Internal Translocation Research Articles

Inorganic nitrogen uptake kinetics and whole-plant nitrogen budget in the seagrass Zostera noltii

The uptake rates of ammonium and nitrate through the leaves and roots, the leaf–root interactions in the nitrogen uptake and the internal translocation of incorporated nitrogen were simultaneously investigated in the seagrass Zostera noltii. Leaf and root uptake rates, which were measured using two-compartment polyethylene chambers that physically separated the leaves from below-ground plant parts, were quantified based on tissue incorporation of 15N-labeled ammonium and nitrate. The maximum leaf uptake rates (V max) of ammonium were 100 times higher than those of nitrate. Both V max and affinity for ammonium were one order of magnitude higher in the leaves (28.3–31.9 μmol g −1 DW h −1 and 0.93–0.99, respectively) than in the roots (2.3–3.0 μmol g −1 DW h −1 and 0.06–0.08, respectively). The uptake of ammonium and nitrate by one plant part did not affect the uptake of the other plant part, and no translocation of inorganic nitrogen was detected between plant parts. The 15N enrichment detected in the rhizomes suggests either a direct uptake of inorganic nitrogen or its transference from the roots. The estimated total inorganic nitrogen uptake of Z. noltii (645 μmol m −2 h −1) in the peak production season (spring) under typical nutrient concentrations, using the rates obtained during the surge uptake phase, exceeded by 3-fold the species estimated nitrogen requirement for growth (236 μmol N m −2 h −1). However, using the stabilized values of the uptake rates obtained after several hours of incubation, the estimated whole-plant nitrogen budget (215 μmol m −2 h −1) was slightly lower than the total nitrogen requirement for growth. We conclude that the growth of Z. noltii in Ria Formosa lagoon is not limited, or is only slightly limited, by nitrogen.

Micro-scale elemental distribution in the thallus of Flavoparmelia caperata transplanted to polluted site

The elemental microdistributions of peripheral and central parts of the lichen Flavoparmelia caperata exposed to industrial pollution were analysed, in order to better understand the elements distribution patterns in relation to the lichen constitution, thereby increasing our knowledge on uptake and release mechanisms. Nuclear microscopy techniques were used to visualize elemental distributions in sample transepts and associate their concentrations to sample morphology. The distribution data of the elements studied suggests there is biological regulation of internal concentrations. Considering thallus parts, element-specific internal translocation should be taken into account as one more factor affecting lichen “memory length”.

Accumulation of trace elements in the peripheral and central parts of two species of epiphytic lichens transplanted to a polluted site in Portugal

This paper compares the dynamics, i.e. the rates of change in element concentrations of young and older lichen thallus parts, of one foliose and one fruticose lichen, during a transplant experiment to a polluted site. Both lichen parts respond to environmental changes. Here, differential accumulation suggests that differential constitution leads to differential uptake and release, and/or the overall behaviour is partly due to internal translocation and regulation mechanisms within the whole lichen. For thallus parts, internal translocation should be taken into account as one more factor affecting lichen "memory length". Young parts of the thallus presented higher rates of change, but different lichen parts accumulate different elements to different extents. Therefore tissue selection in monitoring may depend on the element of interest, and cannot be made into a generalized approach in survey set-ups: the choice depends on the element.

The role of EDTA in phytoextraction of hexavalent and trivalent chromium by two willow trees

