Gas exchange and resource-use patterns along a Mediterranean successional gradient

Abstract. Gas exchange, leaf-nitrogen concentration and water potential were measured in early and late spring in early successional herbaceous plants occurring after cutting and after fire, and in mature woody species from the Mediterranean climax community Quercetum ilicis in central Italy. Net photosynthesis peaked in early spring in all species studied when values for temperature and light were lower but leaf-nitrogen content was higher as compared to late spring, suggesting that nitrogen more than energy input controlled photosynt-hetic rates. Herbaceous pioneer species occurring after cutting showed higher field photo synthetic capacity than evergreen climax trees and shrubs. By contrast, net photosynthesis of herbaceous species occurring in a persistent stage after fire, was in the same range as that of climax trees. This evidence suggests that carbon-gaining appears to be partly related to the dynamic stage of succession and not solely to the growth form.     

Use of the API rapid NFT system for identifying nonfermentative and fermentative marine bacteria.

Thirty-five American Type Culture Collection type strains of marine bacteria were used to evaluate the Rapid NFT system (API Analab Products, Plainview, N.Y.) for use in identifying heterotrophic marine bacteria. The 21 biochemical and assimilation tests on the Rapid NFT test strips were treated according to the manufacturer's protocol, which included use of AUX medium (provided with the Rapid NFT system) for preparing assimilation tests, and by substituting phenol red broth base (BBL Microbiology Systems, Cockeysville, Md.) with and without an oil overlay for the AUX medium. A seven-digit numerical profile was obtained for each NFT test strip from each of the three procedures and matched to its corresponding number in the Rapid NFT identification codebook. Also, all biochemical and assimilation test results were analyzed with SASTAXAN and SAS/GRAPH programs (SAS Institute, Inc., Cary, N.C.); similarity matrices were computed for all 35 strains. For comparison purposes, bacterial strains were grouped at a similarity level of 70%. The results indicated a low efficacy of identification for all three procedures. In addition, similarity matrix analysis showed more cohesive grouping based on results of phenol red broth base-treated strains than for the AUX medium provided by the manufacturer. However, none of the three treatments provided exclusive grouping of type strains at the genus level. Thus, the reliability of the data obtained from the NFT system and modifications thereof should be evaluated carefully when environmental isolates are characterized.     

Dynamics of calmodulin in cerebral structures under the action of modulated UHF electromagnetic fields]

The influence of modulated UHF-electromagnetic fields (low intensity) on calmodulin levels in several brain structures was studied. It was shown that UHF-electromagnetic fields influence calmodulin levels in the hypothalamus and sensorimotor cortex. Its effect depends on modulation regimes.     

Fermentation studies of the secretion of Serratia marcescens nuclease by Escherichia coli

The secretion of a Serratia marcescens nuclease was followed by fermentation with Escherichia coli. A plasmid, p403-SD2, carrying a 1.3-kilobase-pair insert with a 0.4-kilobase-pair region upstream of the nuclease gene caused a growth-phase-regulated expression of nuclease in E. coli in the same way as that seen in S. marcescens. Deletion of the regulatory gene generating plasmid p403-Rsa1 resulted in a constitutive expression of the nuclease. Anaerobiosis stimulated the expression from p403-SD2 in stationary growth phase by a factor of 10 compared with expression stimulated by cultivation in aerobic conditions; no such effect was found for plasmid p403-Rsa1. Different nutritional factors caused the expression level and the amount of extracellular nuclease to vary more when nuclease was expressed from plasmid p403-SD2 than when it was expressed from plasmid p403-Rsa1. A correlation between the regulatory gene and the extracellular secretion of nuclease is proposed.     

Effects of DNA and synthetic oligodeoxyribonucleotides on the binding properties of a cGMP-binding protein from Dictyostelium discoideum

Previously, we identified a cGMP-binding protein (cGBP) in Dictyostelium discoideum that can exist in two forms: a fast-dissociating (F-type) activity and a slow-dissociating (S-type) activity. Moreover, the F-type activity was converted effectively to S-type by the addition of nucleic acids, especially DNA (Parissenti, A.M. and Coukell, M. B. (1989) J. Cell Sci. 92, 291-301). In this study, we examined the effects of heterologous DNA and various synthetic homo-oligodeoxyribonucleotides on the cGMP-binding properties of partially purified F-type activity. Equilibrium and kinetic binding experiments revealed that DNA increased the affinity of the protein for cGMP without altering the number of binding sites. However, the presence of DNA decreased only slightly the apparent Kd of the protein for cGMP because the nucleic acid also reduced the rate of cGMP association. Addition of oligo(dGMP)8 or oligo(dCMP)8 to the protein increased both total cGMP binding and the conversion of F-type activity to S-type; in contrast, oligo(dAMP)8 or oligo(dTMP)8, at the same concentration, had no effect. Oligodeoxycytidylic acids with chain lengths less than about eight nucleotides were also ineffective or inhibitory. Analysis of cGMP binding to intact, filipin-permeabilized cells revealed a binding activity with association and dissociation rates comparable to isolated S-type activity. This observation suggests that in vivo the cGBP might exist in its S-form.