Environmental and hormonal control of turion formation in Myriophyllum verticillatum

The turions of Myriophyllum verticillatum, an aquatic vascularplant, develop in the fall and function in propagation and dispersalas well as in over-wintering. Experiments with controlled evnironmentsindicate that both temperature and photoperiod regulate turionformation. Turions can be induced at 15°C or lower, butnot at 20°C. At 15°C, turions form in both 8- and 12-hrdays, but not in 16-hr days. Plants collected in early springdo not form turions readily in response to short days unlesspreviously exposed to long days; thus, turion formation is along-day-short-day response. This combination of photoperiodand temperature requirements probably prevents turion developmentin early spring when the temperature and photoperiod are similarto those in the fall. Treatment of plants with ABA (10^–5M) enhances turion development under marginally inductive conditions(12-hr days at 15°C) but cannot induce it under long days.On the other hand, the cytokinin benzyladenine (10^–5 M)blocks turion formation. GA3 (10^–5 M) and AMO-1618 (10^–5M) exert only small qualitative effects on turion development,while IAA (10^–5 M) retards it. During turion development,the level of ABAlike activity and of one or two unidentifiedinhibitors increases. Cytokinin activity decreases at the startof turion formation, increases during development, then decreasesat abscission. Thus two lines of evidence suggest that a decreasein cytokinin activity and an increase in acidic inhibitor activityplay important roles in turion induction. ¹Present address: Biological Station, University of Michigan,Ann Arbor, Michigan 48109, U. S. A. (Received December 1, 1975; )     

轮叶狐尾藻的组织培养和快速繁殖

1 植物名称 轮叶狐尾藻（Myriophyllum verticillatumL）。 2 材料类别 带节茎段,植株购于苏州花鸟市场水族馆。     

The discovery of Myriophyllum exalbescens Fernald (Haloragaceae) in Europe and the typification of M.spicatum L. And M.verticillatum L.

Myriophyllum exalbescens Fernald, hitherto regarded as a North American endemic, has been fund to occur widely as a native plant in northern Europe, where it has occasionally been distinguished as a subspecies or variety of M.spicatum L.under the epithet squamosum Linnacus original concept of M.spicalum appears to have included M.exalbescens (and also M. Alterniflorum DC.) but selection of Burser VII(1)79 at UPS as lectotvpe ensures the continued use of the epithet spicatum for the native Eurasian weed species to which it is customarily applied. .M.verlicillalum L., the name of a morphologically similar species, is also lectotypified in a way that preserves its current usage. Distinguishing features of M.exalbescens and M.spicatum are provided along with details of the synonymy and presently known distribution in Europe of M.exalbescens .     

Abscisic-acid-induced turion formation in Spirodela polyrrhiza L. I. Production and development of the turion

Abstract The production, growth, and development of the abscisic-acid-induced turion (a small dormant bud) of Spirodela polyrrhiza were investigated. Addition of ABA to a culture of S. polyrrhiza resulted in growth inhibition at concentrations as low as 10⁻⁶molm⁻³, growth being completely arrested at 10⁻² mol m. Over a single order of magnitude range around I0⁻⁴molm⁻³, ABA also induced the production of turions. The range of turion-producing concentrations of ABA was found to be much narrower than previously reported, turion production having a clearly defined threshold, optimum, and upper limit. The possibility that growth inhibition and turion formation are integrally linked aspects of a single response is discussed. Only primordia ≤0.7 mm long at the time of ABA addition could be induced to develop into turions and the events leading to turion formation were found to be reversible up to 72 h in ABA . It is concluded that in terms of turion formation there is a sensitivity window to abscisic acid lasting some 4–20h in the normal developmental life of frond cells. Providing cells experience the appropriate signal in this sensitivity window they initiate a new programme which eventually leads to turion formation. Microscopical analysis showed that the cells within this sensitivity window were still actively dividing. It is suggested that the developmental switch-over to rapid cell expansion and separation marks the end of this ABA sensitivity window.     

Abscisic-acid-induced turion formation in Spirodela polyrrhiza L. II. Ultrastructure of the turion; a stereological analysis

Abstract The ultrastructural features of the abscisic-acid-induced turion of Spirodela polyrrhiza are briefly described and a comparison between turion and vegetative frond tissue was made by stereological analysis. The turion is characterized by its small size, reniform shape, and dark-brown coloration; the mesophyll is undifferentiated and totally lacking the substantial acrenchyma development found in the vegetative frond. The turion cells have a smaller vacuole and a denser cytoplasm than the cells of the vegetative frond. Stereological analysis showed that the tissues differed quantitatively only in three main respects: air space formation, vacuolation, and starch and cell wall material accumulation. During development, it is suggested that the cells of the turion, while reaching the same final size as the vegetative frond cells, accumulate numerous starch grains, thick cell walls, and large deposits of tannins and anthocyanin pigment at the expense of the vacuolar expansion characteristic of the normal maturity programme. Certain features of the turion ultrastructure indicate a differential cell sensitivity to ABA.     

