Rhizoid Initiation Research Articles

Cytokinins Induce Photomorphogenic Development in Dark-grown Gametophytes of Ceratopteris richardii

The cytokinins benzylaminopurine, kinetin and isopentenyladenine induce photomorphogenesis in dark-grown gametophytes of the fern Ceratopteris richardii. At sub-nanomolar concentrations each altered the rate and pattern of cell division, elongation and differentiation, mimicking aspects of the light-mediated transition from filamentous to prothallial growth. Untreated dark-grown gametophytes grow as narrow, elongate, asexual filaments with an apical meristem. Cytokinin treatments as low as 10(-12) M reduced the length-to-width ratio through decreased cell elongation, increased periclinal cell division and induced the formation of rhizoid initials in the cells immediately below the apical meristem. Higher concentrations (10(-9)-10(-8) M) induced conversion of the meristem from apical to notch morphology. Cytokinins induced both red- and blue-light-mediated photomorphogenic events, suggesting stimulation of both phytochrome and cryptochrome signaling; however, cytokinin treatment only partially substituted for light in that it did not induce hermaphroditic sexual development or spore germination in the dark. Additionally, cytokinins did not increase chlorophyll synthesis in dark-grown gametophytes, which unlike angiosperms are able to produce mature chloroplasts in the dark. Cytokinin treatment had only slight effects on light-grown gametophytes. These results suggest evolutionary conservation between angiosperms and pteridophytes in the role of cytokinins in regulating photomorphogenesis.

Early embryo development in Fucus distichus is auxin sensitive.

Auxin and polar auxin transport have been implicated in controlling embryo development in land plants. The goal of these studies was to determine if auxin and auxin transport are also important during the earliest stages of development in embryos of the brown alga Fucus distichus. Indole-3-acetic acid (IAA) was identified in F. distichus embryos and mature tissues by gas chromatography-mass spectroscopy. F. distichus embryos accumulate [(3)H]IAA and an inhibitor of IAA efflux, naphthylphthalamic acid (NPA), elevates IAA accumulation, suggesting the presence of an auxin efflux protein complex similar to that found in land plants. F. distichus embryos normally develop with a single unbranched rhizoid, but growth on IAA leads to formation of multiple rhizoids and growth on NPA leads to formation of embryos with branched rhizoids, at concentrations that are active in auxin accumulation assays. The effects of IAA and NPA are complete before 6 h after fertilization (AF), which is before rhizoid germination and cell division. The maximal effects of IAA and NPA are between 3.5 and 5 h AF and 4 and 5.5 h AF, respectively. Although, the location of the planes of cell division was significantly altered in NPA- and IAA-treated embryos, these abnormal divisions occurred after abnormal rhizoid initiation and branching was observed. The results of this study suggest that auxin acts in the formation of apical basal patterns in F. distichus embryo development.

Evolutionary patterns in auxin action.

This review represents the first effort ever to survey the entire literature on auxin (indole-3-acetic acid, IAA) action in all plants, with special emphasis on the green plant lineage, including charophytes (the green alga group closest to the land plants), bryophytes (the most basal land plants), pteridophytes (vascular non-seed plants), and seed plants. What emerges from this survey is the surprising perspective that the physiological mechanisms for regulating IAA levels and many IAA-mediated responses found in seed plants are also present in charophytes and bryophytes, at least in nascent forms. For example, the available evidence suggests that the apical regions of both charophytes and liverworts synthesize IAA via a tryptophan-independent pathway, with IAA levels being regulated via the balance between the rates of IAA biosynthesis and IAA degradation. The apical regions of all the other land plants utilize the same class of biosynthetic pathway, but they have the potential to utilize IAA conjugation and conjugate hydrolysis reactions to achieve more precise spatial and temporal control of IAA levels. The thallus tips of charophytes exhibit saturable IAA influx and efflux carriers, which are apparently not sensitive to polar IAA transport inhibitors. By contrast, two divisions of bryophyte gametophytes and moss sporophytes are reported to carry out polar IAA transport, but these groups exhibit differing sensitivities to those inhibitors. Although the IAA regulation of charophyte development has received almost no research attention, the bryophytes manifest a wide range of developmental responses, including tropisms, apical dominance, and rhizoid initiation, which are subject to IAA regulation that resembles the hormonal control over corresponding responses in seed plants. In pteridophytes, IAA regulates root initiation and vascular tissue differentiation in a manner also very similar to its effects on those processes in seed plants. Thus, it is concluded that the seed plants did not evolve de novo mechanisms for mediating IAA responses, but have rather modified pre-existing mechanisms already operating in the early land plants. Finally, this paper discusses the encouraging prospects for investigating the molecular evolution of auxin action.

