Temporal variability of top-down forces and their role in host choice evolution of phytophagous arthropods

The role of top-down forces in host choice evolution of phytophagous arthropods is the subject of a vividly animated debate. Empirical evidence for the evolutionary role of top-down forces comes from studies showing that phytophagous arthropods prefer hosts that entail enemy-free space. The aim of this paper is to draw the attention of plant–arthropod researchers to the potentially, temporally variable nature of third trophic level effects. We show that this aspect is largely neglected in studies on enemy-free space, despite the fact that relative enemy impact varies seasonally among plants in at least some studies. We conclude that rigorous testing of the enemy-free space hypothesis can only be performed when within and between season variation in higher trophic level effects is taken into account.     

Restriction pattern analysis of deoxyribonucleic acid isolated from callus and cell suspension of actinorhizal and non-actinorhizal Betulaceae

Using cell suspensions, a method was elaborated to isolate high-molecular-weight genomic deoxyribonucleic acid (DNA; 65 MDa or more) from members of the Betulaceae: Alnus incana (L.) Moench, Alnus glutinosa (L.) Gaertn. and Betula papyrifera Marsh. The method was also effective for isolation of DNA from callus cells. Based on the chemical lysis of protoplasts, this procedure yielded 130 μg (callus) to 250 μg (cell suspension) of DNA (g fresh cells)⁻¹, with a ratio A₂₀₀/A₂₈ of 1.7–2.0. The purified DNA obtained, formed distinct bands when restricted fragments were electrophoresed. Among the 10 endonucleases used for restriction analysis of Alnus glutinosa, Alnus incana and Betula papyrifera genomes, PvuI1 (EC 3.1.23.33) was unique in giving identical patterns for the two Ainus species. An unusual pattern occurred when Al-2 DNA was restricted with Ava II (EC 3.1.23.4). It formed a ladder with a repeating fragment unit of 181 base pairs long. With the enzymes tested, no differences in restriction patterns were observed among clones of Alnus incana (AI-2 vs AI-2), Betula papyrifera (BP-4 vs BP-8) and subclones of Ainus glutinosa AG-1 (PLFJ709 vs LF1709), suggesting genetic stability of the Betulaceae cultures.     

Cloning and comparison of Aα mating-type alleles of the basidiomycete Schizophyllum commune

Summary An A mating-type allele (A4) was isolated by walking the chromosome from the closely linked PAB1 gene. A cosmid clone containing the A1 allele isolated from the walk was used as a probe to recover the A1 allele from another cosmid library. Cosmids encoding mating-type activity were identified by transforming Schizophyllum cells and screening for activation of A-regulated development. Putative mating-type transformants were confirmed in mating tests and genetic analyses of progeny. The identity of the specific alleles isolated was demonstrated by showing that their effectiveness in transforming for mating type is limited to recipient strains possessing an A allele different from the one encoded by the cloned sequences. Transforming DNA is active in trans, suggesting that A encodes a diffusible product. Restriction mapping shows that A1 and A4 are coded in the same physical region of the genome, but within a subregion that contains extensive sequence divergence. In addition, Southern analyses show that there is only one copy of A1 or A4 per haploid genome, and that they do not cross-hybridize to one another or to any of the other A alleles. A1 and A4 were subcloned as 2.8 and 1.2 kb fragments, respectively, retaining in transformation all the mating-type activity demonstrated of the original cosmids.     

Ontogeny of hormone-secreting cells of the rat pituitary gland: An immunocytochemical study on dissociated cells

Summary An immunocytochemical study was undertaken in foetal, prepubertal and mature rats to determine the time of differentiation of various types of adenohypophyseal cells during development. Freshly dissociated pituitary cells from foetal (18–21 days postconception), neonatal (from birth up to 30 days) and adult rats (more than 8 weeks) were characterized using immunocytochemical methods. All types of hormone-producing cells were present at day 18 postconception, although only 20% of the cells were immunolabelled. Adrenocorticotropin (ACTH)-secreting cells accounted for the highest number of hormone-positive cells. Growth hormone-secreting cells increased remarkably from day 18 postconception onwards. Prolactin-secreting cells were not seen in the foetal adenohypophysis and did not start to increase until 10 days after birth, whereas by that time the number of ACTH, thyrotropin, follicle-stimulating and luteinizing hormone-secreting cells had stopped increasing. By day 30 after birth, 80–95% of the cells were immunoreactive.     

