Gluconeogenesis from amino acids in germinating castor bean endosperm and its role in transport to the embryo

During germination of the castor bean all of the contents of the endosperm are ultimately transported to the embryo through the cotyledon or respired. A net loss of nitrogen from the endosperm begins about the fourth day, i.e. at the time when embryo growth and fat breakdown are also beginning. Amino acid analysis of the exudate from the cotyledons, still enclosed in the endosperm, showed that the amounts of aspartate, glutamate, glycine, and alanine were very low and that glutamine made up 40% of the amino acids in the exudate.

Amino acids labeled with ¹⁴C were applied to intact excised endosperms to follow utilization. Aspartate, glutamate, alanine, glycine, serine, and leucine were converted to sugar to varying extents. Proline, arginine, valine, and phenylalanine were not appreciably converted to sugars. Proline and glutamate were converted to glutamine. When ¹⁴C-glutamate, aspartate, and alanine were added to the outer endosperm of intact seedlings, only sugars and glutamine contained appreciable label in the exudate. When ¹⁴C-valine was added, it was virtually the only labeled compound in the exudate.

The results show that amino acids which on deamination can give rise to intermediates in the pathway of conversion of fat to sucrose are largely converted to sucrose and the nitrogen transported as glutamine. Other amino acids released from the endosperm protein are transported intact into the seedling axis. Some carbon from the gluconeogenic amino acids is also transported as glutamine.

     

Transport of purine and pyrimidine bases and nucleosides from endosperm to cotyledons in germinating castor bean seedlings

During germination and early growth of castor bean (Ricinus communis), all cellular constituents of the endosperm are eventually transferred to the growing embryo. The present results bear on the transport of breakdown products of nucleic acids. The total content of nucleic acids and nucleotides declines rapidly between day 4 and day 8 of seedling development. Concomitant with this decline, a secretion of adenosine, guanosine, and adenine from excised endosperms into the incubation medium takes place, accompanying a much more extensive release of sucrose and amino acids. Release of nucleotides could not be detected. The rates of release were linear for at least 5 hours for all compounds measured, indicating that they were liberated due to a coordinated metabolism. Uptake studies with cotyledons removed from the seedling showed that these have the ability to absorb all the substances released from the endosperm. Besides sucrose and amino acids, both nucleosides and free purine and pyrimidine bases were taken up by the cotyledons with high efficiency. AMP was also transported whereas ATP was not. Kinetic analyses were carried out to estimate the maximal uptake capacities of the cotyledons. Rates of uptake were linear for at least 1 to 2 hours and saturation kinetics were observed for all substances investigated. It is concluded that nucleosides can serve best as transport metabolites of nucleic acids, inasmuch as they are taken up by the cotyledons with the highest efficiency, the V_max/K_m ratios being considerably higher than those found for free purine and pyrimidine bases. For both adenosine and adenine transport, the V_max was about 2 micromoles per hour per gram fresh weight, and the K_m values were 0.12 and 0.37 millimolar, respectively. The rates of metabolite release from the endosperm and the capacity of the absorption system in the cotyledons are shown to account for the observed rates of disappearance of nucleic acids from the endosperm and efficient transport to the growing embryo.     

Sugar uptake and translocation in the castor bean seedling I. Characteristics of transfer in intact and excised seedlings

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.The ability of the cotyledons to absorb sucrose survived removal of the endosperm from the seedling. A series of experiments is described in which the cotyledons of such excised seedlings were immersed in sucrose-(14)C and measurements made of uptake and of translocation to various parts of the seedling. Increasing rates of absorption were observed as the sucrose concentration was raised to 0.5 m and these rates were maintained for several hours. Removal of the embryonic axis (hypocotyl plus roots) drastically altered both the response to sucrose concentration and the time course of absorption by the cotyledons.More than 80% of the sugar normally entering the cotyledons from the endosperm is transmitted to the embryonic axis and this extensive turnover was seen also in pulse/chase experiments with excised seedlings. The cotyledons of excised seedlings absorbed sucrose against high apparent concentration gradients. The absorption was stimulated by phosphate and had a pH optimum at about pH 6.4. It was inhibited by arsenate, azide and 2,4-dinitrophenol.     

