Jeffrey Duckett | Natural History Museum, London (original) (raw)

Papers by Jeffrey Duckett

Restoration Ecology, Jan 17, 2024

American Journal of Botany, Oct 1, 1977

Electron microscopic examination of thin sections showed that the blepharoplast of a young sperma... more Electron microscopic examination of thin sections showed that the blepharoplast of a young spermatid of Phaeoceros consists of two side‐by‐side centrioles and an accumulation of osmiophilic, granular matrix at their proximal ends. Lying between these nearly parallel organelles is a dark‐staining body that will later disappear at the onset of flagellogenesis. For a brief period the centrioles are oriented perpendicular to the nuclear surface so that the granular matrix at their proximal ends is confluent with the nuclear envelope; furthermore, the nucleoplasm immediately in front of the centrioles becomes densely staining. The multilayered structure (MLS) develops directly under the centrioles. It comprises a band of 12 microtubules (the S1 stratum) and three lower strata (S2–4) whose constitutent lamellae are oriented at an oblique angle to the S1 axis. While the S1 tubules grow rearward over the nucleus which forms a beak adjacent to the posterior end of the lamellar strata, the centrioles are transformed into basal bodies with the distal growth of the axonemes and the proximal growth of the central cartwheels and lowermost triplets. The proximal ends of the basal bodies and the S1 tubules overlying the lamellar strata are invested with osmiophilic matrix that extends down to the S2 layer and may temporarily occlude the lamellar plates. At the onset of nuclear elongation an anterior mitochondrion becomes situated close beneath the lamellar strata which extend laterally beyond the S1 tubules.

Journal of Bryology, 1972

Botanical Journal of the Linnean Society, 1980

ABSTRACT

New Phytologist, Jul 1, 1975

SUMMARYElectron microscopy reveals that the multicellular hairs, in the Anabaena‐containing leaf ... more SUMMARYElectron microscopy reveals that the multicellular hairs, in the Anabaena‐containing leaf cavities of Azolla, produce labyrinthine wall ingrowths, and have dense cytoplasm with numerous mitochondria and abundant endoplasmic reticulum. Development of transfer cell morphology, in this location, might be an adaptation facilitating interchange of metabolites between Azolla and its algal partner. Equally prominent wall ingrowths are also found in the absence of Anabaena. It is suggested that they may be either a constitutive feature of Azolla or may be induced as a response to the presence of combined nitrogen sources in the axenic culture medium. The occurrence of plasmalemmasomes, in the developing hair‐cells of Azolla, is compared with their presence in lichens, mycorrhiza and at host‐parasite interfaces.

New Phytologist, Jun 1, 1991

summaryThe lipophilic fluorochrome 3,3′dihexyloxacarbocyanine iodine [DiOC6(3)], previously used ... more summaryThe lipophilic fluorochrome 3,3′dihexyloxacarbocyanine iodine [DiOC6(3)], previously used to visualize mitochondria and ER in animal and plant tells, when applied at concentrations of 0.01–5 μg ml−1selectively stains ascomycetous hyphae in ericaeous roots and in the rhizoids of liverworts in the families Lepidoziaceae (both tropical and temperate species), Calypogeiaceae, Adelanthaceae, Cephaloziaceae and Cephaloziellaceae. Basidio‐mycetes forming endophytic associations with liverworts and ectomycorrhizas in seed plants, are stained with DiOC6(3) only at concentrations at and above 50 μg ml−1. VA mycorrhizal fungi in liverworts, pteridophytes and angiosperms fail to stain. Hyphae of the ericoid mycorrhizal fungus, Hymenoscyphus ericae, grown in axenic culture, are stained with much lower concentrations of DiOC6(3) than are those of a range of ectomycorrhizal fungi, an orchid fungus and Oidiodendron griseum which has been reported occasionally to form ericoid mycorrhizal associations. In contrast to other fluorescent probes that recognize fungal wall components, DiOC6(3) is a vital stain of fungal cytoplasm. Greater membrane permeability, compared to that in other fungi, is the likely basis for the selective staining of Hymenoscyphus ericae and the root and rhizoid‐inhabiting ascomycetes with this dye. DiOC6(3) offers a rapid means for identifying intracellular ascomycetous mycorrhizas and for determining the distribution of living hyphae within these associations.

