QUANTITATIVE PCR DATA FALSIFY THE CHROMOSOMAL ENDOREDUPLICATION HYPOTHESIS FOR VOLVOX CARTERI (VOLVOCALES, CHLOROPHYTA)

Two conflicting hypotheses for chromosome replication in the Volvocaceae, one postulating multiple rounds of replication prior to cell division (endoreduplication) and the other claiming a canonical sequence of one round of nuclear DNA replication preceding each cell division, have been tested experimentally. Competitive PCR of the single-copy actin gene (target) of Volvox carteri f. nagariensis Iyengar and a shortened gene version (competitor) containing the same primer binding sites were used to assess the genome equivalents present in a given number of cells. Determining the molar ratio of the PCR products generated from target DNA (extracted from a known number of cells) and defined numbers of competitor molecules revealed that Volvox embryos between the one- and 16-cell stages possess an average of between one and two—but never more than two—copies of the actin gene. This led us to conclude that the number of genome equivalents per nucleus in dividing Volvox embryos varies only between one and two and that, unlike the case predicted by endoreduplication, the nuclear genome undergoes only one round of replication prior to each cell division.     

Physical properties of microbial suspensions

A way of characterizing cell size distribution in suspensions of single-cell microorganisms is suggested, based on the first and second moments around origin. Suspension density may be predicted on the basis of the mixing law and the density of microbial dry matter, for suspensions ofSaccharomyces cerevisiae, Candida lipolytica, andAspergillus niger. Newtonian viscosities were correlated using regression analysis by η=Aexp(BC _m)exp(D/t); another correlation is presented for the calculation of surface tension in single-cell microbial suspensions. All the relations are valid in the range of concentrations up to 15% (w/v) and for temperatures between 15° and 35°C. The formulae presented may be used in other hydraulic studies.     

Effect of radiation on the biosynthesis of L-Tryptophan from 14C-Anthranilic acid in kohlrabi (Brassica oleracea L., var.gongylodes L.)

The metabolism of¹⁴C-anthranilic acid (¹⁴C-AA) in kohlrabi (Brassica oleracea L. var.gongylodes L.) and the effect of radiation gamma⁶⁰Co on this metabolism was investigated. In hypocotylar segmnents of seven days old etiolated seedlings¹⁴C-AA was metabolised par, tially to its detoxication product¹⁴C-β-glucoside of AA. Simultaneously L-tryptophan was also formed, which in these plants is a precursor of indolic glucosinolates glucobrassicin and neoglucobrassicin. The metabolism of¹⁴C-AA was followed for 97 h. Radiation, applied both to seeds and to seven days old plants did not affect the metabolism of¹⁴C-AA substantially. The intermediary reaction AA → L-tryptophan in the biosynthesis of L-tryptophan is not a radiosensitive part of the synthesis of this amino acid. A not too high radiation sensitivity (max. 45%) was observed in the metabolic pathway leading from L-tryptophan to glucobrassicin.     

Karyological and taxonomic observations onDracocephalum foetidum Bunge andKoenigia islandica L.

Chromosome numbers are reported for two Mongolian species,Dracocephalum foetidum Bunge (2n=12) andKoenigia islandica L. (2n=14). The relationship ofD. foetidum toD. moldavica L. (2n=10) and some patterns of phenotypic variation inK. islandica are briefly discussed. The following new combinations are proposed:K. cyanadra (Diels) Měsí?ek etSoják,K. forrestii (Diels) Měsí?ek etSoják,K. hubertii (Lingelsh.) Měsí?ek etSoják, andK. nummularifolia (Meisn.) Měsí?ek etSoják.     

Changes in the elimination rate of I131-labelled heterologous albumin from the blood of chickens during their postnatal development

The rate of elimination of heterologous albumin from the blood of chickens was found to vary considerably during the first week of age. The half-life obtained for 2-day-old chicks was 1.4 days while that found in birds between 1 and 6 weeks of age ranged from 0.8 to 1.1 days. The results are in agreement with previous observations that the onset of immunological activity of chickens occurs during the first week of age and that their full immunological competence inachieved between the 3rd and 4th weeks of age.     

Cell-pool tryptophan phases in ergot alkaloid fermentation

Three cell-pool tryptophan phases are recorded as characteristics of the alkaloid fermentation byClaviceps paspali grown on a simple defined medium without tryptophan. Within the early phase designated “tryptophan down” the alkaloid-biosynthetic activity of the mycelium attains the maximum, protein synthesis is reduced and extracellular proteases are formed. Cell-pool tryptophan level (b) drops, tryptophan synthetase activity (c) intensifies and sums of logb+logc after different time intervals remain constant. In the subsequent “tryptophan up” phase tryptophan level (b) increases, alkaloid yield (a) becomes a function of time and reaches the top level still tolerable by tryptophan synthetase. The difference of the logb—logc is constant. The tryptophan synthetase diminishes its activity simultaneously with the alkaloid-biosynthetic activity of the mycelium. The district between the “tryptophan down” and “tryptophan up” phase is an especially promising target for the investigation of the regulation of alkaloid formation and continuous fermentation of these compounds. During the third, i.e. “tryptophan over” phase, cell-pool tryptophan accumulates and attains a concentration exerting a negative effect on the alkaloid biosynthesis.