The differential transport of amino acids into the phloem of Ricinus communis L. seedlings as shown by the analysis of sieve-tube sap

The cotyledons of castor bean (Ricinus communis L.) act as absorption organs for amino acids, which are supplied to the medium. The analysis of the sieve-tube sap, which exudes from the cut hypocotyl, demonstrated the ability of the cotyledons to load particular amino acids into the phloem and to reject the loading of others. The sieve-tube sap of cotyledons, which were embedded in the endosperm, contained 150 mM amino acids, with 50 mM glutamine as the major amino acid, and 10–15 mM each of valine, isoleucine, lysine and arginine. Removal of the endosperm led to a drastic decline in the amino-acid content of sieve-tube sap down to 16 mM. Addition of single amino acid species to the medium increased the amino acid concentration in the sieve-tube sap in specific manner: glutamine caused the largest increase (up to 140 mM in exudate), glutamate and alanine smaller increases (up to 60 mM), and arginine the smallest. In addition, the amino acid composition of the sieve-tube sap changed, for instance, glutamine or alanine readily appeared in the sieve-tube sap upon incubation in glutamine or alanine, respectively, whereas glutamate was hardly discernible even in the case of incubation with glutamate; arginine was loaded into the sieve tubes only reluctantly. In general, glutamine and alanine accumulated four- to tenfold in the sieve tubes. The uptake of amino acids and of sucrose into the sieve tubes was interdependent: the loading of sucrose strongly reduced the amino acid concentration in the sieve-tube exudate and loading of amino acids decreased the sucrose concentration. Comparison of the concentrations of various amino acids on their way from the endosperm via the cotyledon-endosperm interface, through the cotyledons and into the sieve tubes showed that glutamine, valine, isoleucine and lysine are accumulated on this pathway, whereas glutamate and arginine are more concentrated in the cotyledons than in the sieve tubes. Obviously the phloem-loading system has a transport specificity different from that of the amino acid uptake system of the cotyledon in general and it strongly discriminates between amino acids within the cotyledons.     

The effect of the embryo axis and exogenous sucrose on lipolysis and glyoxysomal enzyme development in Ricinus communis (castor bean) endosperm and cotyledons

Post-germinative growth in castor bean ( Ricinus communis L. cv. Hale) seedlings was investigated to determine whether lipolytic enzyme synthesis and lipid breakdown was a function of the embryo axis or simply based on a source-sink mechanism connected with sucrose produced during mobilization of storage lipid. Endosperm and cotyledons were excised from the embryo axis at 24 h intervals and were then incubated in Petri dishes containing water or 0.1 M sucrose for 24 h. Excised endosperm showed similar or higher malate synthase (MS, EC 4.1.3.2) and isocitrate lyase (ICL, EC 4.1.3.1) activities and increased lipolysis when compared with endosperm obtained from similarly intact seedlings of the same age. In contrast, cotyledonary ICL and MS activity was up to 50% lower and lipolysis was only slightly affected in excised material when compared with cotyledons obtained from intact seedlings. Incubating endosperm in sucrose had no effect on the development of the above enzyme activities or lipid content, when compared with material incubated in water only. In contrast, cotyledonary MS and ICL activities were up to 70% lower in sucrose and lipolysis substantially inhibited. Lipid breakdown and the development of lipolytic enzyme activity in cotyledons seem to be dependent on the presence of the endosperm. It is concluded that enzyme regulation in castor bean seedlings cannot entirely be explained by axis control or source-sink relationships.     

Osmoregulation in hypocotyls of etiolated mung bean seedlings with or without cotyledons in response to water-deficient stress

Effects of water-deficient stress and cotyledon excision on osmoregulation in hypocotyls of dark-grown mung bean seedlings were studied, and following results were obtained. Water-deficient stress inhibited hypocotyl elongation either in intact or decotylized seedlings. The inhibition was more conspicuous in decotylized seedlings than in intact ones. Water-deficient stress decreased osmotic potential in hypocotyls, while cotyledon excision increased it. The concentrations of soluble sugars, free amino acids and potassium ions in hypocotyls of intact or decotylized seedlings increased in response to water-deficient stress. Cotyledon excision reduced the concentration of soluble sugars and free amino acids, but it did not change the concentration of potassium ions, suggesting that a part of soluble sugars and free amino acids is transported from cotyledons. Unlike cotyledon excision, excision of the apex or roots had no influence on osmoregulation in response to water-deficient stress. Segments excised from hypocotyls had the ability to osmoregulate in response to water-deficient stress. Based on these results, the role of cotyledons in osmoregulation in response to water-deficient stress and quantitative relationships between osmotic potential and hypocotyl elongation in etiolated mung bean seedlings are discussed.     

