Fungal succession in the early decomposition process of pine cones on the floor ofPinus densiflora forests

The fungal succession on pine cones on the floor ofPinus densiflora forest was investigated in the early decomposition process (within ca. 30% decrease in dry weight). The fungal flora was examined by both washing and surface-sterilization methods on artificially placed cones and naturally fallen cones. The decomposition rates of artificially placed cones were 0.081–0.082 yr^–1. On withered cones still attached to the tree,Pestalotiopsis spp. were dominant. These fungi also occurred with higher frequencies after cones had lain on the floor and on cones in the L and FH horizons.Xylaria sp. andPhomopsis sp., which seem to colonize the interior of the tissue, occurred with higher frequencies on the cones on the tree, but their occurrence frequencies decreased after cones had lain on the forest floor. Conversely,Mortierella spp. andTrichoderma spp. newly occurred or their occurrence frequencies increased on lying cones. Of these,Trichoderma koningii increased rapidly and showed high occurrence frequencies.Thysanophora penicillioides, which prefers coniferous substrates, showed higher occurrence frequencies in the early stages of lying on the forest floor. On cones lying on the floor, the fungal flora did not significantly change during the investigation period.     

The proximate/ultimate distinction in the multiple careers of Ernst Mayr

Ernst Mayr's distinction between “ultimate” and “proximate” causes is justly considered a major contribution to philosophy of biology. But how did Mayr come to this “philosophical” distinction, and what role did it play in his earlier “scientific” work? I address these issues by dividing Mayr's work into three careers or phases: 1) Mayr the naturalist/researcher, 2) Mayr the representative of and spokesman for evolutionary biology and systematics, and more recently 3) Mayr the historian and philosopher of biology. If we want to understand the role of the proximate/ultimate distinction in Mayr's more recent career as a philosopher and historian, then it helps to consider hisearlier use of the distinction, in the course of his research, and in his promotion of the professions of evolutionary biology and systematics. I believe that this approach would also shed light on some other important “philosophical” positions that Mayr has defended, including the distinction between “essentialism: and “population thinking.”     

Ernst Mayr: Biologist-historian

Ernst Mayr's historical writings began in 1935 with his essay Bernard Altum and the territory theory and have continued up through his monumentalGrowth of Biological Thought (1982) and hisOne Long Argument: Charles Darwin and the Genesis of Modern Evolutionary Thought (1991). Sweeping in their scope, forceful in their interpretation, enlisted on behalf of the clarification of modern concepts and of a broad view of biology, these writings provide both insights and challenges for the historian of biology. Mayr's general intellectual formation was guided by the GermanBildung ideal, with its emphasis on synthetic and comprehensive knowledge. His understanding of how to write history was inspired further by the example of the historian of ideas Arthur Lovejoy. Some strengths and limitations of this approach are explored here through attention to Mayr's treatment of the French biologist J.-B. Lamarck. It is contended that Mayr's contributions to the history of biology are not restricted to his own very substantial historical writings but also include his encouragement of other scholars, his development of an invaluable archive of scientific correspondence, and his insistence that historians who write about evolution and related subjects acquire an adequate understanding of the principles of Darwinian biology.This paper was originally delivered at the biennial meeting of the International Society for the History, Philosophy, and Social Studies of Biology, held in Brandeis in July 1993, in the special session organized by John Greene on Ernst Mayr's contributions to systematics, evolutionary theory, and the history and philosophy of biology. The paper is presented here with only slight modifications of the original, oral presentation. As indicated in the text, a full assessment of Mayr's historical work, including situating that work in the context of Mayr's other work and contemporary developments in the history of science, would require a much more extensive study than I have been able to undertake here.     

Kinetics of ligand binding to a cluster of membrane-associated receptors

The process of ligand binding to a cluster of membrane-associated receptors is examined theoretically. The theoretical model proposed involves the diffusion of ligands from the solution to the disc-like cluster of receptors on the surface of the spherical cell. When the ligand hits the internal part of the disc-like cluster, it begins to move laterally until it leaves the disc through its outer surface or is bound by one of the receptors inside the disc. If the ligand leaves the cluster, it returns to the solution and hits the disc again after a certain period, etc. According to our model the transition from a diffusion-limited to a reaction-limited process of binding is determined by the dimensionless parameter Dt _c/a ², where D is the lateral diffusion coefficient,t _c is the characteristic time of reaction, anda is the radius of the disc-like cluster. The forward rate constantk _f turns out to be a function of . Comparing the results of our calculations ofk _f with some experimental data we found that agreement is achieved at high , i.e. the process of ligand binding by clustered receptors is predominantly reaction-limited.     

