Nuclear DNA Content Variation in Different Life Cycle Stages of Sugar Kelp,Saccharina latissima

Marine Biotechnology - Ploidy variants can be utilized to increase yield, introduce sterility, and modify specific traits with an economic impact. Despite economic importance of Saccharina species,...     

Sugar transporters in plant biology.

Sugar transporters are key players in many fundamental processes in plant growth and development. Recent results have identified several new transporters that contribute to a wide array of physiological activities, and detailed molecular analysis has provided exciting insights into the structure and regulation of these essential membrane proteins.     

Sugar transport in Coprinus cinereus.

Two transport systems for glucose were detected: a high affinity system with a Km of 27 muM, and a low affinity system with a Km of 3.3 mM. The high affinity system transported glucose, 2-deoxy-D-glucose (Km = 26 muM), 3-O-methylglucose (Km = 19 muM), D-glucosamine (Km = 652 muM), D-fructose (Km = 2.3 mM) and L-sorbose (Km = 2.2 mM). All sugars were accumulated against concentration gradients. The high affinity system was strongly or completely inhibited by N-ethylmaleimide, quercetin, 2,4-dinitrophenol and sodium azide. The system had a distinct pH optimum (7.4) and optimum temperature (45 degrees C). The low affinity system transported glucose, 2-deoxy-D-glucose (Km = 7.5 mM), and 3-O-methylglucose (Km = 1.5 mM). Accumulation again occurred against a concentration gradient. The low affinity system was inhibited by N-ethylmaleimide, quercetin and 2,4-dinitrophenol, but not by sodium azide. The rate of uptake by the low affinity system was constant over a wide temperature range (30--50 degrees C) and was not much affected by pH; but as the pH of the medium was altered from 4.5 to 8.9 a co-ordinated increase in affinity for 2-deoxy-D-glucose (from 52.1 mM to 0.3 mM) and decrease in maximum velocity (by a factor of five) occurred. Both uptake systems were present insporelings germinated in media containing sodium acetate as sole carbon source. Only the low affinity system could initially be demonstrated in glucose-grown tissue, although the high affinity system was restored by starvation inglucose-free medium. The half-ti me for restoration of high affinity activity was 3.5 min and the process was unaffected by cycloheximide. Addition of glucose to an acetate-grown culture inactivated the high affinity system with a half-life of 5--7.5 s. Addition of cycloheximide to an acetate-grown culture caused decay of the high affinity system with a half-life of 80 min. Regulation is thus thought to depend on modulation of protein activity rather than synthesis, and the kinetics of glucose, 2-deoxy-D-glucose and 3-O-methylglucose uptake would be consistent with there being a single carrier showing negative co-operativity. Analysis of transport defective mutants revealed defects in both transport systems although the mutants used were alleles of a single gene. It is concluded that this gene (the ftr cistron) is the structural gene for an allosteric molecule which serves both transport systems.     

Sugar sensing in higher plants.

Sugar repression of photosynthetic genes is likely a central control mechanism mediating energy homeostasis in a wide range of algae and higher plants. It overrides light activation and is coupled to developmental and environmental regulations. How sugar signals are sensed and transduced to the nucleus remains unclear. To elucidate sugar-sensing mechanisms, we monitored the effects of a variety of sugars, glucose analogs, and metabolic intermediates on photosynthetic fusion genes in a sensitive and versatile maize protoplast transient expression system. The results show that sugars that are the substrates of hexokinase (HK) cause repression at a low concentration (1 to 10 mM), indicating a low degree of specificity and the irrelevance of osmotic change. Studies with various glucose analogs suggest that glucose transport across the plasma membrane is necessary but not sufficient to trigger repression, whereas subsequent phosphorylation by HK may be required. The effectiveness of 2-deoxyglucose, a nonmetabolizable glucose analog, and the ineffectiveness of various metabolic intermediates in eliciting repression eliminate the involvement of glycolysis and other metabolic pathways. Replenishing intracellular phosphate and ATP diminished by hexoses does not overcome repression. Because mannoheptulose, a specific HK inhibitor, blocks the severe repression triggered by 2-deoxyglucose and yet the phosphorylated products per se do not act as repression signals, we propose that HK may have dual functions and may act as a key sensor and signal transmitter of sugar repression in higher plants.     

