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Byline: E. Dittmann, U. Pfluger, R. Thehos, M. Baltrusch, M. Buchen Dispersion calculations for regulatory purposes in Germany have been based on a Gaussian-type model for more than 20 years. Within this procedure nearly 88 000 hourly consecutive meteorological situations are evaluated statistically and put into 1944 classes. For each of these classes surface concentrations are calculated and combined to a one-year mean surface concentration field. Another procedure, consisting of the combination of a non-hydrostatic model for the wind field and a Lagrangian dispersion model, is used for 150 different meteorological input datasets. These datasets represent classes of meteorological situations, which are compiled from about 8000 consecutive twice-daily situations by cluster analysis. The two different methods have been applied to a source in the Rhine river valley. The results show differences, in both the value and the location, of the maximum of the mean surface concentration; the difference in location seems to be more significant than that in the maximum value.

Steryl glucosides are characteristic lipids of plant membranes. The biosynthesis of these lipids is catalyzed by the membrane-bound UDP-glucose:sterol glucosyltransferase (EC 2.4.1.173). The purified enzyme (Warnecke and Heinz, Plant Physiol 105 (1994): 1067-1073) has been used for the cloning of a corresponding cDNA from oat (Avena sativa L.). Amino acid sequences derived from the amino terminus of the purified protein and from peptides of a trypsin digestion were used to construct oligonucleotide primers for polymerase chain reaction experiments. Screening of oat and Arabidopsis cDNA libraries with amplified labeled DNA fragments resulted in the isolation of sterol glucosyltransferase-specific cDNAs with insert lengths of ca. 2.3 kb for both plants. These cDNAs encode polypeptides of 608 (oat) and 637 (Arabidopsis) amino acid residues with molecular masses of 66 kDa and 69 kDa, respectively. The first amino acid of the purified oat protein corresponds to the amino acid 133 of the deduced polypeptide. The absence of these N-terminal amino acids reduces the molecular mass to 52 kDa, which is similar to the apparent molecular mass of 56 kDa determined for the purified protein. Different fragments of these cDNAs were expressed in Escherichia coli. Enzyme assays with homogenates of the transformed cells exhibited sterol glucosyltransferase activity.