Illecebrum verticillatum L. in the outer Hebrides

Summary

Scottish habitats are here reviewed in a European context. Examples are selected in order to identify those recognisable as distinctively Scottish as well as others related to Scandinavian or European counterparts. The paper begins with a resumé of the main environmental influences in Scotland, then describes examples of habitats almost unique to, or best represented in Scotland. This is followed by reference to some distinctively western versions of more widely distributed habitats, and others corresponding to related types elsewhere. The bearing of this on site selection for nature conservation is discussed. Hitherto, in the UK selection for National Nature Reserves and Sites of Special Scientific Interest has been based largely on the criteria listed in A Nature Conservation Review (Ratcliffe, 1977). It is important, however, also to review Scottish habitats in a European context, as attempted in this paper. In making proposals (now approaching completion) for Special Areas of Conservation, to be recommended by the UK Government for adoption by the European Commission, it is now our duty to include not only habitats for which we have special responsibility because they are unique to or best represented in Scotland, or have distinctively western features, but also sufficient examples of all the main European types occurring in our country.

Nomenclature of British flowering plants and ferns follows Stace (1991).     

Abscisic-acid-induced turion formation in Spirodela polyrrhiza L III. Specific changes in protein synthesis and translatable RNA during turion development

Abstract The developmental process leading to the formation of the abscisic acid (ABA) induced turion of Spirodela polyrrhiza was accompanied by a repression of nucleic acid and protein synthesis. DNA synthesis in the developing lurion (induced by 10⁻⁴mol m⁻³ ABA) was inhibited within 3h of ABA addition, followed by a repression of protein synthesis after 24 h, while RNA synthesis was not inhibited until 3 d. The inhibitory effect of ABA on protein synthesis was found to be selective and the synthesis of several novel proteins appeared to be induced. These effects were specific to ABA-sensitive tissue. The relationship between the changes in the protein and mRNA profiles during the development of the turion was investigated. The rapid general inhibition of protein synthesis at early stages of lurion formation could not be accounted for by the level of translatable mRNA, indicating an effect of ABA at the translational level. The specific alteration to the pattern of in vivo labelled proteins could have resulted, however, from control of the level of specific mRNAs for those particular proteins. Only after 3 d in ABA, when the developing primordium is committed to the turion developmental pathway, is there a total inhibition in the production of mRNA leading to the shutdown of all primary processes and the onset of the irreversible events leading to the dormant state.     

Abscisic-acid-induced turion formation in Spirodela polyrrhiza L. IV. Comparative ion flux characteristics of the turion and the vegetative frond and the effect of ABA during early turion development

Abstract Using the method of compartmental analysis, the ion fluxes and compartment concentrations of Ca²⁺, K⁺ and Cl^- have been compared in the untreated vegetative frond and the abscisic acid (ABA) induced turion of Spirodela polyrrhiza. The ABA-induced turion is characterized by reduced Ca²⁺ exchange across the tonoplast and low vacuolar Ca²⁺ concentration relative to the vegetative frond. In addition the turion exhibits a higher plasmalemma flux with a correspondingly high Ca²⁺ concentration in the cytoplasm. The concentration of K⁺ and Cl^- is much lower in the cytoplasm of the ABA-induced turion than in the vegetative frond with the influx/efflux ratio at both the plasmalemma and the tonoplast being less than 1, a finding exhibited also in dormant storage tissue. Treatment of vegetative fronds with ABA for 18 h resulted in a reduced K⁺ plasmalemma efflux relative to untreated vegetative fronds and a concomitant increase in the cytoplasmic concentration. There was no rapid effect of ABA on Ca²⁺, K⁺ or Cl^- fluxes through either membrane. These results are consistent with the notion that drastic changes in ion fluxes and concentrations in the turion are a secondary consequence of ABA-induced development, possibly due to prior regulation by ABA of enzymes inherent to processes involved in membrane transport.     

耗散结构理论与农田杂草系统控制策略初探

一、农田杂草系统控制与耗散结构理论耗散结构理论阐明了一个开放系统由混沌无序向有序态进化的过程和规律。生态系统属耗散结构已得到论证。作为农田生态系统,在开放性、非平衡性、相干性和随机涨落机制四方面,与自然生态系统相似,均满足耗散结构的构成条件,因此,农田生态系统也属耗散结构。农田杂草防除实质上是农田生态系统的调     

Effects of stormwater sewer discharges on the aquatic community in urban canals in Lelystad

In urban areas with a separate sewerage system, the stormwater runoff is discharged into surface waters. A study on the effects of stormwater sewer discharges on the composition of the aquatic community in urban waters was carried out in two areas with a primarily residential use in the new town of Lelystad. The aquatic organisms considered included hydrophytes, epiphytic diatoms, filamentous algae and macroinvertebrates.The results indicate that the stormwater sewer discharges cause a slight change in the composition of the aquatic community. The water in the urban surface waters can be characterized as eutrophic and - toa-mesosaprobic. Near stormwater sewer outfalls the water tends to the more polluteda-mesosaprobic state. The shifts in the composition of the aquatic community could be traced primarily on the basis of a number of epiphytic diatoms and macroinvertebrates (in particular some Diptera and Trichoptera). Most hydrophytes, filamentous algae and the remaining epiphytic diatoms and macroinvertebrates (in particular water beetles and water mites) turned out to be of little or no use in this respect.Because the investigation was carried out in an unusually dry summer, the results probably underestimate the effects of stormwater discharges on the aquatic community.     

