Molecular genetics of peripheral populations of Nova Scotian Unionidae (Mollusca: Bivalvia)

Peripheral populations of eight species of freshwater bivalves (Unionidae.) extending their geographic ranges into Nova Scotia, Canada, were examined electrophoretically to determine both the extent of genetic variability within such populations, and whether the hypothesized pathway of colonization across the Isthmus of Chignecto is reflected in patterns of genetic resemblance among these populations. The Nova Scotian species examined could be separated into two groups based on levels of observed heterozygosity and levels of variability in allele frequencies. The first group is characterized by low levels of heterozygosity and polymorphism compared with north-eastern American populations, and in the case of one species, Elliptio complanala, considerable variability in allele frequencies among populations occurring in similar habitats in different drainages. Populations of E. complanata from Nova Scotia can be differentiated from conspecific populations on the southern Atlantic Slope by possession of fast alleles at two loci. Multivariate analyses define subgroups within populations of E. complanata consistent with hypothesis that the species invaded Nova Scotia by way of the Isthmus of Chignecto, and then split into two groups, one of which colonized Cape Breton to the north and the other of which colonized southern areas of the Province. The second group of Nova Scotian species is characterized by little reduction in heterozygosity and polymorphism compared with values observed among north-eastern American conspecifics or congeners, little variability in allele frequencies from population to population, and little evidence to suggest that these species were dependent on the land bridge to invade the Province. The type of dispersal is hypothesized to be responsible, in part, for these differences: larvae of species in the first group rely on a parasitic attachment to fish with territorial habits limited to fresh water, and are thus likely to invade new drainages separated by salt water by chance, in small numbers, and in stepping-stone fashion. Species in the second group parasitize anadromous or saltwater tolerant hosts, are likely to be introduced into new habitats in greater numbers and/or receive greater amounts of gene flow subsequent to colonization, and seem less dependent on land-bridges to colonize new habitats.     

A Comparative Study on the Effects of H2S and SO2 Fumigation on the Growth and Accumulation of Sulphate and Sulphydryl Compounds in Trifolium pratense L., Glycine max Merr. and Phaseolus vulgaris L.

Maas, F. M., De Kok, L. J., Peters, J. L. and Kuiper, P. J.C. 1987. A comparative study on the effects of H₂S and SO₂ fumigationon the growth and accumulation of sulphate and sulphydryl compoundsin Trifolium pratense L., Glycine max Merr. and Phaseolus vulgarisL.—J. exp. Bot. 38: 1459-1469. The effects of 0—25 mm³ dm³ H₂S and SO₂ on growth andsulphur content of shoots of Trifolium pratense, Glycine maxand Phaseolus vulgaris were studied. After 2 weeks of fumigationthe yield of T. pralense was reduced by 32% by H₂S, but notaffected by SO₂. Yield of G. max was not affected by H₂S, butreduced by 20% by SO₂, whereas that of P. vulgaris was increasedby 11% by H₂S and not affected by SO₂. Increases in sulphydrylcontent were already observed after 24 h of exposure to H₂Sand SO₂ in all plants. The increase was greatest in T. pratenseand smallest in P. vulgaris and, except for T. pratense, alwaysgreater in the H₂S-exposed than the SO₂-exposed plants. Oneday of exposure resulted in an increase in sulphate contentonly in the SO₂-fumigated plants, with the highest accumulationin T. pratense and the lowest in P. vulgaris. After 2 weeksan increase in sulphate content was also observed in the H₂S-exposedplants. This increase was also highest in T. pratense and lowestin P. vulgaris. Transpiration rate was not affected by a 24 h exposure to H₂Sor SO₂ and was highest in T. pratense, intermediate in G. maxand lowest in P. vulgaris. The order of theoretical rates of deposition of H₂S and SO₂correlated with the observed increases in sulphydryl contentduring the first 24 h of exposure in both H₂S and SO₂-fumigatedplants and with the increase in sulphate content in the SO₂-exposedplants. The increases in sulphydryl content were only 8% ofthe theoretical H₂S and SO₂-deposition fluxes, whereas sulphateaccumulation accounted for at least 57% of the theoretical SO₂-depositionflux. Key words: Air pollution, clover, French bean, Glutathione, Soybean, sulphur metabolism.     

