Observations on some epibionts of gulf-weed,Sargassum natans (L.) Meyen

The succession of epibionts on gulf-weed, Sargassum natans (L.) Meyen, is described. Only the hydroid Clytia noliformis (McCrady) colonizes the newest algal growth, spreading rapidly from below towards the frond tips by means of stolons. The remaining species — the bryozoon Membranipora tuberculata (Bosc), the spirorbid Janua formosa (Bush) and the blue-green alga Calothrix crustacea Schousb. & Thurs. — establish themselves through a free-swimming phase but, instead of attaching near the meristem as is usual on other algae, the larvae and hormogonia (dispersal phase of Calothrix) settle well away from the growing tip of the Sargassum. Such behaviour is consistent with the view that tannins present in the young thallus inhibit the establishment of the surface microflora which is a pre-requisite for the settlement of larger epibionts.Janua shows a strong preference for the bladders of the Sargassum, and Calothrix for the leaflets; but Membranipora appears to settle equally well on bladders, leaflets, and stem.Observations on young colonies of Membranipora reveal that the metamorphosing larvae were orientated with respect to the axis of the Sargassum leaflets. Water flow, which has previously been considered as likely to provide a directional stimulus for such orientation, cannot be the operative factor in this case.     

Effects of the bryozoan Membranipora tuberculata (Bosc.) on the photosynthesis and growth of Gelidium rex Santelices et Abbott

Several species of Membranipora commonly occur on brown and red algae. It is currently believed that these bryozoans could affect growth of the host plant by modifying incident light. In the present study, we report on the changes that occur in both intensity and quality of light passing through colonies of M. tuberculata (Bosc.) and on the effects of bryozoans on growth of the host plant. M. tuberculata decreases photon-flux density by up to 56% of the incident light and slightly affects the quality of the incident light. Although the bryozoan reduces the photosynthetic rate of Gelidium rex Santelices et Abbott, it does not have a net effect on algal growth. It is concluded that the effects of epifauna on algal growth depend on the nature of the algal structure colonized. Therefore, it cannot be predicted a priori that encrusted thalli should grow at a slower rate than nonencrusted thalli.     

Observations on the ecology of Membranipora (bryozoa) and a major predator Doridella steinbergae (nudibranchiata) along the fronds of Laminaria saccharina at Friday Harbor,washington

The distribution of the bryozoan Membranipora and one of its major predators, the nudibranch Doridella steinbergae (Lance) along the fronds of Laminaria saccharina (L.) Lamour. at Friday Harbor, Washington were studied during the summer (July–August) 1975. Whilst the fronds are most heavily encrusted by the bryozoan in the middle and distal regions, settlement occurs principally in the younger more basal regions of the plants. The distribution pattern of the nudibranch closely parallels that of its prey though there is a tendency for the most distal regions, especially in older plants, to be avoided. An average density of 240 Doridella/plant was found for plants of mean length 91.0 cm. Despite the severe predation pressure imposed by this nudibranch, evidence tends to suggest that these extensive and highly productive Membranipora populations could probably support even higher densities of Doridella than those presently found — at least over that period of the year during which this investigation was made.     

Predator-induced polymorphism in the bryozoan Membranipora membranacea (L.)

Three described species of the bryozoan genus Membranipora, M. membranacea (L.), M. serrilamella Osburn, and M. villosa Hincks, occurring together on brown macroalgae off the west coast of North America are eco-phenotypic variants. These forms should be called M. membranacea on the basis of priority.The presence of spines, an important diagnostic feature separating these Membranipora forms, is induced by two nudibranch predators, Corambe pacifica MacFarland & O'Donoghue and Doridella steinbergae Lance. Spines protect Membranipora zooids against predation by these nudibranchs. The population costs of spine production include lower growth and reproductive rates.     

