Why use population entropy? It determines the rate of convergence

Summary The population entropy introduced by Demetrius is shown to have a precise dynamical meaning as a measure of convergence rate to the stable age distribution. First the Leslie population model is transformed exactly into a Markov chain on a state space of age-classes. Next the dynamics of convergence from a nonequilibrium state to the stable state are analyzed. The results provide the first clear biological reason why entropy is a broadly useful population statistic.     

Length requirements for tRNA-specific enzymes and cleavage specificity at the 3'' end of turnip yellow mosaic virus RNA.

This paper describes the minimum length of the turnip yellow mosaic virus (TYMV) RNA necessary to fulfill the tRNA-like properties of the viral RNA: 50 to 75 nucleotides and 86 nucleotides from the 3' end of TYMV RNA are sufficient for adenylation and valylation respectively by the Escherichia coli system. The size of the tRNA-like fragments obtained in vitro in the presence of an E. coli, a reticulocyte or a chinese cabbage leaf extract has also been determined. Among the major fragments liberated from the 3' end of TYMV RNA by the three systems are fragments of 117 and 112 nucleotides. In addition, the E. coli extract liberates fragments of 139 and 61 nucleotides, and the reticulocyte lysate fragments of 109, 94, 84, 73 and 46 nucleotides. The cleavage of the viral RNA by several systems in vitro to yield RNA fragments encompassing the tRNA-like sequence suggests that such fragments might also be liberated in vivo.     

Inhibition of coupling factor B activity by cadmium ion, arsenite-2,3-dimercaptopropanol, and phenylarsine oxide, and preferential reactivation by dithiols

Coupling factor B activity was measured by the stimulation of the ATP-driven NAD+ reduction by succinate or the 32Pi-ATP exchange activity of Factor B-depleted submitochondrial particles. Half-maximal coupling activity was inhibited by 30 microM cadmium, 5 microM phenylarsine oxide, or 0.3 mM arsenite-2,3-dimercaptopropanol. The inhibition was relieved by slight excess of dithiol but not by a 10-fold molar excess of 2-mercaptoethanol. Inhibition of coupling activity by phenylarsine oxide or cadmium was not due to interference in binding of Factor B to depleted particles. Isolated Factor B binds phenylarsine oxide resulting in loss of ability to stimulate depleted submitochondrial particles. The inhibition was largely overcome by dithiol but not by monothiols. The residual coupling activity of depleted submitochondrial particles was highly resistant to cadmium or arsenical. Moreover, binding of arsenical to the depleted particles per se, did not result in inhibition of Factor B-stimulated activity. Furthermore, the addition of phenylarsine oxide to H+-ATPase resulted in loss of Pi-ATP exchange and stimulation of oligomycin-sensitive ATPase activities. Both effects were further potentiated by 2-mercaptoethanol and reversed by dithiols. These effects parallel uncoupling of oxidative phosphorylation in mitochondria by these inhibitors and point to Factor B as the probable component sensitive to these inhibitors.     

Regulation of starch biosynthesis in normal and opaque-2 maize during endosperm development

The absolute activities of sucrose-UDP glucosyltransferase, glucose-6-phosphate ketoisomerase and soluble and bound ADPG-starch glucosyltransferase have been studied in normal and Opaque-2 maize endosperms during development. In general, the activities of these enzymes except sucrose-UDP glucosyltransferase were higher up to 20 days post-pollination and lower at the 30 day stage in Opaque-2 than in normal maize endosperms. However, sucrose-UDP glucosyltransferase activity was higher in normal maize endosperm up to the 20 day stage while it was lower at subsequent stages than in Opaque-2. It is suggested that the lower level of these enzymes, except sucrose-UDP glucosyltransferase, might be responsible for the reduced accumulation of starch in Opaque-2 endosperm during later stages of endosperm development.     

Some aspects of respiratory metabolism of a penaeid prawn,Penaeus japonicus (Bate) (Crustacea,Decapoda, Penaeidae)

Respiratory metabolism of a marine penaeid prawn, Penaeus japonicus (Bate) was studied in relation to body size, starvation, dissolved oxygen tension, salinity and temperature. Oxygen consumption was significantly (P < 0.03) elevated with decline in body size. The rate of oxygen consumption was decreased significantly (P < 0.05) with an increase in the day of starvation, but the values of the loth and 15th day did not differ significantly (P > 0.05) from each other, indicating adaptation to starved conditions. Respiratory rate was on the ascending scale with an elevation in the surrounding oxygen content. Oxygen consumption increased significantly (P < 0.05) in both hyper- and hypotonic media. Rate of oxygen consumption was significantly (P < 0.05) augmented with an increase in the ambient temperature upto 34°C but a drastic fall was found at both low (18°C) and high (36°C) extreme temperatures. Functional significance of these findings to the prawn, in combating the environmental eddies is discussed.This investigation was supported by I.C.A.R., New Delhi, through a project No. 21 (80)/73-ASR (I)This investigation was supported by I.C.A.R., New Delhi, through a project No. 21 (80)/73-ASR (I)     

