Growth and survival ofAzospirillum brasilense andArthrobacter giacomelloi in binary continuous culture

Summary Azospirillum brasilense andArthrobacter giacomelloi were grown in single and mixed succinate-limited continuous cultures at a partial oxygen pressure of 0.01atm. Growth, viability and survival during nutrient starvation were examined at various dilution rates. At D=0.05 h^–1, K_s values for succinate consumed were calculated.Arthrobacter giacomelloi viability was inversely related to dilution rate whereasAzo. brasilense was directly related. Slightly lower values of viability were obtained in mixed culture, but the ratio between the microorganisms was constant. The survival ofArth. giacomelloi in single culture decreased with increasing growth rate while survival ofAzo. brasilense was directly related to dilution rate. Acetylene reduction activity was generally very low in both single and mixed cultures. Respiration rate was also determined and the mixed culture showed an oxygen uptake rate higher than that of single cultures.Research work supported by CNR, Italy. Special grant I.P.R.A. Sub-project 1. Paper N. 317.     

Effects of insulin treatment on ketone body production and carnitine-palmitoyl-transferase (CPT) activity in the isolated perfused liver from streptozotocin diabetic rats

The aim of the present paper was to evaluate the effects of in vivo insulin treatment of streptozotocin (SZ) diabetic rats on the metabolism of the isolated, perfused liver. Perfused livers from SZ-diabetic rats showed a higher ketone body production and a higher mitochondrial carnitine-palmitoyl-transferase (CPT) activity than controls, while triglyceride (TG) output and free-fatty-acid (FFA) uptake were significantly reduced. In vivo insulin treatment normalized both the ketogenic capacity of the liver and CPT activity, while FFA uptake and TG production were still lower than in controls. A significant correlation was found between total ketone body output and CPT activity. We suggest that In vivo insulin treatment of SZ-diabetic rats can modulate the ketogenic capacity of the isolated, perfused liver.     

Stomatal response to air humidity and its relation to stomatal density in a wide range of warm climate species

The gas exchange of 19 widely different warm climate species was observed at different leaf to air vapour pressure deficits (VPD). In all species stomata tended to close as VPD increased resulting in a decrease in net photosynthesis. The absolute reduction in leaf conductance per unit increase in VPD was greatest in those species which had a large leaf conductance at low VPDs. This would be expected even if stomata of all species were equally sensitive. However the percentage reduction in net photosynthesis (used as a measure of the relative sensitivity of stomata of the different species) was also closely related to the maximal conductance at low VPD. Similarily the relative sensitivity of stomata to changes in VPD was closely related to the weighted stomatal density or crowding index.The hypothesis is presented that stomatal closure at different VPDs is related to peristomatal evaporation coupled with a high resistance between the epidermis and the mesophyll and low resistance between the stomatal apparatus and the epidermal cells. This hypothesis is consistent with the greater relative sensitivity of stomata on leaves with a high crowding index.The results and the hypothesis are discussed in the light of selection, for optimal productivity under differing conditions of relative humidity and soil water availablility, by observation of stomatal density and distribution on the two sides of the leaf.Visiting scientist, plant physiologist and research assitant of the Cassava Program     

Rouleau formation of erythrocytes: A dynamical model

A model is presented for the nonBrownian motion of living erythrocytes suspended in their own plasma as observed by Rowlands et al. On the basis of this model, the formation of rouleaux (contractile fibrils among interacting erythrocytes) can be described in terms of an organization of the molecules (mainly fibrinogen) present in blood plasma; this organization is sustained by the nonlinear propagation of electric vibrations generated by red blood cells (coherent electric vibrations of the Fröhlich type).A number of peculiar experimental features otherwise unexplained can also be taken into account in the framework of the model.     

Isoelectric focusing of brain cortex GSH S-transferase activity in mammals: evidence that polymorphism is absent in man

Specific activities of GSH S-transferase toward different model substrates were determined in the cytosol prepared from rat, guinea pig, rabbit, mouse, sheep, beef, pig and human brain cortex. The GSH S-transferase composition of the eight mammalian brain cortices was studied by using density gradient isoelectric focusing technique. Human brain cortex GSH S-transferase was resolved into a single peak of activity centered at pH 4.6, whereas the supernatants of all other mammals consisted of more than one enzymatic form. The kinetic properties of all forms isolated were compared.     

Peripheral benzodiazepine binding sites in kidney: modifications by diabetes insipidus

Using [3H] diazepam as ligand, it is possible to distinguish neuronal binding sites from those present on glial elements and in peripheral tissues (non-neuronal). The function of the "non-neuronal" binding sites is still obscure. Preliminary data showed a distribution of [3H] diazepam binding sites in kidney that could suggest a localization along the renal tubules. This is the site at which a renal peptide, arginine-vasopressin (AVP) is supposed to act. In an attempt to examine the function of these "non-neuronal" sites, we studied the [3H] diazepam binding in kidney of Brattleboro rats which lack AVP and present the symptoms of diabetes insipidus. The homozygous Brattleboro rats showed an increase in the apparent number of benzodiazepine binding sites (Bmax) compared to Long-Evans control rats. Replacement of AVP in these animals results in a reversal of the electrolyte alterations of diabetes insipidus and in an increase of the affinity of the [3H] diazepam binding. These findings may indicate a possible relationship between benzodiazepine binding sites and vasopressin action in kidney and may support receptor function of these "non-neuronal" binding sites.     

Immobilization of white-tailed deer with xylazine hydrochloride and ketamine hydrochloride and antagonism by tolazoline hydrochloride

Fourteen penned and 17 free-ranging white-tailed deer (Odocoileus virginianus Rafinesque) were singularly or repeatedly immobilized with 100 mg xylazine hydrochloride (HCl) and 300 mg ketamine HCl. The mean times from intravenous injection to ambulation for 1.0, 2.0, and 4.0 mg/kg body weight doses of tolazoline HCl were 13.5, 10.5, and 9.2 min. Deer not receiving tolazoline HCl recovered in an average of 168 min. Heart rates significantly (P less than 0.001) increased from 47 to 83 beats/min after tolazoline HCl administration, representing a return to normal rate. Tolazoline HCl had no effect on respiratory rate. A total of 85 reversals with tolazoline HCl resulted in no apparent adverse reactions.     

Antinociceptive and Met-enkephalin releasing effects of tachykinins and substance P fragments

Substance P (SP), physalaemin, SP4-11, SP5-11 and the SP5-11 analog DiMe-C7 induce an antinociceptive effect in rats after intraventricular administration. Other tachykinins and the N-terminal fragments of SP are inactive. All antinociceptive peptides increase the Met-enkephalin efflux from slices of rat periaqueductal gray matter and their antinociceptive potency is correlated with their capacity to release Met-enkephalin. The results, discussed in the light of current theories on different tachykinin receptors, suggest that the SP-P receptor subtype may be involved in the control of noxious stimulation elicited by SP at supraspinal levels.     

Ultrastructural organization of freeze-fractured interphase nuclei

The morphology of intact or membrane-deprived interphase nuclei has been analysed by freeze-fracture electron microscopy. This method appears particularly useful for providing information on the distribution and organisation of chromatin and ribonucleoproteins in the absence of dehydration and embedding artifacts of conventional electron microscope techniques which, among other effects, appear to affect heterochromatin distribution, inducing its aggregation along the nuclear envelope. The main levels of chromatin superstructure, from nucleosome to solenoid fibres, are detectable in the replicas of freeze-fractured nuclei on the basis of the size of their shadow, a parameter particularly suitable for automated image analyses.