A morphological study of branch development in mosses with special reference to pseudoparaphyllia

The manner of branch development in mosses was studied. Two types of branch development,Bryum-type andClimacium-type, can be distinguished by their morphology at dormancy. In theBryum-type, the branch primordium does not produce leaves and stays as a primordium at dormancy; the primordium is merely a mass of thin-walled cells with an apical cell. However, in theClimacium-type, the branch primordium produces leaves even in the very early stages of development, and it is a bud accompanied by scale-like leaves that goes through dormancy. Though pseudoparaphyllia have been considered to originate from epidermal cells of a stem, results of the present study show that they are, whether filamentous or foliose, produced by the branch primordia. TheBryum-type of dormant branch primordium is accompanied by filamentous pseudoparaphyllia in some species, while, that of theClimacium-type is sometimes accompanied by foliose pseudoparaphyllia. Filamentous pseudoparaphyllia are found to be produced adventitiously from the outermost cell layer of a primordium. Developmental mode of foliose pseudoparaphyllia is left for a future survey.     

Protection of the photosynthetic apparatus against damage by excessive illumination in homoiohydric leaves and poikilohydric mosses and lichens

Experimental work on the control of photosystem II in the photosynthetic apparatus of higher plants, mosses and lichens is reviewed on a background of current literature. Transmembrane proton transport during photoassimilatory and photorespiratory electron flows is considered insufficient for producing the intrathylakoid acidification necessary for control of photosystem II activity under excessive illumination. Oxygen reduction during the Mehler reaction is slow. Together with associated reactions (the water-water cycle), it poises the electron transport chain for coupled cyclic electron transport rather than acting as an efficient electron sink. Coupled electron transport not accompanied by ATP consumption in associated reactions provides the additional thylakoid acidification needed for the binding of zeaxanthin to a chlorophyll-containing thylakoid protein. This results in the formation of energy-dissipating traps in the antennae of photosystem II. Competition for energy capture decreases the activity of photosystem II. In hydrated mosses and lichens, but not in leaves of higher plants, protein protonation and zeaxanthin availability are fully sufficient for effective energy dissipation even when photosystem II reaction centres are open. In leaves, an additional light reaction is required, and energy dissipation occurs not only in the antennae but also in reaction centres. Loss of chlorophyll fluorescence during the drying of predarkened poikilohydric mosses and lichens indicates energy dissipation in the dry state which is unrelated to protonation and zeaxanthin availability. Excitation of photosystem II by sunlight is not destructive in these dry organisms, whereas photosystem II activity of dried leaves is rapidly lost under strong illumination.     

苔藓植物的分子生物学研究

苔藓植物是一类较低等的陆生植物,但由于它生存环境的特殊性及物种本身的特性,在多种领域均具有重要的应用价值。主要从苔藓植物分子生物学的角度介绍国际和我国研究概况．以期为进一步加强认识、提高其利用价值提供帮助。     

Morphogenesis of leaves and cones of male short-shoots of Ginkgo biloba L.

Although the subject of several studies, the phylogeny of Ginkgo biloba is still ambiguous. Most of the morphological and some palaeontological studies assume a close relationship to conifers, but other palaeontological studies regard the origin of Ginkgo biloba in groups that exhibit a pinnate bauplan like Peltaspermales or Dicranophyllales. This divergence has led to controversial interpretations of male sporangiophores and leaves. Attempting to resolve this, here we have investigated the male cones and leaves of short-shoots by SEM and light-microscopy. Our results indicate that the male sporangiophores are simple structures, and the observed formation of thickened cell walls at the sterile adaxial side of the sporangiophores, similar to the endothecium of the sporangia, gives weak support for a precursor of Ginkgo-sporangiophores that displayed simple male sporangiophores with radial arrangement of the sporangia. Thus, our interpretations of the male sporangiophores of Ginkgo biloba allude to a relationship with Coniferales, Gnetales and Cordaitales and reject a close relationship of Ginkgo biloba with pinnate groups like Cycadaceae, as assumed by some molecular studies. In contrast to previous studies on long-shoot leaves, our results on short-shoot leaves give no indication for a compound character of Ginkgo leaves. Moreover, we infer that Ginkgo leaves could be derived from a simple bauplan, by two modifications of the basic growth pattern of conifer leaves, assuming that the dissection of Ginkgo leaves is secondary. Although more comparative investigations are necessary, our results support a coniferophyte origin of the Ginkgoales.     

