Voltage-dependent channels permeable to K+ and Na+ in the membrane ofAcer pseudoplatanus vacuoles

Summary The patch-clamp technique in whole-cell configuration was used to study the electrical properties of the tonoplast in isolated vacuoles fromAcer pseudoplatanus cultured cells. In symmetrical KCl or K₂ malate solutions, voltage- and time-dependent inward currents were elicited by hyperpolarizing the tonoplast (inside negative), while in the positive range of potential the conductance was very small. The specific conductance of the tonoplast at –100 mV, in 100mm symmetrical KCl was about 160 S/cm². The reversal potentials (E _rev) of the current, measured in symmetrical or asymmetrical ion concentrations (cation, anion or both) were very close to the values of the K⁺ equilibrium potential. Experiments performed in symmetrical or asymmetrical NaCl indicate that Na⁺ too can flow through the channels. NeitherE _rev nor amplitude and kinetics of the current changed by replacing NaCl with KCl in the external solution. These results indicate the presence of hyperpolarization-activated channels in tonoplasts, which are permeable to K⁺ as well as to Na⁺. Anions such as Cl^– or malate seem to contribute little to the channel current.     

Sull'evoluzione Dei Mitocondri Nell'endosperma di Semi di Ricino in Germinazione

Abstract

On the behavior of mitochondria in the castor bean seed endosperm during the early phases of germination. — In the endosperm of the castor bean seed the oxidative activity and the protein nitrogen contents of the mitochondrial fraction markedly increase during the first period of germination (Beevers and coworkers). The activation of the mitochondrial system is paralleled by a similar increase of the activity of several soluble enzymes; the latter process is severely depressed by protein synthesis inhibitors (Cornaggia, Aberghina).

The present research is aimed to understand at what extent phenomena of activation and/or, respectively, of « ex novo » synthesis are responsible of the increase of mitochondrial activity. The following aspects of the mitochondrial behavior during the early period of germination were investigated:

a) Changes in the activity of cytochrome oxydase, malate dehydrogenase and of the succinate-citochrome reductase system.

b) Changes in the morphology of mitochondria and other particulated cell structures, as revealed by electron microscopy.

In the mitochondrial preparation all of the three enzymatic activities investigated were found to increase rapidly during the first days of germination. The increase during the first 24 hours was almost as large when measured as specific activity (activity per mg protein in the mitochondrial fraction) than when measured on an absolute (i.e. per seed) basis; moreover, it was not significantly inhibited by puromycin or by actinomycin. The increase of the three activities during the following period of germination (second-third day) was accompanied by an increase of the protein nitrogen (per seed) in the mitochondrial fraction, and was consistently depressed by the protein synthesis inhibitors.

In the mitochondrial preparation all of the three enzymatic activities investigated were found to increase rapidly during the first days of germination. The increase during the first 24 hours was almost as large when measured as specific activity (activity per mg protein in the mitochondrial fraction) than when measured on an absolute (i.e. per seed) basis; moreover, it was not significantly inhibited by puromycin or by actinomycin. The increase of the three activities during the following period of germination (second-third day) was accompanied by an increase of the protein nitrogen (per seed) in the mitochondrial fraction, and was consistently depressed by the protein synthesis inhibitors.

These results, integrated with those of other investigations on the same material are in agreement with the hypothesis that the activation of metabolism in the endosperm during germination depends in a very early phase mainly on the transition of enzyme systems from an inactive to an active state; while in a second phase synthesis « ex novo » of enzymes and cell structures predominates.     

A comparative physiological and transcriptional study of carotenoid biosynthesis in white and red grapefruit (Citrus paradisi Macf.)

Accumulation of lycopene in citrus fruits is an unusual feature restricted to selected mutants. Grapefruit (Citrus paradisi Macf.) is the Citrus specie with greater number of red-fleshed mutants, but the molecular bases of this alteration are not fully understood. To gain knowledge into the mechanisms implicated in this alteration, we conducted a comparative analysis of carotenoid profile and of the expression of genes related to carotenoid biosynthesis and catabolism in flavedo and pulp of two grapefruit cultivars with marked differences in colouration: the white Marsh and the red Star Ruby. Mature green fruit of Marsh accumulated chloroplastic carotenoids, while mature tissues lacked carotenoids. However, accumulation of downstream products such as abscisic acid (ABA) and expression of its biosynthetic genes, 9-cis-epoxycarotenoid dioxygenase (NCED1 and NCED2), increased after the onset of colouration. In contrast, red grapefruit accumulated lycopene, phytoene and phytofluene, while ABA content and NCED gene expression were lower than in Marsh, suggesting a blockage in the carotenoid biosynthetic pathway. Expression analysis of three genes of the isoprenoid pathway and nine of the carotenoid biosynthetic pathway revealed virtually no differences in flavedo and pulp between both genotypes, except for the chromoplast-specific lycopene cyclase 2 (β-LCY2) which was lower in the pulp of the red grapefruit. The proportion in the expression of the allele with high (β-LCY2a) and low (β-LCY2b) activity was also similar in the pulp of both genotypes. Therefore, results suggest that reduced expression of β-LCY2 appears to be responsible of lycopene accumulation in the red Star Ruby grapefruit.     