Sugar Uptake and Translocation in the Castor Bean Seedling II. Sugar Transformations During Uptake

Changes in the dry weights of various parts of the castor bean seedling showed that the rates of transfer of material through the cotyledons to the embryonic axis exceeded 2 mg/hour after 5 to 6 days of germination. The sugar present in the endosperm was predominantly, and in the cotyledon almost exclusively, sucrose. Anatomical features were described which contribute to the efficiency of the cotyledons as organs of absorption and transmittal of sucrose to the embryonic axis, where hexoses are much more prevalent.     

Sugar transport in reversibly hemolyzed avian erythrocytes.

The technique of reversible hemolysis represents one approach which may be used to study transport regulation in nucleated red cells. After 1 h of incubation at 37 degrees C, 88% of the ghosts regained their permeability barrier to L-glucose. In these ghosts, the carrier-mediated rate of entry of 3-O-methylglucose was more than 10-fold greater than the rate in intact cells. Glyceraldehyde-3-phosphate dehydrogenase prevented ghosts from resealing when it was present at the time of hemolysis. Albumin, lactic dehydrogenase and peroxidase did not have this effect. Sugar transport rate could not be tested in the unsealed ghosts. Two possible mechanisms for the effect of hypotonic hemolysis on sugar transport rate were discussed: (1) altered membrane organization and (2) loss of intracellular compounds which bind to the membrane and inhibit transport in intact cells.     

Sugar transport and metabolism in Schistosoma mansoni.

The absorption kinetics of some 14-C-labeled simple sugards in adults of Schistosoma mansoni are described. The influx of fructose and 3-0-methylglucose was by diffusion alone, while glucose, 2-deoxyglucose (2DOG), galactose, glucosamine, and mannose were absorbed by mediated transport as well as by diffusion. Although absorbed glucose was rapidly metabolized, uptake rates of radio-glucose in 2-min incubations corresponded with the amount of glucose (determined chemically) removed from the incubation medium. In 30-min incubations 2DOG was slowly metabolized and accumulated against an apparent concentration difference. The mediated transport of glucose and 2DOG was inhibited in Na+-free media, and by the presence of ouabain, phlorizin, phloretin, and other sugars. Accordingly, influxes of glucose of 2DOG and 22-Na+ were coupled. On a per mg protein basis, female worms transported more 2DOG and glucose, but less glycine, than did males. However, the rate of glucose metabolism by male and female worms incubated together was greater than that of either males or females incubated separately. The nature of sugar transport in schistosomes and other flatworms is similar to that in vertebrates.     

Sugar orthocarbonates

A simple procedure is described for preparing sugar orthocarbonates. It is based on treating the corresponding thionocarbonate in pyridine with cupric acetate and an alcohol, such as methanol, ethanol, or isopropyl alcohol. Treatment of 1,2:5,6-di-O-isopropylidene-D-mannitol 3,4-thionocarbonate with diols, such as 1,2-ethanediol, 1,2-propanediol, or 1,2:5,6-di-O-isopropylidene-D-mannitol, also gave orthocarbonates. Methyl thionocarbonate, S-methyl xanthate, and dithiobis(thioformate) derivatives of 1,2:3,4-di-O-isopropylidene-α-D-galactopyranose all gave the trimethyl orthocarbonate upon treatment with methanol in the presence of pyridine and cupric acetate. The structure of the orthocarbonates was proved by elemental analysis, n.m.r., and mass spectra, and by treatment with mild acid to form carbonates. Treatment of 1,2:5,6-di-O-isopropylidene-3-thio-D-altritol 3,4-thionocarbonate with methanol or ethanol gave the corresponding orthothiocarbonate, but on treatment with 1,2-ethanediol or with sodium ethoxide the 3,4-episulfide resulted.