Resource space partitioning by the Bryozoa of a Fucus serratus L. Community

The spatial distributions of five Bryozoa species encrusting Fucus serratus L. plants in Strangford Lough, Northern Ireland, have been examined in two cross-sectional samples yielding 80 plants and 1326 sampling units drawn from 13 environmentally diverse sites. The co-occurences of Flustrellidra hispida (Fabricius), Alcyonidium hirsutum (Fleming), Electra pilosa (L.), Membranipora membranacea (L.), and Celleporella hyalina (L.) on individual Fucus serratus plants were consistent with independent settlement onto each plant, but their joint distributions within the plants were markedly non-random. Measurements of behavioural interactions between species showed that competitive abilities declined through the sequence Flustrellidra, Alcyonidium, Electra, Membranipora, which parallels the sequence of competition (Levins' α) coefficients calculated from spatial distribution data. Competitive ability varied with position on the plant. Flustrellidra and Alcyonidium reversing their relative competitive superiority between basal and distal regions of the fronds. Flustrellidra and Electra were strongly associated under all conditions. Alcyonidium was also frequently present with this pair, though its numerical abundance was inversely related to that of Flustrellidra. Celleporella tended to co-occur with Electra whilst avoiding Flustrellidra and Alcyonidium. Membranipora numbers were inversely related to those of the other species. Analyses of competition coefficients showed that Flustrellidra, Alcyonidium and Electra each peaked in competitive ability against Membranipora at different points along the frond, such that the latterwaas effectively excluded by direct as well as by diffuse competition. Membranipora populations had a greater dependence on the segment area available for colonization than had any other bryozoan species.     

Glucose induced fractal colony pattern of Bacillus thuringiensis

Growing colonies of bacteria on the surface of thin agar plates exhibit fractal patterns as a result of nonlinear response to environmental conditions, such as nutrients, solidity of the agar medium and temperature. Here, we examine the effect of glucose on pattern formation by growing colonies of Bacillus thuringiensis isolate KPWP1. We also present the theoretical modeling of the colony growth of KPWP1 and the associated spatio-temporal patterns. Our experimental results are in excellent agreement with simulations based on a reaction-diffusion model that describes diffusion-limited aggregation and branching, in which individual cells move actively in the periphery, but become immotile in the inner regions of the growing colony. We obtain the Hausdorff fractal dimension of the colony patterns: D_H.Expt=1.1969 and D_{H, R.D.=}1.1965, for experiment and reaction-diffusion model, respectively. Results of our experiments and modeling clearly show how glucose at higher concentration can prove to be inhibitory for motility of growing colonies of B. thuringiensis cells on semisolid support and be responsible for changes in the growth pattern.     

Phenotypic subunit composition of the tobacco (Nicotiana tabacum L.) vacuolar-type H-translocating ATPase

The model plant tobacco (Nicotiana tabacum L.) was chosen for a survey of the subunit composition of the V-ATPase at the protein level. V-ATPase was purified from tobacco leaf cell tonoplasts by solubilization with the nonionic detergent Triton X-100 and immunoprecipitation. In the purified fraction 12 proteins were present. By matrix-assisted laser-desorption ionization mass spectrometry (MALDI-MS) and amino acid sequencing 11 of these polypeptides could be identified as subunits A, B, C, D, F, G, c, d and three different isoforms of subunit E. The polypeptide which could not be identified by MALDI analysis might represent subunit H. The data presented here, for the first time, enable an unequivocal identification of V-ATPase subunits after gel electrophoresis and open the possibility to assign changes in polypeptide composition to variations in respective V-ATPase subunits occurring as a response to environmental conditions or during plant development.     

Trichoderma spp. alleviate phytotoxicity in lettuce plants (Lactuca sativa L.) irrigated with arsenic-contaminated water

The influence of two strains of Trichoderma (T. harzianum strain T22 and T. atroviride strain P1) on the growth of lettuce plants (Lactuca sativa L.) irrigated with As-contaminated water, and their effect on the uptake and accumulation of the contaminant in the plant roots and leaves, were studied. Accumulation of this non-essential element occurred mainly into the root system and reduced both biomass development and net photosynthesis rate (while altering the plant P status). Plant growth-promoting fungi (PGPF) of both Trichoderma species alleviated, at least in part, the phytotoxicity of As, essentially by decreasing its accumulation in the tissues and enhancing plant growth, P status and net photosynthesis rate. Our results indicate that inoculation of lettuce with selected Trichoderma strains may be helpful, beside the classical biocontrol application, in alleviating abiotic stresses such as that caused by irrigation with As-contaminated water, and in reducing the concentration of this metalloid in the edible part of the plant.     