Cell and Tissue Research, 1973

... I. An Association of the Nuclei with Endoplasmic Reticulum in Post-Meiotic Tetraspore Mother ... more ... I. An Association of the Nuclei with Endoplasmic Reticulum in Post-Meiotic Tetraspore Mother Cells of Corallina officinalis L. * MC Peel, IAN Lucas University College of North Wales, Department 0f Marine Biology, Marine Science Laboratories, Menai Bridge, Anglesey ...

Journal of Bryology, 1972

Botanical Journal of the Linnean Society, Apr 1, 1970

ABSTRACT

Juniperus communis L. (Common Juniper) (Cupressaceae) is a native British species of evergreen di... more Juniperus communis L. (Common Juniper) (Cupressaceae) is a native British species of evergreen dioecious conifer, threatened by extensive grazing, competing tree species and lack of sites to colonise. This study assesses the present status of juniper in the Lake District. Ten large stands recorded as in good condition in 1975 were compared to five smaller stands, and a reference stand protected from grazing for 70 years. Recorded values of the number of berries produced by large stands and seed viability of these berries were combined as a seed viability index. Analysis showed that the seed viability indices of large stands were significantly higher than the small stand values, but significantly lower than the reference stand. These results suggest low reproductive potential may be indicative of a senescing population, and that grazing pressure is limiting reproduction. The absence of regeneration is attributed to stands becoming substantially moribund at a similar time without replacement. Seedling propagation and planting in fenced areas is suggested as the best strategy for juniper conservation.

American Journal of Botany, Apr 1, 1985

The blepharoplast in the young spermatid of Pallavicinia is similar to that of other hepatics in ... more The blepharoplast in the young spermatid of Pallavicinia is similar to that of other hepatics in that it comprises a four‐layered multilayered structure (MLS) and two staggered, dimorphic basal bodies. The spline, approximately 40 μm in length and extending through nearly two full gyres, comprises 20 parallel microtubules at its anterior end and narrows to 17 at the posterior limit of the subjacent lamellar strip (LS). Behind this, the spline shank, approximately 32 μm in length, is reduced to six tubules. The LS curves around the spermatid, following the anterior one‐third of the first gyre of the spine, and is approximately 7.5 μm in length, the longest yet recorded for the bryophytes. It is spatulate in outline, equaling the width of the spline anteriorly but tapering steeply from the right‐hand side behind the anterior basal body (ABB). It then extends posteriorly as a narrow strip beneath the left‐hand margin of the spline. The basal bodies of the greatly staggered flagella are nonoverlapping and separated by a distance of about 4.4 μm. The subapical ABB and PBB measure (including the ventral triplet extensions and transition zones) 1.2 μm and 2.4 μm in length, respectively. A short, narrow aperture equaling one tubule‐diameter in width is located in the spline directly beneath the ABB. The anterior mitochondrion is about 7 μm long and follows the outline of the overlying LS, while a cupshaped posterior mitochondrion is appressed to the plastid. Comparisons with other taxa indicate that major distinguishing features of metzgerialian blepharoplasts are highly staggered, nonoverlapping basal bodies, greatly elongate anterior mitochondria, and six‐tubule shanks. Great differences between the spermatids suggest wide phylogenetic discontinuities between the genera of the Metzgeriales.

Gamete Research, 1980

... Present address of John W. Moser is 110 Main Street, Waveland, Indiana 47989 ... exhaustive h... more ... Present address of John W. Moser is 110 Main Street, Waveland, Indiana 47989 ... exhaustive histo-chemical tests have yet to be performed, there is no evidence from feulgen staining [fol-lowing Feder and O'Brien, 19681 or X-ray microanalysis [Duckett and Chescoe, 19761 that ...

