Properties of glutamate dehydrogenase from Beta vulgaris

Glutamate-NAD oxidoreductase, E.C. 1.4.1.3 (GDH), from seedlings of Beta vulgaris cv. Rota, Jahnsch Peragis Comp., was enzymatically characterized. This enzyme with molecular weight of 2.6 × 10⁵ has a pH optimum of around 8 for animation of α-KGA and around 9.5 for the desamination of glutamate. The apparent K_m for α-KGA is 6.7 × 10^?4M, for NH₃ 2.5 × 10^?3M, for NADH 3.2 × 10^?5M and for NAADPH 5.5 × 10^?4M. NAD¹ inhibits the reaction non-competitively when NADPH serves as substrate. The apparent K¹ is 4.5 × 10^?4M. The data are discussed on relation to the properties of GDH from other plant sources.     

HATCHING GLANDS IN THE TELEOSTS, BRACHYDANIO RERIO. DANIO MALABARICUS, MOENKHAUSIA OLIGOLEPIS AND BARBUS SCHUBERTI

Many teleost embryos produce an enzyme within specialized glands, which facilitate hatching. The enzyme attacks the chorion which becomes so weak that it may be ruptured easily by a blow of the tail.
The embryos of Brachydanio rerio, Danio malabaricus, Moenkhausia oligolepis and Barbus schuberti show some morphological differences in the distribution of the hatching gland cells. More specificity can be found in the ultrastructure of hatching gland cells, which are loaded with enzyme granules prior to hatching. In all four species the nucleus is located near the basis of the cell. The hatching enzyme is contained within granules, which arise from the Golgi body.     

Production of L-DOPA by cell suspension cultures of Mucuna pruriens

The endogenous synthesis of 3-(3,4-dihydroxyphenyl)-L-alanine (L-DOPA) by cell suspension cultures of Mucuna pruriens was found to be influenced by several environmental parameters. The nature of the nitrogen source as well as the concentration of nitrogen containing salts, sucrose and phosphate in the culture medium were found to affect the biosynthesis of L-DOPA. Addition of 2, 4-dichlorophenoxyacetic acid to the medium suppressed L-DOPA production; continuous illumination of the cultures had a strong beneficial effect on L-DOPA production. L-DOPA was accumulated intracellularly by the cell suspension cultures. These observations further demonstrate that for certain products of plant cell suspensions product synthesis can be manipulated by a proper selection of specified nutrients.     

Evaluation of the potential in vivo genotoxicity of quercetin

Quercetin, a naturally occurring flavonol commonly detected in apples, cranberries, blueberries, and onions, has been reported to possess antioxidant, anti-carcinogenic, anti-inflammatory, and cardioprotective properties. While positive results have been consistently reported in numerous in vitro mutagenicity and genotoxicity assays of quercetin, tested in vivo, quercetin has generally produced negative results in such studies. Furthermore, no evidence of carcinogenicity related to the oral administration of quercetin was observed in chronic rodent assays. In order to further define the in vivo genotoxic potential of quercetin, a bone marrow micronucleus assay and an unscheduled DNA synthesis (UDS) assay were conducted in Wistar rats. Administered orally to male rats at dose levels of up to 2000 mg/kg body weight, quercetin did not increase the number of micronucleated polychromatic erythrocytes (MN-PCE) 24 or 48 h following dosing in the micronucleus assay. Likewise, orally administered quercetin (up to 2000 mg/kg body weight) did not induce UDS in hepatocytes of male or female rats. While measurable levels of metabolized quercetin were observed in rat plasma samples for up to 48 h after dosing, peaking at 1 h following treatment administration, the unmetabolized aglycone was not identified in either plasma or bone marrow. With the exception of only a few rats, the aglycone was also not detected in liver tissue. These results demonstrate that quercetin is not genotoxic under the conditions of these assays and further support the negative results of previously conducted in vivo assays.     

Fellow travellers: a concordance of colonization patterns between mice and men in the North Atlantic region

Background

In the Calvin cycle of eubacteria, the dephosphorylations of both fructose-1, 6-bisphosphate (FBP) and sedoheptulose-1, 7-bisphosphate (SBP) are catalyzed by the same bifunctional enzyme: fructose-1, 6-bisphosphatase/sedoheptulose-1, 7-bisphosphatase (F/SBPase), while in that of eukaryotic chloroplasts by two distinct enzymes: chloroplastic fructose-1, 6-bisphosphatase (FBPase) and sedoheptulose-1, 7-bisphosphatase (SBPase), respectively. It was proposed that these two eukaryotic enzymes arose from the divergence of a common ancestral eubacterial bifunctional F/SBPase of mitochondrial origin. However, no specific affinity between SBPase and eubacterial FBPase or F/SBPase can be observed in the previous phylogenetic analyses, and it is hard to explain why SBPase and/or F/SBPase are/is absent from most extant nonphotosynthetic eukaryotes according to this scenario.

Results

Domain analysis indicated that eubacterial F/SBPase of two different resources contain distinct domains: proteobacterial F/SBPases contain typical FBPase domain, while cyanobacterial F/SBPases possess FBPase_glpX domain. Therefore, like prokaryotic FBPase, eubacterial F/SBPase can also be divided into two evolutionarily distant classes (Class I and II). Phylogenetic analysis based on a much larger taxonomic sampling than previous work revealed that all eukaryotic SBPase cluster together and form a close sister group to the clade of epsilon-proteobacterial Class I FBPase which are gluconeogenesis-specific enzymes, while all eukaryotic chloroplast FBPase group together with eukaryotic cytosolic FBPase and form another distinct clade which then groups with the Class I FBPase of diverse eubacteria. Motif analysis of these enzymes also supports these phylogenetic correlations.