Vitamin E sensitive genes in the developing rat fetal brain: a high-density oligonucleotide microarray analysis

Vitamin E (tocopherols and tocotrienols) is essential for normal neurological function. Recently we have reported that the neuroprotective properties of tocotrienols are much more potent than that of the widely studied tocopherols (Sen, C.K., Khanna, S., Roy, S. and Parker, L. (2000) J. Biol. Chem. 275, 13049–13055). The objective of this study was to evaluate whether (i) oral supplementation of tocotrienols during pregnancy is bioavailable to fetal and mother brains; (ii) short-term change in dietary vitamin E levels of pregnant rats influences gene expression profile of developing fetal brains. We report that dietary tocotrienol is bioavailable to both mother and fetal brains. The enrichment is more in fetal brain tissue. Using a GeneChip microarray expression profiling approach we have identified a specific set of vitamin E sensitive genes in the developing rat fetal brain.     

Effects of a brassinosteroid on growth and on H+-extrusion in isolated radish cotyledons: comparison with the effects of benzyladenine

We investigated the effect of 24-epibrassinolide (BR) on the cytokinin-bioassay based on growth of isolated radish ( Raphanus sativus L. cv. Tondo Rosso Quarantino) cotyledons. BR stimulated growth of the cotyledons by about 50% when applied at saturating concentrations (3 μ M ). This effect was much lower than that of saturating concentrations of benzyladenine (BA) which was about 150% at 10 μ M BA. The effects of saturating concentrations of BR and BA were additive. BR, but not BA, stimulated H⁺-secretion by the cotyledons (measured as acidification of the incubation medium) slightly but reproducibly. These results indicate that the modes of action of the two phytoregulators are at least partially different.
BR-induced stimulation of H⁺-secretion was of similar amplitude to that induced by a concentration of fusicoccin (30 n M ) such as to stimulate growth to the same extent as BR. These results suggest that BR-induced stimulation of radish cotyledon growth might depend, at least in part, on BR-induced acidification of the wall space, similar to that observed on Azuki bean epicotyls and maize roots.     

Oxidative addition of 3,6-di-tert-butyl-o-benzoquinone and 4,6-di-tert-butyl-N-(2,6-di-iso-propylphenyl)-o-iminobenzoquinone to SnCl2

Addition of 3,6-di-tert-butyl-o-benzoquinone (3,6-DBBQ) to SnCl₂ in THF leads to the oxidation of Sn(II) to Sn(IV) with formation of catecholate complex (3,6-DBCat)SnCl₂ · 2THF (1), where 3,6-DBCat is 3,6-di-tert-butyl-catecholate dianion. The reaction of 4,6-di-tert-butyl-N-(2,6-di-iso-propylphenyl)-o-iminobenzoquinone (IBQ-Prⁱ) also proceeds on the oxidative-addition mechanism yielding bis-iminosemiquinonato species (ISQ-Prⁱ)₂SnCl₂(2), where ISQ-Prⁱ is anion-radical 4,6-di-tert-butyl-N-(2,6-di-iso-propylphenyl)-o-iminobenzosemiquinolate. The complexes have been characterized by IR, X-band EPR, ¹H NMR (for 1) spectroscopy and magnetochemistry (for 2). X-ray analysis data show the distorted octahedral environment of tin(IV) for both complexes. Complex 1 is diamagnetic (ground state S = 0), while 2 has triplet ground state (S = 1, biradical). Catecholate complex 1 is able to be a spin trap for different organic radicals.     

Dictyostelids from Mediterranean forests of the south of Europe

The first results of a study of dictyostelid diversity in soils of Mediterranean vegetation are presented. Surface soil samples were collected during 2003–2004 from different Mediterranean forests in Spain and Portugal and were plated out for cellular slime moulds. Isolated during this study were 14 species of dictyostelids. One species, Dictyostelium firmibasis is reported for the first time from Europe, and nine (Dictyostelium aureo-stipes, Dictyostelium sp. 1, Dictyostelium fasciculatum, Dictyostelium giganteum, Dictyostelium implicatum, Dictyostelium leptosomum, Dictyostelium sphaerocephalum, Polysphondylium candidum, Polysphondylium pallidum) are new records for the Mediterranean region. Members of the three genera Dictyostelium (ten species), Polysphondylium (three species) and Acytostelium (one species) are present in this region of the world. Comments on their diversity and distribution are included.     

Using Lidar Data to Analyse Sinkhole Characteristics Relevant for Understory Vegetation under Forest Cover—Case Study of a High Karst Area in the Dinaric Mountains

In this article, we investigate the potential for detection and characterization of sinkholes under dense forest cover by using airborne laser scanning data. Laser pulse returns from the ground provide important data for the estimation of digital elevation model (DEM), which can be used for further processing. The main objectives of this study were to map and determine the geomorphometric characteristics of a large number of sinkholes and to investigate the correlations between geomorphology and vegetation in areas with such characteristics. The selected study area has very low anthropogenic influences and is particularly suitable for studying undisturbed karst sinkholes. The information extracted from this study regarding the shapes and depths of sinkholes show significant directionality for both orientation of sinkholes and their distribution over the area. Furthermore, significant differences in vegetation diversity and composition occur inside and outside the sinkholes, which indicates their presence has important ecological impacts.