SCANNING ELECTRON MICROSCOPY OF ANTHERIDIA AND ARCHEGONIA OF ANEMIA MEXICANA KLOTZSCH

Antheridia and archegonia of the fern Anemia mexicana were viewed with scanning electron microscopy (SEM). The mature antheridium is composed of a cap, ring, and basal cell with spermatozoids inside. The archegonium neck is composed of a neck canal cell surrounded by four rows of neck cells. The ventral canal cell and egg were not observed. The neck bends toward the notched meristem. The neck cells usually are uniform in shape and arrangement, but in some archegonia, shape and arrangement of neck cells was irregular. The apex of these archegonia often appeared swollen because of the random cell arrangement. In the presence of water, the antheridium cap is partially detached and the spermatozoids emerge. At this time, the neck cells open at the end of the archegonium in preparation for fertilization. The basic morphology of the antheridia and archegonia is similar to previous reports, although SEM provides more structural detail and a better three-dimensional visualization of these reproductive structures.     

Changes in the Level of the Protein Nitrogen during Growth of the Gametophyte and the Initiation of the Sporophyte of Dryopteris borreri Newm.

Estimations of the amounts of organic nitrogen in spores anddeveloping gametophytes of Dryopteris borreri, a fern reproducingapogamously and lacking archegonia, have shown that the nitrogenin the gametophytes increases exponentially. The logarithmicrate of increase of the nitrogen remains unchanged during theinitiation and emergence of the sporophyte. Gametophytes aboutto produce sporophytes yielded only filamentous growths whentransferred to a medium containing 8-azaguanine, and the increasein their content of organic nitrogen was very small. The resultsare discussed in relation to similar estimations made by otherworkers upon the gametophytes of Dryopteris erythosora(Eat.)Schott, a fern reproducing sexually. The interpretation placedupon the results obtained for D. erytkrosora is questioned,and a new interpretation of these results, together with thosefor D. borreri, is related to the difference in morphology ofthe two generations in the life cycle of the Polypodiaceousferns.     

The Reproductive Biology of Totara (Podocarpus totara) (Podocarpaceae)

A reproductive cycle of totara (Podocarpus totara) in New Zealandis complete within 2 years. After strobilus initiation in September,there is a 9 month period of winter dormancy until emergenceduring the growth flush in July–August of the followingyear. Female strobili bear only one or two ovules which arepollinated mid-October to mid-November at the megaspore tetradstage. Pollen germination and fertilization occur rapidly duringDecember. The pollen tube carries the body cell, sterile andtube nuclei with at least three prothallial nuclei, and branchesout after reaching the archegonia. The four–six archegoniacontain egg nuclei with no distinct perinuclear zone and a largechalazal vacuole. Fertilization by the larger of the two unequalmale gametes is accompanied by a degradation of egg cell cytoplasm.The three-tier proembryo contains a binucleate embryonal tierof only one cell. Soon after embryo penetration into the megagametophyte,the binucleate embryonal-tier cell undergoes mitosis and cellwall formation resulting in four uninucleate cells. Some ovulescontained secondary embryos thought to be the product of suspensorcleavage. Embryo maturation occurs by February.Copyright 1999Annals of Botany Company Podocarpus totara, totara, conifer, podocarp, reproductive biology, embryology.     

The Morphology and Anatomy of Pellia epiphylla considered in Relation to the Mechanism of Absorption and Conduction of Water

1. In Pellia epiphylla water travels in the form of capillary filmsbetween the rhizoids over the under surface, being partly absorbedthere. The remainder passes over the surface and is retainedin the region of the antheridia by the incurved and wavy marginsof the thallus.
2. The antheridia, oospheres, segmenting oospores,and sporogoniaare largely supplied with water from the exterior.This wateris retained in the narrow crevices between antheridialcavityand antheridium, between the flaps of the involucre,and betweenthese and the long necks of the archegonia. Travellingdownthe necks of the archegonia, it reaches the oospheres,and islater available for the developing sporophyte in theform offilms retained between the foot of the segmenting embryoandthe calyptra.
3. In the sporophyte, this water, absorbedby the foot largelyfrom external sources, travels up the seta,into the elaterophore,out to the elaten, and ultimately tothe spores.
4. The sporophyte, therefore, is much less dependenton the gametophytefor supplies of water and raw materials thanmight be expected.

The writer wishes to take this opportunity of thanking ProfessorF. A. Mockeridge for suggesting this work and for her valuableadvice and criticism during its progress.     