Evidence for amino-acid: proton cotransport in Ricinus cotyledons

During germination and early growth of the castor-bean (Ricinus communis L.), protein in the endosperm is hydrolyzed and the amino acids are transferred into the cotyledons and then via the translocation stream to the axis of the growing seedling. The cotyledons retain the ability to absorb amino acids after removal of the endosperm and hypocotyl, exhibiting rates of transport up to 70 mol g^-1 h^-1. The transport of L-glutamine was not altered by KCl or NaCl in low concentrations (0–20 mM). High concentrations of KCl (100 mM) inhibited transport, presumably by decreasing the membrane potential. An increase in the pH of the medium bathing the cotyledons was observed for 10 min following addition of L-glutamine but not with D-glutamine, which is not transported. The rate of proton uptake was dependent on the concentration of L-glutamine in the external solution. Inhibitors and uncouplers of respiration (azide, 2, 4-dinitrophenol, carbonyl cyanide phenylhydrazone and N-ethylmaleimide) inhibited both L-glutamine uptake and L-glutamine-induced proton uptake. Amino acids other than L-glutamine also caused a transient pH rise and the rate of proton uptake was proportional to the rate of amino-acid uptake. The stoichiometry was 0.3 protons per amino acid transported. Addition of sucrose also caused proton uptake but the alkalisation by sucrose and by amino acids were not additive. Nevertheless, when sucrose was added 60 min after providing L-glutamine at levels saturating its uptake system, a rise in pH was again observed. The results were consistent with amino-acid transport and sucrose transport in castor-bean cotyledons both occurring by a proton cotransport in the same membrane system but involving separate carriers.     

Lectins in castor bean seedlings

The amounts of the two lectins (ricin and Ricinus communis agglutinin) in tissues of castor bean seedlings were followed during germination and early growth. For measurement, lectins in extracts were separately eluted from Sepharose columns; an antibody to the agglutinin was also used to detect the lectins by immunodiffusion. The endosperm of the dry seed contains 3.5 mg total lectin (5.6% of the total seed protein), which declines by 50% by day 4 and more rapidly thereafter as the tissue is completely consumed. The cotyledons of the dry seed also contain lectins but the amounts are less than 1% of those in the endosperm, and, as in the endosperm, they are constituents of the albumin fraction of the isolated protein bodies. No lectins were detected in the green cotyledons of 10-day seedlings that had been exposed to light from day 5. The embryonic axes of 2-day seedlings contained very small amounts of lectins but they were not detectable in the aerial parts of seedlings grown for 3 weeks or in cells from endosperm grown in tissue culture.

The ability of proteinases and glycosidases (isolated from endosperm of 4-day seedlings) to hydrolyze the lectins was examined. No hydrolysis of the two lectins was observed, but the subunits, separated by reduction with 2-mercaptoethanol, were hydrolyzed slowly by a proteinase and some release of mannose was observed in the presence of the glycosidases. Ricin was converted to its subunits by cysteine and an enzyme in an endosperm extract accelerated chain separation by glutathione.

     

Characterization of the activity of fatty-acid epoxide hydrolase in seeds of castor bean (Ricinus communis L.)

Epoxide hydrolase (EC 3.3.2.3) activity was measured with [1-¹⁴C]cis-9,10-epoxystearic acid as the substrate. Homogenates were prepared from the endosperm tissue of germinating seeds of castor bean (Ricinus communis L. zanzibariensis). The activity of fatty-acid epoxide hydrolase was characterized with respect to dependence on time, amount of protein, pH and temperature. Analyses of enzyme distribution in endosperm, cotyledons, root and hypocotyl showed the highest total activity in the endosperm, less in the cotyledons and low activity in the root and hypocotyl. The specific activity was similar for cotyledons and endosperm. Analysis of the temporal expression of the enzyme in the endosperm during germination revealed high activity already in the imbibed seed. Activity was maximal between days four to six and then decreased at the end of one week. Subcellular fractionation of endosperm revealed a dual distribution of activity between the glyoxysomal and the cytosolic fractions.     