Morphogenesis of the antenna of the male silkmoth, Antheraea polyphemus. IV. Segmentation and branch formation

The imaginal antenna of the male silkmoth Antheraea polyphemus is a featherlike structure; its flagellum consists of about 30 stem segments each giving off two pairs of side branches. The antenna develops during the pupal stage (lasting in total about 21 days) from a leaf-shaped anlage by incisions proceeding from the periphery towards the prospective antennal stem. Primary incisions, starting about 3 days after apolysis, form double branches, which arethen split into single branches by parallel running secondary incisions. The initial pattern of tracheae and peripheral nerves is completely rearranged during these morphogenetic processes which are finished 9-10 days after apolysis. In Antheraea the dorsal and ventral epithelial monolayers of the antennal anlage are successively subdivided during development into a pattern of repetitive epithelial zones. Within the first day after apolysis alternating stripes of sensillogenic and non-sensillogenic epithelium are differentiating. Then the latter are further subdivided, and at last four different stripelike zones (I-IV) can be discriminated. Long basal protrusions of the epidermal cells ('epidermal feet'), and most probably haemocytes, seem to be involved in the reconstruction of the epithelium: both show characteristic arrangements within the antennal anlage during successive developmental stages.     

Morphogenesis in Marsilea

An account is given of investigations on the development of sporelings of Marsilea using aseptic culture techniques. Special attention was paid to the heteroblastic leaf development and to the conditions leading to the origin of land or water forms. A study was made of the effects of changes in the composition and concentration of the culture medium. The substances tested included sugars, nitrogen compounds, metabolic inhibitors, auxins, gibberellic acid and kinetin.
It was concluded that the changes in leaf segmentation of Marsilea , or heteroplastic development, are correlated with changes in the size of the apical meristematic regions of the shoot, which in turn are influenced by the nutritional status of the plant. On the other hand, the differences between land and water forms are probably due to differences in the available concentration of dissolved carbohydrates in the growing parts. The results are discussed in relation to similar morphogenetic problems in other vascular plants.     

Records of Greek mosses

Abstract

25 mosses are recorded as either new to Greece or to the divisions of the country created by Preston (1984).     

Molecular biology of mosses

Plant Molecular Biology -     

The role of spores in reproduction in mosses

The facility for vegetative reproduction and reproduction by spores was compared in four common mosses by observations on naturally occurring spores, sporclings and juvenile shoots combined with experimental field plantings. In Polytrichum alpestre no evidence of spore germination in the field was obtained, but shoots were formed by regeneration from shoot fragments. Spore germination leading to shoot development, and ultimately to sporophyte production, occurred freely in Funaria hygrometrica. Atrichum undulatum and Bryum argenteum gave intermediate results in that regeneration occurred freely from shoot fragments, and while many spores germinated the sporelings normally failed to develop. There was strong evidence that experimentally planted spores occasionally gave rise to shoot production in both the latter species, however, and shoots commonly developed on protonema planted in the field. The results are discussed in relation to the contrasting life-history strategies shown by the four species.     

Morphogenesis of the antenna of the male silkmoth, Antheraea polyphemus. VI. Experimental disturbance of antennal branch formation

In the male silkmoth Antheraea polyphemus, the formation of the side branches of the quadripectinate antennal flagellum was disturbed by an experimental manipulation. Normally the side branches develop in the pupa via deep incisions which proceed from the periphery towards the centerline of the leaf-shaped antennal anlage. Local removal of the uppermost, pigmented cuticular layers of the pupal antennal pocket ('cuticular window') led to a local standstill of branch formation in the manipulated region of the pocket, most probably caused by increased evaporation of water through the remaining layers of meso- and endocuticle. These parts of the antenna retained an unbranched, plate-like shape. This early morphogenetic stage was conserved by the secretion of antennal cuticle. Besides cuticle formation, development of sensilla is not impeded by the manipulation. In the plate-shaped regions, the initial pattern formed by the sensilla in the antennal epidermis is preserved, because they maturate at their birthplaces. In the individual segments, the pattern of sensilla shows a mirror-like symmetry with respect to the segmental midline. From the edge to the midline, we found large s. trichodea, followed by small s. trichodea, s. basiconica, and s. coeloconica on the dorsal side whereas on the ventral side, there are only large s. trichodea and s. campaniformia. We conclude that the development of the featherlike antennal shape on the one hand and the development of sensilla and cuticle on the other hand are independent processes.     

UV-A protection in mosses growing in continental Antarctica

The simple structure of mosses, a major component of Antarctic terrestrial vegetation, has led to suggestions that they might be exceptionally sensitive to enhanced UV from the ozone hole. The results presented here show that the mosses Ceratodon purpureus and Bryum subrotundifolium are resistant to UV-A and that the latter species can rapidly change its protection to suit the UV environment. The studies were made using a UV-A PAM chlorophyll fluorescence fluorometer that allowed absorption of UV-A before arrival at the chloroplast (i.e. UV-A shielding) to be estimated. Both C. purpureus and B. subrotundifolium have sun and shade forms that differ markedly in colour and their protection from UV-A. Shade forms of B. subrotundifolium, initially low in UV-A protection, achieve full, sun-form levels in about 6 days when exposed to ambient sunlight. These results, taken with other recent studies, suggest that not only are Antarctic mosses well protected from ambient UV, but are also as adaptable to incident UV as higher plants.