Intergeneric pollen – megagametophyte relationships of conifers in vitro

 Germinating pollen from larch (Larix occidentalis), Sitka spruce (Picea sitchensis) and white pine (Pinus monticola) were co-cultured with megagametophytes dissected from cones of other genera (Pseudotsuga menziesii, Larix×eurolepis and Pinus monticola). Pollen was presented to megagametophytes possessing archegonia which were either alive, degenerating or dead. In addition, pollen was presented to fertilized megagametophytes and to megagametophytes that had been cut in half. Megagametophyte penetration by pollen tubes and male gamete release into archegonia were verified by serial sections of glycomethacrylate-embedded specimens. Pollen tubes penetrated through any part of the apex of the megagametophyte. Division of the body cell into the two gametes was regularly observed. Delivery of gametes was confirmed between spruce and larch. Pollen tubes also penetrated fertilized megagametophytes, dead or degenerating archegonia as well as wounded and/or cut surfaces. This demonstrates the inability of the male gametophyte to optimize its mating efforts, since it is unable to differentiate between healthy and unhealthy archegonia. The megagametophyte cells are unable to optimize male selection. They may produce secretions of a generally attractive nature, as pollen is attracted to the apex of the megagametophyte, but archegonia themselves do not produce pollen-specific signals of either a promotive or inhibitory nature. These results open new avenues for the development of novel breeding strategies where natural breeding barriers may be bypassed. Received: 19 March 1998 / Accepted: 29 April 1998     

Root Cell Ultrastructure in Developing Aerenchyma Tissue of Three Wetland Species

Patterns of root cortex cell development and ultrastructurewere analysed in Sagittaria lancifolia L., Thalia geniculataL. and Pontederia cordata L. using scanning and transmissionelectron microscopy (SEM, TEM). In all three species, cortexcells were arranged in radial columns extending from the endodermisto the hypodermis/epidermis. During gas space formation, thecortex cells elongated parallel to the root radius and shrankin the plane perpendicular to the radius leaving long and thinrows of cortex cells extending from the endodermis to the epidermis.Although the cortex cells appeared collapsed in tissue withwell-developed gas spaces, TEM revealed that the cortical cellsas well as the epidermal cells maintained intact membranes andmany normal organelles. Formation of root cortex tissue withwell-developed gas spaces does not require cell death in thesespecies. Living cortex cells in root tissue with mature gasspaces could provide a symplastic pathway for transport betweenthe root stele and the living epidermal cells. Copyright 2000Annals of Botany Company Sagittaria lancifolia, Thalia geniculata, Pontederia cordata, aerenchyma, root, wetland, development     

Megasporogenesis and the Subsequent Cell Lineage Within the Ovule of Taxus baccata L.

Megasporogenesis in Taxus led to a T-shaped tetrad, the mitochondriaand plastids being largely confined to the chalazal megaspore,the only spore to show further development. Germination of themegaspore followed very soon after its formation. The femalegametophyte was initially coenocytic but after about one monthit became cellular, new walls arising between the nuclei inpositions marked out by accumulations of cisternae of endoplasmicreticulum. No ‘secondary spindles’ or other formsof microtubular participation in the siting of these walls couldbe detected. The development of the archegonia could not be resolved withcertainty, but it seemed likely that the cell analogous to thecentral cell of the pteridophyte archegonium eventually becamethe egg cell. The cytoplasm of the egg cell was clearly zoned.Prominent in the outer cytoplasm were granular bodies, 2–5µm in diameter, identifiable with the ‘grandes inclusions’described from the egg cells of conifers. The evidence pointedto their being derived from hypertrophied plastids which hadencapsulated part of the cytoplasm, a view strengthened by thecomplete absence of recognizable plastids from the mature cell.Bundles of microtubules radiating from the nuclear envelopewere a conspicuous feature, possibly stabilizing the zonationof the cytoplasm. Megasporogenesis, Taxus baccata, egg cell, ‘grandes inclusions’     

Cultivation of Excised Anthers in vitro--Effect of Nucleic Acids

Anthers of Allium cepa and Rhoeo discolor, excised at leptotene-zygoteneand diplotene-diakinesis, have been cultured in modified White'smedium supplemented with different concentrations of ribonucleicacid and desoxyribonucleic acid. The best development was obtainedwith ribonucleric acid in which there was a 100 per cent. survivalof the microspore mother cells up to the formation of 1-celledmicrospores. In R. discolor, the time taken by the microsporemother cells to form tetrads in vitri was half of that requiredin nature. All attempts to induce division of the microsporenucleus in vitro failed.     