Advanced sub social behaviour in the scorpionHeterometrus fulvipes Brunner (Arachnida)

Scorpions arc generally non-social, solitary animals that interact with conspecifics at birth, courtship or predation only. The present study reports the presence of advanced sub social behaviour inHeterometrus fulvipes Brunner and evaluates the importance of its burrowing as a cause for such social behaviour.Heterometrus fulvipes constructed deep angular burrows at the base of plants. Burrows provided (i) protection against predation, (ii) increased availability of food and (iii) ideal microclimate for year round activity of the scorpions. No cannibalism was observed in laboratory maintained colonies. The risk of predation and the difficult by immatures to dig tunnels during dry soil conditions may have forced the mother and offspring to live together in the burrow for longer durations. The cohabitation of relative offsprings transforms the burrow into a nest. The members of a colony exhibits division of labour for nest expansion and in foraging. The mother communicates with the immatures through “Buzz” sound and may provide premasticated food. There is food sharing also among colony members. All these behaviours indicate the presence of advanced sub social behaviour inHeterometrus fulvipes.     

Mercury (Hg2+) and zinc (Zn2+): Two divalent cations with different actions on voltage-activated calcium channel currents

Summary 1. We examined the actions of mercury (Hg²⁺) and zinc (Zn²⁺) on voltage-activated calcium channel currents of cultured rat dorsal root ganglion (DRG) neurons, using the whole-cell patch clamp technique.2. Micromolar concentrations of both cations reduced voltage-activated calcium channel currents. Calcium channel currents elicited by voltage jumps from a holding potential of –80 to 0 mV (mainly L- and N-currents) were reduced by Hg²⁺ and Zn²⁺. The threshold concentration for Hg²⁺ effects was 0.1 µM and that for Zn²⁺ was 10µM. Voltage-activated calcium channel currents were abolished (>80%) with 5µM Hg²⁺ or 200µM Zn²⁺. The peak calcium current was reduced to 50% (IC₅₀) by 1.1µM Hg²⁺ or 69µM Zn²⁺. While Zn²⁺ was much more effective in reducing the T-type calcium channel current—activated by jumping from –80 to –35 mV—Hg²⁺ showed some increased effectiveness in reducing this current.3. The effects of both cations occurred rapidly and a steady state was reached within 1–3 min. While the action of Zn²⁺ was not dependent on an open channel state, Hg²⁺ effects depended partially on channel activation.4. While both metal cations reduced the calcium channel currents over the whole voltage range, some charge screening effects were detected with Hg²⁺ and with higher concentrations (>100µM) of Zn²⁺.5. As Zn²⁺ in the concentration range used had no influence on resting membrane currents, Hg²⁺ caused a clear inward current at concentrations µM.6. In the present study we discuss whether the actions of both metals on voltage-activated calcium channel currents are mediated through the same binding site and how they may be related to their neurotoxic effects.     

An improved method for the measurement of total lipid-bound sialic acids after cleavage of α2,8 sialic acid linkage withVibrio cholerae sialidase in the presence of cholic acid,SDS and Ca2+

In the measurement of total lipid-bound sialic acids involving periodic acid oxidation, as in the periodate-resorcinol assay, the inner sialic acids of disialoglycolipids (such as GD₃ and GD₂) are not involved because their 2,8 ketosidic linkages are resistant to periodic acid oxidation, even after acid/enzyme hydrolysis or alkali pretreatment. However, the sialic acids from these glycolipids can be recovered completely after cleavage of 2,8 linkages byV. cholerae sialidase in the presence of cholic acid, sodium dodecyl sulphate and calcium. Interestingly, removal of calcium or detergent(s) or both significantly minimizes the sialidase action on the disialyl residues of these gangliosides. Therefore, we recommend sialidase (Vibrio cholerae) pretreatment of the glycolipids in the presence of cholic acid, SDS and Ca²⁺ for complete recovery of sialic acids from di- and polysialogangliosides and for accurate measurement of total lipid-bound sialic acids by periodate-resorcinol assay.Presented at the Second International Glycobiology Symposium which was held in San Francisco, CA, USA (14 February 1994).     