Journal of Bryology, 1993

... Queen Mary and Westfield College, London, UK ... distinctive feature has been highlighted in ... more ... Queen Mary and Westfield College, London, UK ... distinctive feature has been highlighted in all subsequent studies, not only on this species (eg Mueller, 1909; Goebel, 1905; Nehira ... Nishida, 1978; Noguchi .& Muraoka, 1959) and on the allied genus Theriotia (Nishida, 1980). ...

Cell and Tissue Research, Jun 1, 1983

The stylets of Nilapavarta lugens consist of two maxillae that interlock to form separate food an... more The stylets of Nilapavarta lugens consist of two maxillae that interlock to form separate food and salivary ducts partially surrounded by two mandibles. The ultrastructure of the sensory innervation of the stylets is described. Each maxilla possesses five neurones which extend to the tip of the stylet. The mandibles also contain five neurones, four of which are paired. The paired neurones comprise a shorter dendrite extending part of the way along the stylet and a longer one extending to the tip. The possible functions of these neurones are discussed. Gustatory receptors are located in the small passageway leading from the food duct to the cibarium. The receptors are in two distinct groups on the epipharyngeal side and one group on the hypopharyngeal side of the food canal. Two to five neurones innervate each receptor which connects to the food canal via a small pore.

Botanical Journal of the Linnean Society, 1984

The origins of heterospory: a comparative study of sexual behaviour in the fern Platyzoma rnicrop... more The origins of heterospory: a comparative study of sexual behaviour in the fern Platyzoma rnicrophyllurn R.Br. and Equisetum giganteurn L. 'The heterosporous fern Platyzoma rnicrophyllurn has exosporic photosynthetic gametophytes. Those from the small spores are filamentous, with few rhizoids and produce antheridia alone. The gametophytes from the large spores comprise a massive base bearing numerous rhizoids and an upright spathulate lobe of tissue one cell thick. They initially produce archegonia near the base but subsequently develop antheridia on the lobe. Adventitious outgrowths are produced after prolonged culture. These secondary individuals vary from branched filaments bearing numerous antheridia to spathulate lobes with archegonia near the base. Gametophyte sexuality determined during sporogenesis can be modified by subculturing gametophyte fragments. When isolated, portions of gametophytes from both kinds of spores produce adventitious individuals bearing antheridia or archegonia. The proportions of these secondary male and female outgrowths vary according to the nature of the fragment rather than the kind of spore from which the material was derived. The sexual behaviour of Equiseturn giganteurn follows the. same pattern as in other species of Equiscturn subgenus Hippochaete. Male and female secondary gametophytes may be derived from initially male or female individuals as a result of lamellar proliferation both on intact gametophytes and on subcultures derived from excised lamellae. The antheridia of E. giganteurn are indistinguishable from those of other species of the subgenus but the larnellae and archegonia are distinct for each speries. Detectable genetir load is absent in both Equisefurn and Plafyzomo. O n the basis of the striking similarities in the sexual behaviour of Equiccturn and Plafyzoma it ic suggested that a crucial step in the development of heterospory is an intimate association between gametophyte morphogenesis and sex organ formation. Gametophyte dioecism and dimorphism resulting from this association may have preceded heterospory in evolution.

