The modernistic setting of the campus of the University of East Anglia was the venue for this year’s AGM meeting, though many of the concrete structures that must have looked futuristic in the 1960s are now showing their age, with a attractive veneer of mosses and lichens becoming evident. Thanks are due to all the speakers at this meeting and especially to Mr Richard Fisk, whose efficient and caring organization of the weekend ensured that a good time was had by all. The following summaries of talks have been provided by the authors.
Prof. J.G. Duckett (Queen Mary and Westfield College, London), Mr N.G. Hodgetts (JNCC, Peterborough) & Mr H.W. Matcham (Chichester): Bryologizing in Lesotho.
The object of this trip, funded by the British Council, was to carry out bryophyte surveys on the last remaining substantial piece of forest in the country, Leucosidea woodland in the upper Hlotse valley, and on montane bogs, and also to make bird lists for each locality as far as possible, with the intention of drawing attention to the importance of these habitats for bryophytes and the threats to them, and making recommendations for their conservation. The fieldwork was carried out with the co-operation of the Lesotho Highland Development Authority (LHDA). Additional principal members of the expedition were Mrs Louise Matcham, who listed all the birds seen, and Setenani Nkopane, an ecologist with the LHDA.
Lesotho is little-known bryologically, with a current list of 165 mosses and 39 liverworts. A country of c. 30,000 sq. km (11,700 sq. miles), it is surrounded by South Africa, and is the only country in the world with all its borders over 1000 m. The geology is extremely simple: the western lowlands, which are mostly extremely degraded because of overgrazing and deforestation, being sandstone, the eastern uplands basalt, though there are a few higher sandstone outcrops. There are no native forests left in the lowlands, but much planting of poplars, eucalyptus and pine has taken place. The overgrazing has been so severe in the lowlands that wide ravines, or dongas, have appeared because of erosion. The highland parts of the country, where the vegetation is less degraded, consist of a series of roughly north-south mountain ranges, all of which exceed 3000 m in altitude, culminating in the Drakensbergs on the eastern border with Natal.
Time was found for some general bryology in the lowland sandstone areas around Roma, Maseru, Leribe and Qacha’s Nek. Rock outcrops produced several liverworts new to the country. Reservoir and pool margins were productive for species of Riccia and the strange little Cladophascum gymnomitrioides. Epiphytes were rather few, but where they occurred typical species included Orthotrichum diaphanum, Tortula ammonsiana, T. pagorum and Fabronia pilifera. Other common species included Plagiochasma rupestre, Barbula crinita, Bartramia hampeana, Bryum alpinum, B. torquescens, Brachythecium implicatum, Ptychomitrium cucullatum, Trichostomum brachydontium and members of the Leskeaceae (Pseudoleskea and Lindbergia). Other attractions of the sandstone included some frankly unconvincing dinosaur footprints.
Several days were spent in the woodland of the upper Hlotse valley, where Leucosidea (Rosaceae) is the dominant tree, some specimens of which are up to 300 years old. The woodland here, the only known surviving relic of Leucosidea forest in Lesotho, is unofficially protected by having a large pipeline construction scheme at the bottom, thus preventing access from the villages further down the valley. It is rather Mediterranean in character, fairly dry, with a lot of epiphytic Orthotrichaceae. One almost untouched area was found in a ravine, with bamboo and luxuriant bryophytes. Bryophytes seen included Acanthocoleus chrysophyllus, Plagiochila squamulosa var. crispulo-caudata, Leucolejeunea rotundistipula, Anacolia breutelii, Anoectangium wilmsianum, Haplocladium angustifolium, Orthotrichum subexsertum, Thuidium matarumense and Zygodon leptobolax.
Moving to the north of the country, several of the highland bogs in the Oxbow and Mokhotlong areas were surveyed. There is no Sphagnum in these bogs, but they are peat-forming, composed mainly of a distinctive and attractive suite of vascular plants such as the endemic Aponogeton ranunculiflorus in pools, and a large number of small, flowering herbs. Many of the bogs have deteriorated badly in the last 30 years because of overgrazing. The few we saw that remained relatively intact had a limited but interesting bryophyte flora, much of which had to be extracted from the rather spiky tussocks of Merxmuellera grass. Species included Haplomitrium gibbsiae and Leptodontium proliferum, both new to Africa, as well as more common plants. The high altitude basalt rock crags that often stood over the margins of the bogs were also extremely interesting for bryophytes, particularly on the border with Natal at Sani Pass, where there seemed to be a distinctly Antarctic element to the bryophyte flora. Some of the more notable plants recorded included Adelanthus lindenbergianus, Scapania cuspiduligera, Amphidium tortuosum, Andreaea spp., Anomobryum drakensbergense, Gymnostomum bewsii, Tortella fragilis, and the Drakensberg endemics Quathlamba debilicostata and Orthotrichum oreophilum. The recently described Cryptomitrium oreades was seen on a riverside near Oxbow.