GH3 expression and IAA-amide synthetase activity in pea (Pisum sativum L.) seedlings are regulated by light,plant hormones and auxinic herbicides

The formation of auxin conjugates is one of the important regulatory mechanisms for modulating IAA action. Several auxin-responsive GH3 genes encode IAA-amide synthetases that are involved in the maintenance of hormonal homeostasis by conjugating excess IAA to amino acids. Recently, the data have revealed novel regulatory functions of several GH3 proteins in plant growth, organ development, fruit ripening, light signaling, abiotic stress tolerance and plant defense responses. Indole-3-acetyl-aspartate (IAA-Asp) synthetase catalyzing IAA conjugation to aspartic acid in immature seeds of pea (Pisum sativum L.) was purified and characterized during our previous investigations. In this study, we examined the effect of auxin and other plant hormones (ABA, GA, kinetin, JA, MeJA, SA), different light conditions (red, far-red, blue, white light), and auxinic herbicides (2,4-D, Dicamba, Picloram) on the expression of a putative GH3 gene and IAA-amide synthesizing activity in 10-d-old pea seedlings. Quantitative RT-PCR analysis indicated that the PsGH3-5 gene, weakly expressed in control sample, was visibly induced in response to all plant hormones, different light wavelengths and the auxinic herbicides tested. Protein A immunoprecipitation/gel blot analysis using anti-AtGH3.5 antibodies revealed a similar pattern of changes on the protein levels in response to all treatments. IAA-amide synthetase activity determined with aspartate as a substrate, not detectable in control seedlings, was positively affected by a majority of treatments. Based on these results, we suggest that PsGH3-5 may control the growth and development of pea plants in a way similar to the known GH3 genes from other plant species.     

The effects of laurel (Laurus nobilis L.) on development of two mycorrhizal fungi

Hundreds of aromatic plant species are growing naturally around Mediterranean. Plant essential oils are incorporated in aromatic plant material and follow the litter fall. During litter degradation, the presence of essential oils can affect soil microorganisms. Mycorrhizal fungi have never been investigated so far under the presence of volatile oils. The aim of this study was to explore the effect of aromatic Laurus nobilis L. on development of two mycorrhizal species Glomus deserticola and Glomus intraradices. The response of fungi colonization and host growth were monitored under different concentrations of L. nobilis leaves and essential oil. The major compounds of L. nobilis essential oil were 1,8-cineole (49.6%), sabinene (7.8%), ??-pinene (6.0%), eugenole (5.6%), ??-terpinyl acetate (5.2%) and ??-pinene (5.1%). Both mycorrhizal fungi colonized successfully the host plants whose growth was positively influenced by mycorrhizal fungi. G. deserticola presented higher infection level than G. intraradices. The addition of L. nobilis leaves in the soil resulted in mycorrhiza inhibition. The level of inhibition was positively correlated with the added amount of aromatic leaves in the soil. The essential oil presented a little higher inhibition than the leaves. The presence of this aromatic plant in many different ecosystems could contribute in mycorrhiza inhibition and it is suggested, when it’s possible, reduction of laurel litter before reforestation programs.     

Studies on the growth of LAminaria hyperborea (Gunn.) Fosl. I. Biomass and productivity

Biomass and productivity data for Laminaria hyperborea (Gunn.) Fosl. on the west coast of Scotland are presented. SCUBA diving techniques were used to collect the data which indicate higher values of the biomass than do data from spring grab collections from the same region. The mean biomass values were 20.4 kg fresh weight/m² at 3 m and 7.7 kg/m² at 9 m. Productivities of 16.5 and 8.0 metric tons of organic matter/hectare/year were found at 3 and 9 m, respectively. These values indicate relatively favourable growing conditions for this plant. Analysis of individual plants showed that plants at 3 m depth were only significantly larger than those at 9 m when the shallow population was not very dense. Self-shading is important in more dense populations. Productivity values compared closely with those calculated by other authors for L. hyperborea in regions favourable for algal growth.     