What is Chondriolejeunea?

Abstract Chondriolejeunea , the former subgenus of Cololejeunea is raised to the generic rank on the base that the supposed large styli are in reality underleaves, inserted alternately to the two cell rows of ventral merophytes and having rhizoid initials at their base. Chondriolejeunea pseudostipulata (Schiffn.) Kis & Pocs, Chondriolejeunea shimizui (N. Kitag.) Kis & Pocs, Chondriolejeunea shimizui var. phangngana (N. Kitag.) Kis & Pocs, Chondriolejeunea chinii (Tixier) Kis & Pocs, comb. et stat. nov. Cololejeunea shimizui subsp. shihuishanensis M.L. So & R.L. Zhu, syn. nov. Speculation on the possible ways of evolution of tribe Cololejeuneae .

Physode formation in embryos of Phyllospora comosa and Hormosira banksii (Phaeophyceae)

Phenolic compounds, packaged within vesicles known as physodes, are a major cytoplasmic constituent of eggs and zygotes of the Australasian fucoids Hormosira banksii (Turner) Decaisne and Phyllospora comosa (Labillardière) C Agardh. Light and transmission electron microscopy in conjunction with the actin inhibitors cytochalasin and latrunculin and the Golgi disruptor Brefeldin were used to investigate physode biogenesis in Hormosira and Phyllospora zygotes and embryos. Our results show that physodes are formed in the perinuclear region of the cell. Contrary to many early reports, no evidence was found that physode genesis is associated with chloroplasts. Instead, the Golgi apparatus and the endoplasmic reticulum are implicated in physode formation. Physodes are produced in large quantities around the nucleus just before periods of active wall deposition, particularly during rhizoid initiation and crosswall formation. Subsequently, they move from their central location to the sites of wall deposition.

Spore Age and Sterilization Affects Germination and Early Gametophyte Development of Platycerium bifurcatum

The effects of spore age and sterilization on spore germination and early gametophyte development were investigated in the fern, Platycerium bifurcatum. The highest germination per- centage of sterilized spores was obtained with 2-3 month old spores. Further increase in spore age leads to a decline in germination and primary rhizoid initiation. In contrast, spore age had no effect on the germination of unsterilized spores, where maximum response was observed with spores of both storage periods tested, 2 and 14 months. Increasing spore age delays early game- tophyte development. In cultures of sterilized spores, this was evident from both a decrease in the length of the primary rhizoid and the decreased number of rhizoids and cells per gametophyte. Although longer primary rhizoids developed from unsterilized spores of both ages, after 10 days other growth parameters of gametophytes were similar or even lower compared to those from sterilized spores.

An Autoradiographic Investigation of Protein Synthesis during Rhizoid Differentiation in Pteris vittata

In this autoradiographic study of protein synthesis during rhizoid differentiation in P vittata, total grain counts increase seven-fold, from 42 grains in the non-differentiated stage to 295 in the premitotic corona stage. This almost doubles to 624 in the postmitotic internally- segmented rhizoid stage (irc) and increases five times to 3,079 in the wheel stage that follows; the count then doubles to 6,120 grains in the later protrusion stage and approximately doubles again to 13,487 in the final young rhizoid stage. These results show that rhizoid initiation, differentia- tion, and growth are attended by significant increases in protein syntheses. Although the grain count over the cytoplasm increases seven-fold in the corona when compared to the non-differ- entiated cell, the relative percentage distribution for this compartment remains unchanged. How- ever, grain counts over the cytoplasm of postmitotic stages increase from 80% (irc) to 96% (wheel) to 97% (protrusion) and to 99% (young rhizoid) of the total count. In contrast, nuclear labeling reached a stationary phase in the irc and in the subsequent postmitotic stages. The first rhizoid in Pteris vittata L. is produced when the spore divides mitotically at germination; however, rhizoid formation may be more clearly observed later in gametophyte development, i.e., in the enlarged, vacuolated thallus cells that mature behind the regions of cell division and enlargement (Crotty, 1967). Increases in cytoplasmic RNA in the vicinity of the spore nucleus during primary rhizoid formation in Matteuccia struthiopteris (L.) Tod. were reported by Gantt and Arnott (1965). Extensive cytochemical studies of Pteris vittata by Crotty (1961, 1967) have provided detailed descriptions and analyses of the events at the light microscope level that accompany secondary rhizoid devel- opment, including RNA, protein, and polysaccharide syntheses. Additionally, these studies described a succession of developmental stages that occurred during the pre- and postmitotic rhizoid differentiation process (Fig. 1). Using a precise autoradiographic technique, Cohen and Crotty (1979) reported that the RNA in the anastomosing cytoplasmic strands around the nucleus of the corona (first stage of rhizoid differentiation) originated in the premitotic nu- cleus of this stage. In a later autoradiographic study, Cohen and Crotty (1990) demonstrated the existence of specific patterns of RNA synthesis in the stages of rhizoid differentiation in P vittata. The purpose of this study was to determine if protein synthesis during rhi- zoid differentiation, as measured by radioactive leucine uptake, could also be quantified and resolved into specific patterns. And, if so, can the results show a meaningful relationship to the earlier studies in P. vittata? In fact, the results of this investigation demonstrate that rhizoid differentiation is attended by