The Growth and Reproductive Cycle of Pleurozium schreberi (Brid.) Mitt

The reproductive cycle of the moss Pleurozium schreberi hasbeen investigated by scoring over 600 specimens from Britainand elsewhere, and through regular observations on several populations.P. schreberi is at least functionally dioecious and the stemsare perennial, producing all the inflorescences of a given cycleduring the autumn. On male plants perigonia develop in largenumbers, principally on lateral branches. Relatively few perichaetiaare formed on female stems where they are largely confined tothe main axes. In Britain perigonial development begins in August,the antheridia remaining in the immature stage during the winterresting phase. Young perichaetia are first recorded in Octoberand the archegonia overwinter in the juvenile stage. Rapid gametangialdevelopment takes place in spring prior to the main fertilizationperiod in April and May. Young sporophytes are present fromMay onwards. Setal elongation is delayed until August, but thelate operculum intact stage is reached by October. In Britainthe spores are shed between January and April, nine to twelvemonths after fertilization. Data from the literature and fromFrench, Finnish, and North American specimens suggests a similarcycle in other areas, though with slight differences, notablythat fertilization in parts of Scandinavia may be delayed comparedwith Britain. The results from periodic measurements of marked plants andother techniques suggest that in Britain vegetative growth mayalso show a winter resting phase, stem elongation being recordedonly from April to November.     

Studies on Mature Seeds of Cuscuta pedicellata and C. campestris by Electron Microscopy

The seeds of Cuscuta pedicellata have been investigated by transmissionand scanning electron microscopy. Additional observations havebeen made on seeds of C. campestris by SEM only. The seed coatconsists of an outer single epidermis, two different palisadelayers, and an inner multiparenchyma layer. The outer epidermalwall in C. pedicellata has a thick cuticle and zones rich inpectic substances. The thicker ‘U-shaped’ cell wallsin the outer palisade layer are strengthened by a wall layerof hemicellulose. The inner palisade layer has thick walledcells with a ‘light line’. The inner cell wall ofthe compressed multiparenchyma layer has a thin cuticle. A fairlythick cuticle is positioned directly on the endosperm surface.The aleurone cell walls are different from the remaining endospermwalls. The latter are thick and believed to be of galactomannans.There is a ‘clear’ zone between the plasmalemmaand the cell wall in the aleurone cells. The embryo cells arepacked with lipids and proteins. In Cuscuta campestris mostendosperm has been absorbed during the seed development. Theembryo apex has two minute leaf primordia. The features of theCuscuta seeds are discussed in relation to functional and environmentalconditions. Cuscuta pedicellata, Cuscuta campestris, seed, seed coat, cuticle, cell walls, endosperm, aleurone cells, galactomannan, embryo, TEM, SEM     

Accumulation of Pb and Zn in Gametophytes and Sporophytes of the Moss Funaria hygrometrica(Funariales)

Accumulation of lead and zinc was studied in the moss Funariahygrometrica Hedw. collected from mine tailings. Heavy metalaccumulation in gametophytes and sporophytes was quantifiedby graphite furnace atomic absorption spectrometry (GFAAS) andinductively coupled plasma-atomic emission spectrometry (ICP-AES).Pb and Zn accumulation in the placental zone was analysed byx-ray scanning electron microscopy (SEM) and transmission electronmicroscopy (TEM) microanalysis. Spectrometry showed that whilemoss gametophytes accumulated considerable concentrations ofheavy metals, sporophytes accumulated only small concentrationsof metals. X-ray SEM and TEM showed that the two metals accumulatedin placental transfer cells on both the gametophytic and sporophyticsides. To investigate the uptake pattern for both metals undercontrolled conditions, F. hygrometrica plants collected froma non-polluted site were treated in the laboratory with separatesolutions of Pb and Zn at two concentrations (10^-2and 10^-4 M)for 24 or 168 h. Metal accumulation was analysed separatelyin gametophytes and sporophytes using GFAAS and ICP–AES.Each generation had a different accumulation quotient for bothmetals, and gametophytes accumulated significantly more metalthan sporophytes. Concentrations of Zn in sporophytes were alwayshigher than concentrations of Pb. The findings are discussedin relation to the role performed by the gametophyte and theplacenta in the accumulation and sequestration of Pb and Zn.Copyright 2001 Annals of Botany Company Atomic spectroscopy, Funaria hygrometrica, gametophyte, Pb and Zn accumulation, sporophyte, x-ray TEM and SEM microanalysis     

