Long-term regulation of sucrose intake by the female mosquito, Aedes taeniorhynchius

Newly emerged female Aedes taeniorhynchus were maintained in cups provided with potometers containing 5, 10, and 25% sucrose solutions. Mortality and the ab lib. intake of sucrose were recorded daily and groups were sampled at regular intervals for analysis of energy reserves.After a week of relatively substantial intake of sucrose at all three concentrations, a constancy in daily intake at much lower levels was observed during the next 4 weeks. The caloric intake was highest in the 25% sucrose solution group. There were no differences in mortality rates at these concentrations. Glycogen (0·7–1·0 cal/female) and triglycerides (3·5dash4 cal/female) reserves reached maximum levels after the first week and stabilized thereafter on all three concentrations. In this species the stabilization in intake of sucrose solution after the first week is correlated with the maximum accumulation of stored energy reserves as opposed to decreased activity or subtle changes associated with senescence.     

Oral sucrose stimulation increases accumbens dopamine in the rat

Although taste can influence meal size and body weight, the neural substrate for these effects remains obscure. Dopamine, particularly in the nucleus accumbens, has been implicated in both natural and nonnatural rewards. To isolate the orosensory effects of taste from possible postingestive consequences, we investigated the quantitative relationship between sham feeding of sucrose and extracellular dopamine in the nucleus accumbens with microdialysis in rats. Sucrose intake linearly increased as a function of concentration (0.03 M, 18.07 +/- 2.41 ml; 0.1 M, 30.92 +/- 2.60 ml; 0.3 M, 43.28 +/- 2.88 ml). Sham feeding also stimulated accumbens dopamine overflow as a function of sucrose solution concentration (0.03 M, 120.76 +/- 2.6%; 0.1 M, 140.28 +/- 7.8%; 0.3 M, 146.27 +/- 5.05%). A second experiment used the same protocol but clamped the amount of sucrose ingested and revealed a similar, concentration-dependent dopamine activation in the nucleus accumbens. This is the first demonstration of a quantitative relationship between the concentration-dependent rewarding effect of orosensory stimulation by sucrose during eating and the overflow of dopamine in the nucleus accumbens. This finding provides new and strong support for accumbens dopamine in the rewarding effect of sucrose.     

Energy intake rates and nectar concentration preferences by hummingbirds

Summary In a series of daul choice tests with large volume feeders, rufous hummingbirds preferred sucrose concentrations near those that maximized their instantaneous rates of energy intake. As predicted on theoretical grounds, energy intake rates increased with increasing sucrose concentration to a maximum then decreased above this maximum. Earlier experimental studies suggested that hummingbirds always prefer the highest available concentration. Our results are consistent with the data of these studies, but by using a wider range of concentrations than previous workers, we found that the hummingbirds discriminated against very concentrated solutions.     

Nectar feeding by the ant Camponotus mus: intake rate and crop filling as a function of sucrose concentration

In independent assays, workers of the ant Camponotus mus were conditioned to visit an arena where they found a large drop of sucrose solution of different concentrations, from 5 to 70% weight on weight (w/w). Single ants were allowed to collect the sucrose solution ad libitum, and feeding time, feeding interruptions, crop load, and intake rates were recorded. Feeding time increased exponentially with sucrose concentration, and this relationship was quantitatively described by the increase in viscosity with concentration corresponding to pure sucrose solutions. Ants collecting dilute solutions (5 to 15% w/w) returned to the nest with partial crop loads. Crop filling increased with increasing sucrose concentration, and reached a maximum at 42.6% w/w. Workers collecting highly concentrated solutions (70% w/w) also returned to the nest with a partially-filled crop, as observed for dilute solutions. Nectar intake rate was observed to increase with increasing sucrose concentration in the range 5 to 30% sucrose. It reached a maximum at 30.8%, and declined with increasing sucrose concentration. Results suggest that both sucrose concentration and viscosity of the ingested solution modulate feeding mechanics as well as the worker's decision about the load size to be collected before leaving the source.     

