MOLECULAR AND MORPHOLOGICAL ANALYSIS OF ENTEROMORPHA INTESTINALIS AND E. COMPRESSA (CHLOROPHYTA) IN THE BRITISH ISLES

The very common green seaweeds Enteromorpha intestinalis (L.) Nees and E. compressa (L.) Nees are important fouling organisms and have commonly been used as indicators of eutrophication, but their taxonomic status is problematic. The genus presents extreme difficulties because there is wide intraspecific variation in morphology, but morphological differences between species are small and difficult to detect. In this study, molecular data were used in parallel with morphological characters to resolve the taxonomic problems. Phylogenetic analysis of sequences of the internal transcribed spacers ITS1 and ITS2 and the 5.8S gene distinguished two groups of samples, which were identified by morphological characters as E. compressa (branched) and E. intestinalis (normally unbranched). There was a low level of sequence divergence within each group of samples, but divergence between groups was as great as that between either of the two species and the outgroup E. prolifera. Clades representing E. compressa and E. intestinalis were also found in analyses of an independent molecular data set, chloroplast DNA restriction fragment length polymorphisms (RFLPs). Enteromorpha intestinalis and E. compressa represent two distinct, genetically divergent species. Reinterpretation of published studies shows that these species are reproductively isolated. However, E. compressa and E. intestinalis are sometimes very difficult to distinguish from each other and could be regarded as cryptic species. The presence or absence of branching was the most useful character distinguishing these two species, but there was an element of ambiguity because low salinity or salinity shock can induce branching in E. intestinalis. If environmental factors such as salinity are taken into account, branching can be used to identify the great majority of thalli correctly. This study therefore provides a basis for identifying the two most important marine fouling macroalgae and for their use in environmental monitoring and experimentation. Typification of these two Linnaean species showed that current usage of the names accords with the lectotype and protologue of both species. Samples that resembled E. usneoides did not form a clade in any of the trees, and constraining the data to support the monophyly of this group incurred a penalty. Enteromorpha usneoides appears to be an ecotype of E. compressa.     

PHOTOSYNTHETIC CARBON METABOLISM IN ENTEROMORPHA COMPRESSA (CHLOROPHYTA)1

The intertidal macroalga Enteromorpha compressa showed the ability to use HCO₃^? as an exogenous inorganic carbon (Ci) source for photosynthesis. However, although the natural seawater concentration of this carbon form was saturating, additional CO₂ above ambient Ci levels doubled net photosynthetic rates. Therefore, the productivity of this alga, when submerged, is likely to be limited by Ci. When plants were exposed to air, photosynthetic rates saturated at air-levels of CO₂ during mild desiccation. Based on carbon fixing enzyme activities and Ci pulsechase incorporation patterns, it was found that Enteromorpha is a C₃ plant. However, this alga did not show O₂ inhibited photosynthetic rates at natural seawater Ci conditions. It is suggested that such a C₄- like gas exchange response is due to the HCO₃^? utilization system concentrating CO₂ intracellularly, thus alleviating apparent photorespiration.     

EFFECT OF NITROGEN AND PHOSPHORUS SUPPLY ON GROWTH AND TISSUE COMPOSITION OF ULVA FENESTRATA AND ENTEROMORPHA INTESTINALIS (ULVALES,CHLOROPHYTA)1

The chlorophyte macroalgae Ulva fenestrata (Postels and Ruprecht) and Enteromorpha intestinalis (Linnaeus) Link. were grown under various nutrient regimes in indoor semi-continuous and batch cultures. Tissue nitrogen contents ranged from 1.3–5.4% N (dry wt), whereas tissue P ranged from 0.21–0.56% P (dry wt). Growth in low nitrogen medium resulted in N:P ratios of 5–8, whereas growth in high nitrogen medium resulted in N:P ratios of 21–44. For U. fenestrata, tissue N:P < 16 was indicative of N-limitation. Tissue N:P 16–24 was optimal for growth and tissue N:P > 24 was indicative of P-limitation. Growth of U. fenestrata was hyperbolically related to tissue N but linearly related to tissue P. Phosphorus-limited U. fenestrata maintained high levels of tissue N, but N-limited algae became depleted of P. For E. intestinalis, tissue N remained at maximum levels during P-limitation whereas tissue P decreased to about 85% of maximal levels during N-limitation. Growth rates for U. fenestrata decreased faster during P-limitation than during N-limitation. Simultaneously, tissue P was depleted faster than tissue N. Our results suggest that comparing tissue N and P of macroalage grown in batch cultures is useful for monitoring the nutritional status of macroalgae.     

EXTENSIVE INTRASPECIFIC MORPHOLOGICAL VARIATION IN ENTEROMORPHA MUSCOIDES (CHLOROPHYTA) REVEALED BY MOLECULAR ANALYSIS

Enteromorpha muscoides (Clemente y Rubio) Cremades and E. clathrata Roth (Greville) are morphologically variable species that can easily be distinguished from other Enteromorpha species but not from each other. The key morphological character separating the two species is the presence or absence of spine-like branches: E. muscoides has small spine-like branches throughout the thallus, whereas E. clathrata lacks spines. The spiny branches in E. muscoides are not as obvious in summer as in winter, so summer samples may be difficult to distinguish from those of E. clathrata. In this study, molecular data were used to investigate whether these two species, as defined by morphological characters, might be conspecific. The sequences of the internal transcribed spacers ITS1 and ITS2 and the 5.8S gene differed by 0%–0.6% between all samples of both E. muscoides and E. clathrata. Phylogenetic analysis of these sequences in an alignment with 13 other representatives of both Enteromorpha and Ulva showed that this highly supported monophyletic E. muscoides / E. clathrata clade is separated by long branch lengths from other Enteromorpha and Ulva clades. Based on these results, we suggest that Enteromorpha muscoides (Clemente y Rubio) Cremades and Enteromorpha clathrata Roth (Greville) are conspecific, with the older name E. muscoides taking priority.     

