Endosymbiotic origin and codon bias of the nuclear gene for chloroplast glyceraldehyde-3-phosphate dehydrogenase from maize

Summary The nuclei of plant cells harbor genes for two types of glyceraldehyde-3-phosphate dehydrogenases (GAPDH) displaying a sequence divergence corresponding to the prokaryote/eukaryote separation. This strongly supports the endosymbiotic theory of chloroplast evolution and in particular the gene transfer hypothesis suggesting that the gene for the chloroplast enzyme, initially located in the genome of the endosymbiotic chloroplast progenitor, was transferred during the course of evolution into the nuclear genome of the endosymbiotic host. Codon usage in the gene for chloroplast GAPDH of maize is radically different from that employed by present-day chloroplasts and from that of the cytosolic (glycolytic) enzyme from the same cell. This reveals the presence of subcellular selective pressures which appear to be involved in the optimization of gene expression in the economically important graminaceous monocots.     

Genetic diversity in Cucumis sativus L. assessed by variation at 18 allozyme coding loci

Summary The genetic diversity of the U.S. Cucumis sativus L. germplasm collection [757 plant introductions (PI) representing 45 countries] was assessed using 40 enzymes which represented 74 biochemical loci. Polymorphisms were observed at 18 loci (G2dh-1, Gpi-1, Gpi-2, Gr-1, Gr-2, Idh, Mdh-1, Mdh-2, Mdh-3, Mpi-2, Pepla-2, Peppap-2, Per-4, Pgd-1, Pgd-2, Pgm-1, Pgm-3, and Skdh). Two PIs (285606 and 215589) contained alleles [G2dh-1(1) and Per-4(2), respectively] which did not occur in any other PI. Other alleles which occurred in low frequencies (in < 1% of the PIs) included Gpi-1(3), Gpi-2(3), Gr-1(3), Gr-2(1), Idh(1), Mdh-1(2), Mdh-2(1), Peppap-2(1), and Pgd-1(1). Individual loci containing more than one allele in greater than 20% of the PIs included Mpi-2, Pepla-2, Pgd-2, and Pgm-1. Multivariate analyses aided in the reduction of data (principle components), depicted relationships among PIs (cluster), and identified the most discriminating enzyme loci (Pgm-1, Pepla-2, Gr-1, Pgd-2, Mpi-2, and Skdh) (classification and regression tree).Research partially supported by Asgrow, DeRuiter, Nickerson-Zwaan, Nunhems, and Sun Seed Companies; and the Graduate School, University of Wisconsin, Madison     

Partial characterization of cell wall from a flocculent strain ofKluyveromyces marxianus

Summary Cell walls from aKluyveromyces marxianus either non flocculent or flocculent strain were isolated and analysed for protein, carbohydrates and phosphate content. Alkaline extract of proteins were analysed by SDS-PAGE. The results revealed a higher protein content in the cell walls from the flocculent strain. Electrophoresis of the cell wall proteins of the flocculent strain showed an extra peptide with an apparent molecular weight of 37 KDa which is absent fom non-flocculent cells. The involvement of this protein in cell adhesion during flocculation is discussed.     

Viability of an ectomycorrhizal fungus during cross-flow filtration

Factors affecting the viability and infectivity of an ectomycorrhizal fungus during moderate concentration by cross-flow filtration were determined. Mycelial suspensions were concentrated with three commercial membrane filters (Prostak Millipore Co., M14 Tech-Sep Co. and Ceraflo Norton Co.) under aseptic conditions. Medium components may reduce the filtration rate due to their low solubility. An antifoam agent did not reduce the average flux rates as much as did the malt extract. Clear unobstructed channels (I.D. 6mm) of the tubular modules (Tech-Sep) gave the best results both in terms of performance (filtration rate) and cell viability. Shear stresses caused by pumping and flow through narrow retentate channels were probably responsible for lowering viability and infectivity. There was no linear relationship between permeate fluxes and cell concentration. There is an optimum pore size both in terms of performance (filtration rate) and cell viability. Physical blockage of large pores by hyphae could explain lower permeate flux rates than those obtained with lower pore sizes membranes.     

The preferential uptake of very-low-density lipoprotein cholesteryl ester by rat liver in vivo.

The removal from the blood and the uptake by the liver of injected very-low-density lipoprotein (VLDL) preparations that had been radiolabelled in their apoprotein and cholesteryl ester moieties was studied in lactating rats. Radiolabelled cholesteryl ester was removed from the blood and taken up by the liver more rapidly than sucrose-radiolabelled apoprotein. Near-maximum cholesteryl ester uptake by the liver occurred within 5 min of the injection of the VLDL. At this time, apoprotein B uptake by the liver was only about 25% of the maximum. Maximum uptake of the injected VLDL apoprotein B label was not achieved until at least 15 min after injection, by which time the total uptakes of cholesteryl ester and apoprotein B label were very similar. The results suggest that preferential uptake of the lipoprotein cholesteryl ester by the liver occurred before endocytosis of the entire lipoprotein complex. The fate of the injected VLDL cholesteryl ester after its uptake by the liver was also monitored. Radiolabel associated with the hepatic cholesteryl ester fraction fell steadily from its early maximum level, the rate of fall being faster and more extensive when the fatty acid, rather than the cholesterol, moiety of the ester was labelled. By 30 min after the injection of VLDL containing [3H]cholesteryl ester, over one-third of the injected label was already present as [3H]cholesterol in the liver. When VLDL containing cholesteryl [14C]oleate was injected, a substantial proportion (about 25%) of the injected radiolabelled fatty acid appeared in the hepatic triacylglycerol fraction within 60 min: very little was present in the plasma triacylglycerol fraction at this time.