Microbiological and chemical properties of soil associated with macropores at different depths in a red-duplex soil in NSW Australia

Some agricultural soils in South Eastern Australia with duplex profiles have subsoils with high bulk density, which may limit root penetration, water uptake and crop yield. In these soils, a large proportion (up to 80%) of plant roots maybe preferentially located within the macropores or in the soil within 1–10 mm of the macropores, a zone defined as the macropore sheath (MPS). The chemical and microbiological properties of MPS soil manually dissected from a 1–3 mm wide region surrounding the macropores was compared with that of adjacent bulk soil (>10 mm from macropores) at 4 soil depths (0–20 cm, 20–40 cm, 40–60 cm and 60–80 cm). Compared to the bulk soil, the MPS soil had higher organic C, total N, bicarbonate-extractable P, Ca⁺, Cu, Fe and Mn and supported higher populations of bacteria, fungi, actinomycetes, Pseudomonas spp., Bacillus spp., cellulolytic bacteria, cellulolytic fungi, nitrifying bacteria and the root pathogen Pythium.In addition, analysis of carbon substrate utilization patterns showed the microbial community associated with the MPS soil to have higher metabolic activity and greater functional diversity than the microbial community associated with the bulk soil at all soil depths. Phospholipid fatty acids associated with bacteria and fungi were also shown to be present in higher relative amounts in the MPS soil compared to the bulk soil. Whilst populations of microbial functional groups in the MPS and the bulk soil declined with increasing soil depth, the differentiation between the two soils in microbiological properties occurred at all soil depths. Soil aggregates (< 0.5 mm diameter) associated with plant roots located within macropores were found to support a microbial community that was quantitatively and functionally different to that in the MPS soil and the bulk soil at all soil depths. The microbial community associated with these soil aggregates thus represented a third recognizable environment for plant roots and microorganisms in the subsoil.     

Acetyl coenzyme A carboxylase in species of Triticum of different ploidy

The cellular amounts and cellular activities of acetyl CoA carboxylase (ACC; EC 6.4.1.2.) were determined in the first leaves of diploid, tetraploid and hexaploid species of Triticum (wheat). Per leaf the ACC activities were very similar in T. monococcum (2 ), T. dicoccum (4 ) and T. aestivum (6 ). The ACC activity per chloroplast also showed little variation between species of different ploidy but since chloroplast number increases with ploidy, the ACC activities and ACC amounts per cell also increased with ploidy. These cellular increases in ACC amounts associated with increases in gene dosage were highly co-ordinated in the diploids T. monococcum and T. tauschii and their respective autotetraploids so the specific activity of ACC was highly conserved in these plants. The relevance of these findings to attempts to genetically manipulate lipid biosynthesis in chloroplasts is discussed.Abbreviation ACC acetyl CoA carboxylase We are very grateful to Dr. Kevin Pyke and Miss Jo Marrison for many helpful discussions and to Dr. Collin Law for the generous gift of seeds.     

Biosynthesis of monogalactosyl diglyceride by chloroplasts from spinacia oleracea and from some gramineae

Synthetic diglycerides which differed in unsaturation of fatty acids gave the same incorporation of [¹⁴C]galactose from UDP-[¹⁴C]galactose when added to acetone powders of spinach chloroplasts up to about 0·6 mg diglyceride/20 mg acetone powder. Diolein and the endogenous diglyceride isolated from the acetone extract of chloroplasts stimulated galactolipid biosynthesis to a similar extent. With all diglycerides used, monogalactosyl diglyceride was the main product with little accompanying synthesis of digalactosyl diglyceride. The radioactivity in the monogalactosyl diglyceride synthesized from UDP-[¹⁴C]galactose by whole chloroplasts was distributed widely among the monogalactosyl diglycerides with different fatty acid composition. It is concluded that the enzyme which catalyses the transfer of galactose from UDP-galactose to diglyceride is not specific for polyunsaturated diglycerides and that the polyunsaturated monogalactosyl diglycerides arise either by desaturation of the fatty acyl residues after monogalactolipid synthesis or by transacylation. Acetone powders of chloroplasts prepared from several Gramineae did not exhibit transferase activity although whole chloroplasts were active.     

Amino terminal fragments of human progastrin from gastrinoma

Two peptides which copurified from a human gastrinoma were found to correspond to the amino acid sequence deduced for the amino terminal portion of human and porcine progastrin. The sequence of peptide A is Ser-Trp-Lys-Pro-Arg-Ser-Gln-Gln-Pro-Asp-Ala-Pro-Leu-Gly-Thr-Gly-Ala-Asn- Arg-Asp-Leu-Glu-Leu which is identical to an amino terminal portion of human progastrin. The sequence of peptide. B is identical to that of peptide A except it is missing the first five amino acids. If peptide A corresponds to the amino terminus of progastrin, the signal peptidase cleaves at an Ala-Ser bond.