Conclusions

There are two evolutionarily distant classes of eubacterial bifunctional F/SBPase. Eukaryotic FBPase and SBPase do not diverge from either of them but have two independent origins: SBPase share a common ancestor with the gluconeogenesis-specific Class I FBPase of epsilon-proteobacteria (or probably originated from that of the ancestor of epsilon-proteobacteria), while FBPase arise from Class I FBPase of an unknown kind of eubacteria. During the evolution of SBPase from eubacterial Class I FBPase, the SBP-dephosphorylation activity was acquired through the transition ??from specialist to generalist??. The evolutionary substitution of the endosymbiotic-origin cyanobacterial bifunctional F/SBPase by the two light-regulated substrate-specific enzymes made the regulation of the Calvin cycle more delicate, which contributed to the evolution of eukaryotic photosynthesis and even the entire photosynthetic eukaryotes.     

Inverse Correlation between ABA Content and Germinability throughout the Maturation and the In Vitro Culture of the Embryo of Phaseolus vulgaris

Prevost, I. and Le Page-Degivry, M. Th. 1985. Inverse correlationbetween ABA content and germinability throughout the maturationand the in vitro culture of the embryo of Phaseolus vulgaris.—J.exp. Bot. 36: 1457–1464. Changes in embryo abscisic acid (ABA) content during the maturationof the seed of Phaseolus vulgaris cv. Contender were followed,using a radio-immunoassay. The pattern of change is similarto that already described in several species: a rapid increase(from the 18th to 29th day after anthesis), was followed bya decrease, the ABA level being ten times lower on the 48thday than on the 29th. Embryos isolated from the 18th to the48th day after anthesis were able to ‘germinate’when cultivated on a mineral medium supplemented with sucroseand agar. The development pattern varied throughout the embryogenesisand could be correlated with the differentiation of the embryoat the time of isolation. Before germination could take place,we observed a lag phase, the duration of which could be correlatedwith embryo ABA content. As ABA content increased in the youngestembryos the duration of the lag phase increased. In the sameway, the number of days to germination was shown to diminishas ABA content decreased. Inverse correlation between ABA contentand germinability was thus demonstrated throughout the developmentof the embryo. During in vitro culture, free ABA content decreased in the embryoand reached low values a few days before germination occurred.So the beginning of root elongation in culture was again wellcorrelated with the disappearance of free endogenous ABA. Atransfer experiment inducing an earlier germination associatedwith a more limited development suggests that the lag phaseis associated with an active continuation of embryonic development Key words: Embryo maturation, abscisic acid, germinability     

Relationships between Adsorption, Chemical State and Fluxes of Cadmium Applied as Cd(NO3)2 in Isolated Xylem Cell Walls of Tomato

Wolterbeek, H. Th. 1987. Relationships between adsorption, chemicalstate and fluxes of cadmium applied as Cd(NO₃)₂ in isolatedxylem cell walls of tomato.—J. exp. Bot. 38: 419–432. Isolated xylem cell wall pieces were applied as membranes inion diffusion experiments. The cell walls were isolated fromtomato internodes (Lycopersicon esculentum Mill, cv. Tiny Tim)and sealed in a two-compartment diffusion system. In flux andadsorption calculations, the cell wall was regarded as a leakymembrane with parallel fluxes through Donnan Free Space (DFS)and Water Free Space (WFS). During the experiments absorptioninto and diffusion across the walls was determined of Cd^{2 +}, applied as ¹¹⁵Cd(NO₃)₂. Flux experiments with ⁸²Br^–indicated that excluded volume effects and path tortuosity resultedin apparent WFS diffusion coefficients in the walls which were0·012 times as high as in water. The free proton concentration in the DFS was shown to be relatedto a complex formation between fixed charges and Cd^{2 +}. Thecell wall permeability for Cd^{2 +} and NO₃^– varied withapplied and absorbed concentrations, and the Cd^{2 +} flux curveshowed an inflexion point coinciding with a buffered degreeof dissociation of fixed charges in the DFS. The necessary couplingof fluxes of opposite charges resulted in relatively high NO₃^–and small Cd^{2 +} permeability of the DFS for strongly dilutedsolutions (P = 10^–4 m s^–1 and 10^–11 m s^–1for NO₃^– and Cd^{2 +} respectively). The results demonstratethe possible regulatory effects of the cell wall in processesof ion transfer from xylem vessels, or ion uptake in plant tissues. Key words: Cadmium, chemical state, DFS, WFS, ion flux, permeability, xylem cell walls, tomato, bromium, nitrate     

The Import and Redistribution of Several Cations and Anions in Tomato Leaves

Wolterbeek, H. Th. and De Bruin, M. 1986. The import and redistributionof several cations and anions in tomato leaves.—J. exp.Bot. 37: 331–340. The upward movements in the xylem and redistribution from theleaf of Na⁺ , K⁺ , Rb⁺, Cs⁺ and four anions were examined insub-systems of tomato plants (Lycopersicon esculentum, Mill.cv. Tiny Tim). There was a delay with respect to the redistributionof newly imported elements from the source leaf of about 16–20h for all four alkali ions. This is considerably less than theapparent delay for the anions Sb(SO₄)^– WO₄^2– Mo₇O₂₄^6–and AsO₄^3– The prolonged delay for the anions is suggestedto be a consequence of metabolic transformation in the leaf.Reduction of the source-sink activity ratio did not decreasethe delay period from the source leaf, but apparently causedincreased Na⁺ transfer from the xylem. It is concluded thatthe application of a detailed mathematical descnption of upwardelement movement has considerable potential possibilities forunderstanding circulation of nutrients in the plant. Key words: Alkali ions, anions, xylem, phloem, redistribution, tomato