Effects of the synthetic chelator ethylenediamine tetraacetate (EDTA) on uptake and internal translocation of hexavalent and trivalent chromium by plants were investigated. Two different concentrations of EDTA were studied for enhancing the uptake and translocation of Cr from the hydroponic solution spiked with K(2)CrO(4) or CrCl(3) maintained at 24.0 +/- 1 degrees C. Faster removal of Cr(3+) than Cr(6+) by hybrid willows (Salix matsudana Koidz x Salix alba L.) from the plant growth media was observed. Negligible effect of EDTA on the uptake of Cr(6+) was found, but significant decrease of the Cr concentration in roots was measured. Although the translocation of Cr(6+) within plant materials was detected in response to EDTA concentration, the amount of Cr(6+) translocated to the lower stems was considerably small. EDTA in the nutrient media showed a negative effect on the uptake of Cr(3+ )by hybrid willows; the removal rates of Cr(3+ )were significantly decreased. Translocation of Cr(3+) into the stems and leaves was undetectable, but roots were the exclusive sink for Cr(3+) accumulation. Weeping willows (Salix babylonica L.) showed lower removal rates for both chemical forms of Cr than hybrid willows. Although EDTA had a minor effect on Cr(6+ )uptake by weeping willows, positive effect on Cr(6+ )translocation within plant materials was observed. It was also determined that EDTA in plant growth media significantly decreased the amount of Cr(3+) taken up by plants, but significantly increased Cr(3+) mobilization from roots to stems. Results indicated that EDTA was unable to increase the uptake of Cr(6+) by both plant species, but translocation of Cr(6+)-EDTA within plant materials was possible. Addition of EDTA in the nutrient media showed a strong influence on the uptake and translocation of Cr(3+) in both willows. Cr(3+)-EDTA in tissues of weeping willows was more mobile than that in hybrid willows. The information has important implications for the use of metal chelator in plant nutritional research.

Heavy metal concentrations (Cd, Cu and Pb) in five aquatic plant species in Tasik Chini, Malaysia

The purpose of this study was to determine the levels of heavy metals namely cadmium (Cd), copper (Cu) and lead (Pb) in the five aquatic plants. For this purpose, the concentration of heavy metals were measured in water and in the five aquatic plant species, Lepironia articulata, Pandanus helicopus, Scirpus grossus, Cabomba furcata and Nelumbo nucifera, in 15 sites from Tasik Chini. The concentrations were different among the plant species as well as among the parts of plants. The highest concentration of heavy metals among the aquatic plants and plant parts was found in the roots of S. grossus. The concentrations of Cd in the leaves and stems of submerged aquatic plant, C. furcata, were higher than concentration of Cd in the leaves and stems of emergent aquatic plant and floating leaf plant. The concentration of Cu in the stem of C. furcata was greater than that in the leaf, while the concentration of Cd was more in the leaf than in the stem. The heavy metal contents of the aquatic plants were in descending order of Pb > Cu > Cd. The metal concentration quotient of leaves/roots and stems/roots (ML/MR and MS/MR) were calculated. The highest internal translocation was found in P. helicopus, while the lowest internal translocation was found in S. grossus.

Effects of burial and erosion on the seagrass Zostera noltii

The effects of experimental burial and erosion on the seagrass Zostera noltii were assessed through in situ manipulation of the sediment level (− 2 cm, 0 cm, + 2 cm, + 4 cm, + 8 cm and + 16 cm). Shoot density, leaf and sheath length, internode length, C and N content and carbohydrates of leaves and rhizomes were examined 1, 2, 4 and 8 weeks after disturbance. Both burial and erosion resulted in the decrease of shoot density for all the sediment levels. The threshold for total shoot loss was between 4 cm and 8 cm of burial, particularly during the 2nd week. A laboratory experiment confirmed that shoots did not survive more than 2 weeks under complete burial. There was no evidence of induced flowering by burial or erosion. As well, no clear evidence was found of sediment level effects on leaf and sheath length. Longer rhizome internodes were observed as a response to both burial and erosion, suggesting a plant attempt to relocate the leaf-producing meristems closer to sediment surface or in search of new sediment avoiding the eroded area. The C content of leaves and rhizomes, as well as the non-structural carbohydrates (mainly the starch in rhizomes), decreased significantly along the experimental period, indicating the internal mobilization of carbon to meet the plant demands as a consequence of light deprivation. The significant decrease of N content in leaves, and its simultaneous increase in rhizomes, suggests the internal translocation of nitrogen from leaves to rhizomes. About 50% of the N lost by the leaves was recovered by the rhizomes. Our results indicated that Z. noltii has a high sensitivity to burial and erosion disturbance, which should be considered in the management of coastal activities.