Respiratory Changes During Seed Germination. Histological Distribution of Respiratory Enzymes and Mobilization of Fat Reserves in Castor Bean Endosperm and Peanut Cotyledons

Germinating peanut cotvledons and germinating castor bean endosperm have been compared with respect to their rates of fat dissimilation and with respect to the anatomical distribution of respiratory activity. The lipid mobilization is much slower in peanut cotyledons than in castor bean endosperm. Light has essentially no effect on either system. As germination progresses, the majority of the succinic dehydrogenase and cytochrome oxidase activities become localized in the vein regions of peanut cotyledons. In the castor bean endosperm these two activities are uniformly distributed throughout the storage parenchyma and increase with germination until the organ becomes soft and visibly senescent.     

Stimulation of phosphatidylethanolamine exchange by castor bean cytosol proteins

Cytosol proteins prepared from castor bean endosperm (4-day-old) seedlings stimulate the exchange of [³H]phosphatidylethanolamine between liposomes and mitochondria. The acceleration of the exchange depends on the quantity of cytosol proteins, the time of incubation, and the respective amounts of liposomes and mitochondria. On a per seedling basis, the active proteins are essentially located in the endosperm, whereas the roots and the cotyledons are less rich in these proteins.     

Diverse transporters for neutral amino acids in Ricinus communis L. seedlings

Uptake mechanisms for neutral amino acids were investigated by expression of mRNA isolated from seedlings of Ricinus communis L. in Xenopus laevis oocytes. After injection of mRNA from root, hypocotyl and cotyledon currents elicited by saccharose and neutral amino acids ranged from 0.3 nA up to 2 nA depending on the respective substrate and the source of mRNA. These currents were due to expression of low affinity uptake mechanisms and the KM values found for amino acid induced charge flow range from 1 to 2 mM. The abundance and/or the specificity of the expressed mechanisms differ in the various tissues. Currents of similar magnitude were recorded for alanine and glutamine with mRNA isolated from root, hypocotyl and cotyledons. Serine and proline induced currents after injection of mRNA from hypocotyl and roots, in case of α-aminoisobutyric acid (AIB) induced currents were generally small with mRNA from all tissues tested. In addition, differential sensitivity of glutamine and AIB uptake in the high affinity range was evident towards the amino acid analogue 2-chloro-aminophenoxybutyric acid which indicated an additional set of carriers operating in the micromolar concentration range. The results suggest that multiple transporters for neutral amino acids exist in various tissues of the plant differing in specificity of charge flow and in sensitivity towards the inhibitor 2-chloro-aminophenoxybutyric acid. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mechanism of amino Acid uptake by sugarcane suspension cells

The amino acid carriers in sugarcane suspension cells were characterized for amino acid specificity and the stoichiometry of proton and potassium flux during amino acid transport.

Amino acid transport by sugarcane cells is dependent upon three distinct transport systems. One system is specific for neutral amino acids and transports all neutral amino acids including glutamine, asparagine, and histidine. The uptake of neutral amino acids is coupled to the uptake of one proton per amino acid; one potassium ion leaves the cells for charge compensation. Histidine is only taken up in the neutral form so that deprotonation of the charged imidazole nitrogen has to occur prior to uptake. The basic amino acids are transported by another system as uniport with charge-compensating efflux of protons and potassium. The acidic amino acids are transported by a third system. Acidic amino acids bind to the transport site only if the distal carboxyl group is in the dissociated form (i.e. if the acidic amino acid is anionic). Two protons are withdrawn from the medium and one potassium leaves the cell for charge compensation during the uptake of acid amino acids. Common to all three uptake systems is a monovalent positively charged amino acidproton carrier complex at the transport site.