Selective site segregation in Patelloida (Chiazamea) Pygmaea (Dunker) and P.(C.) Lampanicola Habe (gastropoda: Patellacea) on a Hong Kong shore

Although originally described as a separate species, Patelloida (Chiazacmea) lampanicola Habe has subsequently been regarded as a “form” of P. (C.) pygmaea (Dunker). The conical shape of the shell in the former was assumed to result from the settlement and growth of some individuals of the population upon shells of intertidal Batillaria (Potamididae).This paper reports upon an analysis of a population of limpets resident on a small sand flat in Hong Kong and it is concluded that Patelloida (C.) lampanicola is distinct from P. (C.) pygmaea. This conclusion is based upon differences in radula teeth structure, shell morphometrics and behaviour. Furthermore it has been demonstrated that the earlier confusion surrounding these species results from a very nice example of selective site segregation. P. (C.) pygmaea inhabits stones and empty shells (in this region of its total range) embedded in the sand but can occasionally does reside, up to a length of 4.2 mm, upon Batillaria shells. Thereafter the flattened form of the limpet shell, on a round substratum, presumably makes such individuals more susceptible to either predation or dislodgement. The high-coned Patelloida (C.) lampanicola, on the other hand, almost exclusively colonizes living Batillaria (particularly B. zonalis and B. multiformis) shells but can, with little or no significant alteration in form, also colonize stones. Patelloida (C.) lampanicola has a positive behavioural response towards Batillaria and is clearly living in symbiotic association with the potamid. The benefits accrued by both are discussed.Thus, the limited hard substratum of a primarily soft shore environment has been segregated by these two limpets; one occupies the stones and oyster shells, the other the dense cover of epifaunal potamid snails.     

Centella asiatica (L.) urban from Nepal: Quali-quantitative analysis of samples from several sites,and selection of high terpene containing populations for cultivation

Centella asiatica (L.) Urban is widely used in traditional medicine in many countries and in the formulation of drugs and cosmetics, and is therefore suitable as a trade item for the development of medicinal plants for the population of Nepal. The aim of this work was to select plant populations of C. asiatica with high contents of secondary metabolites growing in various localities in Nepal, and to enhance knowledge of the cultivation of this plant. Quali-quantitative analysis of bioactive triterpenes (asiaticoside and asiatic acid) and phenol derivatives (flavonoids and caffeoyl esters) was performed by HPLC-DAD-ELSD. The highest quantities of triterpenes and phenols were found in samples from the Gorkha and Chitwan districts. Regarding cultivated plants, soil fertilisation is critical, since over-rich soils affect secondary metabolite content. Plants growing in sand-rich soils produce more terpenes. This work provides indications on how to select high-terpene producing germplasm and recommendations for plant cultivation.     

黄土塬区不同品种玉米间作群体生长特征的动态变化

不同玉米品种间作,品种间的竞争对群体结构和产量可能有促进作用.为了明确不同密度下品种间作对不同生育期群体生长特征的影响,以及在不同生育期的变化规律,选用郑单958和沈单16两个不同株型的玉米品种在中、高两种密度条件下进行隔行间作田间试验.研究结果表明:不同密度间作群体叶面积指数(Leaf Area Index,LAI)显著增加,同密度不同品种间作LAI在生育后期显著增加,有利于形成合理的冠层结构以获得更多的光照;中等密度下品种间作单株叶面积较单作显著增加,而高密度间作显著降低了单株叶面积;中等密度下,品种间作地上部干物质积累量显著增加,郑单958尤为突出,但高密度间作时的增加幅度较小,这与高密度下株高、茎粗相对减小有关.品种株高、茎粗随间作密度的增加而有所增加,对间作竞争的响应与品种特性密切相关;在不同生育期,郑单958和沈单16号表现不同的生长规律,前者在整个营养生长过程中对间作竞争的响应明显、持续和稳定,而进入生殖期后,间作的生长优势逐渐消失;后者在营养生长期干物质积累量大,但持续时间较短,表现出较弱的竞争性.品种间作可有效改善群体冠层结构,增加群体物质生产力,更好的为增产鉴定基础.     

Effects of salinity on leaf growth and survival of the Mediterranean seagrass Posidonia oceanica (L.) Delile

The main aim of this study was to estimate the effects of salinity variation on the Mediterranean seagrass Posidonia oceanica (L.) Delile and its attached epiphytes. Leaf growth and survival of this plant were tested in several short-term (15 days) mesocosms experiments under controlled conditions between February 2001 and November 2001. Plants collected from shallow meadows at Alicante (SE Spain), with an ambient salinity of 36.8-38.0 psu, were placed in tanks of 300 L with an additional overhead light and exposed to different salinity treatments (ranging from 25 to 57 psu) during 15 days. To estimate the mortality and growth recuperation, in some experiments shoots were returned to control salinity (38 psu). Leaf growth was measured in the laboratory where epiphytic fauna and flora were removed from leaves, with a razor blade, to determine their biomass.P. oceanica was negatively influenced by increased salinity. Shoots showed a significant decrease in growth and survival, whereas epiphyte biomass did not show a clear response because of their high variability. Maximum leaf growth occurred between 25 and 39 psu. In addition, plants suffered considerable mortality at salinities above 42 psu and below 29 psu, with 100% mortality at 50 psu. In salinities between 39 and 46 psu, surviving plants were able to regain their original growth rate when returned to normal seawater salinity (38 psu). These results suggest that P. oceanica is one of the most sensitive seagrasses to salinity increments it is more tolerant to salinity reductions (25.0-36.4 psu), perhaps due to the terrestrial origin of seagrasses.     