Philosophical transactions of the Royal Society of London, Feb 25, 1977

The male gamete of Equisetum is the largest and structurally most complex of those so far known i... more The male gamete of Equisetum is the largest and structurally most complex of those so far known in living pteridophytes. The ultrastructure of the mature gametes, is described with particular reference to the influence of the multilayered structure (MLS) on its form. In Equisetum this organ elle comprises a band of over 300 microtubules, underlain along its anterior edge by a lamellar strip, 15-20 pm in length, and forming a sinistral spiral of 2 \ gyres. The tubules extend from the strip, at an angle of about 40°, to form a broad sheath around the twisted pyriform nucleus located in the posterior half of the cell. From the an terior tip of the lamellar strip to the posterior end of the nucleus the gamete completes a helix of 3 | gyres, traversed throughout by the microtubular band. As a result of growth of this band during spermatid metamorphosis, and the 40° angle between the plates of the lamellar strip and the microtubules, the strip is displaced anteriorly and laterally relative to the nucleus. In the mature gamete, although the strip and the nucleus remain interconnected by the microtubular band, only the posterior half of the strip lies directly above the anterior third of the nucleus. The precise interrela tionship between nucleus and MLS is illustrated by reconstructions which display the spermatozoids as they would appear if uncoiled. The 80-120 flagella are inserted outside that part of the microtubular band lying anterior to the nucleus. Their basal bodies retain the proximal cartwheel and stellate transition regions found already in spermatids, but in the mature gametes they are invested with collars of osmiophilic material. The axonemes depart at 10° tangentially from the helix and extend backwards parallel with the tubules of the microtubular band. In consequence of the overlapping gyres of the helix the flagella lie in a spiral groove, similar to that found in cycad spermatozoids. From this groove the plasma membrane closely follows the external surface of the microtubular band. Contrasting with other archegoniates, maximal structural differentiation of the MLS is found in the mature spermatozoid. Flat-bottomed keels are present on the microtubules overlying the lamellar strip in which three distinct strata can be recog nized. The two outer, consisting of alternating plates of electron-opaque and electrontransparent material, are separated by a continuous electron-opaque sheet. The innermost stratum comprises a continuous layer of finely granular material. Overlying the external anterior rim of the microtubular band is an osmiophilic crest. This retains the regularly banded substructure found in spermatids, but in mature spermatozoids is far more prominent than at any other time during spermatogenesis. It contains an electron-transparent lumen and is continuous with both the anterior ends of the microtubules and the anteriormost lamellar plates. Between the inner gyres of the MLS the crest is confluent with extensive sheets of smooth endoplasmic reticulum. Underlying the lamellar strip is a spiral mitochondrion with prominent dilated cristae. The central cytoplasm contains at least 100 pleomorphic mitochondria, to gether with from 15 to 25 amyloplasts and a few microbodies. In the nucleus, in addition to condensed chromatin, are several spherical electron-opaque bodies and aggregations of membrane-bound vesicles. Structures identical in appearance with the former also occur in the cytoplasm, and it is suggested that they may be nuclear in origin, as are similar bodies in animal spermatogenesis. The vesicles may represent portions of redundant nuclear envelope whose extrusion into the cytoplasm was prevented by the ensheathing microtubular band. Pores are still present in the nuclear envelope, where this is not invested by the band. The mature spermatozoids are liberated from antheridia within mucilaginous sacs bounded by fibrillar cell wall material, thought to contain lipid droplets promoting their dispersal when in contact with water. On escaping from the sacs the spermato zoids elongate slightly, and profiles of disrupted flagella are frequently encountered. Occasionally the microtubular band ensheathing the posterior part of the nucleus also becomes disorganized. There is no evidence of the utilization of amyloplast starch as an energy source during motility, and, in contrast to ferns and bryophytes, there is no sequestration of the central cytoplasm by the swimming spermatozoids.

Gamete Research, 1979

ABSTRACT

Journal of Bryology, 1984

ABSTRACT

Cell and Tissue Research, Mar 1, 1983

The ultrastructure of the sensory receptors located on the labium of the rice brown planthopper i... more The ultrastructure of the sensory receptors located on the labium of the rice brown planthopper is described; possible functions of individual receptors are suggested on morphological grounds. Uniporous chemosensilla which may or may not possess a mechanoreceptive dendrite, domed multiporous chemosensilla, and mechanoreceptive pegs are present on the flattened labial tip. Mechanoreceptive pegs are distributed over the labium. The fine structure of a multilobed sensillum located on either side of the labium is also described.

