Antioxidants and antioxidative enzymes in wild-type and transgenic Lycopersicon genotypes of different chilling tolerance

The Mehler–Ascorbate–Peroxidase cycle is a protection system against reactive oxygen species (ROS) occurring during over-excitation of the photosynthetic apparatus. In the cultivated tomato, Lycopersicon esculentum, long-term chilling under moderate light leads to oxidation of the Calvin cycle key enzyme, ribulose-1,5-bisphosphate carboxylase (rubisco), presumably by generation of ROS. In contrast, high-altitude lines of the wild tomato species L. peruvianum were tolerant against the same chilling stress. In the present study, we analysed leaf contents of antioxidants (ascorbate, glutathione) and activities of enzymes of the Mehler–Ascorbate–Peroxidase cycle in the two Lycopersicon species. While antioxidant levels and activities of chloroplast superoxide dismutase (SOD) and ascorbate peroxidase (APX), both inducible by chilling stress, were similar in chilling-tolerant and chilling-sensitive genotypes, chilled L. esculentum showed lower glutathione reductase (GR) activities than high-altitude L. peruvianum. We constructed transgenic plants overexpressing an Escherichia coli GR in the chloroplast (approximately 60-fold of the wild-type (WT) activity). However, these plants resembled identical chilling sensitivity of the photosynthetic apparatus as WT plants as measured after a photoinhibition treatment and by the effect of long-term chilling on rubisco activity. We conclude that the Mehler–Ascorbate–Peroxidase cycle is not the limiting factor for the sensitivity of the photosynthetic apparatus of L. esculentum towards long-term chilling under moderate light. We suggest that a possible cause for the higher chilling tolerance of L. peruvianum is prevention of ROS formation by better conversion of light energy to photochemistry at suboptimal temperatures.     

Molecular Cloning and Expression of a Human Phosphodiesterase 4C

A cDNA coding for a human phosphodiesterase 4C (PDE4C2) was isolated from the mRNA prepared from the glioblastoma cell line, U87. The cDNA contained an ORF of 1818 bp corresponding to a 605 amino acid polypeptide. The sequence differed at the 5′ end from the human PDE4C previously reported (Engels, P. et al, 1995 FEBs Letters 358, 305-310) indicating that it represents a novel splice variant of the human PDE4C gene. Evidence was also obtained for a third 5′ splice variant. The PDE4C2 cDNA was transfected into both COS 1 cells and yeast cells, and shown to direct the expression of an 80 kD polypeptide by Western blotting using a PDE4C specific antiserum. The activity of cell lysates was typical of PDE4 being specific for cAMP and inhibitable by the selective inhibitor, rolipram. However, the K_m for cAMP of the enzyme produced in COS cells was 0.6 μM compared to 2.6 μM for the yeast 4C activity. In addition the COS cell PDE4 activity was much more sensitive to R rolipram than the yeast PDE4 enzyme (IC₅₀ of 23 nM compared to 1648 nM). This difference in rolipram sensitivity was associated with the detection of a high affinity [³H] R rolipram binding site on the COS cell 4C enzyme but not on the yeast expressed enzyme. The results indicate that the enzyme can adopt more than one active conformation, which are distinguished by their interaction with rolipram.     

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Ohne Zusammenfassung     

Physiologische und biochemische Beiträge zur Taxonomie der GattungChlorella

Salt tolerance was found to be a species-specific character in the genus Chlorella. The most resistant species, C. luteoviridis, is able to grow in nutrient media containing up to 5% NaCl. The limit for C. protothecoides and C. saccharophila is at 4% NaCl. C. vulgaris var. vulgaris, C. fusa var. vacuolata and C. fusca var. rubescens grow in the presence of 3%, and C. fusca var. fusca, C. kessleri and C. vulgaris f. tertia in the presence of 2% NaCl. C. zofingiensis and C. minutissima are only capable of growing in media containing up to 1% NaCl, and C. homosphaera does not even tolerate 1% NaCl. Those strains, which are able to synthesize secondary carotenoids, turn orange in salt concentrations close to the limit of their tolerance.     

Die Verteilung der Haptoglobin-Phänotypen und Haptoglobin-Allele bei der Lungentuberkulose

Summary The frequency of the three most common haptoglobin-phenotypes and haptoglobin-alleles has been determined in 684 propositi with pulmonary tuberculosis. The distribution in this disease has been compared with 685 serum samples of healthy inhabitants of Süd-Niedersachsen with a Hp¹ frequency of 0.4058. The frequency of the gene Hp¹ in pulmonary tuberculosis is 0.4232, in open pulmonary tuberculosis (n=328) 0.4278 and in closed pulmonary tuberculosis (n=356) 0.4199. The differences are statistically not significant in the several comparsions. There are no correlations between serum haptoglobins and pulmonary tuberculosis.

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(Direktor: Prof. Dr. med. P. E. Becker)