Jasmonic acid promotes division of fern protoplasts, elongation of rhizoids and early development of gametophytes

The effects of jasmonic acid (JA) on spore germination, early gametophyte development and sporophytic protoplast culture of the fern Platycerium bifurcalum (Cav.) C. Chr. were investigated. JA and no influence on spore germination and primary rhizoid initiation, but significantly promoted early gametophyte development, which was evident from the longer primary rhizoids as well as the higher number of rhizoids and cells per gametophyte. Jasmonic acid (1 μM) also promoted the transition of gametophytes from a filamentous to a planar growth. Optimal primary rhizoid elongation and highest cell division activities in the gametophytes were observed at 0.01–1 μM JA, while the highest number of rhizoids on gametophytes was obtained at 0.1–1 μM JA. Jasmonic acid (0.01 μM) also stimulated initial protoplast divisions. Except for the experiment in which the effect of JA on germination was tested. JA concentrations exceeding 1 μM did not promote cell elongation or cell division but were instead inhibitory. On the basis of these findings, we propose that JA may be involved in early stages of P. bifurcatum development.

Polar distribution of annexin-like proteins during phytochrome-mediated initiation and growth of rhizoids in the ferns Dryopteris and Anemia.

Although the calcium requirement of phytochrome-mediated fern spore germination and early rhizoid growth is well established, the calcium-binding proteins that serve as transducers for these responses are not known. Here we report the presence of annexin-like proteins in germinating spores of Dryopteris filix-mas (L.) Schott and Anemia phyllitidis (L.) Sw. and evidence that they may be important participants in early photomorphogenic changes in gametophytes. Immunolocalization and immunoblot assays of these proteins were carried out using polyclonal antibodies raised either against a 35-kDa annexin-like protein from pea or against anchorin CII from chicken. Western-blot analysis showed that crude protein extracts obtained from both species after red-light treatment contained two cross-reactive protein bands with molecular weights around 70 kDa. These proteins were annexin-like in that they bound to a phosphatidylserine affinity column in a calcium-dependent fashion. Using this column, two protein bands around 70 kDa, i.e. 67 and 73 kDa, were partially purified together with proteins at 36 kDa and a doublet at 54 kDa. Proteins of these latter molecular weights are suggested to be members of the annexin family, but no cross-reactivity could be found between these and the two antibodies used in our investigations. Immunodetectable levels of these proteins were observed only after light-mediated induction of spore germination. Imaging of the immuno-localization patterns observed with both antibodies showed that the annexin-like proteins are concentrated at the extreme tips of the rhizoids in D. filix-mas and A. phyllitidis during rhizoid initiation and all stages of elongation. We suggest that these proteins may play a major role in the tip-oriented exocytosis events that are critical for the initiation and growth of fern rhizoids.