Activation of potassium-dependent H+ efflux from mitochondria by cadmium and phenylarsine oxide

Addition of Cd²⁺ or phenylarsine oxide (PhAsO) to respiring rat liver mitochondria results first in acidification of the medium (H⁺ efflux) followed by disappearance of H⁺ (discharge of the pH gradient or uncoupling). The first phase of H⁺ efflux is dependent upon the presence of K⁺ in the medium, and is not seen in the presence of valinomycin, which is consistent with the conclusion that H⁺ efflux is linked to membrane potential-dependent uptake of K⁺. These effects are abolished by low levels of 2,3-dimercaptopropanol but potentiated by excess of 2-mercaptoethanol, showing involvement of a dithiol type of group in the response. Mersalyl produces only the H⁺ efflux, and subsequent addition of Cd²⁺ or PhAsO produces collapse of the pH.Abbreviations BAL British Anti-Lewisite or 2,3-dimercaptopropanol - 2-ME 2-mercaptoethanol - PhAsO phenylarsine oxide - FCCP carbonylcyanide trifluoromethoxyphenylhydrazone - HEPES N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid     

Strain-Specific Inhibition of nod Gene Induction in Bradyrhizobium japonicum by Flavonoid Compounds

A broad-host-range plasmid, pEA2-21, containing a Bradyrhizobium japonicum nodABC'-'lacZ translational fusion was used to identify strain-specific inhibitors of the genes required for soybean nodulation, the common nod genes. The responses of type strains of B. japonicum serogroups USDA 110, USDA 123, USDA 127, USDA 129, USDA 122, and USDA 138 to nod gene inhibitors were compared. Few compounds inhibited nod gene expression in B. japonicum USDA 110. In contrast, nod gene expression in strains belonging to several other serogroups was inhibited by most of the flavonoids tested. However, the application of two of these strain-specific compounds, chrysin and naringenin, had little effect on the pattern of competition between indigenous and inoculum strains of B. japonicum in greenhouse and field trials. Preliminary studies with radiolabeled chrysin and naringenin suggest that the different responses to nod gene inhibitors may be partly due to the degree to which plant flavonoids can be metabolized by each strain.     

Spatial distribution of oil in groundnut and sunflower seeds by nuclear magnetic resonance imaging

Abstract. The nuclear magnetic resonance imaging technique has been used to obtain images of different transverse and vertical sections in groundnut and sunflower seeds. Separate images have been obtained for oil and water components in the seeds. The spatial distribution of oil and water inside the seed has been obtained from the detailed analysis of the images. In the immature groundnut seeds obtained commercially, complementary oil and water distributions have been observed. Attempts have been made to explain these results.     

Sibling rivalry between seeds within a fruit: Some population genetic models

Competition between seeds within a fruit for parental resources is described using one-locus-two-allele models. While a “normal” allele leads to an equitable distribution of resources between seeds (a situation which also corresponds to the parental optimum), the “selfish” allele is assumed to cause the seed carrying it to usurp a higher proportion of the resources. The outcome of competition between “selfish” alleles is also assumed to lead to an asymmetric distribution of resources, the “winner” being chosen randomly. Conditions for the spread of an initially rare selfish allele and the optimal resource allocation corresponding to the evolutionarily stable strategy, derived for species with n-seeded fruits, are in accordance with expectations based on Hamilton’s inclusive fitness criteria. Competition between seeds is seen to be most intense when there are only two seeds, and decreases with increasing number of seeds, suggesting that two-seeded fruits would be rarer than one-seeded or many-seeded ones. Available data from a large number of plant species are consistent with this prediction of the model. Based on a talk given at the Haldane Centenary Symposium held on 6 November 1992 at Ahmedabad as part of the 58th Annual Meeting of the Indian Academy of Sciences.     

Purification and characterization of E. histolytica antigen for diagnosis of amoebiasis

Entamoeba histolytica soluble crude antigen was fractionated by gel filtration on Sephacryl S-300 into four fractions, viz. F1(669 kDa); F2(51.2 kDa); F3(25.1 kDa) and F4(10.5 kDa). F1 fraction was observed to be more sensitive and specific for the detection of antibody in amoebiasis than the crude and other fractions of purified antigens employing IHAT and ELISA. ELISA was found to be better than IHAT since it could detect antibody in the sera (3/6) of asymptomatic cyst passers. The cross reaction of crude antigen with toxocariasis (1/4) and toxoplasmosis (2/5) sera were associated with F4 fraction. F3 and F4 were having low molecular weight and were not sensitive in detection of antibody in amoebiasis. Biochemical characterization revealed glycoprotein nature of the specific (F1) antigen fraction.