Microscopic characterization of early nodulation events in a non-nodulating soybean mutant (NN5) and lack of response to high inoculum dose

The microscopic events leading to nodulation in normally nodulatingsoybean [Glycine max (L.) Merr.] genotypes, and the effectsof Bradyrhizobium strain and inoculum dose on nodulation, wereexamined in the NN5 non-nodulating mutant derived from cv. Williams.The NN5 mutant possesses the recessive genes rj₅ and ,rj₆. BradyrhizoblumJaponicum strain USDA 110 cells attached normally to the rootsurface of NN5, many in a polar manner as in its wild-type parent,but failed to induce root hair curling and sub-epidermal celldivision in the root. Co-culturing NN5 and Williams did notmodify nodulation of either genotype. Hydroponically-grown NN5seedlings did not nodulate at a high inoculum dose (1 x 10¹⁰cells seedling^–1) of any B. japonicum strain tested (USDA110, USDA 26, USDA 136, and the tryptophan metabolic variantsB-14075 and ta 11 Nod⁺). A higher inoculum dose of 3 x 10 USDA136 cells seedling also failed to induce nodulation in NN5 andnod139 (a non-nodulating mutant of cv. Bragg). The lack of nodulationof NN5 at any inoculum dose is contrary to previous observationsof sparse nodulation of other non-nodulating mutants at highinoculum dose. Genetic control of non-nodulation in NN5 is probablysimilar to nodl39. Key words: Nodulation events, non-nodulating mutant, soybean     

Plant Chromatin Replicated in the Absence of Protein Synthesis

The aim of the present work is to detect possible differencesin the chromatin of plants replicated in the absence of proteinsynthesis. The kinetics of nuclease digestion in Allium cepa L., evaluatedafter making the cells permeable, was faster for the chromatinof meristem cells replicated in the presence of 1.0 µgml^–1 cycloheximide than in control cells. In order to have a synchronous population in the meristems,cells were labelled as binucleate by a short treatment with5.0 mM caffeine. Treated cells failed to increase both theircontent in dense chromatin and intranuclear histones. Thesefacts suggest that chromatin replicated in the presence of cycloheximidedid not incorporate histones and was unable to be integratedinto dense chromatin patches. Key words: Allium cepa L., Chromatin replication, Protein synthesis     

Isolation and Characterization of the Olfactory Epithelial Cells of the Catfish

A preparation enriched in olfactory receptor cells has beenobtained from the olfactory mucosa of the catfish (Ictaluruspunctatus). The tissue was treated successively with trypsin,DNase, trypsin inhibitor, EDTA in Ca^{+ +} , Mg^{+ +} free mediumaccording to a method derived from that of Cohen, et al.⁽¹⁾.After mechanical disruption of the isolated olfactory lamellae,the cells were isolated by centrifugation on a Ficoll gradient.Each type of cell was morphologically identified by comparingin situ and in vitro preparations by SEM. Small round cellswere collected on 10% Ficoll. The nature of these cells is notknown but part of them are certainly basal cells which havebeen shown⁽²⁾ to be the precursors of the constantly regeneratingolfactory neurons. Respiratory cells settled mainly on 20% Ficoll.A fraction containing 60% sustentacular cells was collectedon 33% Ficoll. Olfactory cells characterized by an axon, a dendriteand several cilia, were found on 37% Ficoll. This fraction alsocontains up to 40% sustentacular cells. A yield of 20% was measuredfor olfactory cell isolation. Vital staining and ability tosynthesize RNA indicate a viability of the final preparationof 70% to 80%. Further identification of the cells was performedby measuring the binding activity of a series of amino acidsto a preparation enriched in olfactory cells. A good correlationwas determined between the extent of the binding and the reportedelectrophysiological activities of these amino acids recordedin vivo. Although the final olfactory cell suspension is notpure, it constitutes the first step in the study of the olfactoryreceptor sites.     

The occurrence of polysety in relation to the number of archegonia in the female inflorescences of Phascum cuspidatum Hedw.