     

Characteristics and development of leucine transport activity in the scutellum of germinating barley grain

Scutella separated from grains of Himalaya barley after germination for 3 days rapidly took up l-leucine from aerated incubation media; with 1 millimolar leucine the rate varied between 4 and 14 micromoles per gram per hour and the pH optimum was at 3.5 to 5, both depending on buffer composition and prewashing time. The rate of the uptake increased with increasing concentration of leucine in a complex manner, which could be interpreted as multiphasic kinetics with apparent K(m) values of 3.4 and 15.5 millimolar below and above 3 millimolar leucine, respectively. The uptake took place against a concentration difference (highest estimated ratio 270: 1) and was strongly inhibited by dinitrophenol. Uptake was apparently due to active transport requiring metabolic energy.The development of the uptake activity during germination was studied using Pirkka barley. A low activity was present in the scutella of ungerminated grains. It began to increase after 6 hours imbibition, and the increase was biphasic, the major changes occurring during days 0 to 3 and 4 to 6. The total increase was about 20-fold.The regulation of the development was studied by allowing separated embryos to germinate on agar gel. The increase of uptake activity was strongly inhibited by inhibitors of RNA or protein synthesis. Increase did not require the presence of the embryo proper, and was not affected by gibberellic or abscisic acid. Removal of the endosperm greatly accelerated the increase of uptake activity, and the presence of 5 or 20 millimolar glutamine counteracted the removal of the endosperm. The results suggest that the availability of glutamine or amino acids in general in the endosperm may regulate the development or the activity of the transport system.     

INFLUENCE OF AMMONIUM AND NITRATE ON THE PROTEIN- AND FREE AMINO ACIDS IN SHOOTS OF WHEAT SEEDLINGS

Weissman , Gerard S. (Rutgers U., Camden, N. J.) Influence of ammonium and nitrate on the protein- and amino acids in shoots of wheat seedlings. Amer. Jour. Bot. 46(5): 339–346. 1959.—Total and protein nitrogen per shoot of wheat seedlings grown with endosperm attached increased at a steady rate during a 96-hr. growth period, and protein nitrogen, as a percentage of total nitrogen, remained constant at about 53%. Total and protein nitrogen concentration was greatest for 24-hr. shoots and declined as the shoots became older. Total and protein nitrogen were determined in 96-hr. shoots of seedlings grown with endosperm attached but also supplied with ammonium, nitrate, or both in the culture solution. Total nitrogen was greatest in shoots supplied with ammonium, but only 38% was in the form of protein. Maximum protein synthesis occurred in shoots grown in both ammonium and nitrate and protein nitrogen as a percentage of total nitrogen approximated that achieved in shoots lacking nitrogen in the culture solution. The protein amino acid composition of 48-, 72-, and 96-hr. shoots was very similar but differed from 24-hr. shoots which contained higher percentages of arginine and lysine and lower percentages of alanine and threonine. This may be correlated with the higher proportion of meristematic cells in 24-hr. shoots. The protein amino acids in shoots grown with ammonium resembled that of shoots lacking nitrogen in the culture solution, but nitrate shoot protein contained a higher percentage of arginine and a lower percentage of lysine. Nitrate may stimulate the formation of enzymes, possibly of a nitrate-reducing system, with high arginine- low lysine content. Free asparagine and glutamine were both at a maximum in ammonium shoots and at a minimum in nitrate shoots, but asparagine predominated in shoots supplied with ammonium while glutamine was greatest in nitrate shoots. Aspartic acid, asparagine, and glutamine appeared to have ammonia-storage functions, but glutamic acid appeared to be primarily concerned with protein synthesis. Amino acid accumulation was greatest in shoots supplied with both ammonium and nitrate. Protein synthesis in these appeared to be limited by inadequate concentrations of glutamic acid and proline. A hypothesis is proposed in explanation of the high glutamic acid concentration in shoots provided with ammonium and nitrate.     

Gradients of turgor, osmotic pressure, and water potential in the cortex of the hypocotyl of growing ricinus seedlings : effects of the supply of water from the xylem and of solutes from the Phloem

