The mite Varroa jacobsoni does not transmit American foulbrood from infected to healthy colonies

The present study was conducted to determine whether Varroa jacobsoni can transmit American foulbrood (AFB), caused by the bacterium Paenibacillus larvae to healthy colonies by the surface transport of spores. Five two-storey Langstroth colonies of Apis mellifera ligustica were infested by placing a sealed brood comb, with 10% Varroa prevalence, between the central brood combs of each colony. Two months later the colonies were inoculated with P. larvae by adding brood comb pieces with clinical signs of AFB (45±5 scales per colony). After 60 days the brood area was completely uncapped by means of dissecting needles and tweezers, separating the Varroa mites from the larvae and the collected mites were introduced at a rate of 51 per colony into four recipient hives placed in an isolated apiary. Twenty female Varroa specimens were separated at random and observed by SEM. Paenibacillus larvae spores were found on the dorsal shield surface and on idiosomal setae. All colonies died after 4–5 months due to a high incidence of varroosis. No clinical AFB symptoms or P. larvae spores were observed in microscopic preparations. It is concluded that Varroa jacobsoni does not transmit AFB from infected to healthy colonies; it does, however transport P. larvae spores on its surface.     

Fluctuating temperatures have different effects on embryonic sensitivity to ABA in Sorghum varieties with contrasting pre-harvest sprouting susceptibility

The effect of fluctuating temperatures on the germination ofimmature caryopses of two Sorghum varieties presenting contrastingsusceptibility to pre-harvest sprouting was investigated. Fluctuatingtemperatures were able to stimulate germination of immaturecaryopses of both varieties from early stages of development(i.e. 15 d after pollination). Isolated embryos from both varietiesgerminated well in water irrespective of the thermal regimeof incubation. However, the ability of ABA to block germinationin Redland B2 (sproutingsusceptible) isolated embryos was significantlyreduced when embryos were incubated under fluctuating temperaturesfrom 23 DAP onwards. No such effect was found in IS 9530 (sprouting-resistant)embryos. No differences in the pattern with which embryonicABA content decreased during whole grain incubation were foundin 25 and 35 DAP grains from both varieties incubated underconstant or fluctuating temperatures. Therefore, these resultsindicate that alternating temperatures can promote germinationthrough different mechanisms. One of them is the decrease inembryo sensitivity to ABA inhibition which appears to be actingin Redland B2 caryopses from 23 DAP onwards; the other one seemsto be independent of ABA level and sensitivity and is activeat very early stages of development in one variety (RedlandB2) and throughout seed development in the other (IS 9530). Key words: Germination, dormancy, fluctuating temperatures, abscisic acid, seed development, Sorghum bicolor     

Loose binding of testicular mitochondrial ATPase to the inner membrane

Rat testis mitochondrial ATPase was not inhibited by oligomycin at pH 7.5. It was inhibited only at higher alkaline pH's, and showed a lower sensitivity both to oligomycin and N,N′-dicyclohexylcarbodiimide and a higher one to efrapeptin. In submitochondrial particles, testis ATPase was only slightly inhibited by oligomycin, ossamycin, and efrapeptin. The possibility of a loose binding of F₁ to the membrane was supported by its recovery from the supernatant of the submitochondrial particles. Furthermore, by electron microscopy, after hypoosmotic shock and negative staining of the mitochondrial preparations, most of the inner mitochondrial membranes showed only a few “knobs” or none at all. The capacity of the testis mitochondrial preparation to produce ATP was tested and compared to that from liver. ATP synthetase/ATPase activity ratio was $\text{30}\text{1}$ in liver mitochondria, whereas in the testis it was $\text{3}\text{1}$. In spite of this large difference, at least part of the testis ATPase must be firmly bound to the membrane, since it is able to form ATP. The rest seems to be loosely bound and its functional significance is still unknown.     