Effect of Reduction of Sink Strength in Developing Seeds on Vein Loading Patterns of Photoassimilate in Source Leaves of Pisum sativum L

The effect of sink strength reduction in developing seeds onvein loading of photoassimilate has been studied in Pisum sativumL. The sink strength was manipulated by means of the ‘openseed coat technique’. Sink strength of the operated ovuleswas controlled by the osmolality of a substitute medium replacingthe embryo. A high osmolality of the medium (400 mM mannitol)or a low osmolality of the medium (without mannitol) was usedto maintain a high or low sink strength, respectively. To studythe effect of sink strength reduction on vein loading, macro-autoradiographywas used. After applying ¹⁴CO₂ to the source leaf for 10 to20min autoradiographs of plants with different sink strengthshowed differences in distribution of ¹⁴C-photoassimilate overthe mesophyll and the veins. Under low sink strength conditionsvein loading of ¹⁴C-photoassimilate was reduced. After longertime spans (40 to 60 min) no clear differences in vein loadingwere visible in the autoradiographs. However, measurement of¹⁴C in plant parts along the path of transport from source tosink showed a decrease of the rate of export of ¹⁴C from thesource leaf under low sink strength conditions. Apparently,accumulation of ¹⁴C-photoassimilate into the phloem and exporttowards sink regions can be reduced by lowering the sink strength.A signal must have been transferred from sink all the way tothe source regions. The mechanism of such a signal is discussed. Key words: Pisum sativum, phloem loading, photoassimilate transport, seed development, sink-source interactions     

PARASITISM AND THE UNIONACEA (BIVALVIA)

It is proposed that the incorporation of a unique parasitic stage in the life-cycle of unionaceans which involves an obligate relationship between a vertebrate host, usually a fish, and a highly modified larval stage, the glochidium, has had far-reaching consequences with respect to overall morphology, extent of species' geographic ranges, and rate of speciation in the group. Glochidia are separable into three main types with respect to overall shape and attachment features, and are retained in variously modified brood pouches. When mature, glochidia are released in several different ways which reflect various adaptations involved in either attracting the fish host and/or increasing the probability of attachment. Glochidia do not seem capable of host selection, and the reaction of the host to the parasite seems to be the main factor in determining specificity. Release of glochidia is synchronized to correspond to periods of predictable host availability, such as during spawing migrations and nesting behaviour. Other adaptations include modifications of glochidial conglutinates to mimic host food items, and modifications of the unionacean mantle edges to attract hosts. In all cases, a good correlation exists between the type of lure used and host food preferences, but, despite these adaptations, host specificity among unionaceans seems low. Parasitism among unionaceans is postulated to be mainly advantageous in terms of predictability of dispersal by habitat-specific hosts, but parasitism is hypothesized to entail constraints in terms of the degree to which shell shape and life-habit can be diversified among unionaceans. The type of host parasitized is considered to affect the rate of diversification among populations and speciation among unionaceans: those that parasitize strictly freshwater hosts are more likely to exhibit highly individualistic populations in different drainages with respect to molecular genetic and soft-part characters, while those that parasitize anadromous or saltwater-tolerant hosts show little differentiation among widely distributed populations.     

Glycolipid Degradation in Leaves of the Thermophilic Cucumis sativus as Affected by Light and Low-Temperature Treatment

Treatment of Cucumis leaf discs with light and low temperature (1°C) resulted in degradation of the total lipids. In addition, a decrease of the linolenic acid content of the glycolipids of leaves and leaf discs took place while at the same time an increase in the content of unidentified degradation products from the glycolipids was observed. The decrease of the linolenic acid content was not due to galactolipase activity, since no monogalactosyl diglyceride acyl hydrolase activity was found. Dark and low temperature did not alter the fatty acid composition. Blue light and low temperature resulted in a decrease of the linolenic acid content, while yellow-, red- and far red light in combination with low temperature were ineffective.     