Several days were spent examining Leucosidea woodland in Natal, where, because of climatic factors, the bryophyte flora was quite different from that of the Lesotho woodland, being generally richer in species and more luxuriant, and including tropical elements such as members of the Lejeuneaceae and Meteoriaceae.
The expedition was therefore successful purely as a bryophyte collecting trip, with many species found new to Lesotho, several new to southern Africa and to the continent, and at least one probably new to science. It is hoped that our findings (in the form of a report to the British Council) will contribute to the conservation of some of the unique and highly threatened areas examined.
Mr K.I. Kingham, Prof. J.G. Duckett, Dr A.R. Leitch and Dr M.C.P. Glyn (Queen Mary and Westfield College, London): Nuclear and cytoplasmic differentiation in the protonemata of Funaria hygrometrica.
Different cell types have nuclei that vary in shape, volume, structure (Bennett, 1984), organization of chromatin (Manueldis & Borden, 1988) and distribution of nuclear proteins (Zirbil et al., 1993).
In this study, the changes in cytoplasmic organization and interphase nucleus reorganization are being examined in the caulonemata of the moss Funaria hygrometrica Hedw. Moss caulonemata are ideal for investigating inter-relationships between nuclear and cytoplasmic differentiation as these single files of differentiating cells show consistent developmental features. Fully differentiated caulonemal cells are morphologically similar to the food conducting tissues of gametophytes and sporophytes of mosses (Ligrone & Duckett, 1994) and parallel the development of phloem in the stele of tracheophytes. Kingham et al. (1995) found that, near the apices of caulonemal filaments, phenomena such as polarized tip growth, nuclear and cell division and side branch initiation are associated with haploid nuclei (IC DNA amount, 0.5 pg). These are spherical or slightly oval, with no blocks of condensed chromatin, and have a large nucleolus consisting mainly of a granular component. As caulonemal cells mature, the plastids become suspended along endoplasmic strands, the cell walls become thickened and pigmented and the majority of the organelles lie towards the apical ends of the cells. These cytoplasmic changes occur alongside major reorganization of the nucleus, which becomes endoreduplicated by amplification of the IC genome to give mature nuclei of between 4-8C. This amplification is associated with increased nuclear volume whilst elongation of the nucleus results in a larger surface area of the nuclear envelope. Within the nucleolus, amplified ribosomal RNA genes form blocks of heterochromatin, there is an overall reduction in nucleolar volume due to a diminution in the granular component and nucleolar components become spatially separate. During this major reorganization, there is a stable distribution of the ‘D’ polypeptide involved in pre-mRNA splicing.
DNA methylation is thought to be a control element for gene expression (Watt & Molly, 1988) and is involved in many fundamental processes, including genomic imprinting (Lock et al., 1987) and embryo development (Li et al., 1992). It is also strongly implicated in regulating developmental transitions in higher plants (Burn et al., 1993), where expression patterns are correlated with differential methylation of the alleles or their promoter regions. To understand further the role of nuclear differentiation in development of Funaria hygrometrica caulonemata, we have treated the genome with drugs that reduce the levels of DNA methylation. Methylation is a post-synthetic modification of the DNA performed by methyltransferase; in plants it can occur by methylation of the cytosine base in CG dinucleotides and in CXG triplets (Gruenbaum et al., 1981). Using 5-azacytidine (5azaC) and dihydroxypropyladenine (DHPA) to hypomethylate the genome, we are able to perturb normal development. 5-azaC, a base analogue of cytosine, inhibits methylation (preferentially at CG dinucleotides) by incorporating into the genome and inhibiting methyltransferase activity (Li et al., 1970). DHPA inhibits S-adenosyl hydrolase (a down stream enzyme in methylation metabolism), causing feedback inhibition of CXG methylation (Benes et al., 1984). Our investigations are showing considerable changes to nuclei and cytoplasm following hypomethylation with both 5-azaC and DHPA.
Benes M, Holly A, Melichor O. 1984. Effect of 9-(2,3-dihydroxypropyl) adenine (DHPA) on seedling roots of Vicia faba L. in comparison with adenine, adenosine and some cytokinins. Biologia Plantarum (Praha) 26: 144-150.
Bennett MD. 1984. Nuclear architecture and its manipulation. In: Gustafson JP. (ed), Gene manipulation in plant improvement. New York: Plenum Publishing Corporation, 469-502.