Selective choice of sucrose solution concentration by the hovering hawk mothMacroglossum stellatarum

To determine the preference of the hovering hawk mothMacroglossum stellatarum for different sugar concentrations, the foraging behavior of adults were analyzed under laboratory conditions. Six sucrose concentrations (range, 10–60%, w/w) were simultaneously offered in six artificial ab libitum feeders. The number of feeding bouts and the duration of each visit were automatically recorded and stored in a computer. Results showed that the frequency of visits to the feeders did not vary among the different solutions offered, but the gathered volume by the group attained a maximum at between 20 and 50% (w/w). Moths invested more time in front of the feeder with the more concentrated sugar solutions. It was assumed that factors different from maximizing energy intake, such as water balance and viscosity of concentrated nectars, have to be considered in order to understand the observed patterns of nectar choice.     

Increased oral and decreased intestinal sensitivity to sucrose in obese, prediabetic CCK-A receptor-deficient OLETF rats

CCK-A receptor-deficient Otsuka Long-Evans Tokushima fatty (OLETF) rats are hyperphagic and develop obesity and Type 2 diabetes. In this strain, taste preference functions have not been investigated. Therefore, a series of short-access, two-bottle tests were performed in age-matched prediabetic OLETF and nonmutant Long-Evans Tokushima Otsuka (LETO) rats to investigate preference for sucrose (0.03, 0.1, 0.3, or 1.0 M) presented with a choice of water. To discern orosensory from postgastric factors that may contribute to this preference, in a separate experiment, rats were allowed to sham feed sucrose in the absence or presence of duodenal sucrose infusion (0.3, 0.6, or 1.0 M). In the two-bottle real-feeding tests, OLETF rats exhibited a greater preference for 0.3 M sucrose (91.2 +/- 1.7 and 78.5 +/- 3.4% for OLETF and LETO, respectively; P < 0.01) and 1.0 M sucrose (65.3 +/- 1.2 and 57.5 +/- 2.7% for OLETF and LETO, respectively; P < 0.05) than LETO rats. OLETF rats also sham fed less of the lowest (0.03 M; 33.8 +/- 4.8 and 58.3 +/- 7.3 ml for OLETF and LETO, respectively; P < 0.05) and more of the highest (1.0 M; 109.9 +/- 6.5 and 81.0 +/- 3.9 ml for OLETF and LETO, respectively; P < 0.01) concentration of sucrose relative to LETO rats. Finally, intraduodenal sucrose infusions (0.6 and 1.0 M) produced a smaller reduction of 0.3 M sham sucrose intake [14.1 +/- 8.1 vs. 52.5 +/- 3.3 ml and 49.4 +/- 8.0 vs. 82.4 +/- 3.2 ml for 0.6 M (P < 0.01) and 1.0 M (P < 0.05) infusions in OLETF and LETO, respectively]. These findings demonstrate that OLETF rats display an increased preference for sucrose, an effect that is at least partially influenced by the orosensory stimulating effect of sucrose. This enhanced responsiveness to oral stimulation, coupled with the deficit in responding to the postingestive feedback of intestinal sucrose, may contribute additively to the development of hyperphagia and weight gain in OLETF rats.     

Sucrose dilution of frozen mouse embryos: interaction of glycerol and sucrose concentrations

Several concentrations of glycerol for cryoprotection and several concentrations of sucrose for cryoprotectant dilution were examined with frozen, thawed and cultured mouse embryos. Four hundred and eighty late morulae to early blastocyst stage embryos were collected from 35 superovulated mice (B6D2 x Swiss Webster crosses back-crossed to Swiss Webster males) 3-1/2 days after breeding. The embryos were transferred through increasing concentrations of glycerol in modified Dulbecco(1)s phosphate buffered saline (MDPBS) to reach three final concentrations of 1.0 M, 1.4 M and 1.8 M. The embryos were loaded in 0.5-ml French straws appropriately filled with the cryoprotectant and sucrose solutions for each treatment. The straws were cooled with a standard fast-freezing program to -35 degrees C, then plunged into liquid nitrogen. After 58 days of storage at -196 degrees C the straws were thawed in a 37 degrees C water bath. Cryoprotectant dilution was accomplished with a standard step-wise procedure or in the straw with one of three concentrations of sucrose solution (0.25 M, 0.5 M, 1.0 M) in MDPBS. The embryos were then washed twice in MDPBS, twice in Whitten's media for embryo culture and then placed in microdrops of Whitten's media under paraffin oil in a water saturated 5% CO(2) in air atmosphere at 37 degrees C. Embryos were observed 24 hours later for development to the expanded blastocyst stage. The proportion of embryos developing in vitro from the three glycerol concentrations were not significantly different with standard step-wise dilution procedures for glycerol removal. After step-wise cryoprotectant removal, blastocyst expansion occurred in 49%, 44% and 52% of embryos frozen in 1.0 M, 1.4 M and 1.8 M glycerol, respectively. The 1.0 M sucrose dilution of 1.0 M glycerol showed the highest development (60.5%) in vitro but was not significantly different from any of these three step-wise diluted glycerol concentrations. The step-wise dilution of the three glycerol concentrations and dilution of the 1.0 M glycerol and 1.0 M sucrose were all superior (P < 0.01) to any other dilution procedure examined.     

