Change in the chemical signature of the ant leptothorax lichtensteini bondroit with time

The cuticular hydrocarbons of foraging workers of the ant Leptothorax lichtensteini have been identified by gas chromatography-mass spectrometry. Characterization of these compounds at regular intervals, by gas chromatography, has shown a change with time in the relative proportions of some of the hydrocarbons: n-hexacosane, 4-methylhexacosane, 4-methyloctacosane, 3-methylnoncosane. Some of which constitute a part of the colony signature. These changes occur in a synchronous manner, and in the same way for all the individuals of a colony tested at the same time. The changes also appear in queenless colonies; nevertheless, the presence of a queen seems to accelerate the change over the course of 1 yr. Certain hypotheses are formulated as to the mode of regulation of the synthesis of cuticular hydrocarbons responsible for these changes with time and as to the role played by the queen in this regulation. The implications of such a dynamic system for the process of nestmate recognition are discussed.     

A single bout of exercise induces beta-adrenergic desensitization in human adipose tissue

This study was designed to assess whether physiological activation of the sympathetic nervous system induced by exercise changes adipose tissue responsiveness to catecholamines in humans. Lipid mobilization in abdominal subcutaneous adipose tissue was studied with the use of a microdialysis method in 11 nontrained men (age: 22. 3 +/- 1.5 yr; body mass index: 23.0 +/- 1.6). Adipose tissue adrenergic sensitivity was explored with norepinephrine, dobutamine (beta(1)-agonist), or terbutaline (beta(2)-agonist) perfused during 30 min through probes before and after 60-min exercise (50% of the maximal aerobic power). The increase in extracellular glycerol concentration during infusion was significantly lower after the exercise when compared with the increase observed before the exercise (P < 0.05, P < 0.02, and P < 0.01, respectively, for norepinephrine, dobutamine, and terbutaline). In a control experiment realized without exercise, no difference in norepinephrine-induced glycerol increase between the two infusions was observed. To assess the involvement of catecholamines in the blunted beta-adrenergic-induced lipolytic response after exercise, adipose tissue adrenergic sensitivity was explored with two 60-min infusions of norepinephrine or epinephrine separated by a 60-min interval. With both catecholamines, the increase in glycerol was significantly lower during the second infusion (P < 0.05). The findings suggest that aerobic exercise, which increased adrenergic activity, induces a desensitization in beta(1)- and beta(2)-adrenergic lipolytic pathways in human subcutaneous adipose tissue.     

Stoichiometry and compartmentation of NADH metabolism in Saccharomyces cerevisiae

In Saccharomyces cerevisiae, reduction of NAD(+) to NADH occurs in dissimilatory as well as in assimilatory reactions. This review discusses mechanisms for reoxidation of NADH in this yeast, with special emphasis on the metabolic compartmentation that occurs as a consequence of the impermeability of the mitochondrial inner membrane for NADH and NAD(+). At least five mechanisms of NADH reoxidation exist in S. cerevisiae. These are: (1) alcoholic fermentation; (2) glycerol production; (3) respiration of cytosolic NADH via external mitochondrial NADH dehydrogenases; (4) respiration of cytosolic NADH via the glycerol-3-phosphate shuttle; and (5) oxidation of intramitochondrial NADH via a mitochondrial 'internal' NADH dehydrogenase. Furthermore, in vivo evidence indicates that NADH redox equivalents can be shuttled across the mitochondrial inner membrane by an ethanol-acetaldehyde shuttle. Several other redox-shuttle mechanisms might occur in S. cerevisiae, including a malate-oxaloacetate shuttle, a malate-aspartate shuttle and a malate-pyruvate shuttle. Although key enzymes and transporters for these shuttles are present, there is as yet no consistent evidence for their in vivo activity. Activity of several other shuttles, including the malate-citrate and fatty acid shuttles, can be ruled out based on the absence of key enzymes or transporters. Quantitative physiological analysis of defined mutants has been important in identifying several parallel pathways for reoxidation of cytosolic and intramitochondrial NADH. The major challenge that lies ahead is to elucidate the physiological function of parallel pathways for NADH oxidation in wild-type cells, both under steady-state and transient-state conditions. This requires the development of techniques for accurate measurement of intracellular metabolite concentrations in separate metabolic compartments.     

MassFlowDyn I: A Carbon Transport and Partitioning Model for Root System Architecture

Carbon partitioning is important for understanding root developmentbut little is known about its regulation. Existing models suggestthat partitioning is controlled by the potential sink strength.They cannot, however, simulate hierarchical uptake other thanby using absolute priorities. Moreover, they cannot explainthat the changes in photoassimilate partitioning result fromchanges in photosynthesis. In this paper we present a modelof phloem sieve circulation, based on the model of Minchin etal. (Journal of Experimental Botany44: 947–955, 1993).The root system was represented by a network of segments towhich meristems were connected. The properties of the segmentswere determined by the differentiation stage. Photoassimilateimport from each organ was assumed to be limited by a metabolicprocess and driven by Michaelis–Menten kinetics. The axialgrowth was proportional to meristem respiration, which drivesthe flux of new cells required for root elongation. We usedthe model to look at trophic apical dominance, determinate andindeterminate root growth, the effect of the activity of a rooton competition with its neighbours, and the effect of photoassimilateavailability on changes in partitioning. The simulated phloemmass flow yielded results of the same order of magnitude asthose generally reported in the literature. For the main wellvascularized axis, the model predicted that one single apicalmeristem larger than its neighbouring laterals, was enough togenerate a taprooted system. Conversely, when the meristem oflaterals close to the collar had a volume similar to that ofthe taproot, the predicted network became fibrous. The modelpredicted a hierarchical priority for organ photoassimilateuptake, similar to that described in the literature, duringthe decline in photosynthetic activity. Our model suggests thatdeterminate growth of the first laterals resulted from a localshortage of photoassimilate at their meristem, as a result ofthe limited transport properties of the developed roots. Copyright2000 Annals of Botany Company Münch theory, phloem transport model, photoassimilate-partitioning, root growth, root system architecture, translocation