Unusual amino acids VI. Substituted arylamino acids by asymmetric hydrogenation of N-Cbz and N-Boc protected dehydroamino acid derivatives

Substituted N-Cbz and N-Boc protected arylamino acrylic acids and esters have been prepared and used in asymmetric hydrogenations catalyzed by PROPRAPHOSRh. Stereoselectivities > 90% ee could be achieved, the rate of which is dependent on the position of the substituent in the aromatic ring. The N-Boc derivatives provide advantages compared with the N-Cbz analogues. The amino acid derivatives were fully characterized by ¹⁹F, ¹³C, and ¹H NMR spectroscopy. © 1996 Wiley-Liss, Inc.     

Effect of Carbohydrate Demand on the Remobilization of Starch in Stolons and Roots of White Clover (Trifolium repens L.) after Defoliation

White clover plants were grown from stolon tips in growth cabinetsand then defoliated. Thereafter, changes in the contents ofnon-structural carbohydrates such as starch, sucrose, glucose,fructose, maltose, and pinitol in stolons and roots were monitored.Initial contents of carbohydrate reserves, photosynthetic supplyof new carbohydrates and carbohydrate demand after defoliationwere varied by growing the plants at various CO₂ partial pressures,by varying the extent of defoliation and by removing eitherroots or stolon tips at the time of defoliation. Remobilization of carbohydrate reserves in stolons increasedproportionally to their initial contents and was greater whenplants had been severely defoliated, suggesting that carbohydrateswere remobilized according to availability and demand. Starchwas the predominant reserve carbohydrate. Starch degradationwas associated with decreased contents of sucrose, glucose andfructose in young stolon parts and roots but not in old stolonparts suggesting that starch degradation was not strictly controlledby the contents of these sugars. A decrease in the demand forcarbohydrates by removal of roots did not decrease starch degradationbut increased the contents of sucrose, glucose, and fructose.Removal of stolon tips decreased starch degradation and contentsof sucrose, glucose, and fructose. The results suggest thatstarch degradation was controlled by a factor other than sucrose,glucose, and fructose which was exported from stolon tips, e.g.gibberellin. Key words: White clover, storage carbohydrates, remobilization, regrowth     

Comparison of phosphorus deficiency indices during a spring phytoplankton bloom in a eutrophic reservoir

1. Phosphorus limitation was studied along the eutrophic, canyon-type ?ímov reservoir (Czech Republic) during a spring phytoplankton bloom. Concentration of soluble reactive phosphorus (SRP), C:P molar ratio in seston, extracellular alkaline phosphatase activity (APA), and P limitation (bioassay) were used as indices for phosphorus deficiency in the phytoplankton. 2. SRP, C:P, APA, and P limitation indicated a moderate P deficiency in the downstream, but not upper, part of the reservoir. 3. Significant correlations between these parameters were found in the downstream part. Chlorophyll a concentration correlated with APA and P limitation in the upper part. 4. APA was significantly enhanced in the phosphorus-deficient phytoplankton. However, APA was apparently not related to total biomass or species composition of the phytoplankton. 5. Generally, APA was closely correlated with pH in the reservoir. However, extracellular alkaline phosphatases, with a pH optimum above 9.0, were induced and active only during the phytoplankton bloom, whereas low background activity of extracellular phosphatases was found at low chlorophyll a concentrations (winter, clear-water phase).     

Degradation of subunits of the Sec61p complex, an integral component of the ER membrane, by the ubiquitin-proteasome pathway.

We have investigated the degradation of subunits of the trimeric Sec61p complex, a key component of the protein translocation apparatus of the ER membrane. A mutant form of Sec6lp and one of the two associated proteins (Sss1p) are selectively degraded, while the third constituent of the complex (Sbh1p) is stable. Our results demonstrate that the proteolysis of the multispanning membrane protein Sec61p is mediated by the ubiquitin-proteasome pathway, since it requires polyubiquitination, the presence of a membrane-bound (Ubc6) and a soluble (Ubc7) ubiquitin-conjugating enzyme and a functional proteasome. The process is proposed to be specific for unassembled Sec61p and Sss1p. Thus, our results suggest that one pathway of ER degradation of abnormal or unassembled membrane proteins is initiated at the cytoplasmic side of the ER.     

The Function of Urease in Citrullus Seeds

Urease is present in considerable quantity in the cotyledonsof Citrullus, though elsewhere in the plant it is present onlyin traces or is absent; urease activity in the cotyledons changesduring growth, showing an initial rise followed by an abruptdrop almost to zero. These changes, under a wide variety ofconditions, are not correlated with those in the major nitrogenfractions; they are, however, closely correlated with cell extensionand the associated changes in water content and respiration.A connexion with chlorophyll formation is possible but unlikely.It is suggested that the changes in cotyledonary urease constitutemerely one aspect of the ‘protoplasmic differentiation’that takes place as a cell matures.     

Characterization of new microsatellite loci from Vitis vinifera and their conservation in some Vitis species and hybrids

We present here characterization data for seven new microsatellite markers designed from new microsatellite loci isolated from a microsatellite‐enriched DNA library from Vitis vinifera. The observed heterozygosity varied from 0.73 up to 0.93 and the number of alleles per locus ranged from 12 to 26. This high polymorphism makes these new markers interesting for use in genotyping studies and completing the set of microsatellite markers already available for V. vinifera. Additionally these seven new markers appear to be conserved in four other Vitis species and 15 Vitis hybrids used as rootstocks for V. vinifera cultivation.