Ectomycorrhizal Pisolithus albus inoculation of Acacia spirorbis and Eucalyptus globulus grown in ultramafic topsoil enhances plant growth and mineral nutrition while limits metal uptake

Ectomycorrhizal fungi (ECM) isolates of Pisolithus albus (Cooke and Massee) from nickel-rich ultramafic topsoils in New Caledonia were inoculated onto Acacia spirorbis Labill. (an endemic Fabaceae) and Eucalyptus globulus Labill. (used as a Myrtaceae plant host model). The aim of the study was to analyze the growth of symbiotic ECM plants growing on the ultramafic substrate that is characterized by high and toxic metal concentrations i.e. Co, Cr, Fe, Mn and Ni, deficient concentrations of plant essential nutrients such as N, P, K, and that presents an unbalanced Ca/Mg ratio (1/19). ECM inoculation was successful with a plant level of root mycorrhization up to 6.7%. ECM symbiosis enhanced plant growth as indicated by significant increases in shoot and root biomass. Presence of ECM enhanced uptake of major elements that are deficient in ultramafic substrates; in particular P, K and Ca. On the contrary, the ECM symbioses strongly reduced transfer to plants of element in excess in soils; in particular all metals. ECM-inoculated plants released metal complexing molecules as free thiols and oxalic acid mostly at lower concentrations than in controls. Data showed that ECM symbiosis helped plant growth by supplying uptake of deficient elements while acting as a protective barrier to toxic metals, in particular for plants growing on ultramafic substrate with extreme soil conditions. Isolation of indigenous and stress-adapted beneficial ECM fungi could serve as a potential tool for inoculation of ECM endemic plants for the successful restoration of ultramafic ecosystems degraded by mining activities.     

Uptake of glycollate by Skeletonema costatum (Grev.) Cleve in bacterized culture

Glycollic acid, supplied at a concentration of 1 mg l^?1, increased the relative growth rate of Skeletonema costatum (Grev.) Cleve growing in bacterized culture at limiting light intensities. There was little or no such effect at intensities approaching saturation. The presence in the medium of alumina, an adsorbent for glycollate, prolonged the lag phase, the cells remaining viable for up to 5 days. Uptake of glycollate was not appreciably affected by the bicarbonate concentration of the medium. After 3 h, 80–92% of the glycollate carbon assimilated was found in the alcohol and benzene insoluble fraction of the cells. This is in agreement with the supposition that glycollate carbon is as-similated directly by the diatom rather than after degradation by bacteria to carbon dioxide.     

Seasonal changes in the activity of certain enzymes in crude tissue extracts of two common cirripedes, Balanus balanoides (L.) and B. balanus (L.).

The activity of glutamate-oxaloacetate transaminase (GOT), glutamate-pyruvate transaminase (GPT), lactate dehydrogenase (LDH), malate dehydrogenase (MDH), isocitrate dehydrogenase (ICDH), and aldolase in tissue extracts of Balanus balanoides (L.) and B. balanus (L.) have been determined at regular intervals over a year, and an attempt made to relate the results to known biochemical changes in the animals.The work was ecologically orientated. Preliminary studies on the effects of extractant, dialysis, and possible endogenous interference were made and the subsequent procedure rigorously standardized.Transamination was investigated by TLC. LDH and aldolase show striking seasonal changes; an abundance of the former is associated with the production of semen. MDH, concerned in carbohydrate and lipid metabolism, was present in considerable quantities but there were no marked seasonal changes. GPT activity is high when reproductive products are being produced from reserves of food and the activity is also related to the production of semen. GOT showed no clear seasonal trends.The results are discussed relative to the metabolism of crustaceans: the part played by proteins and lipids is stressed.