Modulation of maize roots H+-ATPase by sulfated polysaccharides

Vesicles derived from maize roots retain a membrane bound H⁺-ATPase that is able to pump H⁺ at the expense of ATP hydrolysis. In this work it is shown that heparin, fucose-branched chondroitin sulfate and dextran sulfate 8000 promote a shift of the H⁺-ATPase optimum pH from 6.0 to 7.0. This shift is a result of a dual effect of the sulfated polysaccharides, inhibition at pH 6.0 and activation at pH 7.O. At pH 6.0 dextran 8000 promotes an increase of the apparent K_m for ATP from 0.28 to 0.95 mM and a decrease of the V_max from 14.5 to 7.1 mol P_i/mg · 30 min^–1. At pH 7.0 dextran 8000 promotes an increase in V_max from 6.7 to 11.7 mol Pi/mg · 30 min^–1. In the presence of lysophosphatidylcholine the inhibitory effect of the sulfated polysaccharides observed at pH 6.0 was not altered but the activation of pH 7.0 decreased. It was found that in the presence of sulfated polysaccharides the ATPase became highly sensitive to K⁺ and Na⁺. Both the inhibition at pH 6.0 and the activation promoted by the polysaccharide were antagonized by monovalent cations (K⁺>Na⁺Li⁺).Abbreviations Mops 4-morpholinopropanesulfonic acid - EDTA ethylenediaminetetraacetic acid - ACMA 9-amino-6-chloro-2-methoxyacridine - FCCP carbonyl cyanide p(trifluoromethoxy)-phenylhyrazone     

Surface hydrography and phytoplankton of the Brazil-Malvinas currents confluence

Results are presented on the phytoplankton species compositionand abundance from bottle samples collected in September 1989near the confluence of the Brazil and Malvinas currents offArgentina. The phytoplankton assemblages were dominated by diatomsand dinoflagellates. A surface diatom bloom was found alongthe west side of the Brazil Current, and was dominated by Thalassiosiradelicatula Ostenfeld emend. Hasle (cell numbers up to 5.5 x10⁵ cells 1^–1) The bloom was associated with strong temperaturegradients separating Brazil and Malvinas waters, and with thepresence of a cyclonic eddy near the confluence of the currents.These features were detected in satellite imagery coincidentwith the in situ sampling dates.     

Isolation and promoter characterization of barley geneItr1 encoding trypsin inhibitor BTI-CMe: differential activity in wild-type and mutantlys3a endosperm

The geneItr1, encoding trypsin inhibitor BTI-CMe, has been obtained from a genomic library ofHordeum vulgare L. The gene has no introns and presents in its 5-upstream region 605 bp that are homologous to the long terminal repeats (LTR) of the copia-like retro-transposon Bare-1. Functional analysis of theItr1 promoter by transient expression in protoplasts derived from different barley tissues, has shown that in this system theItr1 promoter retains its endosperm specifity and thetrans-regulation mediated by theLys3a gene. The proximal promoter extending 343 bp upstream of the translation initiation ATG codon is sufficient to confer fullGUS expression and for endosperm specifity. In protoplasts derived from thelys3a mutant, Risø 1508,GUS activity was less than 5% of that obtained with the same constructs in the protoplasts of wild-type Bomi from which it derives. Gel retardation experiments, after incubation with proteins obtained from both types of endosperm nuclei, also show differential patterns. Possible reasons for these differences are discussed.Equal authours     

Bacterial expression of an active class Ib chitinase from Castanea sativa cotyledons

Ch3, an endochitinase of 32 kDa present in Castanea sativa cotyledons, showed in vitro antifungal properties when assayed against Trichoderma viride. The characterization of a cDNA clone corresponding to this protein indicated that Ch3 is a class Ib endochitinase that is synthesized as a preprotein with a signal sequence preceding the mature polypeptide. Bacterial expression of mature Ch3 fused to the leader peptide of the periplasmic protein ompT resulted in active Ch3 enzyme. A plate assay was adapted for semi-quantitative determination of chitinase activity secreted from cultured bacteria, which should facilitate the identification of mutants with altered capacity to hydrolyse chitin.     