Response to auxin by cells of Riella helicophylla during reversible arrest in different cell-cycle phases

When cells of the unistratose meristem of Riella helicophylla (Bory et Mont.) Mont. are reversibly arrested at G1/S transition by treatment with the inhibitor of thymidylate synthase 5-fluorodeoxyuridine, with the inhibitor of DNA polymerase α, aphidicolin, or with an inhibitor of late DNA synthesis, 5-aminouracil, they continue to expand. Simultaneous supply of auxin enhances cell expansion, while simultaneous addition of the auxin antagonistp-chlorophenoxyisobutyric acid prevents cell enlargement. When the meristematic cells are reversibly arrested during G1 phase by treatment with chlorsulfuron, an inhibitor of acetolactate synthase, cell size remains unchanged, but it increases when auxin is supplied simultaneously. Simultaneous application of chlorsulfuron during treatment with 5-fluorodeoxyuridine, aphidicolin or 5-aminouracil, prevents cell expansion. After recovery from 5-fluorodeoxyuridine, aphidicolin or 5-aminouracil treatment, the cellular pattern of the meristem is severely disturbed, while in combination withp-chlorophenoxyisobutyric acid or chlorsulfuron, meristem differentiation is almost unaffected. During reactivation of divisional functions in mature cells induced by isolation of tissue fragments, blockage of DNA synthesis by aphidicolin causes an augmentation of rhizoid initials which are characterized by enhanced RNA synthesis. Exogenous supply of auxin is required for outgrowth of these rhizoid initials, while, in untreated fragments, auxin for rhizoid growth is provided probably by the dividing cells. When reactivation of divisional functions in tissue fragments is reversibly inhibited by chlorsulfuron, no changes in the cells are discernible and application of auxin has no effect; after release from blockage the cells regenerate like those in untreated fragments. The results suggest that the phases of the cell cycle differ with regard to auxin synthesis and competence to respond to auxin. Probably, during cycle inhibition at G1/S or S a rising auxin level causes disintegration of cell-cycle events.

Effects of salinity and bromine on zygotes and embryos of Fucus vesiculosus from the Baltic Sea

Zygotes and young embryos derived from Fucus vesiculosus collected in the archipelgo of Stockholm in 1990, growing at a salinity of 6 to 7‰ S, were cultured under different salinity conditions and in media of different bromine concentrations. Optimum salinity was 10 to 12‰ S for germination (rhizoid initiation) while apical hair formation showed a broader tolerance curve with an optimum at 8 to 14‰ S. Bromine caused inhibition of early development of F. vesiculosus. At 6‰ salinity a 50% reduction in germination took place at 10.0 mM Br and at 1.25 mM Br only 4.7% of the embryos developed apical hairs, as compared to 32.7% in the control. Bromine toxicity decreased at higher salinities. The results indicate that F. vesiculosus in the Baltic Sea has diverged from its Atlantic progenitors and to some extent acclimated to low salinity. Still, the salinity in the normal environment of the tested population is lower than optimum, leading to a lower degree of germination of zygotes, a lower growth rate of young embryos and probably also a higher sensitivity to additional stress factors such as chemical pollution.

The anthocerote chloroplast: a review

SUMMARYThis review covers previous data, together with new information from our laboratories, on the subject of the anthocerote chloroplast. Unlike all other archegoniates, most species of anthocerote have pyrenoids in their chloroplasts. The pyrenoid is the site of accumulation of the first enzyme in the C3 photosynthetic cycle, ribulose bispbosphate carboxylase/oxygenase. Unlike most algae, the hornwort pyrenoid is composed of distinct subunits, numbering up to several hundred. Pyrenoid morphology is quite variable among the genera in shape, fine structure, and distribution of inclusions. Another unique feature of the anthocerote chloroplast is the presence of thylakoids that connect adjacent granal stacks at right angles to the long axis of the granum (so‐called channel thylakoids), resulting in a 'spongy’arrangement of the thylakoid system. The granal stacks of anthocerotes are like the‘pseudograna’of green algae because they lack the highly‐curved end membranes typical of all other embryophytes. The channel thylakoids are enriched in photosystem (PS) I and the grana are enriched in PS II. The chloroplast envelope is a double membrane structure with regions of appression, much like that of other green plants. The apieal cell of the gametophyte contains chloroplasts similar to the mature chloroplasts of the thallus, although certain gametophytic tissues may contain underdeveloped plastids. Chloroplasts in cells around Nostoc colonies and in cells invaded by mycorrhizal fungi have thylakoids mainly in pairs, and small or absent pyrenoids. A number of similarly reduced plastids are noted in the placental cells at the sporophyte/gametophyte junction and in developing spores. The greatest reduction is observed in spermatid cell plastids, which at maturity consist of only a small starch grain surrounded by the envelope. Chromoplast‐like organelles are found in the cells of the antheridial jacket in some genera; these contain numerous osmiophilic globules that are probably pigment aggregations. Colourless bead‐like plastids occur in the rhizoids; these seem to develop by fragmentation of the single chloroplast in the rhizoid initials, concomitant with the loss of chlorophyll. Chloroplast division is a tightly controlled process and, in uniplastidic species, always occurs just before nuclear division, with the participation of a unique system of chloroplast‐associated microtubules. The number of chloroplasts per cell is quite variable in some genera, although most species have but a single chloroplast in each cell of the gametophyte. Chloroplast shape is also variable from ellipsoidal, dumbbell‐shaped, to irregular. These data indicate that the anthocerote chloroplast is unique among the embryophytes and are in line with the notion of an isolated position in the plant kingdom. Certain features of chloroplast morphology appear to be typical of certain genera and might prove useful in taxonomic decisions at the generic level.

