Response of pelagic cyanobacteria to iron additions--enclosure experiments from Lake Erken

In this study, low epilimnetic iron availability during thesummer stagnation period was concluded to be a limiting factorfor cyanobacterial development in Lake Erken. In three enclosureexperiments, different combinations of phosphate, nitrate andammonium additions were tested both with and without additionsof dissolved iron. The addition of iron increased the growthof diazotrophic cyanobacteria significantly compared with enclosuresnot receiving iron. This was especially evident for the colony-formingcyanobacterium Gloeotrichia echinulata. In one experiment, coloniesof G.echinulata disappeared in enclosures not receiving iron,while the abundance of this species increased in those enclosuresto which iron was added.     

Genotypical Variability for the Tasks of Water Collecting and Scenting in a Honey Bee Colony

The polyandrous mating behaviour of the honey bee queen increases the genotypical variability amongst her worker offspring. Microsatellite DNA analyses revealed a total of 16 subfamilies in one colony of honey bees. The subfamilies were represented in significantly different proportions in two subgroups of bees, water collecting bees and scenting bees, indicating a genetic component in task choice.     

Mobile Link Organisms and Ecosystem Functioning: Implications for Ecosystem Resilience and Management

Current natural resource management seldom takes the ecosystem functions performed by organisms that move between systems into consideration. Organisms that actively move in the landscape and connect habitats in space and time are here termed “mobile links.” They are essential components in the dynamics of ecosystem development and ecosystem resilience (that is, buffer capacity and opportunity for reorganization) that provide ecological memory (that is, sources for reorganization after disturbance). We investigated the effects of such mobile links on ecosystem functions in aquatic as well as terrestrial environments. We identify three main functional categories: resource, genetic, and process linkers and suggest that the diversity within functional groups of mobile links is a central component of ecosystem resilience. As the planet becomes increasingly dominated by humans, the magnitude, frequency, timing, spatial extent, rate, and quality of such organism-mediated linkages are being altered. We argue that global environmental change can lead to (a) the decline of essential links in functional groups providing pollination, seed dispersal, and pest control; (b) the linking of previously disconnected areas, for example, the spread of vector-borne diseases and invasive species; and (c) the potential for existing links to become carriers of toxic substances, such as persistent organic compounds. We conclude that knowledge of interspatial exchange via mobile links needs to be incorporated into management and policy-making decisions in order to maintain ecosystem resilience and hence secure the capacity of ecosystems to supply the goods and services essential to society. Received 23 April 2001; accepted 17 June 2002.     

The Garifuna Journey

The Garifuna Journey. 1998. 47 minutes, color. video by Andrea E. Leland and Kathy L. Berger. For more information contact Leland/Berger Productions, 1200 Judson, Evanston, IL 60202.     

Autophagic sequestration of [C]sucrose introduced into isolated rat hepatocytes by electrical and non-electrical methods

Isolated rat hepatocytes were found to become permeable to [¹⁴C]sucrose at 0 °C under three different conditions:

1. 1. Immediately following their liberation from the collagenase-perfused liver.

2. 2. Following a short incubation under hypoxic conditions.

3. 3. After electropermeabilisation.

All three conditions were characterised by the formation of small protuberances (blebs) indicative of localised cell surface damage, and it is possible that the stretched plasma membrane of such blebs acted as a high-permeability region. Disappearance of blebs and restoration of normal plasma membrane impermeability could be achieved by a short (15 min) incubation at 37 °C.It could be shown that [¹⁴C]sucrose introduced into rat hepatocytes by non-electrical means was autophagically sequestered at the same rate as [¹⁴C]sucrose introduced electrically. In both cases the sequestration was inhibited by the specific autophagy inhibitor 3-methyladenine to a similar extent. The subcellular distribution of sequestered isotope in metrizamide/sucrose density gradients was found to be independent of the conditions of its introduction into cells.     

A second form of adenine phosphoribosyltransferase in Arabidopsis thaliana with relative specificity towards cytokinins

Adenine phosphoribosyltransferase (APRTase) is an important enzyme for its ability to convert adenine, a by-product of many biochemical reactions, into AMP. By functional complementation of an Escherichia coli mutant, cDNAs encoding two APRTases have been cloned from Arabidopsis thaliana. One of the cDNAs (ATapt1)has been previously identified while the second (ATapt2) is of a previously unknown type. Kinetic analysis of the two enzymes purified from E. coli expressing the two cDNAs indicates that ATapt2 has a higher affinity for cytokinin than the ATapt1. RNase protection studies indicate that the ATapt2, is not expressed in leaves. Analysis of the gene structure indicates that ATapt2 has identical intron positions to ATapt1, but neither the intron sequence nor intron size are conserved between the two genes. The implications of a second, differentially expressed APRTase with affinity for both adenine and cytokinin are discussed.