Significance of the inactivation of transport in thermal death of Escherichia coli.

Cells of Escherichia coli ML308-225, harvested from the exponential phase, were heated in 50 mM potassium phosphate, and the loss in viability and inability to transport lactose, proline, and alpha-methylglucoside was compared. After cells were heated at 48 degrees C for 15 min, there was a 16% loss in viability and a similarly small reduction in the steady-state accumulation of lactose at 25 degrees C. The initial rates of lactose and proline transport were severely inhibited by heating at either 48 or 50 degrees C, but substantial recovery occurred within 5 to 7 min at 25 degrees C. Heating at 50 degrees C for 15 min caused an 86% loss in viability, but only a 53% decrease in the steady-state accumulation of lactose and only a 24% reduction in the initial rate of alpha-methylglucoside uptake. Twice as much alpha-methylglucoside was accumulated at 50 degrees C as at 25 degrees C. Although alpha-methylglucoside phosphate leaked from the cells at 50 degrees C, the concentration retained within the cells was about 500 times that externally, when only about 14% of the cells were viable. Overall, these results indicate that cells made nonviable by heating at 50 degrees C still have significant membrane integrity.     

Inhibition of IAA-induced elongation in Avena coleoptile segments by lead: a physiological and an electron microscopic study.

A high resolution growth measuring apparatus was used to demonstrate the inhibition of auxin-induced cell elongation in oat coleoptile segments (Avena sativa L. var Holden) by lead at concentrations ranging from 2 x 10-6 M to 2 x 10-3 M. The inhibition was immediate, having no measurable lag period. Electron micrographs of lead-treated and control segments revealed that in the treated material, lead became localized as electron-dense granules in the cell walls and in vesicles associated with dictyosomes. These granules were found to be lead hydroxide phosphate by electron diffraction techniques. The possible significance of this localization and identification with regard to phosphatase activity is discussed.     

In vitro metabolism or testosterone by breast microcysts

Breast microcysts are considered to be a normal findings in the adult female breast without any increased risk of developing carcinomatous change. Breast cysts fluid contains steroid but not studies have been reported on the ability of breast microcysts to metabolise steroid hormones. It was, therefore, the aim of this study to identify the metabolites formed on incubation of radiolabelled testosterone with microcysts. In all instances dihydrotestosterone and androstenedione were formed. Oestrogens were not identified. Tis study, therefore, provides evidence for th presence of 5-alpha-reductase and 17-oxidoreductase enzyme systems in breast microcysts.     

Burrowing dynamics and energy cost of transport in the soft-bodied marine invertebrates Polyphysia crassa and Priapulus caudatus

The dynamics and mechanical forces generated during burrowing in Polyphysia crassa (Annelida: Polychaeta) and Priapulus caudatus (Priapulida) were investigated. Both animals live in soft marine muds and burrow by utilizing a direct peristaltic wave alternating with a high internal pressure event which thrusts the anterior part of the body into the substratum. Forces generated during the various phases of a typical burrowing cycle were measured in animals moving beneath the natural substratum at 5±3 °C using electronic transducers and recorder. During 'head' advance Polyphysia generated 0.027 N, and during 'tail' advance 0.020 N, with peak internal pressures averaging 0.95 kPa (= 0.095 N/cm²). Force by Priapulus during head advance and tail advance was 0.081 N and 0.121 N, respectively, with peak internal pressures averaging 2.47 kPa (= 0.247 N/cm²). Polyphysia moves more slowly (0.24 cm/min) than does Priapulus (0.76 cm/min) and expends more energy on mass moved per unit distance. These force measurements during a burrowing cycle were used in place of respirometry as a basis for computation of net cost of transport (NCT) for each animal. NCT for Polyphysia was 635 J kg^-1 m^-1 and for Priapulus was 314Jkg^-1m^-l. Cost of transport for all burrowing animals thus far investigated is high compared to swimming, running and flying. For soft-bodied invertebrates that live an entirely buried existence this high cost must be interpreted in the broader context of the adaptive value of infaunal life, especially protection against predation, and not as simply a means of moving about.