Burn JE, Bagnall DJ, Metzger JD, Dennis ES, Peacock, WJ. 1993. DNA methylation, vernalization, and the initiation of flowering. Proceedings of the National Academy of Science USA 90: 287-291.
Gruenbaum Y, Cedar H, Razin A. 1981. Sequence specificity of methylation in higher plants. Nature 292: 860-862.
Kingham, K.I., Duckett, J.G., Glyn, M.C.P. & Leitch, A.R. 1995. Nuclear differentiation in the filamentous caulonema of the moss Funaria hygrometrica. New Phytologist (in press).
Li E, Bestor TH, Jaenisch R. 1992. Targeted mutation of the DNA methyltransferase gene results in embryonic lethality. Cell 69: 915-926.
Li LH, Olin EJ, Buskirk HH, Reinetic LM. 1970. Cytotoxicity and mode of action of 5-azacytidine on L1210 leukemia. Cancer Research 30: 2760-2769.
Ligrone R, Duckett JG. 1994. Cytoplasmic polarity and endoplasmic microtubules associated with the nucleus and organelles are ubiquitous features of food conducting cells in bryoid mosses (Bryophyta). New Phytologist 127: 601-614.
Lock LF, Takagi FN, Martins GR. 1987. Methylation of Hprt gene on the inactive X occurs after chromosome inactivation. Cell 48: 39-46.
Manuelidis L, Borden J. 1988. Reproducible compartmentalization of individual chromosome domains in human CNS cells revealed by in situ hybridization and three-dimensional reconstruction. Chromosoma 96: 397-410.
Watt F, Molly PI. 1988. Cytosine methylation prevents binding to DNA of HeLa cell transcription factor required for optimal expression of adenovirus major late promoter. Genes and Development 2: 1136-1143.
Zirbil RM, Mathieu UR, Kurz A, Cremer T, Lichter P. 1993. Evidence for a nuclear compartment of transcription and splicing located at chromosome domain boundaries. Chromosome Research 1: 93-106.
Dr A. Russell, Dr M. Leech & Dr T. Wang (The John Innes Centre): Searching for a signal for plant hormone action in the moss Physcomitrella patens.
The plant hormone cytokinin is known to be involved in a number of processes in higher plants, such as shoot formation and chloroplast biogenesis. To date, however, very little is known concerning the action of cytokinins in promoting these effects. Cytokinins are present in mosses and cause single-celled protonemal side-branches to undergo the morphogenetic transition to meristematic buds. We are therefore using this system to try to gain insights into how the cytokinin signal is translated into a response by the cell.
Time-lapse video microscopy has been used to record the timing of the change from side-branch initial to gametophore-bud initial. This has also revealed that the fate of cell divisions of a developing gametophore is established when the bud is still a single cell. From such microscopy, it appears that the main early effects of cytokinin in P. patens are the inhibition of polarized tip growth and an increase in the numbers of chloroplasts.
It has been suggested that, similar to hormones in animals, cytokinins might work by a signal transduction system in which calcium acts as a ‘secondary messenger’. To try to detect any increase in calcium in cells incubated in cytokinin, moss protonema have been microinjected with calcium-sensitive fluorescent dyes. Images of calcium distribution in protonemal cells have been obtained but calcium increases in cells incubated in cytokinin have not been visualized using these dyes.
Experiments with the calcium ionophore A23187, which facilitates the transport of calcium across the cell membrane, have suggested that calcium may be a messenger involved in responses to light such as side-branch formation. Increasing the calcium concentration of protonemal cells in this manner does not mimic cytokinin-induced bud formation, contrary to earlier reports (Saunders & Hepler, 1982).
- patens has been tranformed with the gene for apoaequorin from the jellyfish Aequorea victoria. This compound produces luminescence on binding to calcium in the presence of coelenterazine. Transformed moss does not respond to plant hormones with a rise in cytosolic calcium as indicated by aequorin, but does respond to touch and cold-shock with with considerable transient changes in cytosolic calcium. These responses are similar to those found for tobacco (Knight et al., 1991) and show that plants are extremely sensitive to touch stimuli. Experiments with transformed moss have also demonstrated that moss can cope with large changes in cytoplasmic calcium levels.
As well as exploring possible roles for signal molecules in cytokinin signalling, we are taking a molecular approach and looking for changes in gene expression associated with plant hormones. A gene has been isolated in P. patens that corresponds to a gene involved in flowering in higher plants. Results indicate that this is a gene associated with the development of gametophores. Further work is required to determine whether plant hormones are involved in the regulation of this gene.
