Regulation of nitrate uptake by amino acids in maize cell suspension culture and intact roots

The effect of amino acids on nitrate transport was studied in Zea mays cell suspension cultures and in Zea mays excised roots. The inclusion of aspartic acid, arginine, glutamine and glycine (15mM total amino acids) in a complete cell-culture media containing 1.0 mM NO₃ ^- strongly inhibited nitrate uptake and the induction of accelerated uptake rates. The nitrate uptake rate increased sharply once solution amino acid levels fell below detection limits. Glutamine alone inhibited induction in the cell suspension culture. Maize seedlings germinated and grown for 7 days in a 15 mM mixture of amino acids also had lower nitrate uptake rates than seedlings grown in 0.5 mM Ca(NO₃)₂ or 1 mM CaCl₂. As amino acids are the end product of nitrate assimilation, the results suggest an end-product feed-back mechanism for the regulation of nitrate uptake.     

Non-lethal secondary product release from transformed root cultures of Beta vulgaris

Transformed root tissue of Beta vulgaris (Detroit Dark Red) was permeabilized to stimulate the release of intracellularly stored betanin without adverse affects on tissue viability as measured by biomass accumulation. Product release of up to 15% (w/w) was achieved by heat treatment at 42°C for 45 min with minimal effect on viability. Higher levels of product release were obtained with increasing temperature and exposure, but at the expense of viability. Viability was measured by comparing dry weight increases of permeabilized tissue 3 days after treatment vs non-permeabilized tissue over the same time interval. Recovery of heat-treated tissue was improved by addition of CaCl₂ (20 mm for 10 min) post-heat treatment. Betanin release up to 15% was also obtained at ambient temperature (25°C) by addition of up to 20 mm (NH₄)₂SO₄ in the presence of 1 mm ethylenediaminetetraacetic acid (EDTA). Correspondence to: A. A. DiIorio     

DEVELOPMENTAL PLASTICITY,GENETIC VARIATION,AND THE EVOLUTION OF ANDROMONOECY IN SOLANUM HIRTUM (SOLANACEAE)

Studies of andromonoecious species have shown that sex expression (proportions of hermaphrodite and staminate flowers) is quite variable. It is not known, however, whether this variation is due to variation among individuals for genetically fixed patterns of allocation to staminate and hermaphrodite flowers (population level variation) and/or to developmental plasticity of individuals in a heterogeneous environment (organismal level variation). Distinguishing between these two levels of variation is important for understanding the evolution of andromonoecy. This study investigates levels of variation in sex expression in the andromonoecious Solanum hirlum. Sex expression in this species is shown to be plastic among individuals of the same genotype (organismal level variation) and determined, in part, by the resource status of the individual. Among the genotypes examined there is also genetic variation for developmental plasticity. Thus, developmental plasticity can potentially respond to selection, and the evolution of this developmental system may have been instrumental in the establishment and maintenance of andromonoecy in S. hirtum.     

Aspects of the biology of Pantinonemertes californiensis,a high intertidal nemertean

I studied the distribution, feeding biology, and reproductive biology of Pantinonemertes californiensis, described as a semi-terrestrial nemertean, along the central California coast. At the sites used in this study, maximal tidal height is about 2 m, and P. californiensis typically occurred under boulders between 1.3 and 1.7 m tidal height. Worms fed primarily on the semi-terrestrial amphipod Traskorchestia traskiana. Distribution of nemerteans was similar to that of the prey, although prey extended higher on the beach than did the worms. Nemerteans were largest and most abundant at the site with highest abundance of T. traskiana and smallest and least abundant at the lowest prey abundance site. In laboratory feeding trials, nemerteans from the site with lowest prey abundance fed most readily. Non-reproductive nemerteans lived for at least a week when submerged in sea water; some prey died within a week of being submerged. Nemerteans only lived minutes when submerged in fresh water; 50% of prey lived 4.5 h. Eggs are approximately 90–100 μm in diameter and hundreds to thousands are shed per female. Larvae are planktonic and apparently planktotrophic, and are morphologically similar to other marine hoplonemertean larvae. At the sites studied life history characteristics of P. californiensis provided little evidence of adaptations to terrestrial life in these worms and were not helpful in elucidating the role of semi-terrestrial nemerteans in the evolution of terrestrial nemerteans.     

An adaptive, object oriented strategy for base calling in DNA sequence analysis.