Modulation of platelet responsiveness through selective phosphorylation of plasma membrane proteins: Antagonistic eeffects of cyclic AMP and cyclic GMP

³²P phosphorylation of plasma membranes from human blood platelets, under conditions that closely resemble physiological ones (endogeneous phosphate donors and intact platelets in homologous plasma), result in the incorporation of the label mainly in a membrane glycoprotein of apparently high molecular weight (greater than 400 000). Dibutyryl cyclic AMP, an inhibitor of platelet aggregation, specifically increases the degree of phosphorylation of this glycoprotein. Moreover, it has been found that prostaglandin E₁ one of the most potent inhibitors of platelet aggregation which also increases phosphorylation of the same glycoprotein, is significantly more effective than cyclic AMP.Cyclic GMP does not have any apparent effect on platelet aggregation. However, incubation of platelet-rich plasma with both cyclic GMP and cyclic AMP results in a partial recovery of the platelet responsiveness towards ADP-induced aggregation. Coincidently, the degree of phosphorylation of the high molecular weight glycoprotein under these conditions, although still higher than in controls (no nucleotides added), is significantly decreased as compared with cyclic AMP-treated cells. Furthermore, cyclic GMP inhibits the cyclic AMP-dependent protein kinase activity in isolated platelet plasma membranes.These results suggest a central role for this membrane phosphoglycoprotein in the triggering of platelet aggregation and, furthermore, suggest that modulation of its degree of phosphorylation may be exerted through some cyclic AMP/cyclic GMP relationship, which in the basal state might be critical for platelet responsiveness.     

Coprophilous fungi of the horse

A total of 1267 microfungi, including 35 Myxomycetes, were recorded from the fecal samples of the 60 horses; of these 395 were found on 20 saddle-horse feces, 363 on 20 race-horses and 509 on 20 working-horses. Eighty two species representing 53 genera were recorded; of these 7 were Zygomycetes, 18 Ascomycetes, 1 Basidiomycetes and 25 Fungi Imperfecti: 2 Myxomycetes. Common coprophilous fungi are in decreasing orderPilobolus kleinii, Saccobolus depauperatus, Mucor hiemalis, Lasiobolus ciliatus, Podospora curvula, Petriella guttulata, M. circinelloides, Coprinus radiatus, Dictyostelium mucoroides, Sordaria fimicola, C. miser, C. stercorarius, Acremonium sp., Coprotus granuliformis, Graphium putredinis, Iodophanus carneus, Chaetomium murorum, Podospora communis, P. inaequalis, P. setosa, Saccobolus versicolor andCladosporium cucumerinum. Species ofMyrothecium verrucaria, Actinomucor elegans, Kernia nitida, Spiculostilbella dendritica andMucorparvispora were found exclusively in working-horses feces.Badhamia sp., Anixiopsis stercoraria, Echinobotryum state ofD. stemonitis, Geotrichum candidum andOidiodendron sp. were found only in saddle-horses feces.Chlamidomyces palmarum andPhilocopra sp. were found exclusively in race-horses feces.Notes on infrequent or interesting fungi includeThamnostylum piriforme, Phialocephala dimorphospora, Rhopalomyces elegans andSpiculostilbella dendritica.     

Properties of a major α-globulin of rice endosperm

Globulin was isolated from milled rice (Oryza sativa, line IR480-5-9) by 5% NACl extraction and was precipitated by (NH₄)₂SO₂ or by dialysis against water. The extract was purified by repeated isoelectric precipitation at pH 4.5. The major globulin fraction (40%) exhibited one band by electrophoresis at pH 4.5 but two bands at pH 8.3. Similarly, one sharp peak was shown by sedimentation corresponding to 1.41S (α-globulin) in acetic acid (pH 2) and NaOH (pH 11.7) but a broad asymmetric peak was obtained at pH 6.7, 8.3 and 8.9. Gel filtration of the α-globulin at pH 6.5 exhibited 2 proteins with MW 20 000 and 98 000. The results suggest a pH dependent aggregation phenomenon. The two proteins could not be separated by DEAE-cellulose chromatography. SDS-polyacrylamide electrophoresis of α-globulin revealed one subunit with MW 18 000. This α-globulin is poorer in lysine and histidine but richer in cystine, methionine, arginine, tyrosine and glutamic acid than whole milled rice proteinfa]Taken part from the M.S. thesis of AAP from the University of the Philippine at Los Baños (1977).     

