geranium carolinianum and G. dissectum. †Methods Seeds of G. carolinianum and G. dissectum were stored under different temperature regimes to test the effect of storage temperature on PY-break. The role of temperature and moisture regimes in regulating PY-break was investigated by treatments simulating natural conditions. Greenhouse (non-heated) experiments on seed germination and burial experiments (outdoors) were carried out to determine the PY-breaking behaviour in the natural habitat. †Key Results Irrespective of moisture conditions, sensitivity to the PY-breaking step in seeds of G. carolinianum was induced at temperatures ≥20 8C, and exposure to temperatures ≤20 8C made the sensitive seeds permeable. Sensitivity of seeds increased with time. In G. dissectum, PY-break occurred at temperatures ≥20 8C in a single step under constant wet or dry conditions and in two steps under alternate wet–dry conditions if seeds were initially kept wet. †Conclusions Timing of seed germination with the onset of autumn can be explained by PY-breaking processes involving (a) two temperature-dependent steps in G. carolinianum and (b) one or two moisture-dependent step(s) along with the inability to germinate under high temperatures in G. dissectum. Geraniaceae is the third of 18 families with PY in which a two-step PY-breaking process has been demonstrated.

  • the autumn effect timing of physical dormancy break in seeds of two winter annual species of Geraniaceae by a stepwise process
    Annals of Botany, 2012
    Co-Authors: N S Gamaarachchige, Jerry M. Baskin, Robert L. Geneve, Carol C. Baskin
    Abstract:

    BACKGROUND AND AIMS: The involvement of two steps in the physical dormancy (PY)-breaking process previously has been demonstrated in seeds of Fabaceae and Convolvulaceae. Even though there is a claim for a moisture-controlled stepwise PY-breaking in some species of Geraniaceae, no study has evaluated the role of temperature in the PY-breaking process in this family. The aim of this study was to determine whether a temperature-controlled stepwise PY-breaking process occurs in seeds of the winter annuals Geranium carolinianum and G. dissectum. METHODS: Seeds of G. carolinianum and G. dissectum were stored under different temperature regimes to test the effect of storage temperature on PY-break. The role of temperature and moisture regimes in regulating PY-break was investigated by treatments simulating natural conditions. Greenhouse (non-heated) experiments on seed germination and burial experiments (outdoors) were carried out to determine the PY-breaking behaviour in the natural habitat. KEY RESULTS: Irrespective of moisture conditions, sensitivity to the PY-breaking step in seeds of G. carolinianum was induced at temperatures ≥20 °C, and exposure to temperatures ≤20 °C made the sensitive seeds permeable. Sensitivity of seeds increased with time. In G. dissectum, PY-break occurred at temperatures ≥20 °C in a single step under constant wet or dry conditions and in two steps under alternate wet-dry conditions if seeds were initially kept wet. CONCLUSIONS: Timing of seed germination with the onset of autumn can be explained by PY-breaking processes involving (a) two temperature-dependent steps in G. carolinianum and (b) one or two moisture-dependent step(s) along with the inability to germinate under high temperatures in G. dissectum. Geraniaceae is the third of 18 families with PY in which a two-step PY-breaking process has been demonstrated.

  • acquisition of physical dormancy and ontogeny of the micropyle water gap complex in developing seeds of geranium carolinianum Geraniaceae
    Annals of Botany, 2011
    Co-Authors: N S Gamaarachchige, Jerry M. Baskin, Robert L. Geneve, Carol C. Baskin
    Abstract:

    †Background and Aims The ‘hinged valve gap’ has been previously identified as the initial site of water entry (i.e. water gap) in physically dormant (PY) seeds of Geranium carolinianum (Geraniaceae). However, neither the ontogeny of the hinged valve gap nor acquisition of PY by seeds of Geraniaceae has been studied previously. The aims of the present study were to investigate the physiological events related to acquisition of PY and the ontogeny of the hinged valve gap and seed coat of G. carolinianum. †Methods Seeds of G. carolinianum were studied from the ovule stage until dispersal. The developmental stages of acquisition of germinability, physiological maturity and PY were determined by seed measurement, germination and imbibition experiments using intact seeds and isolated embryos of both fresh and slow-dried seeds. Ontogeny of the seed coat and water gap was studied using light microscopy. †Key Results Developing seeds achieved germinability, physiological maturity and PY on days 9, 14 and 20 after pollination (DAP), respectively. The critical moisture content of seeds on acquisition of PY was 11 %. Slowdrying caused the stage of acquisition of PY to shift from 20 to 13 DAP. Greater extent of cell division and differentiation at the micropyle, water gap and chalaza than at the rest of the seed coat resulted in particular anatomical features. Palisade and subpalisade cells of varying forms developed in these sites. A clear demarcation between the water gap and micropyle is not evident due to their close proximity. †Conclusions Acquisition of PY in seeds of G. carolinianum occurs after physiological maturity and is triggered by maturation drying. The micropyle and water gap cannot be considered as two separate entities, and thus it is more appropriate to consider them together as a ‘micropyle–water-gap complex’.

  • identification and characterization of the water gap in physically dormant seeds of Geraniaceae with special reference to geranium carolinianum
    Annals of Botany, 2010
    Co-Authors: N S Gamaarachchige, Jerry M. Baskin, Robert L. Geneve, Carol C. Baskin
    Abstract:

    BACKGROUND AND AIMS: Physical dormancy in seeds of species of Geraniaceae is caused by a water-impermeable palisade layer in the outer integument of the seed coat and a closed chalaza. The chalazal cleft has been reported to be the water gap (i.e. location of initial water entry) in innately permeable seeds of Geraniaceae. The primary aim of this study was to re-evaluate the location of the water gap and to characterize its morphology and anatomy in physically dormant seeds of Geraniaceae, with particular reference to G. carolinianum. METHODS: Length, width, mass, anatomy and germination of two seed types (light brown and dark brown) of G. carolinianum were compared. Location, anatomy and morphology of the water gap were characterized using free-hand and microtome tissue sectioning, light microscopy, scanning electron microscopy, dye tracking, blocking and seed-burial experiments. KEY RESULTS: Treatment with dry heat caused a colour change in the palisade cells adjacent to the micropyle. When placed in water, the 'hinged valve' (blister) erupted at the site of the colour change, exposing the water gap. The morphology and anatomy in the water-gap region differs from those of the rest of the seed coat. the morphology of the seed coat of the water-gap region is similar in G. carolinianum, G. columbinum, G. molle and G. pusillum and differs from that of the closely related species Erodium cicutarium. CONCLUSIONS: Dislodgment of swollen 'hinged valve' palisade cells adjacent to the micropyle caused the water gap to open in physically dormant seeds of G. carolinianum, and it was clear that initial water uptake takes place through this gap and not via the chalazal opening as previously reported. This water gap ('hinged valve gap') differs from water gaps previously described for other families in morphology, anatomy and location in the seed coat.

Robert L. Geneve - One of the best experts on this subject based on the ideXlab platform.

  • PART OF A HIGHLIGHT SECTION ON SEEDS Identification and characterization of the water gap in physically dormant seeds of Geraniaceae, with special reference to Geranium carolinianum
    2020
    Co-Authors: N. S. Gama-arachchige, Jerry M. Baskin, Robert L. Geneve, Carol C. Baskin
    Abstract:

    †Background and Aims Physical dormancy in seeds of species of Geraniaceae is caused by a water-impermeable palisade layer in the outer integument of the seed coat and a closed chalaza. The chalazal cleft has been reported to be the water gap (i.e. location of initial water entry) in innately permeable seeds of Geraniaceae. The primary aim of this study was to re-evaluate the location of the water gap and to characterize its morphology and anatomy in physically dormant seeds of Geraniaceae, with particular reference to G. carolinianum. †Methods Length, width, mass, anatomy and germination of two seed types (light brown and dark brown) of G. carolinianum were compared. Location, anatomy and morphology of the water gap were characterized using free-hand and microtome tissue sectioning, light microscopy, scanning electron microscopy, dye tracking, blocking and seed-burial experiments. †Key Results Treatment with dry heat caused a colour change in the palisade cells adjacent to the micropyle. When placed in water, the ‘hinged valve’ (blister) erupted at the site of the colour change, exposing the water gap. The morphology and anatomy in the water-gap region differs from those of the rest of the seed coat. The morphology of the seed coat of the water-gap region is similar in G. carolinianum, G. columbinum, G. molle and G. pusillum and differs from that of the closely related species Erodium cicutarium. †Conclusions Dislodgment of swollen ‘hinged valve’ palisade cells adjacent to the micropyle caused the water gap to open in physically dormant seeds of G. carolinianum, and it was clear that initial water uptake takes place through this gap and not via the chalazal opening as previously reported. This water gap (‘hinged valve gap’) differs from water gaps previously described for other families in morphology, anatomy and location in the seed coat.