The importance of atmospheric deposition, charge and atomic mass to the dynamics of minor and rare elements in developing, ageing, and wilted leaves of beech ( Fagus sylvatica L.)

The amounts of sixty elements in developing, maturing, senescent and wilting leaves, and in the wintering dead leaves attached to the branches, are reported for a beech ( Fagus sylvatica) forest on mor Podzol in south Sweden, a site with no local sources of pollution or geological anomalies. The amounts (contents per leaf) of K (potassium), Rb (rubidium), Cs (caesium), Cu (copper) and P (phosphorus) were highest in young leaves, decreasing throughout the growing season and usually in the subsequent winter. The entirely opposite pattern with a continuous, mostly even increase of the amounts was measured with Be (beryllium), Ba (barium), Hg (mercury), Al (aluminium), Tl (thallium), Pb (lead), Bi (bismuth), V (vanadium), W (tungsten), As (arsenic), Sb (antimony), and Se (selenium). Amounts of rare-earth elements and some transition metals, such as Co (cobalt), Ti (titanium), and the actinides Th (thorium) and U (uranium) were more stable during the growing season, after an initial increase in early summer, but increased greatly in the winter. This winter increase in dead attached leaves has to be accounted for by uptake from long-distance transported constituents in dry and wet deposition. It was similar to deposition rate estimates using moss carpets from the same locality. A passive uptake was positively related to ionic charge and atomic mass. However, the amounts of several, mainly non-essential elements, such as Ni (nickel), Sc (scandium), Zr (zirconium), Cr (chromium), Ag (silver), and Cd (cadmium) were not much lower in the young or maturing leaves than in the wintered dead leaves of this deciduous (hardwood) forest and a proportion apparently originated from internal translocation in the trees. Seasonal fluxes or cycling of many of the scarce or rare elements reported here have never been studied before in forest ecosystems.

Unique Substrate Recognition by Botulinum Neurotoxins Serotypes A and E

Botulinum neurotoxins (BoNTs) are zinc proteases that cleave SNARE proteins to elicit flaccid paralysis by inhibiting the fusion of neurotransmitter-carrying vesicles to the plasma membrane of peripheral neurons. There are seven serotypes of BoNT, termed A-G. BoNT serotype A and serotype E cleave SNAP25 at residues 197-198 and 180-181, respectively. Unlike other zinc proteases, the BoNTs recognize extended regions of SNAP25 for cleavage. The basis for this extended substrate recognition and specificity is unclear. Saturation mutagenesis and deletion mapping identified residues 156-202 of SNAP25 as the optimal cleavage domain for BoNT/A, whereas the optimal cleavage domain for BoNT/E was shorter, comprising residues 167-186 of SNAP25. Two sub-sites were resolved within each optimal cleavage domain, which included a recognition or active site (AS) domain that contained the site of cleavage and a binding (B) domain, which contributed to substrate affinity. Within the AS domains, the P1', P3, and P5 sites of SNAP25 contributed to scissile bond cleavage by LC/A, whereas the P1' and P2 sites of SNAP25 contributed to scissile bond cleavage by LC/E. These studies provide insight into the development of strategies for small molecule inhibitors of the BoNTs.

Dehydration versus volume depletion

To the Editor: In his recent Nephrology Forum, Dr. Friedman1 makes a number of interesting and cogent observations regarding enteral and parenteral fluid and electrolyte therapy in infants and children. However, I believe discussions of fluid and electrolyte disorders, and their treatments, become much clearer and more easily understood when terms such as "hydration," "dehydration," "volume depletion," and "volume expansion" are used in a more exacting and restricted fashion. As Menge et al2 describe in their article, "hydration" is best used to define the ratio between total body solute and total body water, and is usually reflected by the sodium concentration. In the absence of internal water translocations such as those produced by hyperglycemia, hyponatremia indicates that body water is increased in relation to solute and overhydration exists, while hypernatremia indicates a relative deficit of water, or excess of sodium, and indicates dehydration. In contradistinction, volume depletion defines contraction of the ECF and vascular spaces as may result from blood loss or the loss of salt and volume due to diarrhea, and is appropriately treated by the infusion of volume expanding solutions such as saline or blood.