Protein-lipid interactions and differential scanning calorimetric studies of bacteriorhodopsin reconstituted lipid-water systems

Bacteriorhodopsin has been reconstituted at various molar concentrations into liposomes of dimyristoyl- and also of dipalmitoylphosphatidylcholine. Differential scanning calorimetry indicates that as the protein concentration within the lipid bilayer increases, the cooperativity of the lipid phase transition is reduced, i.e. the transition is broadened, while the midpoint transition temperature remains virtually unchanged. Freeze-fracture electron microscopy of our preparation shows, in agreement with previous data from other laboratories, that extensive protein aggregation occurs when the liposome is cooled below the T_c transition temperature of the lipid. Laser flash photolysis measurements of protein rotation of the bacteriorhodopsin show, especially in the case of protein-rich recombinants, that protein aggregates exist even above T_c. The perturbation caused by the presence of bacteriorhodopsin in the lipid bilayer is similar to that produced by other intrinsic proteins. The difficulty of correlating the observed calorimetric enthalpy data with a simple concept of a ‘boundary lipid layer’ based upon consideration of a single isolated protein is discussed in view of the occurrence of protein aggregates both above and below T_c. It is concluded that the reduction of enthalpy is related to the number of lipids which solvate the protein aggregates within the protein-lipid patches and are thereby removed from the cooperative melting and enthalpy of the remaining regions of pure lipid.     

Fructose 1,6-bisphosphatase: Dissociation of AMP cooperativity and AMP inhibition by carbamylation

Selective treatment of pig kidney fructose 1,6-bisphosphatase with potassium cyanate leads to the formation of an active carbamylated enzyme that has lost the cooperative interactions among AMP sites, but retains sensitivity to inhibition of catalytic activity by the regulator AMP. Incorporation data on [¹⁴C]KNCO indicate that the loss of enzyme cooperativity at the AMP sites is related to selective carbamylation of four lysine residues per mole of tetrameric enzyme. Exhaustive carbamylation suggests that a second lysine residue per subunit is essential for AMP inhibition.     

Progressive changes in the structure and dynamics of the phytoplankton community along a pollution gradient in a lowland river — a multivariate approach

The phytoplankton of the River Lujan (Buenos Aires, Argentina) was studied for a period of 18 months, together with physical and chemical variables, in relation to a pollution gradient. 167 taxa were recorded within a seasonal succession characterized by dominance of diatoms with a brief summer green algae facies. A combination of several biotic indices and multivariate analysis was employed to assess the impact of pollution on the phytoplankton community. The biotic indices used were species diversity and richness, algal quotients (green algae/diatom ratio, Centrales/Pennales ratio) and the SD succession rate index. Multivariate procedures included cluster analysis and ordination by PCA of both species and samples, stepwise discriminant analysis and multiple discriminant analysis of variance (MANOVA). Results indicate that community dynamism is attenuated at the more polluted sites, concomitant with an increased predominance of a broad-tolerance algal assemblage, co-dominated by Cyclotella meneghiniana and Nitzschia stagnorum. The changes in the community structure and dynamics described herein involved alterations in the distribution and relative proportions of the algae, rather than modifications in the basic species composition. These changes may not be readily detectable by methods which over-simplify the ecological information, such as systems of indicator species and biotic indices, designed to assess the degree of pollution. The suitability of multivariate analysis and biotic indices in river phytoplankton studies is further discussed.