Restoration Ecology, Jan 17, 2024

American Journal of Botany, Oct 1, 1977

Electron microscopic examination of thin sections showed that the blepharoplast of a young sperma... more Electron microscopic examination of thin sections showed that the blepharoplast of a young spermatid of Phaeoceros consists of two side‐by‐side centrioles and an accumulation of osmiophilic, granular matrix at their proximal ends. Lying between these nearly parallel organelles is a dark‐staining body that will later disappear at the onset of flagellogenesis. For a brief period the centrioles are oriented perpendicular to the nuclear surface so that the granular matrix at their proximal ends is confluent with the nuclear envelope; furthermore, the nucleoplasm immediately in front of the centrioles becomes densely staining. The multilayered structure (MLS) develops directly under the centrioles. It comprises a band of 12 microtubules (the S1 stratum) and three lower strata (S2–4) whose constitutent lamellae are oriented at an oblique angle to the S1 axis. While the S1 tubules grow rearward over the nucleus which forms a beak adjacent to the posterior end of the lamellar strata, the centrioles are transformed into basal bodies with the distal growth of the axonemes and the proximal growth of the central cartwheels and lowermost triplets. The proximal ends of the basal bodies and the S1 tubules overlying the lamellar strata are invested with osmiophilic matrix that extends down to the S2 layer and may temporarily occlude the lamellar plates. At the onset of nuclear elongation an anterior mitochondrion becomes situated close beneath the lamellar strata which extend laterally beyond the S1 tubules.

Journal of Bryology, 1972

Botanical Journal of the Linnean Society, 1980

ABSTRACT

New Phytologist, Jul 1, 1975

SUMMARYElectron microscopy reveals that the multicellular hairs, in the Anabaena‐containing leaf ... more SUMMARYElectron microscopy reveals that the multicellular hairs, in the Anabaena‐containing leaf cavities of Azolla, produce labyrinthine wall ingrowths, and have dense cytoplasm with numerous mitochondria and abundant endoplasmic reticulum. Development of transfer cell morphology, in this location, might be an adaptation facilitating interchange of metabolites between Azolla and its algal partner. Equally prominent wall ingrowths are also found in the absence of Anabaena. It is suggested that they may be either a constitutive feature of Azolla or may be induced as a response to the presence of combined nitrogen sources in the axenic culture medium. The occurrence of plasmalemmasomes, in the developing hair‐cells of Azolla, is compared with their presence in lichens, mycorrhiza and at host‐parasite interfaces.

New Phytologist, Jun 1, 1991

summaryThe lipophilic fluorochrome 3,3′dihexyloxacarbocyanine iodine [DiOC6(3)], previously used ... more summaryThe lipophilic fluorochrome 3,3′dihexyloxacarbocyanine iodine [DiOC6(3)], previously used to visualize mitochondria and ER in animal and plant tells, when applied at concentrations of 0.01–5 μg ml−1selectively stains ascomycetous hyphae in ericaeous roots and in the rhizoids of liverworts in the families Lepidoziaceae (both tropical and temperate species), Calypogeiaceae, Adelanthaceae, Cephaloziaceae and Cephaloziellaceae. Basidio‐mycetes forming endophytic associations with liverworts and ectomycorrhizas in seed plants, are stained with DiOC6(3) only at concentrations at and above 50 μg ml−1. VA mycorrhizal fungi in liverworts, pteridophytes and angiosperms fail to stain. Hyphae of the ericoid mycorrhizal fungus, Hymenoscyphus ericae, grown in axenic culture, are stained with much lower concentrations of DiOC6(3) than are those of a range of ectomycorrhizal fungi, an orchid fungus and Oidiodendron griseum which has been reported occasionally to form ericoid mycorrhizal associations. In contrast to other fluorescent probes that recognize fungal wall components, DiOC6(3) is a vital stain of fungal cytoplasm. Greater membrane permeability, compared to that in other fungi, is the likely basis for the selective staining of Hymenoscyphus ericae and the root and rhizoid‐inhabiting ascomycetes with this dye. DiOC6(3) offers a rapid means for identifying intracellular ascomycetous mycorrhizas and for determining the distribution of living hyphae within these associations.