Processes, dynamics and modelling of radiocaesium cycling in a chronosequence of Chernobyl-contaminated Scots pine ( Pinus sylvestris L.) plantations

In a large forested area affected by the Chernobyl radioactive fallout, especially in CIS, the lasting recycling of radiocaesium ( 137Cs) by the trees is a source of long-term contamination of woody products. The quantitative description of the 137Cs dynamics in contaminated forest is a prerequisite to predictive modelling and further management of such territories. Three even-aged mono-specific Scots pine stands (17, 37 and 57 years old) were selected in a contaminated woodland in southeastern Belarus to constitute an adequate chronosequence. We determined the potassium and radiocaesium annual fluxes involved in the biological cycling in each stand using a well-documented calculation methodology. Qualitatively, 137Cs was shown to be rapidly recycled in trees through the same pathways as K and to redistribute similarly between the tree components. Compared to K, a higher fraction of 137Cs, corresponding to about the half of the annual uptake, is immobilised in perennial organs. With tree development, trunk wood and bark become prevailing sinks for 137Cs since they represent an increasing pool of biomass. In the pine chronosequence, the current root absorption, respectively, mobilizes 0.53, 0.32 and 0.31% year −1 of the total 137Cs pool in soil. Variations in the 137Cs uptake do not reflect differences in the 137Cs balance between stands. In the two older stands, 51 and 71% of the current tree contamination are related to earlier accumulation subsequent to the initial fallout interception and recycling. The soil is the dominant source of long-term tree contamination. A simple modelling based on the measured 137Cs fluxes indicates that, for young stands, radioactive decay-corrected contamination would stabilize after reaching a maximum of 25 years after the 137Cs deposition. Stemwood presents a maximum of 15 years after the deposition and decrease afterwards mainly through radioactive decay. In the older stands, the decontamination is constant without local maximum of 137Cs level in the wood. The 137Cs contamination of tree components is the result of different influential processes like root uptake, internal translocation and immobilisation. For more accurate predictions, the calibration of existing models would be benefited by comparing with the 137Cs annual fluxes instead of the simple transfer factor coefficients. In the perspective of other applications, there is a need of such data for other radionuclides as well as for heavy metals.

Nitrogen uptake and translocation by Chara

The potential for above-ground and below-ground uptake and subsequent internal translocation of ammonium (NH 4 +) and nitrate (NO 3 −) by the macroalga Chara spp. was investigated. In a two compartment experimental set-up separating above-ground and below-ground algal parts, the charophytes were exposed to various combinations of 15 N -labelled NH 4 + and NO 3 −. Uptake in one compartment and translocation to the other were measured. Chara spp. was able to take up and translocate nitrogen between below-ground and above-ground parts. Uptake of 15 NH 4 + in rhizoids was two-fold higher than that of 15 NO 3 − , indicating a preferential uptake of 15 NH 4 + . Translocation after 5 days was always less in the direction from above-ground to below-ground parts (on average 2% of total 15 N uptake), than in the below-ground to above-ground direction (on average 29%). Translocation occurred when the ratio of 15 N -atomic percentage in the algal material in the exposed compartment roughly exceeded 2%, and was thus more determined by the internal gradient in the 15 N content than by the nature of the N source (either NH 4 + or NO 3 −). Translocation of 15 N from the below-ground to the above-ground compartment also occurred when the charophytes were exposed to high concentrations of either NO 3 − or NH 4 + in the above-ground compartment. The results of this study are supportive for a mechanism with preferential uptake of NH 4 + over NO 3 −, and subsequent passive diffusion between cells as the dominant transport mechanism.

Nutrient dynamics throughout the rotation of Eucalyptus clonal stands in Congo.

