Photosynthate costs associated with the utilization of different nitrogen–forms: influence on the carbon balance of plants and shoot–root biomass partitioning

The photosynthate costs of processes (amino acid and protein synthesis and turnover, and pH regulation) associated with the utilization of nitrate (NO₃⁻), ammonium (NH₄⁺) or glutamine (Gln) for plant growth were estimated. Based on these estimates, the effects of these forms of nitrogen (N) on the carbon balance of plants and on shoot–root biomass allocation were evaluated. The results indicated that NO₃⁻ as an N source for plant growth is not substantially more expensive to utilize than either NH₄⁺ or Gln, particularly in the long term when costs due to protein turnover dominate the total costs of N utilization. It is also suggested that the photosynthate use in processes associated with N assimilation has little impact on the carbon balance of plants, and hence on shoot–root biomass allocation.     

Alternate Positions for the Sulphydryl Group in β-Lactoglobulin: the Significance for Sulphydryl Location in Other Proteins

EARLIER studies of the location of the single cysteine residue and the two disulphide bridges in bovine β-lactoglobulins A and B¹, for each of which the monomer is a single chain of 162 residues and 18,000 molecular weight^2,3, led to the conclusion that the sulphydryl group is at position 69 and that the disulphides bridge positions 123 to 160 and 57 to 70. These results were based on diagonal peptide studies⁴ and on the composition of peptides in which the sulphydryl group had been labelled with ¹⁴C-iodoacetamide, the disulphide bridges being left intact. Use was made of the partial amino-acid sequence given by Frank and Braunitzer⁵ and the reasonable assumption was made that the sulphydryl occurred in only one position. Subsequently, Shaw⁶ has shown that the sequence of Frank and Braunitzer⁵ showing Cys residues adjacent at positions 69 and 70 is incorrect and that they are separated by a glutamine, the sequence for positions 67 to 71 for the Bvariant being Ala.Cys.Gln.Cys.Leu. Autoradiography of the dansyl amino-acid derivatives formed during the sequence determination of this pentapeptide indicated that both residues 68 and 70 seemed to have been labelled and so we have given further consideration to the sulphydryl location. It has been found that although it does occur at 68, with 57 and 70 disulphide bridged, there is also an equal amount of protein present with the sulphydryl at 70, with 57 and 68 disulphide bridged. We discuss this additional finding here and the significance for the determination of the location of sulphydryl groups in other proteins.     

AFM IMAGING AND ELASTICITY MEASUREMENTS ON LIVING RAT LIVER MACROPHAGES

The authors investigated the morphology and the elastic properties of living cultured rat liver macrophages (Kupffer cells) with an atomic force microscope (AFM). Continuous imaging and elasticity mapping of individual cells in physiological buffer was carried out for several hours without damaging the cells as judged by their persistent undisturbed morphology. Dynamic events such as protrusive activity were observed in time course. The importance of the cytoskeleton for the mechanical properties of the cell has been investigated by measuring the cell's elasticity as a function of position. Chemical disassembly of the actin network by applying 10μg/ml cytochalasin B decreased the cell's average elastic modulus seven-fold within less than 40 minutes. Treating the cells with 0.1μg/ml latrunculin A resulted in a two-fold decrease in the elastic modulus merely in the perinuclear region after 40 minutes, whereas other parts of the cell were not affected.     

ROUTINE RESAZURIN TEST RESULTS AND THERMODURIC BACTERIAL CONTENT OF MILK SAMPLES AS A MEASURE OF MILK PRODUCTION CONDITIONS

The milk production conditions on 44 farms (18 designated and 26 non-designated) have been assessed by score-card marks for visual conditions, facilities, equipment, and methods. Over a period of one year fortnightly samples from these farms were subjected to routine resazurin tests and laboratory pasteurized counts. The results were compared with the total score-card marks and the equipment assessments of the farms. It was found that neither test alone sufficed to detect unsatisfactory production, but failure on the two tests combined agreed well with the production conditions and facilities.
The relation of season and mean shade atmospheric temperature to the thermoduric bacterial content of the milk was studied but no clear association was observed.     

A CARBONIFEROUS SYNZIPHOSURINE (XIPHOSURA) FROM THE BEAR GULCH LIMESTONE, MONTANA, USA

Abstract:  A new synziphosurine, Anderella parva gen. et sp. nov., extends the known range of this group from the Silurian to the Carboniferous and is the youngest known so far from the fossil record. Previously the youngest synziphosurine, Kasibelinurus , was from the Devonian of North America. Anderella parva has a semi-oval carapace with pointed genal regions, nine freely articulating opisthosomal segments and a long styliform tail spine. It is the third xiphosuran genus to be described from the Bear Gulch Limestone and its discovery highlights this deposit as containing an unusually diverse xiphosuran biota. It is also the only known locality where synziphosurines occur alongside the more derived xiphosurids. Xiphosurans reached their greatest diversity in the Carboniferous when the xiphosurids began to occupy brackish and freshwater habitats and became dominant over the synziphosurines. The discovery of the only known Carboniferous synziphosurine in marine sediments may indicate their inability to exploit these same environments.