Electromotive chloride transport and gastric acid secretion in the frog

The total active transport of chloride ions across the gastric mucosa can be considered as the sum of two fractions; an acidic one which is equivalent to the acid secreted, and an electromotive one which accounts for the electric energy generated by the gastric mucosa. In the present studies, the relationship between this electromotive chloride transport and acid secretion has been investigated, using specific inhibitors. The rate of electromotive chloride transport was found to be essentially unaffected by changes in the rate of acid secretion, and also by inhibition of acid secretion by thiocyanate. On the other hand, diamox, in combination with histamine, was shown to depress or abolish the gastric electromotive force and to inhibit partially the total chloride transport, while acid was secreted at an almost normal rate. This kind of inhibition is undefined as to its mechanism but seems to be more specific for the gastric chloride transport than any other inhibitor known. It is concluded that acid secretion and electromotive chloride transport involve two different mechanisms, and are not absolutely essential for each other. The present results do not support the view that carbonic anhydrase is essential for acid secretion. They rather suggest an important function of this enzyme in the mechanism of active chloride transport.     

Life-long growth of Quercus ilex L. at natural CO2 springs acclimates sulphur, nitrogen and carbohydrate metabolism of the progeny to elevated pCO2

The aim of the present study was to analyse whether offspring of mature Quercus ilex trees grown under life‐long elevated pCO₂ show alterations in the physiological response to elevated pCO₂ in comparison with those originating from mature trees grown at current ambient pCO₂. To investigate changes in C‐ (for changes in photosynthesis, biomass and lignin see Polle, McKee & Blaschke Plant, Cell and Environment 24, 1075–1083, 2001), N‐, and S‐metabolism soluble sugar, soluble non‐proteinogenic nitrogen compounds (TSNN), nitrate reductase (NR), thiols, adenosine 5′‐phosphosulphate (APS) reductase, and anions were analysed. For this purpose Q. ilex seedlings were grown from acorns of mother tree stands at a natural spring site (elevated pCO₂) and a control site (ambient pCO₂) of the Laiatico spring, Central Italy. Short‐term elevated pCO₂ exposure of the offspring of control oaks lead to higher sugar contents in stem tissues, to a reduced TSNN content in leaves, and basipetal stem tissues, to diminished thiol contents in all tissues analysed, and to reduced APS reductase activity in both, leaves and roots. Most of the components of C‐, N‐ and S‐metabolism including APS reductase activity which were reduced due to short‐term elevated pCO₂ exposure were recovered by life‐long growth under elevated pCO₂ in the offspring of spring oaks. Still TSNN contents in phloem exudates increased, nitrate contents in lateral roots and glutathione in leaves and phloem exudates remained reduced in these plants. The present results demonstrated that metabolic adaptations of Q. ilex mother trees to elevated pCO₂ can be passed to the next generation. Short‐ and long‐term effects on source‐to‐sink relation and physiological and genetic acclimation to elevated pCO₂ are discussed.     

Microtubular Structures in Macronuclei of Synchronously Dividing Tetrahymena pyriformis

SYNOPSIS. When heat-synchronized cultures of Tetrahymena pyriformis , amicronucleate strain GL, were examined by electron microscopy, intramacronuclear microtubules were observed in dividing cells. These tubules have a diameter of 180–230 A and occur either singly or packed together in bundles. They are predominantly associated with outpocketings and invaginations of the nucleus. Sections as well as negatively stained preparations of isolated macronuclear envelopes indicate that the microtubules are inserted at the inner nuclear membrane.
The findings suggest that microtubules of the spindle type participate in the process of macronuclear division.     

Single RNA Polymerase Binding Site Isolated

One approach to study the structure of promoter regions^1–3 is to isolate RNA polymerase binding sites. Several attempts have been made to isolate such sites as protected DNA fragments^4–10, but so far the DNA isolated has not definitely shown to be only one or a few specific sites. We report here the isolation of a single RNA polymerase binding site from the replicative form (RF) DNA of bacteriophage fd. The site as isolated is a short double-stranded DNA with a unique nucleotide sequence.     

Differential expression of specific sulphate transporters underlies seasonal and spatial patterns of sulphate allocation in trees

Sulphate uptake and its distribution within plants depend on the activity of different sulphate transporters (SULTR). In long‐living deciduous plants such as trees, seasonal changes of spatial patterns add another layer of complexity to the question of how the interplay of different transporters adjusts S distribution within the plant to environmental changes. Poplar is an excellent model to address this question because its S metabolism is already well characterized. In the present study, the importance of SULTRs for seasonal sulphate storage and mobilization was examined in the wood of poplar (Populus tremula × P. alba) by analysing their gene expression in relation to sulphate contents in wood and xylem sap. According to these results, possible functions of the respective SULTRs for seasonal sulphate storage and mobilization in the wood are suggested. Together, the present results complement the previously published model for seasonal sulphate circulation between leaves and bark and provide information for future mechanistic modelling of whole tree sulphate fluxes.