Internal Translocation Research Articles

Oncogenes in Human Leukemias

Eukaryotic cells contain a family of genes termed cellular oncogenes or proto-oncogenes thought to regulate normal cell growth and development. In some abnormal circumstances, such as following transduction by retroviruses, activation of these genes causes leukemias in animals. Possible mechanisms of activation of cellular oncogenes include: point mutation, deletion, or insertion; amplification; activation by internal rearrangement, chromosomal translocation, or promoter insertion; recombinatorial events resulting in the formation of novel chimeric genes; among others. In this review, we consider data implicating activation of cellular oncogenes in the pathogenesis of leukemia in humans. We discuss possible mechanisms whereby oncogene activation may induce leukemias, as well as potential diagnostic and therapeutic implications.

Accumulation of cadmium and selenium and their mutual interaction in the shore crab Carcinus maenas (L.)

The accumulation of cadmium and selenium and their mutual interaction was measured in hepatopancreas, gills, chela muscle, and carapace in six groups of shore crabs Carcinus maenas (L.), exposed to combinations of cadmium and selenite concentrations in the sea water. The highest concentrations of cadmium occurred in gills and hepatopancreas; muscle and carapace accumulated cadmium to lower levels. The cadmium concentrations in hepatopancreas varied inversely with the cadmium concentrations in muscle and carapace. The cadmium concentrations in muscle and carapace varied in parallel. The presence of selenite in the sea water augmented the concentrations of cadmium in the gills. When selenite was added to the sea water the selenium level rose in gills and carapace, while no increase was observed in hepatopancreas and muscle. The presence of cadmium in the sea water augmented the accumulation of selenium in the gills. In the presence of cadmium in the sea water selenium wa; accumulated in gills and carapace in proportion to the ambient selenite concentration. Exposing crabs 10 selenile and cadmium resulted in a positive correlation between the concentration of these elements in the gills and hepatopancreas. Furthermore, a positive correlation was found between the selenium and cadmium concentrations in carapace within each experimental group. The data are discassed as regards mode of uptake, internal translocations, accumulation, me'abolism, and excretion of the elements investigated.

Internal Cycling of Nitrogen in Shortgrass Prairie

Study was made of the rates at which and the routes by which nitrogen once taken up by the plant moves into litter and soil compartments and from them to new plant growth. Field mini-plots were given an initial pulse treatment with '5N, following which destructive removals were made over the next 5 growing seasons. In the year of application, 15N moved primarily to the green herbage; 0.58 of all 15N recovered in plant materials the 1st year was in such herbage. There was late season translocation of N from aboveground to belowground plant parts. The pulse N peaked in the aboveground dead compartment in the winter months following the first and preceding the second growing season. Transfer of '5N from the aboveground litter occurred principally during the second growing season. The '5N content of crowns and live roots did not change significantly during the 5 seasons; that of senescent and detrital roots increased significantly during the same interval. It was concluded that the annual N requirement in ungrazed blue grama is met by a combination of 4 nitrogen-supplying mechanisms. One of these is that of internal translocation whereby N of one season is stored over winter belowground and then moved to new growth in the next growing season. Another is that of mineralization of easily decomposable organic materials; among these are certain herbage components, roots exudates and exfoliates, and short-lived unsuberized roots. A third is mineralization of organic nitrogen synthesized by microorganisms that grow on energy-rich materials such as those named in the immediately preceding sentence. Finally, not all of the plant and micro- bially synthesized organic N undergoes quick release to the available N pool; a portion of it undergoes polymerization and becomes humic nitrogen, from which there is slow release to the available N pool. It is the first 3 mechanisms that promote quick recycling of N in the blue grama system. Once a given N atom makes its initial entry into the blue grama plant, there is greatly increased probability that the atom will again enter new herbage growth in each of several following years. Nitrogen that enters the soil humus is very slowly recycled into new plant growth.