Light-Dependent Inhibition of Cell Division and Rhizoid Elongation in Gemmae of the Fern, Vittaria graminifolia

Gametophytes of the shoe-string fern Vittaria graminifolia produce linear, six-celled propagules called gemmae. The terminal cells of each gemma elongate into primary rhizoids in culture, and the inner body cells divide asymmetrically to produce prothallial or rhizoid initials. The initiation of both asymmetric cell division and rhizoid elongation is delayed by light intensities greater than 2 w/m2. The maximal rates of cell division and rhizoid elongation are unaltered. A 24-hr pulse of high light intensity delays cell division and rhizoid elongation to the same extent, whenever applied during the first 3 d of culture. The model we propose for cell division hypothesizes the existence of a preparatory phase of finite duration prior to mitosis that is sensitive to light intensity. If a cell is irradiated by light intensities greater than 2 w/m2 while in the preparatory phase, its entrance into mitosis is delayed. A similar model is proposed for the initiation of rhizoid elongation. Despite the fact that both cell division and rhizoid elongation are dependent on photosynthesis, direct measurements of CO2-uptake rates show that the inhibitory effects of high light intensities are not due to an inhibition of photosynthesis.

LIGHT‐DEPENDENT INHIBITION OF CELL DIVISION AND RHIZOID ELONGATION IN GEMMAE OF THE FERN, VITTARIA GRAMINIFOLIA

Gametophytes of the shoe‐string fern Vittaria graminifolia produce linear, six‐celled propagules called gemmae. The terminal cells of each gemma elongate into primary rhizoids in culture, and the inner body cells divide asymmetrically to produce prothallial or rhizoid initials. The initiation of both asymmetric cell division and rhizoid elongation is delayed by light intensities greater than 2 w/m2. The maximal rates of cell division and rhizoid elongation are unaltered. A 24‐hr pulse of high light intensity delays cell division and rhizoid elongation to the same extent, whenever applied during the first 3 d of culture. The model we propose for cell division hypothesizes the existence of a preparatory phase of finite duration prior to mitosis that is sensitive to light intensity. If a cell is irradiated by light intensities greater than 2 w/m2 while in the preparatory phase, its entrance into mitosis is delayed. A similar model is proposed for the initiation of rhizoid elongation. Despite the fact that both cell division and rhizoid elongation are dependent on photosynthesis, direct measurements of CO2‐uptake rates show that the inhibitory effects of high light intensities are not due to an inhibition of photosynthesis.

Effects of osmotic stress on gamete size, rhizoid initiation and germling growth in fucoid algae

Effects of osmotic stress on gamete size were studied for Fucus vesiculosus; spermatozoids behaved as osmometers when the osmotic pressure of the external artificial seawater medium (ASP12S) was changed. The non-osmotic volume was approximately 44% of the spermatozoid volume in full-strength ASP12S. Unfertilized eggs behaved as osmometers but with a relatively small change in volume. The apparent non-osmotic volume of the egg was approximately 93% of the volume in full-strength ASP12S. The significance of these observations and their possible implications for fertilization and cross-fertilization in situ is discussed. Rhizoid initiation in zygotes of Fucus spiralis and F. vesiculosus decreased with increasing salinity. A decrease also occurred when F. vesiculosus was incubated in low salinity media, though this was not the case in F. spiralis. Subsequent growth patterns of the germlings of both fucoid algae were similar, although F. vesiculosus had a higher growth rate than F. spiralis. Both species showe...

