Polyamine Content in Relation to Embryo Growth and Dedifferentiation in Barley (Hordeum vulgare L.)

Putrescine, spermidine, and spermine content were analysed inzygotic embryos of barley (Hordeum vulgare L.). Changes in polyaminecontent were observed during zygotic embryo growth. In two cultivars,‘Bomi’ and ‘Golden Promise’, the totalpolyamine content in the embryos was 2.6–2.9 nmol mg^–1fresh weight 10 d after anthesis, the highest content observed.It dropped to 1.3 nmol mg^–1 fresh weight 14 d after anthesis.This drop was caused by decreases in all three polyamine concentrations.From 14 to 35 d after anthesis the putrescine content continuedto decrease while the spermidine and spermine content increased,thus the total polyamine content remained constant until 35d after anthesis. The mutant ‘Ris? 1508’ showeda constant polyamine content around 1.3 nmol mg^–1 freshweight from 14 to 35 d after anthesis. The polyamine patternwas conserved in all three lines throughout the period of investigationshowing a spermidine content higher than putrescine contentwhich was, in turn, higher or equal to the spermine content.The polyamine content measured as nmol µg^–1 proteindecreased from 14 to 21 d post anthesis in all three lines,because the protein content (µg mg^–1 fresh weight)increased during the period. In dedifferentiating zygotic embryoscultured in vitro the putrescine content (nmol mg^–1 freshweight) rose by a factor of nine and the spermidine contentdoubled within the first week of cultivation, whereas sperminecontent did not change. For embryoderived calli a repeated patternof change in polyamine content was observed throughout the subculturingperiod. Key words: Polyamines, Hordeum vulgare L., embryo development     

Benthic resources are the key to Daphnia middendorffiana survival in a high arctic pond

1. Shallow arctic lakes and ponds have simple and short food webs, but large uncertainties remain about benthic–pelagic links in these systems. We tested whether organic matter of benthic origin supports zooplankton biomass in a pond in NE Greenland, using stable isotope analysis of carbon and nitrogen in the pond itself and in a ¹³C‐enrichment enclosure experiment. In the latter, we manipulated the carbon isotope signature of benthic algae to enhance its isotopic discrimination from other potential food sources for zooplankton. 2. The cladoceran Daphnia middendorffiana responded to the ¹³C‐enrichment of benthic mats with progressively increasing δ¹³C values, suggesting benthic feeding. Stable isotope analysis also pointed towards a negligible contribution of terrestrial carbon to the diet of D. middendorffiana. This agreed with the apparent dominance of autochthonous dissolved organic matter in the pond revealed by analysis of coloured dissolved organic matter. 3. Daily net production by phytoplankton in the pond (18 mg C m^?2 day^?1) could satisfy only up to half of the calculated minimum energy requirements of D. middendorffiana (35 mg C m^?2 day^?1), whereas benthic primary production alone (145 mg C m^?2 day^?1) was more than sufficient. 4. Our findings highlight benthic primary production as a major dietary source for D. middendorffiana in this system and suggest that benthic organic matter may play a key role in sustaining pelagic secondary production in such nutrient‐limited high arctic ponds.     

The outcome of the invasion of Florida lakes by Daphnia lumholtzi

1. We examined 7–12 years of monthly to quarterly historical data from 15 lakes in FL, U.S.A. to determine the extent and outcome of invasion by the alien cladoceran Daphnia lumholtzi Sars. 2. The alien species was found in 10 of the 15 lakes, including Florida’s three largest lakes: Okeechobee, George and Apopka. All the surveyed lakes had resident populations of the smaller native species Daphnia ambigua Scourfield. 3. In most of the lakes, D. ambigua occurred seven to ninefold more often in plankton samples than D. lumholtzi, and at 10‐ to 100‐fold higher maximal densities. One exception was a small lake in central Florida (Lake Jesup), where D. lumholtzi attained high densities on several occasions in the 10 years of sampling. 4. In Lake Okeechobee, where data were of sufficient quality and quantity to perform statistical analyses, the results of canonical correlation analysis indicated that high densities of D. lumholtzi were correlated with lower concentrations of suspended solids, high algal biomass and higher temperature, whereas the opposite conditions were correlated with high densities of D. ambigua. 5. Based on the majority of data, D. lumholtzi has successfully invaded many lakes in Florida, yet it has not become a substantive component of the zooplankton. Additional research is needed to determine whether resources, fish predation or some other factor is responsible for this outcome of invasion.     

Validation of Fecal Glucocorticoid Metabolite Assays for South African Herbivores

ABSTRACT Fecal glucocorticoid metabolite (FGM) assays are a popular means of monitoring adrenocortical activity (i.e., physiological stress response) in wildlife. Species-specific differences in glucocorticoid metabolism and excretion require assay validation, including both laboratory and biological components, before assay use in new species. We validated a commercially available radioimmunoassay (MP ¹²⁵I corticosterone RIA kit [MP Biomedicals, Solon, OH]) for measuring FGMs of several South African herbivores, including giraffe (Giraffa camelopardalis), impala (Aepyceros melampus), nyala (Tragelaphus buxtoni), kudu (Tragelaphus strepsiceros), wildebeest (Connochaetes taurinus), and zebra (Equus burchelli). These herbivores are important in South African parks and reserves for ecotourism and as a prey base for predators and serve an integral role in ecosystem processes. Standard biochemical validations (e.g., recovery of exogenous corticosterone, intra- and interassay variation, and parallelism) demonstrated that the assay accurately and precisely measured FGMs of all 6 herbivore species. Our biological validations demonstrated that the assay was sensitive enough to detect changes in FGM production associated with season. Samples collected during the dry season (Jun-Aug) contained higher FGM concentrations than those from the wet season (Dec-Feb) in all species. We established optimal sample dilutions and reference FGM levels for these 6 herbivores, which can now be used to monitor the effects of management and ecotourism activities on the stress responses of these herbivores.