... are some evolutionary trends, particularly in the modes of corolla tube formation and ovulemo... more ... are some evolutionary trends, particularly in the modes of corolla tube formation and ovulemorphology. ... corolla lobes (or there are fewer sta-mens) and a coenocarpous gynoecium of mostly ... Within the Convolvulaceae, in Di-chondra and Cuscuta, there is no corolla tube, but ...
ABSTRACT To follow the movement of Erwinia amylovora in plant tissue without dissection, this bac... more ABSTRACT To follow the movement of Erwinia amylovora in plant tissue without dissection, this bacterium was marked with either the lux operon from Vibrio fischeri or the gfp gene from the jellyfish Aequorea victoria, both carried on multicopy plasmids and expressed under the control of the lac promoter from Escherichia coli. Movement of the pathogen was visualized in leaves, stems, and roots of apple seedlings, and migration of E. amylovora was traced from inoculation sites in the stem to as far as the roots. Green fluorescent E. amylovora cells were observed in the xylem and later appeared to break out of the vessels into the intercellular spaces of the adjacent parenchyma. Inoculation in the intercostal region of leaves caused a zone of slow necrosis that finally resulted in bacterial invasion of the xylem vessels. Labeled bacteria could also be seen in association with the anchor sites of leaf hairs. Distortion of the epidermis adjacent to leaf hairs created openings that were observed by scanning electron microscopy. As the intercostal region, the bases of leaf hairs provided E. amylovora access to intact xylem vessels, which allowed further distribution of the pathogen in the host plant.
... Pollen is deposited onto orchid stigmata either when whole pollinia become trapped in a roste... more ... Pollen is deposited onto orchid stigmata either when whole pollinia become trapped in a rostellum notch or when the adhesion between pollen and stigmatic mucilage breaks away whole pollinia, individual massulae or parts of soft pollen masses. ...
The correct assessment of homology is an important prerequisite for reconstructing phylogenetic r... more The correct assessment of homology is an important prerequisite for reconstructing phylogenetic relationships and character evolution. Old World Papaveroideae (Papaver, Meconopsis, Roemeria, Stylomecon) show substantial diversity in gynoecium and capsule morphology. In particular, capsules can have distinct styles (Meconopsis p.p., Stylomecon) or a sessile stigmatic disc (Papaver). Molecular phylogenetic analyses of Old World Papaveroideae had shown that neither taxa with styles nor those with stigmatic discs represent monophyletic lineages. We here investigate whether either styles or stigmatic discs have arisen repeatedly during the diversification of Old World Papaveroideae. We investigated gynoecium ontogeny in Papaver rhoeas, P. californicum, Meconopsis cambrica, and Stylomecon heterophylla by scanning electron microscopy for the first time. Our observations were interpreted on the background of a well-resolved molecular phylogeny of the taxa investigated. Papaver rhoeas and P. californicum share the presence of a developmentally complex garland-like stage in gynoecium ontogeny. The styles of M. cambrica and S. heterophylla result from growth in a ring-like zone beneath the carpel tips. This zone is also present in Papaver. In M. cambrica, traces of a garland-like stage can be seen. Style formation and stigma formation begin more or less simultaneously in M. cambrica, but style formation clearly precedes stigma formation in S. heterophylla. The styles present in M. cambrica and S. heterophylla are considered to have arisen in parallel from ancestors with a stigmatic disc. We speculate that style formation may have been a means to reduce selfing.
Disintegration of the Scrophulariaceae due to molecular data resulted in re-circumscriptions, res... more Disintegration of the Scrophulariaceae due to molecular data resulted in re-circumscriptions, resurrection and new descriptions of families to encompass the monophyletic lineages. In some of these families floral morphological/ontogenetic data, however, are largely missing, as, for example, in Paulowniaceae. This study reveals a set of distinctive features that were up to now unknown in Paulowniaceae: In the lateral flowers of the inflorescence, initiation sequence in calyx and corolla is unidirectional in identical direction, starting at the adaxial side; the formation of sympetaly is late but ledges connecting the separate petals arise relatively early. Of importance are particularly the occurrence of: crescent-shaped archespore and pollen sacs with a pollen sac placentoid, secretory tapetum, a several cell layers thick endothecium, endothecium-like cells situated all over the tissue of the theca except in the placentoid, undivided placenta originating in each locule on the septum only, a tubular stigma with papillae inside a dilated chamber (in this character Paulownia differs from all other members of the Lamiales-clade!), nectary in the basal part of the superior ovary, and small, winged seeds whose testa possesses protrusions that laterally expand into several sinuate wings, gradually increasing in extension towards the two margins.