An algorithm has been developed for the determination of nucleotide sequence from data produced in fluorescence-based automated DNA sequencing instruments employing the four-color strategy. This algorithm takes advantage of object oriented programming techniques for modularity and extensibility. The algorithm is adaptive in that data sets from a wide variety of instruments and sequencing conditions can be used with good results. Confidence values are provided on the base calls as an estimate of accuracy. The algorithm iteratively employs confidence determinations from several different modules, each of which examines a different feature of the data for accurate peak identification. Modules within this system can be added or removed for increased performance or for application to a different task. In comparisons with commercial software, the algorithm performed well.     

Mutants in dolichol synthesis: conversion of polyprenol to dolichol appears to be a rate-limiting step in dolichol synthesis

Chinese hamster ovary (CHO) cells of the Lec9 recessive complementationgroup display a distinctive profile of resistance to a varietyof toxic lectins. In addition, they accumulate cis--unsaturatedpolyprenol and use mainly polyprenol rather than dolichol tosynthesize the glycosylated lipids used in asparagine-linkedglycosylation of proteins. The primary defect in these cellsis thought to result from a deficiency in polyprenol reductaseactivity. Three new mutants were isolated and determined tohave qualitatively, although not quantitatively, similar lectinresistance profiles to Lec9 cells. Two of these mutants (Abr^Rand Ric^R) also contained polyprenol rather than dolichol. Thelectin resistance profile of an independent mutant which accumulatespolyprenol, F2A8, was also found to be qualitatively similarto the Lec9 pattern. The relationship among these mutants wasanalysed in more detail by construction of cell—cell hybrids.Lectin resistance profiles of the hybrids demonstrated thatAbr^R, Ric^R and F2A8 fell into the Lec9 complementation group.Analysis of prenols in the hybrids also showed that F2A8 wasa member of the Lec9 group. Surprisingly, a significant fractionof the prenols found in Lec9 Parent hybrids was polyprenol(up to 30% of the neutral fraction), whereas the prenols foundin Parent Parent hybrids were nearly exclusively dolichol(97% of the neutral lipid fraction). Therefore, reduction ofpolyprenol to dolichol appears to be a rate-limiting step inthe synthesis of dolichol since hybrids with differing numbersof wild-type alleles can be biochemically distinguished. CHO cells dolichol lectins mutants polyprenol reductase     

Human non-secretory ribonucleases. II. Structural characterization of theN-glycans of the kidney, liver and spleen enzymes by NMR spectroscopy and electrospray mass spectrometry

The N-glylycans have been removed by peptide-N-glycosidase F(PNGase F) from purified human non-secretory RNases derivedfrom kidney, liver and spleen. The spleen RNase was purifiedby two procedures, one of which did not include the usual acidtreatment step (0.25 M H₂SO₄, 45 min, 4C), to determine ifacid treatment alters the carbohydrate moieties. TheN-glycansof the RNases were fractionated by Bio-Gel P-4 chromatographyand analysed by 600 MHz ¹H-NMR spectroscopy and electrospraymass spectrometry. All four non-secretory RNase preparationscontained the following structures: The relative amounts of the trisaccharide, pentasaccharide andhexasaccharide appeared to vary slightly in the different tissueRNases. The overall results indicate: (i) that acid treatmentduring purification does not alter the N-glycans of non-secretoryRNases; (ii) that the N-glycans from kidney, liver and spleennon-secretory RNases are very similar, if not identical, toone another, but different from the N-glycan structures reportedfor secretory RNase. N-glycans non-secretory RNases     

Drosophila acidic ribosomal protein rpA2: Sequence and characterization

A cDNA encoding the Drosophila melanogaster acidic ribosomal protein rpA2 was cloned and sequenced. rpA2 is homologous to the Artemia salina acidic ribosomal protein eL12′. In situ hybridization to salivary gland polytene chromosomes localizes the rpA2 gene to band 21C. It is a single copy gene, with an mRNA of 0.8 kb. Two-dimensional gel electrophoresis of Drosophila ribosomal proteins followed by immuno-blotting showed that the rpA2 protein has an apparent relative mobility in SDS of 17 kD and an isoelectric point less than pH 5.0. Although the Drosophila gene rp21C may be the same as rpA2, the reported sequences differ. Comparisons of the aligned nucleotide sequences coding for the acidic ribosomal proteins rpA1 and rpA2 of Drosophila with those of other eukaryotes support the view of two separate, though closely related, groups of acidic proteins. Comparison with the Artemia homologues suggests that nucleotide identity may have been conserved by some constraint that acts in addition to the requirement for substantial similarity of amino acid sequences. © 1993 Wiley-Liss, Inc.