The transport of radiolabeled indoleacetic acid and its conjugates in nodal stem segments of Phaseolus vulgaris L.

The transport of radiolabeled indoleacetic acid (IAA), and some of its conjugates, was investigated in nodal stem segments of Phaseolus vulgaris L. Donor agar blocks containing either [2-acetyl-¹⁴C]-IAA; [2-acetyl-¹⁴C]-indole-3-acetyl-L-aspartate (IAAsp); [2-acetyl-¹⁴C]-indole-3-acetyl-L-glycine (IAGly); or [2-acetyl-¹⁴C]-indole-3-acetyl-L-alanine (IAAla) were placed on either the apical or basal cut surface of stem segments each bearing an axillary bud at the midline. In some experiments, a receiver block was placed on the end opposite to the donor. After transport was terminated, the segments were divided into five equal sections plus the bud, and the radioactivity of donors, receivers and each part of the stem segment was counted.For all four substances tested, the amount of ¹⁴C transported to the axillary bud from the base was the same or greater than that from the apical end. After basipetal transport, the distribution of ¹⁴C in the segment declined sharply from apex to base. The inverse was true for acropetal transport. Transport for the three IAA conjugates did not differ substantially from each other.The IAA transport inhibitor, N-1-naphthylphthalamic acid (NPA), inhibited basipetal ¹⁴C-IAA transport to the base of the stem segment but did not alter substantially the amount of ¹⁴C-IAA recovered from the bud. Transport of ¹⁴C-IAA from the apical end to all parts of the stem segment declined when the base of the section was treated with nonradioactive IAA. Taken together with data presented in the accompanying article [Tamas et al. (1989) Plant Growth Regul 8: 165–183], these results suggest that the transport of IAA plays a role in axillary bud growth regulation, but its effect does not depend on the accumulation of IAA in the axillary bud itself.     

A spatial model of the evolution of quorum sensing regulating bacteriocin production

Like any form of cooperative behavior, quorum sensing (QS) inbacteria is potentially vulnerable to cheating, the occurrenceof individuals that contribute less but still profit from thebenefits provided by others. In this paper, we explore the evolutionarystability of QS as a regulatory mechanism of antibiotics productionin a spatially structured population, using cellular automaton(CA) modeling. QSg is supposed to regulate the excretion ofa bacteriocin (anticompetitor toxin) in a population of bacteriapolymorphic for the ability to produce and to be immune to thebacteriocin. Both the social interactions resulting from QSand the competitive interactions resulting from the bacteriocinexcretion are supposed to be only effective at the local scale,that is, restricted to the immediately neighboring cells. Thisimplies a rather diffuse kind of group selection. The CA modelis contrasted to a model assuming no spatial structure but withotherwise identical assumptions. Our analysis predicts thatQS as a regulatory mechanism of bacteriocin excretion is evolutionarilyunstable when the competitive interactions between bacteriocin-producing,resistant, and sensitive strains only involve closely relatedstrains which can share the signaling and responding genes involvedin QS. However, when the competition is between unrelated strainsand the QS alleles can only be carried by the bacteriocin-producingstrains, stable QS may evolve provided its costs are small andthe critical quorum threshold is neither too low nor too high.     

Ethanol potentiates the inhibitory effect of D-galactosamine on protein synthesis in isolated hepatocytes

The effect of the combined addition of D-galactosamine and ethanol on hepatic protein synthesis was studied in isolated mouse hepatocytes. 2.5 mM D-galactosamine or 40 mM ethanol alone caused slight or no inhibition of amino acid incorporation into proteins. However, a profound inhibition (about 80%) was observed if D-galactosamine of the same dose was added after a preincubation of the cells with 40 mM ethanol and vice versa. It shows that there is a strong mutual potentiation between D-galactosamine and ethanol in the inhibition of protein synthesis.     

Acetylarsenocholine: A Cholinergic Agonist

Abstract: The pharmacological properties of acetylarsenocholine, an arsenic analogue of acetylcholine, were investigated. Acetylarsenocholine behaved as a cholinergic ligand both in the central and peripheral nervous system. It bound to nicotinic receptors in rat medulla-pons with a K _D of 15 μ M and to muscarinic receptors in rat cerebral cortex with a K _D of 10 μ M . It behaved also as an agonist at presynaptic muscarinic receptors in guinea pig ileum myenteric plexus preparation. Arsenocholine is an alternative substrate for choline acetyltransferase and acetylarsenocholine is an alternative substrate for acetylcholinesterase.