GROWTH-INHIBITORS AND GROWTH-PROMOTERS IN ENTEROMORPHA COMPRESS A (CHLOROPHYTA)1

Methanol extracts from the alga Enteromorpha compressa (L.) Grev. contain substances which inhibit the elongation of Lepidium roots. Chromatographic separation of the inhibiting substances revealed that one of the inhibitory zones of the chromatograms had properties of the so-called inhibitor β. Neither abscisic acid (ABA) nor lunularic acid proved to be responsible for the growth-inhibiting property of this zone. Moreover, the extracts contain substances which promote the elongation of Avena coleoptile segments. One of these substances could be tentatively identified as indole-3-acetic acid by thin-layer and gas-liquid chromatography. (In addition to indole-3-acetic acid a second growth-promoting factor with the properties of the so-called accelerator α could be detected.)     

The role of lateral roots in bypass flow in rice (Oryza sativa L.)

Although an apoplastic pathway (the so‐called bypass flow) is implicated in the uptake of Na⁺ by rice growing in saline conditions, the point of entry of this flow into roots remains to be elucidated. We investigated the role of lateral roots in bypass flow using the tracer trisodium‐8‐hydroxy‐1,3,6‐pyrenetrisulphonic acid (PTS) and the rice cv. IR36. PTS was identified in the vascular tissue of lateral roots using both epifluorescence microscopy and confocal laser scanning microscopy. Cryo‐scanning electron microscopy and epifluorescence microscopy of sections stained with berberine‐aniline blue revealed that the exodermis is absent in the lateral roots. We conclude that PTS can move freely through the cortical layers of lateral roots, enter the stele and be transported to the shoot via the transpiration stream.     

Gill chloride cell surface-area is greater in freshwater-adapted adult sea trout (Salmo trutta, L.) than those adapted to sea water

An increase in the apical surface-area exposed to the environment in sea trout ( Salmo trutta , L.) branchial chloride cells, examined by scanning electron microscopy after adaptation to fresh water, indicates that salt-uptake may be dependent upon apical membrane morphology.     

Chemical and physical-chemical characteristics of dietary fibres from Ulva lactuca (L.) Thuret and Enteromorpha compressa (L.) Grev.

Dietary fibres from Ulva lactuca (L.) Thuret (sea lettuce) and Enteromorpha compressa (L.) Grev. (A.O. nori) were measured according to a ‘standard’ method and a ‘physiological’ protocol simulating the gastric and intestinal environments. U. lactuca contained 15.8–8.0% soluble and 24.2–32.6% insoluble fibres according to the ‘standard’ and ‘physiological’ methods, respectively. For E. compressa, these values were 14.9–15.9 and 21.6–28.7%, respectively. For both algae, the composition suggests that the soluble fibres were xylorhamnoglycuronans sulphates and insoluble fibres were essentially composed of glucans. No marked chemical compositional variation was observed between soluble fractions extracted under the simulated gastric and intestinal conditions. Fibres in both algae are hydrophilic but the water holding capacities were higher after extraction of soluble fibres (5.5–9.5 g g⁻¹ for the dry algae; 14.0–16.0 g g⁻¹ for the standard insoluble fibres). Water soluble fibres demonstrated low intrinsic viscosities at 37 °C in buffers, particularly those from E. compressa (36.0–36.5 ml g⁻¹), and was affected by pH for those of U. lactuca (147.5 ml g⁻¹ at pH 3.0 and 175.0 ml g⁻¹ at pH 7.3).     

Silicon absorption by wheat (Triticum aestivum L.)

Although silicon (Si) is a quantitatively major inorganic constituent of higher plants the element is not considered generally essential for them. Therefore it is not included in the formulation of any of the solution cultures widely used in plant physiological research. One consequence of this state of affairs is that the absorption and transport of Si have not been investigated nearly as much as those of the elements accorded 'essential' status. In this paper we report experiments showing that Si is rapidly absorbed by wheat (Triticum aestivum L.) plants from solution cultures initially containing Si at 0.5 mM, a concentration realistic in terms of the concentrations of the element in soil solutions. Nearly mature plants (headed out) 'preloaded' with Si absorbed it at virtually the same rate as did plants grown previously in solutions to which Si had not been added. The rate of Si absorption increased by more than an order of magnitude between the 2-leaf and the 7-8 leaf stage, with little change thereafter. This revised version was published online in June 2006 with corrections to the Cover Date.     

Behaviour of roach (Rutilus rutilus L.) altered by Ligula intestinalis (Cestoda: Pseudophyllidea): a field demonstration

1. We studied the influence of a cestode parasite, the tapeworm Ligula intestinalis (L.) on roach ( Rutilus rutilus L.) spatial occupancy in a French reservoir (Lake Pareloup, South-west of France).
2. Fish host age, habitat use and parasite occurrence and abundance were determined during a 1 year cycle using monthly gill-net catches. Multivariate analysis [generalized linear models (GLIM)], revealed significant relationships ( P  < 0.05) between roach age, its spatial occupancy and parasite occurrence and abundance.
3. Three-year-old roach were found to be heavily parasitized and their location toward the bank was significantly linked to parasite occurrence and abundance. Parasitized fish, considering both parasite occurrence and abundance, tended to occur close to the bank between July and December. On the contrary, between January and June no significant relationship was found.
4. These behavioural changes induced by the parasite may increase piscivorous bird encounter rate and predation efficiency on parasitized roach and therefore facilitate completion of the parasite's life cycle.