Accumulation of amyloplasts on the bottom of normal and inverted rhizome tips of Caulerpa prolifera (Forssk�l) Lamouroux

Caulerpa prolifera (Chlorophyta) exhibits a gravimorphogenetic response to inversion by switching the site of new rhizoid initiations to correspond with the new direction of the gravity stimulus. When plants were fixed at 6 and 24 h after being held in either a normal or an inverted position the switch in the site of organ differentiation, upon inversion, was found to be preceded by the accumulation of starch-containing amyloplasts on the bottom of the rhizome. Approximately 1.5-2.0 times as many amyloplasts were found at the bottom of normal or inverted rhizomes as compared with the top in a region extending from 200 to 1,000 μm behind the rhizome tip. All new rhizoid initials were located in the region of amyloplast accumulation and each rhizoid initial contained numerous amyloplasts.

Chlorotetracycline-binding surface regions in gemmalings of Riella helicophylla (Bory et Mont.) Mont.

The unistratose thallus of the gemmaling of Riella helicophylla is divided into an apical growth lobe with the meristem, an intermediate pillar, and a basal rhizoidal lobe. This organization can be correlated with a distinct fluorescence pattern of wall and membrane after treatment with chlorotetracycline. Mature cells of the growth lobe are distinguished by two chlorotetracycline-binding surface regions (CSR) with a diameter of 6-12 μm in the middle of both outer cell surfaces. Meristematic cells are devoid of CSR. The same is true for cells of the pillar which elongate under low light intensity. Rhizoid initials have an enlarged CSR on the site where the rhizoidal tube will emerge, whereas the opposite cell surface lacks any chlorotetracycline fluorescence. With the beginning of the extension of the rhizoid, CSR remains as a ring around the base of the tube. Darkness, plasmolysis, and sulfhydryl reagents inhibit the fluorescence of CSR, whereas calcium antagonists in addition suppress the fluorescence of the rhizoids. Cytochemical methods demonstrate that sulfhydryl proteins and anionic polysaccharides are involved in adsorbing chlorotetracycline in this region. Surface electron-microscopic preparations reveal a local depression of the wall covered with amorphous material.

Transport of 14 C-indoleacetic Acid in the Hepatic Marchantia polymorpha

Tracer experiments using exogenous 14C-indoleacetic acid showed that its transport is localized in the midrib cells of Marchantia polymorpha vege- tative thalli. Transport occurs both acropetally and basipetally at approximately the same velocity, but basipetal transport is significantly greater in intensity. In- terference with energy-yielding metabolism due to anaerobic conditions, iodoacetic acid or sodium fluoride reduced basipetal transport by 40-50%. Disruption of cel- lular integrity via centrifugation or cytochalasin B reduced basipetal transport by 30-40%. IAA transport in M. polymorpha gametophytes is essentially the same as in vegetative axes of flowering plants with respect to all parameters compared. The presence of naturally occurring auxin in gametophytic tissue of Marchantia poly- morpha has been demonstrated by both chemical methods and bioassays. As early as 1956, an endogenous compound was isolated from thalli that gave positive results with the Avena curvature test (La Rue & Narayanaswami 1957). Schneider et al. (1967) isolated an Erlich and Salkowski-positive ethanol-soluble compound with an Rf corresponding to indoleacetic acid (IAA). La Rue and Narayanaswami (1957) also present evidence for the localized synthesis of auxin in the apical region of the thallus, and Maravolo (1976) dem- onstrated that IAA was the major transport form in Marchantia. Endogenous growth regulators exert correlative action over developmental processes in bryophytes analogous to their action in tracheophytes. Their correlative activity is dependent upon absolute concentrations, gradients, differential rates of synthesis, inacti- vation and the direction and intensity of transport. The polar distribution of auxin in Marchantia polymorpha assumes an important regulatory role in apical dominance, gem- mae-cup formation and rhizoid initiation through its influence on the balance between cell division and elongation (Maravolo & Voth 1966; Binns & Maravolo 1972; Davidonis & Munroe 1972; Rota & Maravolo 1975). Hebant (1970) and Scheirer (1977) demonstrated that some bryophytes possess spe- cialized cells within the midrib tissue with morphological characteristics of phloem sieve tube cells. Translocation of auxin in Marchantia is conducted in a similar transport system. This transport is strictly basipetal, and was adversely affected by triiodobenzoic acid, cinnamic acid and ethylene, all inhibitors of polar transport in tracheophytes (Maravolo 1976). The present investigation derives from the latter and investigates the nature of several aspects of the auxin transport mechanism in Marchantia.