The dynamics of the main nutrient fluxes of the biological cycle were quantified in a clonal Eucalyptus plantation throughout the whole planted crop rotation: current annual requirements of nutrients, uptake from the soil, internal translocations within trees, return to soil (litterfall and crown leaching) and decomposition in the forest floor. As reported for other species, two growth periods were identified in these short-rotation plantations: (1) a juvenile phase up to canopy closure, during which the uptake of nutrients from the soil reserves supplied most of the current requirements; and (2) a second phase up to harvest, characterized by intense nutrient recycling processes. Internal translocation within trees supplied about 30 % of the annual requirements of N and P from 2 years of age onwards, and about 50 % of the K requirement. The mineralization of large amounts of organic matter returned to the soil with litterfall during stand development represented a key process providing nutrients to the stand at the end of the rotation. The importance of the recycling processes was clearly shown by the small amounts of nutrients permanently immobilized in the ligneous components of trees, compared with the total requirements accumulated over the stand rotation which were two to four times higher. Small pools of nutrients circulating quickly in the ecosystem made it possible to produce high amounts of biomass in poor soils. The sustainability of these plantations will require fertilizer inputs that match the changes in soil fertility over successive rotations, mainly linked to the dynamics of organic matter in this tropical soil.

Changes in Production and Nutrient Cycling across a Wetness Gradient within a Floodplain Forest

Floodplain forest ecosystems are highly valuable to society because of their potential for water quality improvement and vegetation productivity, among many other functions. Previous studies have indicated that hydrology influences productivity but that the relationship between hydroperiod and productivity is a complex one. Consequently, we compared multiple indexes of productivity, nutrient circulation, and hydroperiod among three communities on the Flint River floodplain, Georgia, that differed in terms of inundation frequency. We hypothesized that (a) the wettest community would have the lowest total net primary production (NPP) values because of saturated soil conditions; (b) as wetness increases, nutrient circulation in litterfall would decrease because of the hypothesized lower productivity in the wetter community; and (c) as wetness increases, internal translocation would become more efficient. The study site was partitioned into three wetness types—somewhat poorly drained (SPD), intermediate (I) and poorly drained (PD). We found that belowground biomass was greatest on the SPD, litterfall was similar for all three sites, and that woody biomass current annual increment (CAI) was greatest in the PD community. However, when the three variables were totaled for each site, the PD had the greatest NPP, thus disproving hypothesis (a). For hypothesis (b), we observed that P content in litterfall, although not significant, followed the predicted trend; nitrogen (N) content displayed the opposite pattern (PD > I > SPD). As wetness increased, internal translocation became more efficient for phosphorus (support for hypothesis [c]), but the SPD community was more efficient at retranslocating N (contradiction of hypothesis [c]).

COLONY INTEGRATION DURING REGENERATION IN THE STONY CORALFAVIA FAVUS

Modular organisms consist of repeated building blocks. An important con- sequence of modularity may be reflected in the ability of a colony to continually reallocate priority of resource transport among its units in response to stress. Hermatypic corals, the main organisms constructing tropical reefs, are prone to damage by a multitude of agents. Since colonization of lesions by competitors is a potent threat to colonial organisms, fast recovery is an important component of colony survival. Previous regeneration studies have claimed that the energy requirements of this essential process are fueled only by the polyps directly bordering the injured area. This ''localized regeneration hypothesis'' rejects the necessity for wide colony integration during regeneration and sees no advantage to large colony size. The objective of the present study was to test an alternative regeneration hypothesis that argues, in contrast, that injury repair (i.e., closure of lesions by newly formed tissues) in corals may require extended colony integration (i.e., internal translocation of resources from sites of acquisition to sites of maximal demand). To test our hypothesis we examined: (1) the relationship between colony size and percentage recovery of lesions differing in size and shape; and (2) the effect of different sized lesions on the fecundity of polyps located at increasing distances from the lesion site. Both experiments were conducted on the common, spherically shaped coral Favia favus in the Red Sea near Eilat, Israel. The relatively small lesions ( , 1c m 2 ) were the only ones to support the localized regeneration hypothesis, since their recovery was unaffected by colony size. However, the two larger lesion types (approximate sizes of 2 cm 2 and 3c m 2 ) confirmed the importance of large colony size for achieving fast recovery. In the second experiment we found that small lesions, repeated monthly, caused only a localized reduction in fecundity, while larger monthly repeated lesions caused significant reductions in fecundity up to a distance of 15 cm away from their site. Both experiments indicate that regeneration from injury may require an extended magnitude of energy integration throughout the colony, and that the extent of this integration is regulated by the colony in accordance with lesion characteristics. It is also concluded that in long-lived organisms such as corals, there is a priority of energy allocation to recovery rather than to reproduction. Our findings reveal the existence of injury thresholds within a colony that determine energy allocation and intra-colonial trans- location of energy products toward regions of maximal demand. We suggest that such injury thresholds may characterize many other coral species and that colony integration during stress is a basic life-preserving ability and one of the most important advantages of clonal and colonial organisms.