Cell and Tissue Research, 1973

... I. An Association of the Nuclei with Endoplasmic Reticulum in Post-Meiotic Tetraspore Mother ... more ... I. An Association of the Nuclei with Endoplasmic Reticulum in Post-Meiotic Tetraspore Mother Cells of Corallina officinalis L. * MC Peel, IAN Lucas University College of North Wales, Department 0f Marine Biology, Marine Science Laboratories, Menai Bridge, Anglesey ...

Journal of Bryology, 1972

Botanical Journal of the Linnean Society, Apr 1, 1970

ABSTRACT

Juniperus communis L. (Common Juniper) (Cupressaceae) is a native British species of evergreen di... more Juniperus communis L. (Common Juniper) (Cupressaceae) is a native British species of evergreen dioecious conifer, threatened by extensive grazing, competing tree species and lack of sites to colonise. This study assesses the present status of juniper in the Lake District. Ten large stands recorded as in good condition in 1975 were compared to five smaller stands, and a reference stand protected from grazing for 70 years. Recorded values of the number of berries produced by large stands and seed viability of these berries were combined as a seed viability index. Analysis showed that the seed viability indices of large stands were significantly higher than the small stand values, but significantly lower than the reference stand. These results suggest low reproductive potential may be indicative of a senescing population, and that grazing pressure is limiting reproduction. The absence of regeneration is attributed to stands becoming substantially moribund at a similar time without replacement. Seedling propagation and planting in fenced areas is suggested as the best strategy for juniper conservation.

American Journal of Botany, Apr 1, 1985

The blepharoplast in the young spermatid of Pallavicinia is similar to that of other hepatics in ... more The blepharoplast in the young spermatid of Pallavicinia is similar to that of other hepatics in that it comprises a four‐layered multilayered structure (MLS) and two staggered, dimorphic basal bodies. The spline, approximately 40 μm in length and extending through nearly two full gyres, comprises 20 parallel microtubules at its anterior end and narrows to 17 at the posterior limit of the subjacent lamellar strip (LS). Behind this, the spline shank, approximately 32 μm in length, is reduced to six tubules. The LS curves around the spermatid, following the anterior one‐third of the first gyre of the spine, and is approximately 7.5 μm in length, the longest yet recorded for the bryophytes. It is spatulate in outline, equaling the width of the spline anteriorly but tapering steeply from the right‐hand side behind the anterior basal body (ABB). It then extends posteriorly as a narrow strip beneath the left‐hand margin of the spline. The basal bodies of the greatly staggered flagella are nonoverlapping and separated by a distance of about 4.4 μm. The subapical ABB and PBB measure (including the ventral triplet extensions and transition zones) 1.2 μm and 2.4 μm in length, respectively. A short, narrow aperture equaling one tubule‐diameter in width is located in the spline directly beneath the ABB. The anterior mitochondrion is about 7 μm long and follows the outline of the overlying LS, while a cupshaped posterior mitochondrion is appressed to the plastid. Comparisons with other taxa indicate that major distinguishing features of metzgerialian blepharoplasts are highly staggered, nonoverlapping basal bodies, greatly elongate anterior mitochondria, and six‐tubule shanks. Great differences between the spermatids suggest wide phylogenetic discontinuities between the genera of the Metzgeriales.

Gamete Research, 1980

... Present address of John W. Moser is 110 Main Street, Waveland, Indiana 47989 ... exhaustive h... more ... Present address of John W. Moser is 110 Main Street, Waveland, Indiana 47989 ... exhaustive histo-chemical tests have yet to be performed, there is no evidence from feulgen staining [fol-lowing Feder and O'Brien, 19681 or X-ray microanalysis [Duckett and Chescoe, 19761 that ...