Serotonin type-3 receptors mediate cholecystokinin-induced satiation through gastric distension

We have previously shown that serotonin type-3 (5-HT3) receptors mediate cholecystokinin (CCK)-induced satiation and that this effect is dependent on postoropharyngeal feedback. However, the independent contributions of gastric and intestinal feedback in 5-HT3 receptor mediation of suppression of food intake by CCK have not been determined. Using a sham-feeding preparation combined with intraduodenal sucrose infusion, we show that blockade of 5-HT3 receptors by ondansetron (1 mg/kg ip) had no effect on suppression of sham feeding by intraduodenal 15% sucrose infusion (4 ml/10 min), CCK (2 microg/kg ip) administration, or the combination of the two treatments. In separate experiments consisting of either sham-feeding rats that received gastric distension with the use of a balloon or real-feeding rats whose stomachs were distended using gastric loads of saline after the occlusion of the pylorus, we tested the hypothesis that gastric feedback signals are necessary for activation of 5-HT3 receptors. Ondansetron significantly attenuated suppression of sham sucrose intake after a 10-ml gastric balloon distension (30.5 +/- 2.2 vs. 20.2 +/- 2.2 ml, respectively) and gastric distension combined with CCK (21.9 +/- 1.4 vs. 12.0 +/- 1.7 ml, respectively). When intestinal feedback was eliminated in a real-feeding paradigm by closing the pylorus using a cuff preparation, ondansetron attenuated suppression of sucrose intake produced by a 10-ml saline gastric load (6.8 +/- 0.7 vs. 4.2 +/- 0.4 ml, respectively). Finally, when CCK (1 microg/kg) was administered in combination with a 5-ml saline gastric load in a real-feeding preparation, ondansetron significantly attenuated suppression of sucrose intake by CCK (9.0 +/- 0.9 vs. 6.3 +/- 0.5 ml, respectively), as well as the enhanced suppression of intake by CCK plus gastric load (6.9 +/- 0.6 vs. 4.6 +/- 0.5 ml, respectively). These findings demonstrate that CCK-induced activation of 5-HT3 receptors requires gastric, but not intestinal feedback.     

Single amino acids in sucrose rewards modulate feeding and associative learning in the honeybee

Obtaining the correct balance of nutrients requires that the brain integrates information about the body’s nutritional state with sensory information from food to guide feeding behaviour. Learning is a mechanism that allows animals to identify cues associated with nutrients so that they can be located quickly when required. Feedback about nutritional state is essential for nutrient balancing and could influence learning. How specific this feedback is to individual nutrients has not often been examined. Here, we tested how the honeybee’s nutritional state influenced the likelihood it would feed on and learn sucrose solutions containing single amino acids. Nutritional state was manipulated by pre-feeding bees with either 1 M sucrose or 1 M sucrose containing 100 mM of isoleucine, proline, phenylalanine, or methionine 24 h prior to olfactory conditioning of the proboscis extension response. We found that bees pre-fed sucrose solution consumed less of solutions containing amino acids and were also less likely to learn to associate amino acid solutions with odours. Unexpectedly, bees pre-fed solutions containing an amino acid were also less likely to learn to associate odours with sucrose the next day. Furthermore, they consumed more of and were more likely to learn when rewarded with an amino acid solution if they were pre-fed isoleucine and proline. Our data indicate that single amino acids at relatively high concentrations inhibit feeding on sucrose solutions containing them, and they can act as appetitive reinforcers during learning. Our data also suggest that select amino acids interact with mechanisms that signal nutritional sufficiency to reduce hunger. Based on these experiments, we predict that nutrient balancing for essential amino acids during learning requires integration of information about several amino acids experienced simultaneously.     