During the last 15 years enormous progress had been made in understanding the genetic and molecul... more During the last 15 years enormous progress had been made in understanding the genetic and molecular regulation of flower development. The classical A-B-C model, which describes how the activities of three classes of genes coding for transcription factors (A, B, C) alone or coordinately specify the different floral organs, has been expanded by class D genes involved in ovule development and class E genes required for the identities of all floral organs. The molecular quartet model advances the genetic A-B-C-D-E model by describing the presumed interactions between floral MADS-domain proteins. Although the basic developmental program appears to be quite conserved, in non-core eudicots modifications such as ``sliding-boundary'' and ``fading borders'' models had to be established. Since the identity of floral organs is strictly dependent on the activity of the MADS-box genes, duplication and diversification within these genes must have been key processes in flower evolution. Hence, insights into the phylogeny of the floral homeotic genes may help to better understand the evolution of flowers (``evo-devo'').
In angiosperm reproduction, pollen tubes elongate from the stigma through the stylar transmitting... more In angiosperm reproduction, pollen tubes elongate from the stigma through the stylar transmitting tissue to the ovary to deliver the male gametes for fertilization. This article reviews different forms of pollen tube transmitting tracts within the style as well as possibilities for bridging the gap from the transmitting tissue to the ovule. The pollen tube transmitting tissue is the place of possible pollen tube competition. Often the number of pollen grains deposited onto the stigma or stigmata of a flower exceeds the number of ovules in the ovary of the pollinated flower. In the styles of most taxa investigated, a reduction in number of the pollen tubes occurs from the stigma to the ovary (pollen tube attrition): the pollen tubes compete for entry into the embryo sac of the ovules within the ovary. A prediction of the extent of pollen tube competition can be partially equated to the P-S/O ratio. This ratio relates the total number of pollen grains (P) deposited onto the stigmata (S) at the end of the female phase of anthesis (stigma receptivity) to the number of ovules (O) present in the ovary. Some quantitative data on pollen load on the stigma or stigmata and resulting pollen tube competition will be demonstrated especially in the choricarpous gynoecium of Geum rivale (Rosaceae) and in the coenocarpous gynoecium of Cichorium intybus (Asteraceae). Data from this study are compared with data of other taxa obtained from the literature.
... are some evolutionary trends, particularly in the modes of corolla tube formation and ovulemo... more ... are some evolutionary trends, particularly in the modes of corolla tube formation and ovulemorphology. ... corolla lobes (or there are fewer sta-mens) and a coenocarpous gynoecium of mostly ... Within the Convolvulaceae, in Di-chondra and Cuscuta, there is no corolla tube, but ...
ABSTRACT To follow the movement of Erwinia amylovora in plant tissue without dissection, this bac... more ABSTRACT To follow the movement of Erwinia amylovora in plant tissue without dissection, this bacterium was marked with either the lux operon from Vibrio fischeri or the gfp gene from the jellyfish Aequorea victoria, both carried on multicopy plasmids and expressed under the control of the lac promoter from Escherichia coli. Movement of the pathogen was visualized in leaves, stems, and roots of apple seedlings, and migration of E. amylovora was traced from inoculation sites in the stem to as far as the roots. Green fluorescent E. amylovora cells were observed in the xylem and later appeared to break out of the vessels into the intercellular spaces of the adjacent parenchyma. Inoculation in the intercostal region of leaves caused a zone of slow necrosis that finally resulted in bacterial invasion of the xylem vessels. Labeled bacteria could also be seen in association with the anchor sites of leaf hairs. Distortion of the epidermis adjacent to leaf hairs created openings that were observed by scanning electron microscopy. As the intercostal region, the bases of leaf hairs provided E. amylovora access to intact xylem vessels, which allowed further distribution of the pathogen in the host plant.
... Pollen is deposited onto orchid stigmata either when whole pollinia become trapped in a roste... more ... Pollen is deposited onto orchid stigmata either when whole pollinia become trapped in a rostellum notch or when the adhesion between pollen and stigmatic mucilage breaks away whole pollinia, individual massulae or parts of soft pollen masses. ...
