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.     

X-ray microanalytical detection of iron in pigmentation of oral mucosa.

A patient was referred to the Charles Clifford Dental Hospital with a grey metallic pigmentation of the hard palate. Conventional histopathological examination was inconclusive, suggesting the presence of either an ephelis (freckle) of pigmentation resulting from a stainless steel upper denture. Material from the pathological specimen was dewaxed and reembedded in Spurr's resin. Examination in the TEM revealed electron dense deposits in the cytoplasm of macrophages. Energy dispersive X-ray microanalysis demonstrated that these inclusions contained iron. The results suggested that the iron was in a form similar to haemosiderin and had arisen from the steel denture.     

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.     

Renal uptake and excretion of epidermal growth factor from plasma in the rat

The rat excretes around 2 nmol epidermal growth factor (EGF) in the urine per 24 h. The urinary EGF might be derived from plasma and/or might be synthesized in the kidneys. We have used the rat to study the renal uptake and excretion of homologous EGF from plasma. I.v. injected 125I-EGF was removed from the circulation within a few minutes. 5 min after the injection, the kidneys contained 12% of the 125I-EGF. The kidneys seemed to degrade most of the 125I-EGF which they accumulated from blood, as only 4% of the injected label was excreted as intact 125I-EGF in the urine. The amount of endogenous EGF in plasma was under the detection limit of our enzyme-linked immunosorbent assay (0.03 nmol/l) and it remained so after bilateral nephrectomy. Even if plasma EGF was 0.03 nmol/l excretion of EGF from plasma could account for less than 5% of the urinary EGF. This study shows that the kidneys are able to accumulate EGF from plasma and excrete a part of it as intact EGF in the urine. However, excretion of immunoreactive EGF from plasma can only account for a minor part of the urinary EGF.     

Multiattribute evaluation of regional cotton variety trials

Summary The Australian Cotton Cultivar Trials (ACCT) are designed to investigate various cotton [Gossypium hirsutum (L.)] lines in several locations in New South Wales and Queensland each year. If these lines are to be assessed by the simultaneous use of yield and lint quality data, then a multivariate technique applicable to three-way data is desirable. Two such techniques, the mixture maximum likelihood method of clustering and three-mode principal component analysis, are described and used to analyze these data. Applied together, the methods enhance each other's usefulness in interpreting the information on the line response patterns across the locations. The methods provide a good integration of the responses across environments of the entries for the different attributes in the trials. For instance, using yield as the sole criterion, the excellence of the namcala and coker group for quality is overlooked. The analyses point to a decision in favor of either high yields of moderate to good quality lint or moderate yield but superior lint quality. The decisions indicated by the methods confirmed the selections made by the plant breeders. The procedures provide a less subjective, relatively easy to apply and interpret analytical method of describing the patterns of performance and associations in complex multiattribute and multilocation trials. This should lead to more efficient selection among lines in such trials.     

Metabolic consequences of positive inotropy in rat and guinea-pig hearts

The metabolic and physiological responses of hearts from male rats and guinea-pigs to isoprenaline and SK&F 94120 (a phosphodiesterase III inhibitor), have been studied. Doses which gave similar chronotropic stimulation gave different inotropic responses. In both species, isoprenaline generated a greater increase in developed tension than SK&F 94120. With both drugs the inotropic response in the rat was less than than in the guinea-pig. 31P-NMR investigation of high-energy phosphate levels showed reduction in PCr concentration and an accompanying acidosis in the isoprenaline-perfused rat heart only. In both species, lactate production was stimulated by SK&F 94120 but not by isoprenaline. These results are discussed with reference to G-protein activation of ion channels and differences in Ca2+ handling by the two species.     

The use of a drug resistance cartridge for in vitro insertion and deletion mutagenesis of a cosmid clone

A drug-resistant cartridge was employed in the construction of families of insertion mutants of a cosmid clone. The cartridge contains a cml gene and has identical restriction enzyme sites, EcoRI, BamHI, SalI, and PstI, on both ends. The families of mutants were made by ligation of the cartridge to the cosmid, which was linearized or partially digested, followed by in vitro packaging and transduction. From these families we selected cosmid derivatives which either have a unique BamHI site at a predetermined site in the cosmid or have deletions covering different portions of the original clone. The extent of a large gene cluster cloned into the original cosmid was identified by confirming the gene function in some of the deletion mutants. The possibility for further and various uses of this cartridge is discussed.     

Mutagenesis of the NH2-terminal domain of elongation factor Tu

Mutagenesis was carried out in the N-terminal domain of elongation factor Tu (EF-Tu) to characterize the structure-function relationships of this model GTP binding protein with respect to stability, the interaction with GTP and GDP, and the catalytic activity. The substitutions were introduced in elements around the guanine nucleotide binding site or in the loops defining this site, in the intact molecule or in the isolated N-terminal domain (G domain). The double substitution Val88----Asp and Leu121----Lys, two residues situated on two vicinal alpha-helices, influences the basic activities of the truncated factor to a limited extent, probably via long-range interactions, and induces a destabilisation of the G domain structure. The functional alterations brought about by substitutions on the consensus sequences 18-24 and 80-83 highlight the importance of these residues for the interaction with GTP/GDP and the GTPase activity. Mutations concerning residues interacting with the guanine base lead to proteins in large part insoluble and inactive. In one case, the mutated protein (EF-TuAsn135----Asp) inhibited the growth of the host cell. This demonstrates the crucial role of the base specificity for the active conformation of EF-Tu. The obtained results are discussed in the light of the three-dimensional structure of EF-Tu.