Water restriction and fluid temperature alter preference for water and sucrose solutions

The role of diet temperature in ingestive behavior is poorly understood. We examined the importance of stimulus temperature and water-restriction state on the preference for and intake of water and sucrose. Using custom-designed equipment that allows us to monitor and maintain solution temperatures during testing (±0.1 °C), we conducted a series of 2-bottle preference tests (10 °C water vs. sucrose 10-40 °C) and brief access tests (10-40 °C water and sucrose). Water-restricted rats preferred cold water over any sucrose concentration (0.0-1.0 M) if the sucrose was 30 or 40 °C, whereas the same rats preferred sucrose at all concentrations and temperatures when unrestricted suggesting that the water-restriction state interacts with temperature preference. In a series of brief-access tests using a Davis Rig (MS-180), rats reduced licking to cold sucrose compared with 20 °C sucrose, suggesting that unlike water, cold temperature reduced the palatability of sucrose.     

Sugar preferences, absorption efficiency and water influx in a Neotropical nectarivorous passerine, the Bananaquit (Coereba flaveola)

Nectarivory has evolved repeatedly in a number of unrelated bird taxa throughout the world and nectar feeding birds, regardless of their taxonomic affiliation, display convergent foraging and food processing adaptations that allow them to subsist on weak sugar solutions. However, phylogeny influences sugar type preferences of nectarivores. We investigated sugar preferences, assimilation efficiency and water flux in a Neotropical honeycreeper, the Bananaquit (Coereba flaveola; Coerebidae), a member of a radiation of tanagers and finches. Bananaquits showed no preference for nearly equicaloric (25% w/v) sucrose, glucose, fructose or glucose-fructose mixtures in pair-wise choice tests. In agreement with this lack of preference, they were equally efficient at absorbing sucrose and both hexoses. Apparent assimilation efficiency of these sugars was around 97.5%. In pair-wise tests, Bananaquits displayed a strong preference for the most concentrated sucrose solution when the lowest concentration ranged from 276 to 522 mM. Between 522 and 1120 mM sucrose solution concentrations, Bananaquits were able to adjust their volumetric food intake in order to maintain a constant energy intake. At solution concentration of 276 mM, birds could not maintain their rate of energy intake by increasing food consumption enough. We consider that at low sugar concentrations, Bananaquits faced a physiological constraint; they were unable to process food at a fast enough rate to meet their energy needs. We also explored the possibility that dilute nectars might be essential to sustain high water needs of Bananaquits by allowing them to control osmolarity of the food. Between 276 and 1120 mM sucrose solution concentrations, average amount of free water drunk by Bananaquits was independent of food concentration. They drank very little supplementary water and did not effectively dilute concentrated nectars. The evidence suggests that water bulk of dilute nectars is a burden to Bananaquits.     

Nectar concentration preferences and sugar intake in the white-bellied sunbird, <Emphasis Type="Italic">Cinnyris talatala</Emphasis> (Nectariniidae)

Plant nectar is a simple food consumed by many different animals. Preferences regarding its components, especially sugars, have been studied for many species, but the preferences of nectar-feeding birds for different sugar concentrations are less well known than their sugar type preferences. The concentration preferences of white-bellied sunbirds, Cinnyris talatala, were examined using paired solutions of either sucrose or equicaloric 1:1 mixtures of glucose and fructose. Preferences were tested over a broad concentration range of 0.25–2.5 M sucrose equivalents (using 0.25 or 0.5 M differences between pairs). On both sucrose and hexose diets, the higher concentration was preferred up to 1 M, but there were no significant preferences above this concentration, except that birds preferred 1.5 to 2 M sucrose. As with other nectar-feeding vertebrates, the laboratory preferences of sunbirds do not explain the low concentration of their natural nectars. We recorded apparent excess sugar consumption during 6 h preference tests involving concentrated hexose diets; this could be due to digestive constraints or viscosity differences between sucrose and hexose solutions.     

Taste responses of Drosophila melanogaster

The amounts of sugar solution consumed by Drosophila melanogaster flies were determined. Starved and desiccated flies of a wild type strain (QA) consume 7?9 × 10^?2 λ of a 0.3 M sucrose solution per fly during the first hour and less later. They consume more of the 0.3 M sucrose solution than of the more diluted and the more concentrated solutions. In preference-aversion tests the flies discriminated between water and various sugar solutions, and between different sugar concentrations. Contrary to other fly species these flies did not prefer 0.05 M fructose over 0.05 M glucose. 0.3–0.5 M NaCl added to 0.1 M sucrose turned a preference over 0.01 sucrose into an aversion. A mutant, Lot-94, selected for its increased consumption of a 1 M NaCl solution was found to consume more of all test solutions. The amount of NaCl that had to be added to 0.1 M sucrose to turn the preference over 0.01 M sucrose by the mutant flies into aversion was not different from that found for the wild type flies.     