Saunders MJ, Hepler PK. 1982. Calcium ionophore A23187 stimulates cytokinin-like mitosis in Funaria. Science 217: 943-945.
Knight MR, Campbell AR, Smith SM, Trewavas AJ. 1991. Transgenic plant aequorin reports the effects of touch and cold-shock and elicitors on cytoplasmic calcium. Nature 352: 524-526.
Mr R.C. Stern (Chichester): Fifteen years of BBS meetings.
Slides of most of the twenty-seven spring and summer meetings attended by R.C. Stern between 1979 and 1984 were shown. These included group photographs taken at many of these (often including overseas members), prints of which are lodged with the BBS Photographic Archivist (Prof. M.R.D. Seaward). In several cases, individual members or small groups were shown, as well as views of the more attractive and interesting localities visited and a few of the bryophytes seen.
Among the meetings illustrated were the excursion to the Algarve in Portugal in March 1989, the international meeting based at Aigas House near Inverness in July 1988 and the IAB/BBS Sphagnum tour to various localities in Britain in July 1991.
Mr C.R. Stevenson (Kings Lynn): Recording in Norfolk.
A brief outline of the history of recording in the county was followed by an account of progress made and difficulties encountered. Recent recording had established that some species were much more widespread than previously suspected, whilst a trickle of new VCRs continue to be made, even in such a well-worked county. Other species appeared to have suffered major declines, possibly to the point of extinction, although in many cases the lack of recent records probably reflected a mixture of genuine rarity and insufficient fieldwork.
After this factual introduction the talk assumed a more amusing tone, and speculated on the purpose of publishing regional floras, who they were liable to be used by and for what purposes. The appropriateness of trying to cover an area the size of Norfolk in detail was questioned, when it might perhaps be more appropriate to make detailed records of key sites of conservation interest. The talk concluded with a discussion of the appropriateness of writing accounts of the ecology of species which added little, if anything, to the store of already available information.
Mr R. Woods (Countryside Council for Wales, Llandrindod Wells): Bryophyte communities.
Under this all-embracing title, our current understanding of plant communities dominated by mosses and liverworts was reviewed. The National Vegetation Classification, now nearing completion, has revitalised an interest in plant communities. No environmental assessment of a site would be considered adequate without a description of its vegetation communities, in addition to a description of the species it supports.
Unfortunately, the NVC as yet fails to cover a number of important bryophyte-dominated communities and includes in its floristic tables barely a third of the British bryophyte flora. Notable omissions identified include epiphytic and many epilithic communities.
The lichenologists have available a preliminary conspectus of lichen communities in the British Isles by James, Hawksworth and Rose in Lichen Ecology, edited by Seaward (Academic Press, London, 1977). A proposal was aired that BBS members should consider collecting data to enable a comparable conspectus for bryophyte-dominated communities to be produced. A possible outline of epiphytic communities based on available data was presented.
Field excursion to Flordon Common and Ashwellthorpe Lower Wood, 10 September 1995
Despite earlier predictions, a cloudless blue sky and warm sunshine were an encouraging start for the day’s excursion. First stop was at Flordon Common, just to the south of Norwich. It is renowned for being the site of the discovery of Leiocolea rutheana in Britain and, during the First World War, Sphagnum was collected from the Common in some quantity for use in first aid dressings. Drainage and other changes have left only one small wet area but this produced plenty of interest. After some discussion the ‘Drepanocladus revolvens‘ was pronounced as D. cossonii and some fine Moerckia hibernica with perianths tempted Harold’s camera into the open. Other species recorded included Campylium stellare, Fissidens adianthoides, Rhizomnium pseudopunctatum, Scorpidium scorpioides, Sphagnum palustre, S. subnitens, Aneura pinguis, Calypogeia fissa and Pellia endiviifolia.
Our second site was at Lower Wood, Ashwellthorpe. This is a recent acquisition by the Norfolk Wildlife Trust and was bryologically unknown. It consists of 93 acres of mainly ash but with some hornbeam, which is at its northern limit as a native species. Unfortunately, recent rains had not revived the bryophytes after the long hot spell so well as a certain brand of lager would have, if one believes the advertisements. Jeff Duckett spotted Ulota phyllantha almost as soon as we entered the wood but other species seen were typical of an East Anglian wood on boulder clay. These included Cirriphyllum piliferum, Eurhynchium pumilum, E. striatum, Homalia trichomanoides, Isothecium myurum, Rhytidiadelphus triquetrus and Metzgeria furcata. Most members had a long journey home, so the meeting broke up in the early afternoon after a very enjoyable day in the field, and just before rain arrived to spoil it.