The correct assessment of homology is an important prerequisite for reconstructing phylogenetic r... more The correct assessment of homology is an important prerequisite for reconstructing phylogenetic relationships and character evolution. Old World Papaveroideae (Papaver, Meconopsis, Roemeria, Stylomecon) show substantial diversity in gynoecium and capsule morphology. In particular, capsules can have distinct styles (Meconopsis p.p., Stylomecon) or a sessile stigmatic disc (Papaver). Molecular phylogenetic analyses of Old World Papaveroideae had shown that neither taxa with styles nor those with stigmatic discs represent monophyletic lineages. We here investigate whether either styles or stigmatic discs have arisen repeatedly during the diversification of Old World Papaveroideae. We investigated gynoecium ontogeny in Papaver rhoeas, P. californicum, Meconopsis cambrica, and Stylomecon heterophylla by scanning electron microscopy for the first time. Our observations were interpreted on the background of a well-resolved molecular phylogeny of the taxa investigated. Papaver rhoeas and P. californicum share the presence of a developmentally complex garland-like stage in gynoecium ontogeny. The styles of M. cambrica and S. heterophylla result from growth in a ring-like zone beneath the carpel tips. This zone is also present in Papaver. In M. cambrica, traces of a garland-like stage can be seen. Style formation and stigma formation begin more or less simultaneously in M. cambrica, but style formation clearly precedes stigma formation in S. heterophylla. The styles present in M. cambrica and S. heterophylla are considered to have arisen in parallel from ancestors with a stigmatic disc. We speculate that style formation may have been a means to reduce selfing.
Disintegration of the Scrophulariaceae due to molecular data resulted in re-circumscriptions, res... more Disintegration of the Scrophulariaceae due to molecular data resulted in re-circumscriptions, resurrection and new descriptions of families to encompass the monophyletic lineages. In some of these families floral morphological/ontogenetic data, however, are largely missing, as, for example, in Paulowniaceae. This study reveals a set of distinctive features that were up to now unknown in Paulowniaceae: In the lateral flowers of the inflorescence, initiation sequence in calyx and corolla is unidirectional in identical direction, starting at the adaxial side; the formation of sympetaly is late but ledges connecting the separate petals arise relatively early. Of importance are particularly the occurrence of: crescent-shaped archespore and pollen sacs with a pollen sac placentoid, secretory tapetum, a several cell layers thick endothecium, endothecium-like cells situated all over the tissue of the theca except in the placentoid, undivided placenta originating in each locule on the septum only, a tubular stigma with papillae inside a dilated chamber (in this character Paulownia differs from all other members of the Lamiales-clade!), nectary in the basal part of the superior ovary, and small, winged seeds whose testa possesses protrusions that laterally expand into several sinuate wings, gradually increasing in extension towards the two margins.
During the last 15 years enormous progress had been made in understanding the genetic and molecul... more During the last 15 years enormous progress had been made in understanding the genetic and molecular regulation of flower development. The classical A-B-C model, which describes how the activities of three classes of genes coding for transcription factors (A, B, C) alone or coordinately specify the different floral organs, has been expanded by class D genes involved in ovule development and class E genes required for the identities of all floral organs. The molecular quartet model advances the genetic A-B-C-D-E model by describing the presumed interactions between floral MADS-domain proteins. Although the basic developmental program appears to be quite conserved, in non-core eudicots modifications such as ``sliding-boundary'' and ``fading borders'' models had to be established. Since the identity of floral organs is strictly dependent on the activity of the MADS-box genes, duplication and diversification within these genes must have been key processes in flower evolution. Hence, insights into the phylogeny of the floral homeotic genes may help to better understand the evolution of flowers (``evo-devo'').
In angiosperm reproduction, pollen tubes elongate from the stigma through the stylar transmitting... more In angiosperm reproduction, pollen tubes elongate from the stigma through the stylar transmitting tissue to the ovary to deliver the male gametes for fertilization. This article reviews different forms of pollen tube transmitting tracts within the style as well as possibilities for bridging the gap from the transmitting tissue to the ovule. The pollen tube transmitting tissue is the place of possible pollen tube competition. Often the number of pollen grains deposited onto the stigma or stigmata of a flower exceeds the number of ovules in the ovary of the pollinated flower. In the styles of most taxa investigated, a reduction in number of the pollen tubes occurs from the stigma to the ovary (pollen tube attrition): the pollen tubes compete for entry into the embryo sac of the ovules within the ovary. A prediction of the extent of pollen tube competition can be partially equated to the P-S/O ratio. This ratio relates the total number of pollen grains (P) deposited onto the stigmata (S) at the end of the female phase of anthesis (stigma receptivity) to the number of ovules (O) present in the ovary. Some quantitative data on pollen load on the stigma or stigmata and resulting pollen tube competition will be demonstrated especially in the choricarpous gynoecium of Geum rivale (Rosaceae) and in the coenocarpous gynoecium of Cichorium intybus (Asteraceae). Data from this study are compared with data of other taxa obtained from the literature.
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