Electrical signals during nectar sucking in the carpenter ant Camponotus mus

Ants of the same size can vary their intake rate of a given sucrose solution depending on the colony's needs for carbohydrates. As this capacity has not yet been described for another insect, the question of how they can do that was the focus of our work. When viscosity and ant-morphometry remain constant, changes in intake rate can only be attributed to the sucking forces. The aim of this study was to analyze the nectar sucking activity in the ant Camponotus mus. Feeding behavior seems to be under motivational control; therefore, we developed a non-invasive experimental device. We recorded the electrical signal generated during nectar feeding by offering ants sucrose solutions of different concentrations (from 10%w/w to 70%w/w). The signal frequency was between 2 and 12 peaks/s. We could distinguish two different patterns of electrical signal during feeding depending on the solution concentration. Only the more concentrated solutions reached frequencies higher than 7 peaks/s and the signal performance was quite irregular. For the other concentrations (10%, 30% and 50%), signal frequencies were lower than 6 peaks/s and the signal pattern was sinusoidal, regular and decreased with intake in all cases. We discuss the possible implications of these two signal patterns.     

Reduction of food intake by intestinal macronutrient infusion is not reversed by NMDA receptor blockade

Rats increase their intake of food, but not water, after intraperitoneal injection of MK-801, a noncompetitive antagonist of N-methyl-D-aspartate-activated ion channels. We hypothesized that MK-801 might enhance intake by interfering with intestinal chemosensory signals. To test this hypothesis, we examined the effect of the antagonist on 15% sucrose intake after an intraduodenal infusion of maltotriose, oleic acid, or phenylalanine in both real- and sham-feeding paradigms. MK-801 (100 microg/kg) significantly increased sucrose intake regardless of the composition of the infusate during real feeding. Furthermore, MK-801 had no effect on reduction of sucrose intake by intestinal nutrient infusions in sham-feeding rats. These results indicate that MK-801 does not increase meal size and duration by interfering with signals activated by intestinal macronutrients.     

Expression of Fos during sham sucrose intake in rats with central gustatory lesions

For humans and rodents, ingesting sucrose is rewarding. This experiment tested the prediction that the neural activity produced by sapid sucrose reaches reward systems via projections from the pons through the limbic system. Gastric cannulas drained ingested fluid before absorption. For 10 days, the rats alternated an hour of this sham ingestion between sucrose and water. On the final test day, half of them sham drank water and the other half 0.6 M sucrose. Thirty minutes later, the rats were killed and their brains immunohistochemically stained for Fos. The groups consisted of controls and rats with excitotoxic lesions in the gustatory thalamus (TTA), the medial (gustatory) parabrachial nucleus (PBN), or the lateral (visceral afferent) parabrachial nucleus. In controls, compared with water, sham ingesting sucrose produced significantly more Fos-positive neurons in the nucleus of the solitary tract, PBN, TTA, and gustatory cortex (GC). In the ventral forebrain, sucrose sham licking increased Fos in the bed nucleus of the stria terminalis, central nucleus of amygdala, and the shell of nucleus accumbens. Thalamic lesions blocked the sucrose effect in GC but not in the ventral forebrain. After lateral PBN lesions, the Fos distributions produced by distilled H(2)O or sucrose intake did not differ from controls. Bilateral medial PBN damage, however, eliminated the sucrose-induced Fos increase not only in the TTA and GC but also in the ventral forebrain. Thus ventral forebrain areas associated with affective responses appear to be activated directly by PBN gustatory neurons rather than via the thalamocortical taste system.     

