Cadmium accumulation in populations of Thlaspi caerulescens and Thlaspi goesingense

The capacity to accumulate cadmium (Cd) and zinc (Zn) was compared in Thlaspi goesingense and four populations of Thlaspi caerulescens . Two populations of T. caerulescens were grown in hydroponics at five concentrations of Cd. In addition, plants were grown in pots containing compost in which three different concentrations of Cd and two concentrations of Zn were added. A field trial was conducted to compare Zn and Cd uptake by three populations of T. caerulescens on nine selected plots of the Woburn Market Garden Experiment (UK) which had been contaminated to different degrees with heavy metals owing to past applications of sewage sludge. Results show that the four populations of T. caerulescens had the same ability to hyperaccumulate Zn but were significantly different in terms of Cd accumulation. Two populations of T. caerulescens from Southern France accumulated much more Cd than the populations from Prayon (Belgium) and Whitesike (UK). Generally, uptake of Cd was not decreased by increased concentrations of Zn in the substrate. These results indicate that the mechanisms of Cd and Zn hyperaccumulation are not identical in this species. This is the first report of hyperaccumulation of Cd by T. goesingense , but the growth of this species was markedly reduced by the large concentrations of Zn in the substrate. Future work should focus on the differences between Cd and Zn uptake in hyperaccumulator plants at the species and population level.     

The Effect of Carbohydrate and Nitrogen Concentration on Phenol Synthesis in Paul's Scarlet Rose Cells Grown in Tissue Culture

The effects of exogenous concentrations of glucose and nitrate on total ethanol extractable phenols and leucoanthocyanins were studied in Paul's Scarlet Rose cells grown in either liquid suspension or solid culture. Aliquots of liquid suspension cultured cells were harvested during logarithmic, early stationary, and late stationary periods of growth for determination of fresh weight, dry weight, total ethanol extractable phenols and leucoanthocyanins. Cells produced phenols during all phases of growth, but at stationary phase, the production was greatest. Increasing concentrations of exogenous glucose in the culture medium resulted in an increased synthesis of total phenols in logarithmic cells, and an increased synthesis of total phenols and leucoanthocyanin in stationary cells. Addition of increased concentrations of exogenous nitrate to the stationary cells grown in suspension culture markedly reduced synthesis of leucoanthocyanins although total phenol synthesis was not significantly affected. Similar observations were made in cells cultured on solid medium in respect to exogenous glucose concentration, however these cells differed from the suspension cultured cells by having increased amounts of total phenol synthesis and decreased synthesis of leucoanthocyanins in the presence of increasing concentrations of exogenous nitrate in the culture medium.     

Using plant analysis to predict yield losses caused by sulphur deficiency

Yield losses in agricultural crops as a result of sulphur deficiency are increasing in the UK, because of the decrease in sulphur dioxide emissions and changes in fertiliser practices. Therefore, there is a need for a reliable and practical diagnostic indicator to predict early in the growing season whether it is necessary to apply S fertiliser, but also to avoid the application of fertiliser when not necessary. A successful diagnostic indicator should be reliable and stable throughout plant development, but also easily measured with great accuracy and as little effort as possible. In this paper the difficulties and problems with currently used diagnostic tests for S deficiency, such as total S, sulphate or the N:S ratio, will be discussed. A more reliable and practical indicator of S deficiency is the malate: sulphate peak area ratio which is at present being developed for use by commercial laboratories and their customers.     

RECRUITMENT AND GROWTH OF THE BLUE-RAYED LIMPET, HELCION PELLUCIDUM (L.), IN SOUTH EAST IRELAND

This account reports on recruitment, growth and population structureof the macroherbivorous gastropod Helcion pellucidum (L.) onan exposed rocky shore in S.E. Ireland, with particular referenceto the pellucidum form. Recently settled Helcion spat were foundinitially on living crustose lithothamnia in pools and on openrock, on the lower shore, during February-April and subsequentlyrecruited to macro-algal fronds. By May they were found in abundanceon Mastocarpus stellatus and Laminaria spp. Helcion was markedlyseasonal in its occurrence on Mastocarpus, being most abundantduring May-August. A complementary pattern was evident on growingHimanthalia receptacles, with limpets abundant from July onwards.It is suggested that Helcion may migrate from Mastocarpus toHimanthalia as they grow. Data on growth rates are presentedfor Helcion in the various habitats studied. Growth rates werehighest on the Laminaria spp. (Received 21 February 1992; accepted 8 June 1992)     

Population structure of the yellow-footed rock-wallaby Petrogale xanthopus (Gray, 1854) inferred from mtDNA sequences and microsatellite loci

The yellow-footed rock-wallaby Petrogale xanthopus is considered to be potentially vulnerable to extinction. This wallaby inhabits naturally disjunct rocky outcrops which could restrict dispersal between populations, but the extent to which that occurs is unknown. Genetic differences between populations were assessed using mitochondrial DNA (control region) sequencing and analysis of variation at four microsatellite loci among three geographically close sites in south-west Queensland (P. x. celeris) and, for mtDNA only, samples from South Australia (P. x. xanthopus) as well. Populations from South Australia and Queensland had phylogenetically distinct mtDNA, supporting the present classification of these two groups as evolutionarily distinct entities. Within Queensland, populations separated by 70 km of unsuitable habitat differed significantly for mtDNA and at microsatellite loci. Populations separated by 10 km of apparently suitable habitat had statistically homogeneous mtDNA, but a significant difference in allele frequency at one microsatellite locus. Tests for Hardy-Weinberg equilibrium and micro-geographical variation at microsatellite loci did not detect any substructuring between two wallaby aggregations within a colony encircling a single rock outcrop. Although the present study was limited by small sample sizes at two of the three Queensland locations examined, the genetic results suggest that dispersal between colonies is limited, consistent with an ecological study of dispersal at one of the sites. Considering both the genetic and ecological data, we suggest that management of yellow-footed rock-wallabies should treat each colony as an independent unit and that conservation of the Queensland and South Australian populations as separate entities is warranted.