Accumulation of mansonones E and F in seedlings of Ulmus americana in response to inoculation with Ophiostoma ulmi

Summary The accumulation of mansonones E and F was investigated in Ulmus americana L. seedlings 5 weeks after inoculation with three aggressive and three non-aggressive isolates of Ophiostoma ulmi (Buism.) Nannf. The three non-aggressive isolates stimulated significantly more mansonone E and F accumulation than the three aggressive isolates of O. ulmi. Mansonone induction also varied within both the aggressive and the non-aggressive groups. Aggressive and non-aggressive isolates were recovered in equal frequencies from the inoculation wounds, whereas the aggressive isolates were recovered more frequently than the non-aggressive isolates 15 cm and 25 cm up the seedlings' stem. Vascular browning in the outer xylem of the seedlings correlated with mansonone E and F accumulation. Mansonone accumulation in U. americana seedlings is therefore associated with vascular browning and a reduction in fungal spread.     

Further resolution of the low density lipoprotein spectrum in normal human plasma: physicochemical characteristics of discrete subspecies separated by density gradient ultracentrifugation

The molecular basis of the heterogeneity of plasma low density lipoproteins (LDL, d 1.024-1.050 g/ml) was evaluated in 40 normolipidemic male subjects following fractionation by isopycnic density gradient ultracentrifugation into eight major subspecies. The mass profile of our subjects' LDL uniformly displayed single symmetric or asymmetric peaks as a function of density; the peak occurred most frequently (20 subjects) in subfraction 7 (d 1.0297-1.0327 g/ml). Several physicochemical properties (hydrodynamic behavior, electrophoretic mobility, chemical composition, size and particle heterogeneity, and apolipoprotein heterogeneity) of the LDL subfractions were examined. Hydrodynamic analyses revealed unimodal distributions and distinct peak Sf degree rates in individual subfractions. Such behavior correlated well with particle size and heterogeneity data, in which LDL subspecies were typically resolved as unique narrow bands by gradient gel electrophoresis. Subspecies with average densities of 1.024 to 1.0409 g/ml ranged from 229 to 214 A in particle diameter. LDL protein content increased in parallel with density while the proportion of triglyceride diminished; cholesteryl esters predominated, accounting for approximately 40% or more by weight. Distinct differences in net electric charge were demonstrated by electrophoresis in agarose gel, the subspecies with average density of 1.0314 g/ml displaying the lowest net negative charge. ApoB-100 was the major apoprotein in all subspecies, and constituted the unique protein component over the density interval 1.0271-1.0393 g/ml. ApoE and apo[a] were detected at densities less than 1.0271 and greater than 1.0393 g/ml. While apoE was evenly distributed within these two regions, representing up to 2% of apoLDL, the distribution of apo[a] was skewed towards the denser region, in which it amounted to 3-7% of apoLDL. ApoC-III was detectable as a trace component at densities greater than 1.0358 g/ml. Calculation of the number of molecules of each chemical component per LDL subspecies showed the presence of one copy of apoB-100 per particle, in association with decreasing amounts of cholesteryl ester, free cholesterol, and phospholipid. These data indicate that a similar overall molecular organization and structure is maintained in a unimodal distribution of LDL particle subspecies over the density range approximately 1.02 to 1.05 g/ml. In sum, our data may be interpreted to suggest that microheterogeneity in the physicochemical properties of human LDL subspecies reflects dissimilarities in their origins, intravascular metabolism, tissular fate, and possibly in their atherogenicity.     

Circadian and Ultradian Rhythms in Blood Glucose and Plasma Insulin of Healthy Adults

The circadian and ultradian variations of blood glucose and plasma insulin have been characterized individually and as a group phenomenon in five healthy young adults studied while adhering as closely as possible to their usual routine of sleep, activity, meal content and timing. Three complementary methods were used to analyze the data: displaying raw data as a function of time; cosinor method according to Nelson and Halberg; and time series analyses as proposed by De Prins and Malbecq. The subjects were studied in the laboratory and their life routine were controlled, but very close to that of their habitual routine. They had mainly ultradian rhythms of blood glucose (mainly about 6 hr) and circadian rhythms of immunoreactive insulin (I.R.I.). Blood glucose ultradian rhythms seem to be mainly but not exclusively mealtime dependent, while I.R.I, circadian rhythms appear to be primarily endogenous in origin. Therefore, the role played by insulin in the control of blood glucose levels seems to be programmed on a circadian basis rather than by a time independent feedback phenomenon as postulated by the conventional homeostatic hypothesis. The advantage of this chronophysiologic approach is to consider circadian rhythms of both I.R.I. and insulin effectiveness as an adaptive phenomenon able to maintain blood sugar changes in the ultradian domain of rhythms.