Use of Avermectins for the Control of Meloidogyne incognita on tomatoes

The efficacy of avermectins B₁ and B₂ for control of Meloidogyne incognita on tomato was studied in pots and field plots for two seasons. Avermectins were applied as granules and liquid in furrows or by low pressure drip irrigation systems, at rates ranging from 0.093 to 0.34 kg a.i./ha, as single or multiple applications. Levels of control comparable to those obtained by oxamyl and aldicarb at 3.36 kg a.i./ha were achieved by the avermectin with only 1/10 the volume of chemicals applied to the environment. Avermectin protection of the roots remained constant throughout the first 5 weeks giving slightly longer protection than oxamyl or aldicarb.     

DNA topoisomerase activities in concanavalin A-stimulated lymphocytes

Topoisomerase activities have been measured in nuclear extracts of concanavalin A-stimulated lymphocytes. In parallel with the wave of DNA synthesis, type II topoisomerase activity was considerably increased. After 72 h treatment, this activity was stimulated approx. 20-fold over the activity in untreated cells. In contrast, type I topoisomerase was poorly stimulated after 24 h treatment, and 4-5-fold after 72 h. These findings, together with our previous results on regenerating rat liver, suggest a major role of topoisomerase II in DNA replication.     

Mg2+, Asp-, and Glu--effects in the processive and distributive DNA relaxation catalyzed by a eukaryotic topoisomerase.

The salt requirement for the catalysis of DNA relaxation carried out by a eukaryotic DNA topoisomerase I from Candida was reexamined with plasmid pBR322 DNA. Two levels of analysis were considered: the initial velocity of the overall reaction and the mode of this reaction (processivity vs distributivity). When looking at the monovalent salts from the first level, the replacement of Cl- by Glu- or Asp- greatly enhanced the salt range over which the enzyme was active. Moreover, the initial velocity reached an optimal value for a higher salt concentration in this case. For the cationic counterpart, K+ was a little more effective than Na+ and much more so than NH4+. Addition of 4 mM magnesium chloride affected both the range and the optimum of the initial velocity differentially, depending upon the monovalent salt, but with a general stimulating tendency. On the other hand, when the Mg2+ salt was varied, substitution of chloride by aspartate enhanced the optimum of the initial velocity for a fixed KCl concentration. In addition, magnesium aspartate (MgAsp2) and magnesium glutamate (MgGlu2) allowed the reaction to occur even without monovalent salt and over an extended range. Magnesium was also shown to directly interact with the general catalysis (Kd = 2.5 mM). From the second level of analysis, the presence of Mg2+ (except with NH4Glu), the substitution of Cl- by Glu- or Asp-, and a lower monovalent salt concentration than that used for the velocity optimum were required to promote the processive mode.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of group size and group density on trade-offs in resource selection by a group-territorial central-place foraging woodpecker

Trade-offs in resource selection by central-place foragers are driven by the need to balance the benefits of selecting resources against the costs of travel from the central place. For group-territorial central-place foraging birds, trade-offs in resource selection are likely to be complicated by a competitive advantage for larger groups at high group density that may limit accessibility of high-quality distant resources to small groups. We used the group-territorial, central-place foraging Red-cockaded Woodpecker Leuconotopicus borealis (RCW) as a case study to test predictions that increases in group density lead to differences in foraging distances and resource selection for groups of different sizes. We used GPS tracking and LiDAR-derived habitat data to model effects of group size on foraging distances and selection for high-quality pines (≥ 35.6 cm diameter at breast height (dbh)) and lower quality pines (25.4–35.6 cm dbh) by RCW groups across low (n = 14), moderate (n = 10) and high group density (n = 10) conditions. At low and moderate group density, all RCW groups selected distant high-quality pines in addition to those near the central place because competition for resources was low. In contrast, at high group density, larger groups travelled further to select high-quality pines, whereas smaller groups selected high-quality pines only when they were close to the central place and, conversely, were more likely to select lower quality pines at greater distances from the central place. Selection for high-quality pines only when close to the cavity tree cluster at high group density is important to long-term fitness of small RCW groups because it allows them to maximize benefits from both territorial defence and selecting high-quality resources while minimizing costs of competition. These relationships suggest that intraspecific competition at high group density entails substantive costs to smaller groups of territorial central-place foragers by limiting accessibility of distant high-quality foraging resources.     

Pyridoxal 5'-phosphate inactivates DNA topoisomerase IB by modifying the lysine general acid

The present results demonstrate that pyridoxal, pyridoxal 5′-phosphate (PLP) and pyridoxal 5′-diphospho-5′-adenosine (PLP-AMP) inhibit Candida guilliermondii and human DNA topoisomerases I in forming an aldimine with the ε-amino group of an active site lysine. PLP acts as a competitive inhibitor of C.guilliermondii topoisomerase I (K_i = 40 μM) that blocks the cleavable complex formation. Chemical reduction of PLP-treated enzyme reveals incorporation of 1 mol of PLP per mol of protein. The limited trypsic proteolysis releases a 17 residue peptide bearing a lysine-bound PLP (KPPNTVIFDFLGK^*DSIR). Targeted lysine (K^*) in C.guilliermondii topoisomerase I corresponds to that found in topoisomerase I of Homo sapiens (K₅₃₂), Candida albicans (K₄₆₈), Saccharomyces cerevisiae (K₄₅₈) and Schizosaccharomyces pombe (K₅₀₅). In the human enzyme, K₅₃₂, belonging to the active site acts as a general acid catalyst and is therefore essential for activity. The spatial orientation of K₅₃₂–PLP within the active site was approached by molecular modeling using available crystallographic data. The PLP moiety was found at close proximity of several active residues. PLP could be involved in the cellular control of topoisomerases IB. It constitutes an efficient tool to explore topoisomerase IB dynamics during catalysis and is also a lead for new drugs that trap the lysine general acid.