  • the autumn effect timing of physical dormancy break in seeds of two winter annual species of Geraniaceae by a stepwise process
    Annals of Botany, 2012
    Co-Authors: N S Gamaarachchige, Jerry M. Baskin, Robert L. Geneve, Carol C. Baskin
    Abstract:

    †Background and Aims The involvement of two steps in the physical dormancy (PY)-breaking process previously has been demonstrated in seeds of Fabaceae and Convolvulaceae. Even though there is a claim for a moisturecontrolled stepwise PY-breaking in some species of Geraniaceae, no study has evaluated the role of temperature in the PY-breaking process in this family. The aim of this study was to determine whether a temperature-controlled stepwise PY-breaking process occurs in seeds of the winter annuals Geranium carolinianum and G. dissectum. †Methods Seeds of G. carolinianum and G. dissectum were stored under different temperature regimes to test the effect of storage temperature on PY-break. The role of temperature and moisture regimes in regulating PY-break was investigated by treatments simulating natural conditions. Greenhouse (non-heated) experiments on seed germination and burial experiments (outdoors) were carried out to determine the PY-breaking behaviour in the natural habitat. †Key Results Irrespective of moisture conditions, sensitivity to the PY-breaking step in seeds of G. carolinianum was induced at temperatures ≥20 8C, and exposure to temperatures ≤20 8C made the sensitive seeds permeable. Sensitivity of seeds increased with time. In G. dissectum, PY-break occurred at temperatures ≥20 8C in a single step under constant wet or dry conditions and in two steps under alternate wet–dry conditions if seeds were initially kept wet. †Conclusions Timing of seed germination with the onset of autumn can be explained by PY-breaking processes involving (a) two temperature-dependent steps in G. carolinianum and (b) one or two moisture-dependent step(s) along with the inability to germinate under high temperatures in G. dissectum. Geraniaceae is the third of 18 families with PY in which a two-step PY-breaking process has been demonstrated.

  • the autumn effect timing of physical dormancy break in seeds of two winter annual species of Geraniaceae by a stepwise process
    Annals of Botany, 2012
    Co-Authors: N S Gamaarachchige, Jerry M. Baskin, Robert L. Geneve, Carol C. Baskin
    Abstract:

    BACKGROUND AND AIMS: The involvement of two steps in the physical dormancy (PY)-breaking process previously has been demonstrated in seeds of Fabaceae and Convolvulaceae. Even though there is a claim for a moisture-controlled stepwise PY-breaking in some species of Geraniaceae, no study has evaluated the role of temperature in the PY-breaking process in this family. The aim of this study was to determine whether a temperature-controlled stepwise PY-breaking process occurs in seeds of the winter annuals Geranium carolinianum and G. dissectum. METHODS: Seeds of G. carolinianum and G. dissectum were stored under different temperature regimes to test the effect of storage temperature on PY-break. The role of temperature and moisture regimes in regulating PY-break was investigated by treatments simulating natural conditions. Greenhouse (non-heated) experiments on seed germination and burial experiments (outdoors) were carried out to determine the PY-breaking behaviour in the natural habitat. KEY RESULTS: Irrespective of moisture conditions, sensitivity to the PY-breaking step in seeds of G. carolinianum was induced at temperatures ≥20 °C, and exposure to temperatures ≤20 °C made the sensitive seeds permeable. Sensitivity of seeds increased with time. In G. dissectum, PY-break occurred at temperatures ≥20 °C in a single step under constant wet or dry conditions and in two steps under alternate wet-dry conditions if seeds were initially kept wet. CONCLUSIONS: Timing of seed germination with the onset of autumn can be explained by PY-breaking processes involving (a) two temperature-dependent steps in G. carolinianum and (b) one or two moisture-dependent step(s) along with the inability to germinate under high temperatures in G. dissectum. Geraniaceae is the third of 18 families with PY in which a two-step PY-breaking process has been demonstrated.