Internal Nutrient Translocation in Chestnut Tree Stemwood: III. Dynamics Across an Age Series of Castanea sativa(Miller)

Nutrient translocation in chestnut tree stemwood was calculated from the distribution of nutrient content throughout the tissue life-span. The dynamics of internal translocation were followed during the crop rotation by means of an age series of five coppiced stands (2–19 years). N, P, K, Ca and Mg contents in tree rings were estimated from the concentrations along a vertical and radial gradient and from the ring volume obtained using stem ring analysis. Real nutrient translocationwas calculated stepwise between successive stages in the age series; apparent translocationwas computed on a complete tree rotation by comparing the initial content just after the ring was formed with the mineral content in the oldest stand. There was a marked translocation of N, P, K and Ca when the rings were physiologically-active tissues. Real translocation of N, P and K (but not Ca) increased with stand age, obviously in parallel with the enlarged stemwood biomass reaching 23.2 and 20.6 kg ha -1for K and N in the last years of rotation, nearly 5 kg ha -1for Mg and about 3 kg ha -1for Ca and P. Potassium was the most mobile element since translocation reached 60% of the total amount immobilized in the stemwood at the end of the rotation, whereas values for N, P and Mg were approximately 25% and 10% for calcium. Total apparent translocation reached respectively 39.2 and 32.4 kg ha -1for K, N, approximately 12 and 7 kg ha -1for Mg and Ca and only 4.4 kg ha -1for P. Total apparent translocation as a percentage of total wood immobilization was 114% for K, 83% for Mg, 63% for P, but only 39% for N and 24% for calcium.

Nutrient dynamics of chestnut tree ( Castanea sativa Mill.) coppice stands

A chronosequence of chestnut coppice stands was used to study nutrient dynamics in an ecosystem during stand development. The strategy of the ecosystem was demonstrated in this study: to achieve a large biomass production under conditions of limited nutrient availability. Contrary to what is generally expected, forest production has high nutrient requirements. Perennial vegetation fulfilled half its requirements of N, P and K from internal translocation of nutrients that were reused when physiological activity ceased; the remaining part was taken up from available soil reserves. Half of the uptake returned to the soil, mainly as litterfall. As a result, overal immobilization was low. As a consequence, decreasing the rotation length will enhance the depletion of forest soil nutrients, as will harvesting a larger part of the forest biomass and hence the smaller biomass compartments, which contain most of the nutrients in the vegetation. Dynamics of biological fluxes clearly show the importance of tree vegetation on soil mineral functions, especially by continuously returning organic matter and nutrients back to the soil surface.

Genotype–nutrition interactions in field-planted loblolly pine

Four families of loblolly pine (Pinustaeda L.), representing a productivity gradient, were compared to determine inherent differences in productivity and nutrient efficiency for two nutrient regimes. The nutrient regimes consisted of a nonfertilized treatment, representing a deficiency of N, P, and K, and a fertilized treatment, ensuring an adequate supply of N, P, and K. Nutrient efficiency was determined using the traditional measure of nutrient use efficiency and alternative measures, including biomass and nutrient accumulation over time, element ratios, specific absorption rate, internal translocation, and a graphical technique. Family and nutrient regime differences were found in biomass production, biomass allocation, and nutrient efficiency. Of the nutrient efficiency measures, biomass and nutrient accumulation, nutrient use efficiency, and specific absorption rate tended to mirror family productivity differences. Family variation in element ratios, internal translocation, and the graphical technique did not mirror biomass production and, thus, were able to provide additional information on specific nutrient use mechanisms of efficiency that is not provided by traditional nutrient use efficiency calculations, the latter being confounded by biomass production.

