Response to insulin and the expression pattern of a gene encoding an insulin receptor homologue suggest a role for an insulin-like molecule in regulating growth and patterning in Hydra

 A gene encoding a receptor protein-tyrosine kinase closely related to the vertebrate insulin receptor has been identified in the Cnidarian Hydra vulgaris. The gene is expressed in both epithelial layers of the adult polyp. A particularly high level of expression is seen in the ectoderm of the proximal portions of the tentacles and in a ring of ectodermal cells at the border between the foot basal disk and body column. The expression pattern of the gene in asexual buds is dynamic; expression is high throughout the newly emerging bud but the area of high expression becomes restricted to the apex as the bud lengthens. When the bud begins hypostome and tentacle formation, a high level of expression appears at the bases of the emerging tentacles. Finally, a ring of high expression appears just above the foot of the bud, completing the pattern seen in the adult polyp. The presence of this receptor and its pattern of expression suggested that an endogenous molecule related to insulin plays a role in regulating cell division in the body column and in differentiation of the tentacle and foot cells in Hydra, with the switch between the two being determined by the level of the receptor. Treatment of Hydra polyps with mammalian insulin caused an increase in the number of ectodermal and endodermal cells undergoing DNA synthesis. Received: 19 April 1996 / Accepted: 5 July 1996     

Influence of overstory composition on understory colonization by native species in plantations on a degraded tropical site

Abstract. Patterns of understory colonization by native and naturalized trees and shrubs were evaluated in 4.5-year-old plantations of three exotic tree species, Casuarina equisetifolia, Eucalyptus robusta, and Leucaena leucocephala, on a degraded coastal grassland site with reference to overstory composition and understory environmental conditions. 19 secondary forest species were established in the plantation understories (with a total area of 0.52 ha), while no natural regeneration occurred in unplanted, though protected, control areas. The majority of these species (90 %) and the total seedling population (97 %) were zoochorous, indicating the importance of frugivorous bats and particularly birds as facilitators of secondary forest species colonization. Understory species richness and seedling densities were affected significantly by overstory composition, the most abundant regeneration occurring beneath Leucaena and least under Casuarina. Understory colonization rates within mixed-species stands were intermediate between those of single-species stands of the trees comprising their overstories. Significant negative correlations were found between understory species richness and seedling density, and forest floor depth and dry mass, especially for small-seeded ornithochorous species. Higher colonization rates near the peripheries of plantation plots relative to plot interiors were due in part to roosting site preferences by frugivores, particularly bats. The study results indicate that overstory species selection can exert a significant influence on subsequent patterns of colonization by secondary forest species and is an important consideration in the design of plantations for ‘catalyzing’ succession on deforested, degraded sites.     

Nitrogen limitation and amino-acid metabolism of Chlorella symbiotic with green hydra

Chlorella algae symbiotic in the digestive cells of Hydra viridissima Pallas (green hydra) were found to contain less amino-N and smaller pools of free amino acids than their cultured counterparts, indicating that growth in symbiosis was nitrogen-limiting. This difference was reflected in uptake of amino acids and subsequent incorporation into protein; symbiotic algae incorporated a greater proportion of sequestered radioactivity, supplied as ¹⁴C-labelled alanine, glycine or arginine, than algae from nitrogen-sufficient culture, presumably because smaller internal pools diluted sequestered amino acids to a lesser extent. Further experiments with symbiotic algae showed that metabolism of the neutral amino acid alanine differed from that of the basic amino acid arginine. Alanine but not arginine continued to be incorporated into protein after uptake ceased, and while internal pools of alanine were exchangeable with alanine in the medium, those of arginine were not exchangeable with external arginine. Thin-layer chromatography of ethanol-soluble extracts of algae incubated with [¹⁴C]alanine or [¹⁴C]arginine showed that both were precursors of other amino acids. The significance of nitrogen-limiting growth of symbiotic algae is discussed in terms of host-cell regulation of algal cell growth and division.     