Abstract

In Phascum cuspidatum the number of sporophytes per inflorescence was found to increase, up to a certain limit, with increase in the number of archegonia present. The number of archegonia present varies with the age of the inflorescence, and fertilization terminates the production of archegonia. The common occurrence of solitary sporophytes is due to fertilization at a time when only a small number of archegonia is present in most inflorescences. Delayed fertilization, leading to an increase in the average number of archegonia per inflorescence, is a necessary precondition for increased occurrence of polysety. As many as five sporophytes in a single inflorescence formed capsules with spores without significant reduction in the size of capsules. Variation in the frequency of abortive embryos gave evidence of competition amongst sporophytes and this was most severe in the smaller inflorescences. The occurrence of polysety in Tortula muralis appears to be governed by the same rules.     

Increases in Cellular Levels of Cytochrome cd1 in Roseobacter denitrificans upon Irradiation with Green Light during Aerobic Growth

The cellular level of cytochrome cd₁, the nitrite reductaseof the aerobic photosynthetic bacterium Roseobacter denitrificans,increased considerably when the cells were grown aerobicallyunder white light. The action spectrum for the increase, determinedboth spectroscopically and immunologically, revealed that greenlight at 561 nm was most effective, while blue light between400 and 500 nm was fairly effective. Red and far-red light (650–900nm) absorbed by the bacterio-chlorophyll had no effect, eventhough bacteriochlorophyll and carotenoids were formed normallyduring the growth of cells. Diphenylamine, an inhibitor of thebiosynthesis of carotenoids abolished the increase in levelsof the cytochrome, a result that suggests that a carotenoid(s)was responsible for this phenomenon. The bulk carotenoids seem,however, to be unlikely the candidates for the photoreceptorsbecause they did not accumulate in the light-grown cells. Attemptsto detect archaerhodopsin, 11-cis and all-trans retinal by immunologicalor HPLC analysis were unsuccessful. Although we failed to identifythe photoreceptor, it is clear that R. denitrificans has a green-lightsignal-transduction system that controls the expression of cytochromecd₁. (Received April 19, 1993; Accepted July 12, 1993)     

Terminal Motility in Elongating Stolons of Proboscidactyla flavicirrata

Proboscidactyla flavircirrata is a commensal hydroid whose stolonselongate rapidly in the absence of its host. Growth pulsationscomparable to those of other hydroids originate endogenouslyin each stolon tip, although influenced by the to and fro movementsof the hydroplasm. Neither growth pulsations nor elongationappear to depend upon cellular proliferation, because the distalends of stolons lacked mitotic figures and since irradiationsufficient to halt mitosis failed to stop stolon elongation.Cellular migration is also apparently unessential for elongationbecause severed stolon tips, isolated from potential sourcesof reusable cells, nevertheless elongated. Marking experimentssuggested that cells changed shape rather than location as severedtips advanced. In old preparations the stolons became attenuatedbecause the tips continued to progress without adequate recruitmentof cells. Stolons deprived of their tips failed to elongatealthough they were still connected to the remainder of the colonyand contained mitotic cells. Cytochalasin B simultaneously haltedgrowth pulsations and stolon elongation in a reversable manner.Apparently stolon tip locomotion in Proboscidactyla is essentialto the elongation process.     

Effect of desiccation on the germination of akinetes of Anabaena cylindrica

Akinetes of Anabaena cylindrica were more tolerant to desiccationthan vegetative cells. Desiccated akinetes retained the germinationability after storage in darkness for 5 years. Desiccated vegetativecells failed to grow after storage of only 15 days. (Received January 31, 1975; )     

The relation between the occurrence of polysety and the number of archegonia in female inflorescences of Dicranum majus and D. scoparium.

Abstract

Inflorescences of Dicranum scoparium contain 7–9 archegonia on average compared with 13–15 in D. majus. In D. majus polysety was observed in 55% of fertile shoots. There is no evidence that the occurrence of polysety in D. majus is associated with any increase in the number of archegonia. This was interpreted to show that all inflorescences contained four or five ripe archegonia at the time of fertilization. Since monosetous inflorescences were more common than polysetous ones, it was concluded that the supply of antherozoids was not saturating for fertilization. In D. scoparium polysety was observed in only 5% of fertile shoots.     

Appendaged calyptra development in Fontinalis

Abstract

Some species of Fontinalis produce a calyptra which splits below the point of insertion of adjacent archegonia. Therefore accessory archegonia are incorporated into the aerial calyptra. This is especially evident in F. squamosa and less so in species with few archegonia per perichaetium such as F. dalecarlica.