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.     

Comparisons of photosynthesis-related traits among understory lichens,mosses and vascular plant leaves in a high-elevation subalpine forest

对比高海拔亚高山森林林下地衣、藓类及维管植物叶片的光合相关性状 在高海拔亚高山森林中,许多地衣和藓类植物欣欣向荣,甚至成为林地表层的优势物种。尽管它们在森林生态系统中承担着不可替代的功能,但我们对其光合作用相关的功能性状水平知之甚少,对相同生境下藓类植物和维管植物的比较研究也较为匮乏。因此,本研究选择中国青藏高原东缘亚高山林下常见的3种地衣、3种藓类和4种维管植物,测定并对比了它们的碳、氮、磷含量及化学计量比、单位面积光合组织干重、叶绿素含量及光合光响应曲线的异同。研究结果表明,林下地衣的氮含量高于藓类植物,二者的氮、磷、叶绿素、光合速率及光合氮利用效率均低于维管植物叶片。不同种类地衣的光合相关性状与其生长环境相符,而林地表层的3种藓类植物和3种草本植物的功能性状在各自功能群中的种间差异均不显著。总之,这些结果表明高海拔亚高山林下地衣和藓类植物的优势与其光合相关性状关系不大,对严酷环境较强的适应能力可能是它们得以繁荣生长的关键。     

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.     

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.     

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 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 -     

Green light drives photosynthesis in mosses

Temperate forests are characterised by variable light quality (i.e. spectral composition of light) at or near the forest floor. These understory environments have a high concentration of green light, as red and blue light are preferentially absorbed by upper canopy leaves. Understory species may be well-adapted for using green light to drive photosynthesis. Angiosperms have been shown to use green light for photosynthesis, but this ability has not been demonstrated in shade-dwelling bryophytes. In this study, net photosynthetic rate (P_N) of three temperate understory species of moss (Dichodontium pellucidum (Hedw.) Schimp., Leucobryum albidum (Brid. ex P.Beauv) Lindb. and Amblystegium serpens (Hedw.) Schimp.) was measured under green, red?+?blue, and red?+?blue?+?green light to assess green light use efficiency. All three species were capable of photosynthesising beyond their respiratory demands using solely green light, with higher green light use efficiency measured in plants collected from areas with greater canopy cover, suggesting growth in a green light concentrated environment increases green light use efficiency. Each species was also collected from sites differing in their degree of canopy cover and grown under three light treatments (high light, low light, and green light). Photosynthetic efficiency (chlorophyll fluorescence), tissue nitrogen and carbon isotope concentrations were assessed after a short growth period. Growth conditions had little effect on leaf chemistry and monochromatic green light did not significantly degrade photosynthetic efficiency. This study provides the first evidence to date of positive net ‘green light photosynthesis’ in mosses.     

Auxin metabolism in mosses and liverworts

The plant hormone auxin (indole-3-acetic acid, IAA) is involved in the control of many phenomena during plant development. By characterizing steady-state free and conjugated IAA levels using a stable isotope dilution method coupled with gas chromatography- selected ion monitoring- mass spectrometry, this paper provides a detailed characterization of IAA metabolism in five liverworts, four mosses, and two tracheophytes. Long-term IAA conjugation patterns were monitored by incubating actively growing tissue with (14)C-IAA and then analyzing the de novo synthesis of IAA conjugates with radioimaging techniques. The liverworts, mosses, and tracheophytes can be differentiated by the total amount of IAA metabolites, the proportion of free and conjugated IAA, the chemical nature of their IAA conjugates, and the rates of IAA conjugation. Our tentative conclusion is that the liverworts appear to employ a biosynthesis-degradation strategy for the regulation of free IAA levels, in contrast to the conjugation-hydrolysis strategy apparently used by the mosses and tracheophytes. Such alternative metabolic strategies may have profound implications for macroevolutionary processes in these plant groups.     

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.     

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.