Variation in green hydra. A description of three cloned strains of Hydra viridissima Pallas 1766 (Gnidaria: Hydrozoa) isolated from a single site

Three different strains of green hydra were isolated in successive years from a single site in the River Frome, Bristol, England. The strains resembled each other in important taxonomic characters, and were identified as Hydra viridissima by their possession of smooth-walled single-chambered embryothecas, but were smaller, possessed smaller nematocysts and produced fewer eggs per individual than the Western European holotype. It is possible that English green hydra represent a geographical subspecies.
The three strains could be distinguished from each other by differences in rates of bud production and in characters associated with their symbiotic algae. These differences are considered varietal, and it is suggested that H. viridissima is a polytypic species. The possible origins of these variations and their significance is discussed.     

中国水螅属一新种(水螅虫纲:螅形目)

报道采自黑龙江省漠河地区北极村水螅１新种,即漠河水螅Ｈｙｄｒａ ｍｏｈｅｎｓｉｓ ｓｐ．ｎｏｖ．,模式标本保存于哈尔滨师范大学生物学系无脊椎动物教学研究室。     

Molecular characterization of Hydra acetylcholinesterase and its catalytic activity

A full-length cDNA encoding an acetylcholinesterase (AChE) from Hydra magnipapillata was isolated. All of the important aromatic residues that line a catalytic gorge in cholinesterases of other species were conserved, but the sequences of peripheral anionic and choline binding sites were not. Hydra AChE, expressed in Xenopus oocytes, showed AChE activity. The gene was expressed in both ectodermal and endodermal epithelial cells except for the tentacles and basal disk. AChE gene expression was not detected in the regenerating tips in either the head or the foot, indicating that regeneration is controlled by the non-neuronal cholinergic system in Hydra.     

Metamorphosis ofHydractinia echinata Insights into pattern formation in Hydroids

Summary Hydractinia echinata is a marine, colony-forming coelenterate. Fertilized eggs develop into freely swimming planula larvae, which undergo metamorphosis to a sessile (primary) polyp. Metamorphosis can be triggered by means of certain marine bacteria and by Cs⁺. Half a day after this treatment a larva will have developed into a polyp. The induction of metamorphosis can be prevented by addition of inhibitor I, a substance partially purified from tissue ofHydra. The larvae ofH. echinata also appear to contain this substance. Inhibitor I appliedafter the onset of metamorphosis blocks its continuation as long as it remains in the culture medium. Cs⁺ applied within the same period of time also blocks the continuation of metamorphosis. However, these two agents have opposite effects on the body pattern of the resultant polyps. The experiments indicate that application of Cs⁺ triggers the generation of the pre-pattern. Inhibitor I appears to be a factor of this prepattern. A model is proposed which describes the basic features of head and foot/stolon formation not only forHydractinia but also for other related hydroids.     

Anti-fungal activity of essential oils of Ceylon Eucalyptus species for the control of Fusarium solani and Sclerotium rolfsii

The essential oils were extracted from the leaves of Eucalyptus microcorys, Eucalyptus grandis and Eucalyptus robusta which were grown in Sri Lanka and their major chemical compounds were determined. 1,8-Cineole and α-pinene were identified as major aroma compounds in these oils. In this study, the anti-fungal activity of essential oils of E. microcorys, E. grandis and E. robusta, ethanol extract of E. microcorys and 1,8-cineole were evaluated against Sclerotium rolfsii, a fungi responsible for leaf spot disease of indoor plants and Fusarium solani, a fungi responsible for dry rot diseases of potato by poisoned food technique, and minimum inhibitory concentrations (MICs) were determined. The essential oils from three Eucalyptus species showed significant inhibitory effect against S. rolfsii and F. solani than the ethanol extract of E. microcorys. Of treatments, the essential oil of E. grandis showed the best anti-fungal activity with the MIC values of less than 0.1% for S. rolfsii and 0.5% for F. solani. The MICs of the oils of E. microcorys and E. robusta were between 0.3–0.5% against S. rolfsii and 0.5–0.75% for F. solani. The 1,8-cineole did not exhibit inhibition activity as much of Eucalyptus essential oils and hence, it can be assumed that minor chemical components of the oils contribute to the growth inhibition of the tested fungi. This is the first report of anti-fungal activity of Sri Lankan oils of E. microcorys, E. grandis and E. robusta and ethanol extract of E. microcorys against S. rolfsii and F. solani. These findings would be useful for the designing of natural fungicide for agriculture- and food-based industries.