Effect ofLantana camara L. extract on fern spore germination

Extracts of root, stem, leaf and inflorescence ofLantana camara Linn., (Verbenaceae) inhibited exine bursting, rhizoid initiation and protonemal initiation of spores of the fernCyclosorus dentatus (Forsk.) Ching. The leaf extract was found to be qualitatively and quantitatively most potent in its inhibitory effect. Attention is drawn to the fact that further spread ofLantana camara at Mt. Abu, Rajasthan, India may lead to the complete destruction, of the sizeable pteridophytic component in this locality, the richest vegetationally in Rajasthan.

The Rediscovery of Rhabdodontium buftonii (Broth. & Geh. in Broth.) Broth.

A recent collection of Rhabdodontium buftonii (Broth. & Geh. in Broth.) Broth. is reportedfrom a site in northern Tasmania about one hundred miles north of the only two previous collections. Examination of the three known collec- tions requires corrections in the original description: the plant grows submerged in rapidly flowing water; only a very short prostrate axis; prorate cells in the upper lamina; and a basally bistratose leaf lamina. On the basis of these and other observations, very tentative agreement is expressed with the traditional placement of this monotypic genus in the Pterobryaceae. The genus Rhabdodontium is a monotypic Tasmanian endemic that has not been found many years and ... a rediscovery is much to be hoped for (Scott & Stone 1976). The senior author found this plant densely covering several square meters of rocks in very rapid currents of the Mackintosh River in northern Tasmania. An updated descrip- tion of the species and its habitat based upon comparative study of the original collections (Bathurst Harbor, Bufton 91; Hartz Mtn., Bufton 17-BM, HOB), and the recent Mackin- tosh River collection (Norris 33753, 1 February 1974-HSC) is presented. Rhabdodontium buftonii (Broth. & Geh. in Broth.) Broth. (Fig. 1-9) Plants aquatic, glossy, dark-green to reddish brown. Prostrate stem extensively branched with the branches tangled in a rhizoid-covered cushion. Prostrate stem segments black and denuded of leaves, mostly less than 5 mm long, then arching away from the substratum as flexuose streamers in the water currents. These stems extend to 15 cm with radially inserted branches up to 2 cm long arranged in a more or less planar, loosely plumose system. Leafy axes very strongly julaceous, 1.5-2.0 mm in diameter, abruptly attenuate at the condensed-fusiform apex. Lower portions of stems denuded of leaves with contiguous younger portions having the leaves lacerated into numerous linear strips. Plant not at all heterophyllous but basal leaves of stems and branches small and gradually enlarged in the more distal regions. Leaves ecostate, spirally 5-ranked, 1.8-2.3 x 0.7-0.9 mm, deeply concave above the sheathing lower 1/6. Leaf attached along about 1500 of stem circumference with the line of attachment nearly straight and perpendicular to the long axis of the stem. Leaves obovate to ovate, abruptly expanded above the sheathing base and broadest above the middle; obtuse to bluntly short- acuminate. Margin plane to erect, entire to minutely crenulate by projecting cell angles. Alar cells irregularly rectangular, 2-6:1, 8-9 ~m wide, lumen/wall ratio 2-4:1, not or sparingly pitted, poorly and gradually different from median cells. Median and basal, juxtacostal cells spinulose, 10-18:1, 6- 7 um wide, lumen/wall ratio 1.5-3:1, prominently pitted especially at cell ends, lightly prorate. Leaf bi- or tristratose in lower 1/4 with bistratose streaks often extending to mid-leaf. Paraphyllia and gemmae lacking. Pseudoparaphyllia filamentose, quickly deciduous from the bases of developing branches. Rhizoids restricted to prostrate stems, stem bases and branch insertions, pale to reddish- brown, smooth and thick-walled, sparingly branched. Rhizoid initials isodiametric, 12-14 /m in di- ameter, arising secondarily (by dedifferentiation) in adaxial, median portions of leaf insertion and then increasing in number and lateral extent to form a swollen blackish callus. Axillary hairs 12-14 pm wide by 0.9-1.0 mm long, numerous, equally spaced in median 2A of leaf insertion with 3-5 basal