Uptake and Transport of Calcium and Phosphorus in Lolium perenne in Response to N Supplied to Halves of a Divided Root System

AbstractThe uptake and transport of Ca2+ and HPO42− from roots of Lolium perenne L. was studied using variable N nutrition supplied to halves of a divided root system. Plants were grown for 4 weeks in solution containing 0.11 mM NO3−–N; then one‐half of the root system was supplied with either 4.0 mM NO3−–N or 0.28 mM NH4+–N while the other half of the root system remained in low‐N solution.Uptake and transport of Ca2+ increased and uptake of HPO42− declined in root halves supplied with high NO3−–N for 16 h. After supply of high NO3−–N or NH4+–N to half the root system for 6 days, the roots supplied with high‐N exhibited significantly higher rates of uptake and percentage transport to shoots of both Ca2+ and HPO42−–. However, in neither the 16‐h nor 6‐day treatment did Ca2+ or HPO42− uptake of the root half supplied with low N differ significantly from the control (low N supplied to both halves of the root).Significantly higher N concentrations were found in low‐N supplied roots (compared to the control) as a result of internal translocation of N from high‐N supplied roots to low‐N supplied roots. Although N concentration in the low‐N supplied roots increased, uptake rates of Ca2+ or HPO42− did not change implying that external N concentration may be the important factor which influences or governs N mediated uptake responses. This would further suggest that the site of uptake regulation for Ca2+ and HPO42− exists on the outer plasma membrane which is in direct contact with the external solution.Transport of Ca2+ and HPO42− to the shoot was generally increased in low‐N root halves after 6 days of high‐N supply to the other half of the root. This implies that plant growth demand may be a major factor in regulating rates of Ca2+ and HPO42− transport from roots to the shoot. It also reinforces the hypothesis that uptake and transport of ions out of the root are separately controlled or regulated in the plant.

Transport and Distribution of 14CO2 Assimilate in Lolium perenne in Response to Varying Nitrogen Supply to Halves of a Divided Root System

AbstractThe movement of 14C assimilate from shoots to roots and its subsequent metabolism in the root of Lolium perenne L. was studied using variable N nutrition supplied to halves of a divided root system. Half of the N‐deficient root system was supplied with either high NO3‐N or high NH4‐N for 16 hours or 6 days before 14CO2 labeling of the shoots.The distribution of 14C in sugars, ethanol‐soluble nitrogen and organic acids in roots appeared to be related to the N content of the tissue. Supply of high NO3‐N for 6 days resulted in significant internal translocation of N into the low N supplied root half. Both root halves also had similar patterns of 14C distribution among soluble and insoluble metabolites. However, NH4‐N supply for 6 days did not result in a significant increase of N in the low N supplied roots, thus only the high NH4‐N supplied roots displayed stimulated sugar metabolism, similar to that in both root halves in the high NO3‐N supply treatment.Percent transport of 14C assimilates from shoot to root was influenced by form and level of N supplied to root halves. Root halves supplied with either high N source for 6 days accumulated greater amounts of 14C assimilate than the corresponding low N root half. However NH4‐N supply appeared to make roots stronger sinks since NH4 supply resulted in significantly greater 14C accumulation in both the high NH4 supplied and the low N root halves than did NO3‐N supply in corresponding root halves.The data suggest that factors other than root metabolism, such as N mediated metabolism in the shoot, may also influence the percent transport of assimilates to the root. Internal distribution of the incoming assimilate within the root system could be regulated by the metabolic activity or assimilate demand of the roots.

Uptake and translocation of zinc by intact plants

Certain cations were added to nutrient solution cultures, in which intact bean plants were being grown, in an attempt to establish whether they influenced either entry of radiozinc (Zn*) into these plants or translocation of this element from the roots to the tops, or both. The Zn*-level in the culture solution was maintained at 5µM and the concentrations of the added cations were varied from zero through 60µM in the highest treatments. When copper was present as the added cation at the Zn*-level (5µM), Zn*-uptake was severely reduced but internal translocation was not especially altered. When zinc was present as the added cation it exerted the expected competition on Zn*-uptake and in addition exerted an unexpected, suppressing effect on Zn* being translocated to the tops. Manganese, as an added cation, has an effect on Zn*-uptake only at high concentrations (30µM or more) but it did not alter the internal Zn* distribution. Cadmium behaved similarly to copper in its influence on Zn*-uptake and translocation. It is concluded that the general effect of added cations on Zn*-uptake and translocation in intact bean plants is predominantly to inhibit uptake, not internal distribution.