Cloning and expression of transaldolase from potato

We have isolated a cDNA encoding transaldolase, an enzyme of the pentose-phosphate pathway, from potato (Solanum tuberosum). The 1.5 kb cDNA encodes a protein of 438 amino acid residues with a molecular mass of 47.8 kDa. When the potato cDNA was expressed in Escherichia coli a 45 kDa protein with transaldolase activity was produced. The first 62 amino acids of the deduced amino acid sequence represent an apparent plastid transit sequence. While the potato transaldolase has considerable similarity to the enzyme from cyanobacteria and Mycobacterium leprae, similarity to the conserved transaldolase enzymes from humans, E. coli and Saccharomyces cerevisiae is more limited. Northern analysis indicated that the transaldolase mRNA accumulated in tubers in response to wounding. Probing the RNA from various potato tissues indicated that the transaldolase mRNA accumulation to higher levels in the stem of mature potato plants than in either leaves or tubers. These data are consistent with a role for this enzyme in lignin biosynthesis.     

Cloning and expression of soluble epoxide hydrolase from potato

Five cDNAs encoding a putative soluble epoxide hydrolase (sEH) from potato were isolated and characterized. The cDNAs contained open reading frames encoding 36 kDa polypeptides which were highly homologous to the carboxy terminal region of mammalian sEH. When one of the cDNAs was expressed in a baculovirus system a soluble 38 kDa protein with epoxide hydrolase activity was produced. The recombinant enzyme hydrolyzed a commonly used diagnostic substrate for the soluble form of mammalian EH. Inhibitor profiles of the recombinant potato and mammalian sEH were also similar. The expression of sEH in potato was found to be regulated by both developmental and environmental signals. Levels of mRNA for sEH were higher in meristematic tissue than in mature leaves. This mRNA was also observed to accumulate on wounding and application of exogenous methyl jasmonate.     

Flow rate and vertical position influence ingestion rates of colonial zebra mussels (Dreissena polymorpha)

1. Zebra mussels aggregate to form dense colonies where, depending on the flow rate, individuals in different vertical locations within the colony may experience restricted food availability. 2. Using ³²P‐labelled Chlamydomonas angulosa, we found ingestion rates of individual mussels located at the surface to exceed those in the bottom of a 6 cm thick colony by up to 75%. 3. Higher velocities (10 and 20 cm s^?1) increased algal delivery to the colony's middle layer (2–4 cm depth), subsequently increasing ingestion rates to equal those in the surface layer, while increasing ingestion only for the smallest mussels in the bottom (4–6 cm). 4. At all vertical locations within the colonies, smaller mussels showed higher ingestion rates per unit mass than larger mussels, particularly at higher flow rates.     

Nitrate reductase deficient cell lines from haploid protoplast cultures ofNicotiana plumbaginifolia

Summary Nitrate reductase deficient (NR^-) cell lines were selected indirectly by their resistance to 40 mM chlorate in protoplast cultures of haploidNicotiana plumbaginifolia. Frequency of the chlorate resistant clones was 5.8×10^-5 in non-mutagenized cultures, which could be increased up to 25 times by treatment with N-ethyl-N-nitrosourea (NEU) or gamma irradiation.Out of 136 chlorate resistant clones 29 were fully deficient in nitrate reductase. The rest of the clones contained decreased or normal levels of NR activity (91 and 16 clones, respectively).Further characterization was carried out in 9 clones which were fully deficient in NR and in 2 clones containing resisdual (0–5%) NR activity. The clones were tentatively classified as defective in the apoenzyme (7 clones including the 2 with residual NR activity) or the cofactor (4 clones) of NR by the xanthine dehydrogenase activity and in vitro enzyme complementation. The cofactor defectives could be further classified into two groups. In one of these (2 clones) the NR activity could be partially restored by unphysiologically high (0.2–1 mM) molybdate in the culture medium. The other two are new types which have not been described in flowering plants.Plant regeneration was obtained only in the clones which contained residual NR activity.     

Effect of food-deprivation on rat pancreatic islet cells

Somatostatin, insulin and glucagon concentrations in rat pancreas were measured following various intervals of food-deprivation. Tissue concentrations, as measured by radioimmunoassay, were correlated with A-, B-, and D-cell number and size using a scanning integrating image analyzer (Quantimet 720). Alterations in total islet hormone content were not correlated to changes in size or distribution of cells. This implies that changes in tissue content reflect changes in turnover of peptides rather than changes in cell size or number.     

Cloning of the aspartate-β-semialdehyde dehydrogenase structural gene fromEscherichia coli K12

Transformation ofEscherichia coli strains with the recombinant plasmid, prepared by shot gun cloning with pBR322 and containing the geneasd, the structural gene of aspartate--semialdehyde dehydrogenase, results in an increase in specific activity of 65-fold of the enzyme in crude extracts. Approximately 60 mg of pure enzyme may be obtained from 10 g of transformed cells (wet weight) in a simplified purification procedure. The molecular weight, amino acid composition, and kinetic properties of the enzyme appear to be the same as previously reported, and the first 36 amino acids of the N-terminal sequence have been determined.