  • acquisition of physical dormancy and ontogeny of the micropyle water gap complex in developing seeds of geranium carolinianum Geraniaceae
    Annals of Botany, 2011
    Co-Authors: N S Gamaarachchige, Jerry M. Baskin, Robert L. Geneve, Carol C. Baskin
    Abstract:

    †Background and Aims The ‘hinged valve gap’ has been previously identified as the initial site of water entry (i.e. water gap) in physically dormant (PY) seeds of Geranium carolinianum (Geraniaceae). However, neither the ontogeny of the hinged valve gap nor acquisition of PY by seeds of Geraniaceae has been studied previously. The aims of the present study were to investigate the physiological events related to acquisition of PY and the ontogeny of the hinged valve gap and seed coat of G. carolinianum. †Methods Seeds of G. carolinianum were studied from the ovule stage until dispersal. The developmental stages of acquisition of germinability, physiological maturity and PY were determined by seed measurement, germination and imbibition experiments using intact seeds and isolated embryos of both fresh and slow-dried seeds. Ontogeny of the seed coat and water gap was studied using light microscopy. †Key Results Developing seeds achieved germinability, physiological maturity and PY on days 9, 14 and 20 after pollination (DAP), respectively. The critical moisture content of seeds on acquisition of PY was 11 %. Slowdrying caused the stage of acquisition of PY to shift from 20 to 13 DAP. Greater extent of cell division and differentiation at the micropyle, water gap and chalaza than at the rest of the seed coat resulted in particular anatomical features. Palisade and subpalisade cells of varying forms developed in these sites. A clear demarcation between the water gap and micropyle is not evident due to their close proximity. †Conclusions Acquisition of PY in seeds of G. carolinianum occurs after physiological maturity and is triggered by maturation drying. The micropyle and water gap cannot be considered as two separate entities, and thus it is more appropriate to consider them together as a ‘micropyle–water-gap complex’.

  • Acquisition of physical dormancy and ontogeny of the micropyle–water-gap complex in developing seeds of Geranium carolinianum (Geraniaceae)
    Annals of Botany, 2011
    Co-Authors: N. S. Gama-arachchige, Jerry M. Baskin, Robert L. Geneve, Carol C. Baskin
    Abstract:

    †Background and Aims The ‘hinged valve gap’ has been previously identified as the initial site of water entry (i.e. water gap) in physically dormant (PY) seeds of Geranium carolinianum (Geraniaceae). However, neither the ontogeny of the hinged valve gap nor acquisition of PY by seeds of Geraniaceae has been studied previously. The aims of the present study were to investigate the physiological events related to acquisition of PY and the ontogeny of the hinged valve gap and seed coat of G. carolinianum. †Methods Seeds of G. carolinianum were studied from the ovule stage until dispersal. The developmental stages of acquisition of germinability, physiological maturity and PY were determined by seed measurement, germination and imbibition experiments using intact seeds and isolated embryos of both fresh and slow-dried seeds. Ontogeny of the seed coat and water gap was studied using light microscopy. †Key Results Developing seeds achieved germinability, physiological maturity and PY on days 9, 14 and 20 after pollination (DAP), respectively. The critical moisture content of seeds on acquisition of PY was 11 %. Slowdrying caused the stage of acquisition of PY to shift from 20 to 13 DAP. Greater extent of cell division and differentiation at the micropyle, water gap and chalaza than at the rest of the seed coat resulted in particular anatomical features. Palisade and subpalisade cells of varying forms developed in these sites. A clear demarcation between the water gap and micropyle is not evident due to their close proximity. †Conclusions Acquisition of PY in seeds of G. carolinianum occurs after physiological maturity and is triggered by maturation drying. The micropyle and water gap cannot be considered as two separate entities, and thus it is more appropriate to consider them together as a ‘micropyle–water-gap complex’.