The effect of salinity on lipid composition and on activity of Ca2+- and Mg2+-stimulated ATPases in salt-sensitive and salt-tolerant Plantago species

Lipid composition of the roots and the shoot of the salt-sensitive Plantago media L., the salt-tolerant P. maritima L. and the less salt-tolerant P. coronopus L. was followed under saline conditions. In the roots of P. media the level of phospho-, galacto- and sulpholipids decreased strongly with increased NaCl concentration, indicating decreased control of permeability of the root cell membranes. In the roots of the two salt-tolerant species the level of most lipid classes was maintained or even raised up to 75 mM NaCl, and a decrease was noted only at higher NaCl concentrations. In P. maritima, a species from relatively nutrient-rich habitats, decreased lipid levels in the roots and shoot were observed with increasing salinity in combination with a low nutrient availability. The Ca²⁺- and Mg²⁺-stimulated ATPase activities of the microsomal fraction of the roots of P. maritima was decreased at a salinity level in excess of 150 mM, while in P. coronopus they were decreased at all NaCl levels tested. The obtained results are discussed as part of the adaptation of the species to salinity.     

Ca2+ and Mg2+-Stimulated ATPases from Roots of Plantago lanceolata, Plantago media and Plantago coronopus: Response to Alterations of the Level of Mineral Nutrition and Ecological Significance

Growth of Plantago lanceolata L., P. media L. and P. coronopus L. was followed at two levels of mineral nutrition (low-salt and high-salt). In addition the response of transfer of plants from low-salt conditions to high-salt conditions and vice versa was studied. Growth of these Plantago species was not much affected by the nutritional level. P. coronopus showed the least dependence on the level of mineral nutrition. The Ca²⁺- and Mg²⁺-stimulated ATPase activity of microsomal preparations of the roots of Plantago was also studied. A pH optimum at pH 6.5 was observed in all species, together with a relatively high ATPase activation by Mg²⁺ in P. lanceolata, by Ca²⁺ in P. media, and by both ions in P. coronopus. The specific activity of the ATPases was highest in preparations from low-salt roots. The three species all occur in relatively nutrient-poor habitats, but they are at the same time particularly adapted to circumneutral soils (P. lanceolata), to Ca²⁺-rich soils (P. media) and to alternating levels of mineral nutrition (P. coronopus). The properties of the ATPases (K_m, V_max, protein content) and the growth are discussed in relation to these ecological properties of the species.     

Taxonomic studies on Senecio aquaticus (Asteraceae). A recommendation for the taxonomic status of Aquaticus and Barbareifolius

Aquaticus and Barbareifolius are two subgroups of Senecio aquaticus s. l. (Asteraceae) that have been recognized at various taxonomic levels in European taxonomic literature. In this paper we present the results of morphological studies on S. aquaticus s. l. in order to establish the taxonomic status of these two subgroups. Using multivariate morphometric techniques (discriminant analysis and principal component analysis), we examined the diagnostic potential of 60 macro-morphological characters and studied the delimitation of Aquaticus and Barbareifolius. Seven of the characters studied were included in the discriminant function of the stepwise discriminant analysis and are therefore considered to be the most reliable diagnostic characters of Aquaticus and Barbareifolius. Barbareifolius has, amongst other distinguishing traits, a more divaricate inflorescence than Aquaticus. Because both subgroups are distinct but overlapping clusters in multivariate morphometric space, and because clear differences in their geographical distribution are absent, we recommend the taxonomic status of variety to both groups. Following the rules of nomenclature, Aquaticus and Barbareifolius should therefore be named S. aquaticus Hill var. aquaticus and S. aquaticus Hill var. barbareifolius (Krock.) Wimm. & Grab.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 145 , 489–498.