Journal of Bryology, 1993

... Queen Mary and Westfield College, London, UK ... distinctive feature has been highlighted in ... more ... Queen Mary and Westfield College, London, UK ... distinctive feature has been highlighted in all subsequent studies, not only on this species (eg Mueller, 1909; Goebel, 1905; Nehira ... Nishida, 1978; Noguchi .& Muraoka, 1959) and on the allied genus Theriotia (Nishida, 1980). ...

Cell and Tissue Research, Jun 1, 1983

The stylets of Nilapavarta lugens consist of two maxillae that interlock to form separate food an... more The stylets of Nilapavarta lugens consist of two maxillae that interlock to form separate food and salivary ducts partially surrounded by two mandibles. The ultrastructure of the sensory innervation of the stylets is described. Each maxilla possesses five neurones which extend to the tip of the stylet. The mandibles also contain five neurones, four of which are paired. The paired neurones comprise a shorter dendrite extending part of the way along the stylet and a longer one extending to the tip. The possible functions of these neurones are discussed. Gustatory receptors are located in the small passageway leading from the food duct to the cibarium. The receptors are in two distinct groups on the epipharyngeal side and one group on the hypopharyngeal side of the food canal. Two to five neurones innervate each receptor which connects to the food canal via a small pore.

Botanical Journal of the Linnean Society, 1984

The origins of heterospory: a comparative study of sexual behaviour in the fern Platyzoma rnicrop... more The origins of heterospory: a comparative study of sexual behaviour in the fern Platyzoma rnicrophyllurn R.Br. and Equisetum giganteurn L. 'The heterosporous fern Platyzoma rnicrophyllurn has exosporic photosynthetic gametophytes. Those from the small spores are filamentous, with few rhizoids and produce antheridia alone. The gametophytes from the large spores comprise a massive base bearing numerous rhizoids and an upright spathulate lobe of tissue one cell thick. They initially produce archegonia near the base but subsequently develop antheridia on the lobe. Adventitious outgrowths are produced after prolonged culture. These secondary individuals vary from branched filaments bearing numerous antheridia to spathulate lobes with archegonia near the base. Gametophyte sexuality determined during sporogenesis can be modified by subculturing gametophyte fragments. When isolated, portions of gametophytes from both kinds of spores produce adventitious individuals bearing antheridia or archegonia. The proportions of these secondary male and female outgrowths vary according to the nature of the fragment rather than the kind of spore from which the material was derived. The sexual behaviour of Equiseturn giganteurn follows the. same pattern as in other species of Equiscturn subgenus Hippochaete. Male and female secondary gametophytes may be derived from initially male or female individuals as a result of lamellar proliferation both on intact gametophytes and on subcultures derived from excised lamellae. The antheridia of E. giganteurn are indistinguishable from those of other species of the subgenus but the larnellae and archegonia are distinct for each speries. Detectable genetir load is absent in both Equisefurn and Plafyzomo. O n the basis of the striking similarities in the sexual behaviour of Equiccturn and Plafyzoma it ic suggested that a crucial step in the development of heterospory is an intimate association between gametophyte morphogenesis and sex organ formation. Gametophyte dioecism and dimorphism resulting from this association may have preceded heterospory in evolution.