Intravenous infusion of glucagon-like peptide-1 potently inhibits food intake, sham feeding, and gastric emptying in rats

Glucagon-like peptide-1(7-36)-amide (GLP-1) is postulated to act as a hormonal signal from gut to brain to inhibit food intake and gastric emptying. A mixed-nutrient meal produces a 2 to 3-h increase in plasma GLP-1. We determined the effects of intravenous infusions of GLP-1 on food intake, sham feeding, and gastric emptying in rats to assess whether GLP-1 inhibits food intake, in part, by slowing gastric emptying. A 3-h intravenous infusion of GLP-1 (0.5-170 pmol.kg(-1).min(-1)) at dark onset dose-dependently inhibited food intake in rats that were normally fed with a potency (mean effective dose) and efficacy (maximal % inhibition) of 23 pmol.kg(-1).min(-1) and 82%, respectively. Similar total doses of GLP-1 administered over a 15-min period were less potent and effective. In gastric emptying experiments, GLP-1 (1.7-50 pmol.kg(-1).min(-1)) dose-dependently inhibited gastric emptying of saline and ingested chow with potencies of 18 and 6 pmol.kg(-1).min(-1) and maximal inhibitions of 74 and 83%, respectively. In sham-feeding experiments, GLP-1 (5-50 pmol.kg(-1).min(-1)) dose-dependently reduced 15% aqueous sucrose intake in a similar manner when gastric cannulas were closed (real feeding) and open (sham feeding). These results demonstrate that intravenous infusions of GLP-1 dose-dependently inhibit food intake, sham feeding, and gastric emptying with a similar potency and efficacy. Thus GLP-1 may inhibit food intake in part by reducing gastric emptying, yet can also inhibit food intake independently of its action to reduce gastric emptying. It remains to be determined whether intravenous doses of GLP-1 that reproduce postprandial increases in plasma GLP-1 are sufficient to inhibit food intake and gastric emptying.     

Candida mogii and Debaryomyces hansenii yeast development in the presence of metal chlorides

The yeasts Candida mogii 2 and Debaryomyces hansenii 8 isolated from salted fish spawn in the process of its storage were found to be capable of growth in 4 M KCl, 3 M MgCl2, 2.5 M NaCl, 1.5 BaCl2 and 1 M CaCl2. The activity of water (aw) in these solutions varied from 0.983 to 0.719; the maximum osmotic pressure was 380 atm. The cultures grew also in a 3 M sucrose solution, at low concentrations of osmotically active substances and without them. Therefore, they can be regarded as osmotolerant microorganisms. The osmotolerance of the cultures decreased with temperature of solutions. The absence of growth or weak growth in solutions of certain other chlorides should be attributed to toxicity of cations.     

Seasonal changes in the response of wood-ants (Formica lugubris) to sucrose baits

Abstract. 1. The acceptability of sucrose solutions to Formica lugubris Zett. in the field was tested by offering droplets of known concentrations to ants tending aphids.
2. A probit model fitted to the data allowed the computation of the Median Effective Concentration (ED₅₀) and its confidence limits.
3. In spring and early summer ED₅₀ was about 0.15 M sucrose, but the ED₅₀ rose in 1 week at the end of June from 0.2 M to 0.9 M. The change was simultaneous on pine and birch trees. The ED₅₀ fell gradually to about 0.4 M in early November.
4. The increase in ED₅₀ is related to the production of the summer apterae in the aphids tended, Cinara pini (L.) on pines and Symydobius oblongus (von Heyden) on birch. This increases the 'quality' of food resource so that low sucrose concentrations can no longer compete for ant attendance.
5. The increase in ED₅₀ may limit the attendance of wood-ants at the nectaries of bracken, Pteridium aquilinum (L.) Kuhn. and at colonies of some other aphid species which are attended only in early summer.     

Abscisic acid inhibits phloem loading of sucrose

The effect of abscisic acid (ABA) on the uptake of sucrose by discs from castor bean ( Ricinus communis L. cv. Zanzibarensis) cotyledons was investigated. Incubation on ABA solutions for one hour or longer significantly inhibited sucrose uptake. The effect was measurable at ABA concentrations as low as 0.1 μ M . The inhibition was due to a lowering of the apparent V_max of the sucrose-carrier system, the K_m being unaffected. Uptake of sucrose was coupled to proton uptake but ABA had no detectable effect on the latter process. It is suggested that ABA exerts an effect on the phloem loading of sucrose by enhancing the efflux of sucrose. In leaf discs from three other plant species ( Beta vulgaris L., Petunia hybrida L. and Phaseolus vulgaris L.) ABA exerted a similar effect. The results are discussed with respect to source-sink relationships.