Photophysiology of turion germination inSpirodela polyrhiza (L.)Schleiden. The cause of germination inhibition by overcrowding

Red-light-induced (via phytochrome) germination decreased with increasing numbers of turions per germination flask (overcrowding). Three hypotheses concerning the mechanism of this germination inhibition were tested, related to abscisic acid, ethylene, and oxygen deficiency: (i) Although abscisic acid is a powerful inhibitor of turion germination it had to be excluded as a cause, because abscisic acid was not secreted from turions into the nutrient solution, (ii) Ethylene (ethrel) strongly inhibited growth of newly formed sprouts, but germination response itself was not inhibited, (iii) Germination inhibition did not appear if short light pulses were substituted by continuous irradiation. It reappeared in the presence of the photosynthesis inhibitor 3-(3, 4-dichlorophenyl)-l, 1-dimethylurea, but it was not observed in aerated nutrient solutions, or when Petri dishes instead of Erlenmeyer flasks were used. Decreased oxygen concentrations in the nutrient solution were produced by turion respiration. Consequently, anaerobiosis within the nutrient solution caused by turion respiration was the reason for germination inhibition by overcrowding.     

Control of Chenopodium album by soil application of Ascochyta caulina under greenhouse conditions

Effects of soil application of Ascochyta caulina spores on seedlings of Chenopodium album and five cultivated plant species were investigated under greenhouse conditions as a part of a study on biological control of C. album. Application of A. caulina spores to soils resulted in disease development on C. album and to a lesser degree on Spinacia oleracea seedlings, but not on Beta vulgaris subspecies vulgaris, Zea mays, Triticum aestivum and Pisum sativum seedlings. Affected C. album seedlings had an abnormal olive-green colour or necrotic spots on cotyledons and hypocotyls, and were stunted or died. Affected S. oleracea seedlings were pale in colour or had necrotic spots on the cotyledons, but did not die. Time courses of disease incidence and of mortality of C. album could be described by a monomolecular model. Effects of spore density, sowing depth, soil water content, soil type and time of sowing on disease development were examined. Disease incidence and mortality were influenced by spore density, soil water content and soil type, but not by sowing depth. Spores in a moist soil maintained infectivity at least 2 wk. Spore densities of 10⁹ to 10¹⁰ spores m^-2 were required for 50% mortality of emerged C. album plants. Aspects of the development of A. caulina into a soil-applied mycoherbicide are discussed.     

Factors influencing the distribution of aquatic plant communities in Irish canals

Terrestrial tardigrades are often found in the lichens and mosses growing on trees and rocks. The assertion that tardigrades in these habitats are very patchy in their distribution has rarely been backed by quantitative sampling. This study assesses spatial variability in tardigrade populations inhabiting small patches (0.1 cm² to over 5 cm²) of moss and lichen on trees and rocks at three sites in the United States of America. Tardigrades were collected from four replicate rocks in the Ouachita Mountains of Arkansas, with 30 lichen patches collected on two adjacent boulders and 20 moss patches on a second pair of boulders. In Fort Myers and in Citrus Springs, Florida, 30 lichen patches per tree were collected from two pairs of trees. The tardigrades in each sample were extracted, mounted, identified, and counted. The variation in tardigrade abundance among lichen or moss patches within rocks or trees was very high; the only consistent pattern was that very small patches usually lacked tardigrades. Tardigrade diversity and abundance also varied greatly within sites when lichens and mosses of the same species from different rocks and trees were compared (in the most extreme case one tree had numerous individuals of two tardigrade species present while the other had almost no tardigrades). The results of this quantitative sampling support the assertion that tardigrades are very patchy in distribution. Given the considerable time investment required for the quantitative processing of tardigrade samples, this high spatial variability in tardigrade diversity and abundance requires that researches testing ecological hypotheses about tardigrade abundance check variability before deciding how many samples to take.     

Deep evolutionary diversification of semicircular canals in archosaurs

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Inhibition of sodium chloride toxicity in seedlings of Myriophyllum spicatum L. with calcium

Treatment of milfoil seedlings with NaCl results in disruptionof the cell wall and membranes and in depressed photosynthesis,respiration, and Na accumulation. Addition of low levels ofCa to NaCl treatment solutions inhibited these toxic effects. ¹Present address: Department of Anatomy, School of Medicine,Tulane University, New Orleans, Louisiana 70118, U.S.A. (Received January 16, 1974; )