Philosophical transactions of the Royal Society of London, Feb 25, 1977

The male gamete of Equisetum is the largest and structurally most complex of those so far known i... more The male gamete of Equisetum is the largest and structurally most complex of those so far known in living pteridophytes. The ultrastructure of the mature gametes, is described with particular reference to the influence of the multilayered structure (MLS) on its form. In Equisetum this organ elle comprises a band of over 300 microtubules, underlain along its anterior edge by a lamellar strip, 15-20 pm in length, and forming a sinistral spiral of 2 \ gyres. The tubules extend from the strip, at an angle of about 40°, to form a broad sheath around the twisted pyriform nucleus located in the posterior half of the cell. From the an terior tip of the lamellar strip to the posterior end of the nucleus the gamete completes a helix of 3 | gyres, traversed throughout by the microtubular band. As a result of growth of this band during spermatid metamorphosis, and the 40° angle between the plates of the lamellar strip and the microtubules, the strip is displaced anteriorly and laterally relative to the nucleus. In the mature gamete, although the strip and the nucleus remain interconnected by the microtubular band, only the posterior half of the strip lies directly above the anterior third of the nucleus. The precise interrela tionship between nucleus and MLS is illustrated by reconstructions which display the spermatozoids as they would appear if uncoiled. The 80-120 flagella are inserted outside that part of the microtubular band lying anterior to the nucleus. Their basal bodies retain the proximal cartwheel and stellate transition regions found already in spermatids, but in the mature gametes they are invested with collars of osmiophilic material. The axonemes depart at 10° tangentially from the helix and extend backwards parallel with the tubules of the microtubular band. In consequence of the overlapping gyres of the helix the flagella lie in a spiral groove, similar to that found in cycad spermatozoids. From this groove the plasma membrane closely follows the external surface of the microtubular band. Contrasting with other archegoniates, maximal structural differentiation of the MLS is found in the mature spermatozoid. Flat-bottomed keels are present on the microtubules overlying the lamellar strip in which three distinct strata can be recog nized. The two outer, consisting of alternating plates of electron-opaque and electrontransparent material, are separated by a continuous electron-opaque sheet. The innermost stratum comprises a continuous layer of finely granular material. Overlying the external anterior rim of the microtubular band is an osmiophilic crest. This retains the regularly banded substructure found in spermatids, but in mature spermatozoids is far more prominent than at any other time during spermatogenesis. It contains an electron-transparent lumen and is continuous with both the anterior ends of the microtubules and the anteriormost lamellar plates. Between the inner gyres of the MLS the crest is confluent with extensive sheets of smooth endoplasmic reticulum. Underlying the lamellar strip is a spiral mitochondrion with prominent dilated cristae. The central cytoplasm contains at least 100 pleomorphic mitochondria, to gether with from 15 to 25 amyloplasts and a few microbodies. In the nucleus, in addition to condensed chromatin, are several spherical electron-opaque bodies and aggregations of membrane-bound vesicles. Structures identical in appearance with the former also occur in the cytoplasm, and it is suggested that they may be nuclear in origin, as are similar bodies in animal spermatogenesis. The vesicles may represent portions of redundant nuclear envelope whose extrusion into the cytoplasm was prevented by the ensheathing microtubular band. Pores are still present in the nuclear envelope, where this is not invested by the band. The mature spermatozoids are liberated from antheridia within mucilaginous sacs bounded by fibrillar cell wall material, thought to contain lipid droplets promoting their dispersal when in contact with water. On escaping from the sacs the spermato zoids elongate slightly, and profiles of disrupted flagella are frequently encountered. Occasionally the microtubular band ensheathing the posterior part of the nucleus also becomes disorganized. There is no evidence of the utilization of amyloplast starch as an energy source during motility, and, in contrast to ferns and bryophytes, there is no sequestration of the central cytoplasm by the swimming spermatozoids.

Gamete Research, 1979

ABSTRACT

Journal of Bryology, 1984

ABSTRACT

Cell and Tissue Research, Mar 1, 1983

The ultrastructure of the sensory receptors located on the labium of the rice brown planthopper i... more The ultrastructure of the sensory receptors located on the labium of the rice brown planthopper is described; possible functions of individual receptors are suggested on morphological grounds. Uniporous chemosensilla which may or may not possess a mechanoreceptive dendrite, domed multiporous chemosensilla, and mechanoreceptive pegs are present on the flattened labial tip. Mechanoreceptive pegs are distributed over the labium. The fine structure of a multilobed sensillum located on either side of the labium is also described.