To evaluate the possible role of solute transport during extension growth, water and solute relations of cortex cells of the growing hypocotyl of 5-day-old castor bean seedlings (Ricinus communis L.) were determined using the cell pressure probe. Because the osmotic pressure of individual cells (πⁱ) was also determined, the water potential (ψ) could be evaluated as well at the cell level. In the rapidly growing part of the hypocotyl of well-watered plants, turgor increased from 0.37 megapascal in the outer to 1.04 megapascal in the inner cortex. Thus, there were steep gradients of turgor of up to 0.7 megapascal (7 bar) over a distance of only 470 micrometer. In the more basal and rather mature region, gradients were less pronounced. Because cell turgor ≈ πⁱ and ψ ≈ 0 across the cortex, there were also no gradients of ψ across the tissue. Gradients of cell turgor and πⁱ increased when the endosperm was removed from the cotyledons, allowing for a better water supply. They were reduced by increasing the osmotic pressure of the root medium or by cutting off the cotyledons or the entire hook. If the root was excised to interrupt the main source for water, effects became more pronounced. Gradients completely disappeared and turgor fell to 0.3 megapascal in all layers within 1.5 hours. When excised hypocotyls were infiltrated with 0.5 millimolar CaCl₂ solution under pressure via the cut surface, gradients in turgor could be restored or even increased. When turgor was measured in individual cortical cells while pressurizing the xylem, rapid responses were recorded and changes of turgor exceeded that of applied pressure. Gradients could also be reestablished in excised hypocotyls by abrading the cuticle, allowing for a water supply from the wet environment. The steep gradients of turgor and osmotic pressure suggest a considerable supply of osmotic solutes from the phloem to the growing tissue. On the basis of a new theoretical approach, the data are discussed in terms of a coupling between water and solute flows and of a compartmentation of water and solutes, both of which affect water status and extension growth.     

Biosynthesis of nonspecific lipid transfer proteins in germinating castor bean seeds

The biosynthesis of nonspecific lipid transfer proteins (ns-LTPs) in germinating castor bean (Ricinus communis L.) seeds were investigated. Lipid transfer activities of ns-LTPs in the cotyledons, axis, and endosperm increased with growth after germination. The activity increases were accompanied by increased amounts of ns-LTPs in each tissue, as measured by immunoblot using anti-ns-LTP serum. These results suggest that the ns-LTPs are synthesized de novo in each tissue after germination and not activated from inactive proteins synthesized before germination. Comparison of the immunoblot products in each tissue from 4-day-old seedlings indicate the occurrence of tissue-specific isoforms of ns-LTPs; 9 kilodaltons (major) and 7 kilodaltons (minor) in the cotyledons, and 7 kilodaltons (major) and 9 kilodaltons (minor) in the axis, whereas only the 8-kilodalton ns-LTP is present in the endosperm. In vitro translation from poly(A)⁺ RNAs from three tissues of castor bean seedlings and the detection of immunoprecipitated products indicate that translatable mRNAs for ns-LTPs exist in the three tissues a day before the synthesis of ns-LTPs; the translation products, which are 3.5 to 4.0 kilodaltons larger than ns-LTPs, were processed to the mature ns-LTPs. The production of mature ns-LTPs from translatable mRNAs without any delay suggests that gene expression of ns-LTPs in castor bean seedlings is controlled at a step before the formation of translatable mRNAs.     

Mobilization of Endosperm Reserves and Uptake of Sucrose and Valine by the Cotyledons of Euphorbia lathyris L.

Upon germination, the endosperm triacylglycerols and proteinswere converted to sucrose and amino acids. During early postgerminativegrowth, the rate of sucrose and amino acid production exceededthe rate of uptake by the cotyledons. As a result, the levelsof total amino acid and sucrose in the endosperm increased;maximum levels were reached at 7 d and 10 d after imbibition(DAI), respectively. Intact seedlings were used to measure thedevelopment of valine, arginine, glutamic acid, and sucroseuptake rate throughout the course of endosperm depletion. Maximumamino acid uptake rates were measured at around 9 DAI, the highestuptake rate for sucrose was obtained at 12 DAI (just beforedepletion of the endosperm). The daily increase of sucrose andamino acid uptake could be manipulated, by replacing the endospermwith a pre-incubation solution during 1 d. The increase in sucroseuptake in vitro was equal to that measured with intact seedlingswhen the cotyledons were pre-incubated in 10 mol m^–3 sucrose.Higher sucrose concentrations reduced the increase of sucroseuptake; at 300 mol m^–3 sucrose (corresponding to the meanendosperm sucrose concentration) sucrose uptake after pre-incubationwas even lower than before. This reduction was largely counteractedwhen the pre-incubation solution was supplemented with minerals.The development of the valine uptake was hardly affected bysucrose, but was inhibited by several amino acids. Key words: Euphorbia lathyris seedling, sucrose uptake, amino acid uptake, reserve mobilization