Identification and characterization of a low-affinity granulocyte- macrophage colony-stimulating factor receptor on primary and cultured human melanoma cells

Hematopoietic growth factor receptors are present on cells of normal nonhematopoietic tissues such as endothelium and placenta. We previously demonstrated functional human granulocyte-macrophage colony- stimulating factor (GM-CSF) receptors on small cell carcinoma of the lung cell lines, and others have reported that certain solid tumor cell lines respond to GM-CSF in clonogenic assays. In the current study, we examine human melanoma cell lines and fresh specimens of melanoma to determine whether they have functional GM-CSF receptors. Scatchard analyses of 125I-GM-CSF equilibrium binding to melanoma cell lines showed a mean of 542 +/- 67 sites per cell with a kd of 0.72 +/- 0.14 nmol/L. Cross-linking studies in the melanoma cell line, M14, showed a major GM-CSF receptor species of 84,000 daltons. Under the conditions tested, the M14 cells did not have a proliferative response to GM-CSF in vitro, nor was any induction of primary response genes detected by Northern analysis in response to GM-CSF. Studies to determine internal translocation of the receptor-ligand complex indicated less than 10% of the 125I-GM-CSF internalized was specifically bound to receptors. Primary melanoma cells from five surgical specimens had GM-CSF receptors; Scatchard analysis was performed on one sample, showing 555 sites/cell with a kd of 0.23 nmol/L. These results indicate that human tumor cells may express a low-affinity GM-CSF receptor protein that localizes to the cell surface and binds ligand, but lacks functional components or accessory factors needed to transduce a signal.

Identification and Characterization of a Low-Affinity Granulocyte-Macrophage Colony-Stimulating Factor Receptor on Primary and Cultured Human Melanoma Cells

Hematopoietic growth factor receptors are present on cells of normal nonhematopoietic tissues such as endothelium and placenta. We previously demonstrated functional human granulocyte-macrophage colony-stimulating factor (GM-CSF) receptors on small cell carcinoma of the lung cell lines, and others have reported that certain solid tumor cell lines respond to GM-CSF in clonogenic assays. In the current study, we examine human melanoma cell lines and fresh specimens of melanoma to determine whether they have functional GM-CSF receptors. Scatchard analyses of 125I-GM-CSF equilibrium binding to melanoma cell lines showed a mean of 542 +/- 67 sites per cell with a kd of 0.72 +/- 0.14 nmol/L. Cross-linking studies in the melanoma cell line, M14, showed a major GM-CSF receptor species of 84,000 daltons. Under the conditions tested, the M14 cells did not have a proliferative response to GM-CSF in vitro, nor was any induction of primary response genes detected by Northern analysis in response to GM-CSF. Studies to determine internal translocation of the receptor-ligand complex indicated less than 10% of the 125I-GM-CSF internalized was specifically bound to receptors. Primary melanoma cells from five surgical specimens had GM-CSF receptors; Scatchard analysis was performed on one sample, showing 555 sites/cell with a kd of 0.23 nmol/L. These results indicate that human tumor cells may express a low-affinity GM-CSF receptor protein that localizes to the cell surface and binds ligand, but lacks functional components or accessory factors needed to transduce a signal.

Oncogenes and 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 circumstances, such as following transduction by retroviruses, activation of these genes causes tumors and leukemias in animals. Possible mechanisms of cellular oncogene activation include: 1) DNA point mutation, deletion or insertion, 2) gene amplification, 3) gene activation by internal rearrangement, chromosomal translocation or promoter insertion, 4) recombinative events resulting in the formation of novel chimeric genes, and others. In this review, we consider data which implicates cellular oncogene activation in the pathogenesis of leukemia in humans. We discuss possible mechanisms by which oncogene activation may induce leukemias, as well as potential diagnostic and therapeutic implications.