Changes in UsnRNA biosynthesis during rat liver regeneration

Partial hepatectomy (P.H.) induces a partially synchronized growth response of liver under normal regulation of growth. In this phase changes in cellular morphology, radial distribution pattern of cells and other biological as well as major biochemical changes are well documented [24]. Here, we have shown that the cellular content of UsnRNAs altered during this proliferative phase as well. The level of spliceosomal UsnRNAs (U1, U2, U4–U6) gradually decreased by 30–50% upto 48 hrs of P.H. followed by gradual increase to reach the normal level within one month of P.H. The U3 snRNA level on the other hand, was nearly equal to that in normal liver at 48 hrs of P.H. but in 24 and 72 hrs of P.H. its level was high (4 fold) in contrast to that in other UsnRNAs. Thus, it is clear from our data that the level of all the six UsnRNAs decreased during 48 hrs of P.H. compared to that after first 24 hrs. This has been correlated in the kinetics of UsnRNAs' synthesis (in terms of labelling) in isolated hepatocytes, where the rate of labelling of all the six UsnRNAs increased 20–30% in 24 hrs regenerating hepatocytes (R.H.) followed by sharp decrease by 30–50% within next 24 hrs, compared to that in the normal hepatocytes. But from 72 hrs onwards in R.H. the rate of labelling of all the six UsnRNAs again increased by 30–50% (compared to that in normal hepatocytes) followed by decrease of their labelling-rate to reach the normal level in R.H. within one month of P.H. Thus, it may be concluded that the changes in UsnRNAs' level during the proliferative phase of liver regeneration may be either due to the alteration in the rate of synthesis (in terms of labelling) or along with it differential turn over rate; this phenomenon may have some consequences with the regenerative process of liver.This paper was published in Molecular and Cellular Biochemistry131:67–73, 1994. Kluwer Academic Publishers regret the publication of the only partly corrected version.     

2,4,6-trinitrobenzenesulfonic acid modification of the carboxyl-terminal region (C-domain) of calreticulin

The role of the primary amino groups of lysine sidechains in Ca²⁺ binding to calreticulin was evaluated by chemical modification of the amino group with 2,4,6-trinitrobenzenesulfonic acid (TNBS). TNBS binding to calreticulin could be described by two steps: (i) a fast reaction, with low affinity, and (ii) a slow reaction with a relatively high affinity. Inclusion of Ca²⁺ and/or Mg²⁺ decreased both the amount of TNBS bound to calreticulin and the apparent affinity constant of the slower reaction. In contrast, the properties of the faster reaction for TNBS binding were not sensitive to Ca²⁺ and/or Mg²⁺. Analysis of TNBS binding to the carboxyl-terminal (C-domain) and aminoterminal (N-domain) of calreticulin revealed that theC-domain andN-domain are responsible for the slow and fast component of the TNBS binding, respectively. In keeping with this, in the presence of Ca²⁺, TNBS binding to theC-domain was significantly reduced, whereas modification of theN-domain was unaffected. TNBS modification of calreticulin significantly decreased Ca²⁺ binding to the low affinity/high capacity Ca²⁺ binding site(s) which are localized to theC-domain but had no effect on the high affinity/low capacity Ca²⁺ binding localized to theN-domain.In theC-domain of calreticulin, which contains the low affinity/high capacity Ca²⁺ binding sites, acidic residues are interspersed at regular intervals with one or more positively charged lysine and arginine residues. Our results indicate that the aminogroups of the lysine sidechains in theC-domain of calreticulin have a role in the low affinity/high capacity Ca²⁺ binding that is characteristic of this region of the protein and which is proposed to contribute significantly to the capacity of the endoplasmic reticulum Ca²⁺ store. (Mol Cell Biochem130: 19–28, 1994)Abbreviations TNBS 2,4,6-Trinitrobenzenesulfonic Acid - GST Glutathione S-Transferase - SDS-PAGE Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis - EDTA Ethylenediaminetetraacetic Acid - EGTA Ethylene Glycol bis(-aminoethylether)-N,N,N,N-tetraacetic Acid - MOPS 4-Morpholinepropanesulfonic Acid