Effects of low water potentials on some aspects of carbohydrate metabolism in Chlorella pyrenoidosa

Summary Chlorella pyrenoidosa was subjected to low water potentials and the resulting changes in carbohydrate metabolism were measured.Water deficit reduced the incorporation of ¹⁴C-glucose into methanol insoluble compounds, principally starch and increased that into sucrose. Even moderate water deficit, for example potentials of -2.5 and -5 atm, greatly reduced the incorporation of ¹⁴C-glucose into uridine diphosphate glucose, while ¹⁴C levels of the hexose monophosphates changed little, indicating a direct stimulus of sucrose synthesis. This increased sucrose synthesis was one of the earliest effect of water deficit, because potentials of -2.5 and -5 atm did not reduce respiration and glucose uptake.At lower water potentials (-10 atm or less) there was reduced ¹⁴C incorporation into all sugar phosphates. This resulted from a combination of reduced ¹⁴C-glucose uptake and increased sucrose synthesis.Water potentials as low as -20 atm had little effect on acetate uptake, or on the ¹⁴C levels in the intermediates of the TCA cycle. This confirmed that low water potentials do not directly inhibit respiratory pathways in Chlorella.The results are discussed in relation to the effect of water deficit on levels of various metabolites in vascular plants, which have been reported by other workers.     

COMPARISON OF DIMENSIONS AND FIBRIL ANGLES OF LOBLOLLY PINE TRACHEIDS FORMED IN WET OR DRY GROWING SEASONS

Diameter and wall thickness of tracheids and the fibrillar angle in their S₂ layers were investigated at five relative heights within two increment sheaths of one dominant loblolly pine (Pinus taeda L.). The sheaths investigated were formed during extremes of soil moisture availability. In both increment sheaths the radial and longitudinal trends of the respective anatomical features were similar; however, the sheaths differed in the degree and rate at which their size changed from the apex to the base of the tree. Soil moisture conditions directly affected the width of the annual rings, tracheid diameter, and wall thickness but not the fibril angle of tracheid walls.     

Four major saponins from Solidago canadensis.

Four new bisdesmosidic saponins each containing eight carbohydrate units were isolated from Solidago canadensis. GC, GC-MS, FABMS analysis and mainly the use of 2D NMR techniques allowed their identification as bayogeninglycosides (canadensissaponins 1-4) 3-O- [beta-D-glucopyranosyl-(1----3)-beta-D-glucopyranosyl]-28-O-[alpha-L- rhamnopyranosyl-(1----3)-beta-D-xylopyranosyl-(1----4)-[beta-D- xylopyranosyl-(1----3)]-alpha-L-rhamnopyranosyl-(1----2)-[beta-D- apio-D-furanosyl-(1----3)]-beta-D-6-deoxyglucopyranosyl- (1----]-bayogenin; -(1----2)-[beta-D-apio-D-furanosyl-(1----3)]-ara- binopyranosyl-(1----]-bayogenin; -[alpha-L-rhamnopyranosyl-(1----3)]-beta- D-6-deoxyglucopyranosyl-(1----]-bayogenin and - [alpha-L-rhamnopyranosyl- (1----3)]-arabinopyranosyl-(1----]-bayogenin.     

The dependence of isometric tension, isometric ATPase activity, and shortening velocity of limulus muscle on the MgATP concentration.

The dependence of the isometric tension, the velocity of unloaded shortening, and the steady-state rate of MgATP hydrolysis on the MgATP concentration (range 0.01-5 mM MgATP) was studied in Ca-activated skinned Limulus muscle fibers. With increasing MgATP concentration the isometric tension increased to a peak at approximately 0.1 mM, and slightly decreased in the range up to 5 mM MgATP. The velocity of unloaded shortening depended on the MgATP concentration roughly according to the Michaelis-Menten law of saturation kinetics with a Michaelis-Menten constant Kv = 95 microM and a maximum shortening velocity of 0.07 muscle lengths s-1; the detachment rate of the cross-bridges during unloaded shortening was 24 s-1. The rate of MgATP splitting also depended hyperbolically on the MgATP concentration with a Michaelis-Menten constant Ka = 129 microM and a maximum turnover frequency of 0.5-1 s-1. The results are discussed in terms of a cross-bridge model based on a biochemical scheme of ATP hydrolysis by actin and myosin in solution.     

Affinity chromatography of solubilized opioid binding sites using CH-Sepharose modified with a new naltrexone derivative

An affinity gel containing a newly synthesized derivative of naltrexone, beta-naltrexyl-6-ethylenediamine (NED), was used to purify opioid binding sites by 300-450-fold. Binding sites solubilized from brains of toad, rat and cow using digitonin in the presence of 0.5 M NaCl are retained by the gel and can be eluted with naloxone (1-3 microM) in yields of 20-25%. The biospecificity of the interaction of opioid binding sites with modified beads is supported by the following: 1) unmodified beads do not retain the binding sites, 2) binding sites prebound with an opioid are not retained, 3) dilution of NED gels with unmodified Sepharose progressively reduced efficiency of retention and 4) specific receptor ligands elute binding sites retained on the NED gels.     

Characterisation of a chloroplast-encoded secY homologue and atpH from a chromophytic alga. Evidence for a novel chloroplast genome organisation.

secY is a prokaryotic gene that encodes the SecY protein, an integral membrane component of the prokaryotic protein translocation apparatus. A chloroplast-encoded secY homologue has been identified in the unicellular, chromophytic alga, Pavlova lutherii. The gene predicts a protein composed of ten membrane-spanning regions, that is approximately 25% homologous and 50% similar to bacterial and plastid SecY proteins. The secY gene from P. lutherii is independent of the ribosomal protein (rp) gene cluster to which it is closely linked in other organisms. In P. lutherii secY is located 5' to atpI and atpH. Since, in higher plants the atpIHFA gene cluster and the rp gene cluster are separated by approximately 50 kb, we conclude, this indicates a novel chloroplast gene arrangement in P. lutherii.     

Radioautography of binding of tritiated diprenorphine to opiate receptors in the rat

Radioautography of tritiated diprenorphine in rat brain indicates anatomic distribution of receptors with a greater degree of precision than is possible using dissection techniques. The results of this study largely confirm those of others but indicate some differences in receptor distribution in the thalamus. Differential receptor binding in the periaquaductal gray matter with the highest counts lying laterally is an original observation.