Somatic embryogenesis,organogenesis and callus growth kinetics of flax

The effects of plant growth regulators (PGR) on calli induction, morphogenesis and somatic embryogenesis of flax were studied. The organogenic and callus formation capacity were assessed for different types of source explants. Root and shoot explants were equally good material for calli production but the former produced calli without shoot regeneration capacity. Under the experimental conditions tested, 2,4-dichlorophenoxyacetic acid (2,4-D) + zeatin was the most efficient PGR combination on calli induction and biomass production. The calli were green but with no rhizogenic capacity. In contrast, and at similar concentrations, indole-3-butyric acid (IBA) + kinetin induced white or pale green friable calli with a good root regeneration capacity (60%). A factorial experiment with different combinations of 2,4-D + zeatin + gibberellic acid (GA₃) levels revealed that the direction of explant differentiation was determined by specific PGR interactions and concentrations. The results from these experiments revealed that the morphogenetic pathway (shoot versus root differentiation) can be manipulated on flax explants by raising the 2,4-D level from 0.05 to 3.2 mg l^?1 in the induction medium. The induction and development of somatic embryos from flax explants was possible in a range of 2,4-D + zeatin concentrations surrounding 0.4 mg l^?1 2,4-D and 1.6 mg l^?1 zeatin, the most efficient growth regulator combination.     

A new species of Lupinus (Fabaceae: Lupininae) from southeastern Brazil

Lupinus rubriflorus Planchuelo, from Rio Grande do Sul, Brazil, is described and illustrated. This species is related toL. bracteolaris s.l. differing in pubescence, stipules, and floral characters.     

Assessment of populations ofGracilaria chilensis (Graeilariales,Rhodophyta) utilizing RAPDs

Phenotypic variability and mixing of material due to massive cultivation for commercial purposes has contributed to the taxonomic confusion ofGracilaria in Chile. At least four species with cylindrical thalli and similar morphology have been recorded. However, since establishment ofG. chilensis, most of the collected thalli have been attributed to this species despite the lack of diagnostic features. In an attempt to resolve whetherGracilaria from 3 localities where it grows in natural and artificial populations belongs to the same species, gametophytic samples were compared by applying RAPD-PCR to their total DNA. This was analysed using 25 different 10-mer primers from which 21 revealed polymorphism within and between populations. Similarity matrices and cluster analyses were performed based on the presence/absence of bands representing fragments of DNA generated by random amplification. Similarity values between two of the populations were equivalent to those detected within a third, indicating the mixing of genetic material due to transplant between the two former localities. Similarities between samples of ChileanGracilaria andG. tenuistipitata from Sweden are considerably lower (0.45–0.53) than those between populations from Chile (0.74–0.88), confirming the existence of a single specific taxon,G. chilensis, in these three localities.     

Advantages and limitations in the use of hairy root cultures for the production of tropane alkaloids: Use of anti-auxins in the maintenance of normal root morphology

Summary Brugmansia candida hairy roots, obtained by infection withAgrobacterium rhizogenes LBA 9402, exhibit, after subculturing in liquid media, a tendency towards dedifferentiation. It has been found that the following strategies can be applied to inhibit this dedifferentiation and preserve normal root morphology: (a) lowering both the mineral and sucrose concentration in the media employed so as to diminish osmotic stress (a condition to which these roots appear to be particularly susceptible); (b) employing antiauxins in appropriate concentrations; and (c) maintaining the hairy roots on solid media prior to use in production processes in liquid media. The first strategy suggested does not favor alkaloid productivity, but in this case a two-step method could be attempted: biomass with normal root morphology could be obtained in a first stage using low sucrose concentrations, and in a second stage, sucrose could be increased in order to achieve higher productivity. In all the clones ofB. candida obtained, alkaloid production was biased towards scopolamine.     

PGE2 involvement in experimental infection with Trypanosoma cruzi subpopulations

PGE₂ involvement in experimental Trypanosoma cruzi infection depends on the lethal capacity of the parasite subpopulation used. Mice acutely infected with non-lethal K98 displayed an enhancement in PGE₂ serum levels during the acute period, while those infected with lethal T. cruzi subpopulations (RA or K98-2) showed levels not different from normal mice. The enhancement detected in K98 group could be related both to an increased number of CD8+ T cell number and to enhanced PGE₂ release per cell by CD8+; values of PGE₂ release by adherent cells were not altered in this group. Treatment with cyclooxygenase inhibitors enhanced mortality rates of mice infected with K98, and administration of 16,16-dimethyl PGE₂ (dPGE) reversed this effect. However, mice infected with RA did not reduce their mortality rates by administration of diverse doses of dPGE. These findings suggest that PGE₂ could play a role in resistance in mice infected with K98.