SOURCE-SINK RELATIONSHIPS IN THE BLADE OF ALARIA ESCULENTA (LAMINARIALES,PHAEOPHYCEAE)1

The translocation of ¹⁴C-labelled photoassimilate was studied in blades of the kelp, Alaria esculenta (L.) Grev., which had been surgically modified to produce source and sink regions of various sizes. Thirty cm above the blade base a 2.5 cm dia. section of the blade received a 1 h pulse of H¹⁴CO₃^?. Efflux of ¹⁴C-labelled photoassimilate from this “source disc” was monitored over the next 8 days using a Geiger-Müller detector probe. Accumulation of ¹⁴C-labelled solutes by a “sink disc” of similar diameter, 20 cm below the source disc, was also monitored. Rate of ^l4C efflux from the source disc was governed by two factors: (1) total sink size and (2) feed-back from competing sources. In the latter case, source export was depressed if the portion of the blade, just distal to the source disc, was present. While the initial ¹⁴C influx rate into the sink disc was greater when competing sinks were present, the total accumulation of ¹⁴C-photoassimilates was 2–3 times higher in the sink disc when competing sources were not present. Basipetal translocation velocity (1.3–1.7 cm h^?1) was unaffected by competing sources and sinks.     

The influence of externally supplied sucrose on phloem transport in the maize leaf strip

Sucrose (2,5–1000 mmol l^–1), labeled with [¹⁴C]sucrose, was taken up by the xylem when supplied to one end of a 30-cm-long leaf strip of Zea mays L. cv. Prior. The sugar was loaded into the phloem and transported to the opposite end, which was immersed in diluted Hoagland's nutrient solution. When the Hoagland's solution at the opposite end was replaced by unlabeled sucrose solution of the same molarity as the labeled one, the two solutions met near the middle of the leaf strip, as indicated by radioautographs. In the dark, translocation of ¹⁴C-labeled assimilates was always directed away from the site of sucrose application, its distance depending on sugar concentration and translocation time. When sucrose was applied to both ends of the leaf strip, translocation of ¹⁴C-labeled assimilates was directed toward the lower sugar concentration. In the light, transport of ¹⁴-C-labeled assimilates can be directed (1) toward the morphological base of the leaf strip only (light effect), (2) toward the base and away from the site of sucrose application (light and sucrose effect), or (3) away from the site of sucrose application independent of the (basipetal or acropetal) direction (sucrose effect). The strength of a sink, represented by the darkened half of a leaf strip, can be reduced by applying sucrose (at least 25 mmol l^–1) to the darkened end of the leaf strip. However, equimolar sucrose solutions applied to both ends do not affect the strength of the dark sink. Only above 75 mmol l^–1 sucrose was the sink effect of the darnened part of the leaf strip reduced. Presumably, increasing the sucrose concentration replenishes the leaf tissue more rapidly, and photosynthates from the illuminated part of the leaf strip are imported to a lesser extent by the dark sink.Supported by Deutsche Forschungsgemeinschaft     

Clearance rates of bacteria by the rotifer Filinia longiseta (Ehrb.) measured using three tracers

The clearance rates (CRs) of bacteria by Filinia longiseta were measured at 19°C, both in situ in Lake Loosdrecht and in the laboratory during summer. The tracer particles used in the field were: (1) 0.51 µm fluorescent microspheres, and (2) fluorescently labelled bacteria (FLB). A third type of tracer particle, natural [methyl-³H]-thymidine-labelled bacteria (< 1.2 µm), were used as a radiotracer in a laboratory experiment. The uptake of the first two tracer-particle types was measured by microscopic examination of the rotifer guts. In the third case, the uptake of radioactivity was determined by liquid scintillation counting. The rate of uptake of the microspheres decreased 10 min after the start of the experiment, probably because the gut passage time was exceeded. Using a 5 min feeding time, the rate of uptake of microspheres was higher than that of the FLB, though the variation in the uptake in both cases was high. The ingestion rates and CRs of bacteria by F. longiseta based on the fluorescent tracers were: microspheres, 5115 bact.ind^–1 h^–1 and 0.368 µl ind^–1 h^–1; FLB, 2252 bact.ind^–1 h^–1 and 0.162 µl ind^–1 h^–1. The mean CR using the thymidine-labelled natural bacteria and a 10 min feeding time was 0.179 µl ind^–1 h^–1. Thus, the CR based on the microsphere method was twice as high as for the other two methods.     

Kinetics of C-photosynthate translocation in morning glory vines

The movement of ¹⁴C-photosynthate in morning glory (Ipomea nil Roth, cu. Scarlet O'Hara) vines 2 to 5 meters long was followed by labeling a lone mature leaf with ¹⁴CO₂ and monitoring the arrival rate of tracer at expanding sink leaves on branches along the stem. To a first approximation, the kinetic behavior of the translocation profiles resembled that which would be expected from movement at a single velocity (“plug flow”) without tracer loss from the translocation stream. There was no consistent indication of a velocity gradient along the vine length. The profile moved along the vine as a distinct asymmetrical peak which changes shape only slowly. The spatial distribution of tracer along the vine reasonably matched that predicted on the basis of the arrival kinetics at a sink, assuming plug flow with no tracer loss. These observations are in marked contrast to the kinetic behavior of any mechanism describable by diffusion equations.

However, a progressive change in profile shape (a symmetrical widening) was observed, indicating a range of translocation velocities. A minimum of at least two factors must have contributed to the observed velocity gradient: the exchange of ¹⁴C between sieve elements and companion cells (demonstrated by microautoradiography) and the range of velocities in the several hundred sieve tubes which carried the translocation stream. Possible effects of these two factors on profile spreading were investigated by means of numerical models. The models are necessarily incomplete, due principally to uncertainties about the exchange rate between sieve elements and companion cells and the degree of functional connectivity between sieve tubes of different conductivities. However, most of the observed profile spreading may be reasonably attributed to the combined effects of those two factors.

The mass average velocity of translocation (calculated from the mean times of ¹⁴C arrival at successive sink leaves) was about 75% of the maximum velocity (calculated from the times of initial detection at the same sink leaves), which was usually between 0.6 and 1 cm min⁻¹. Owing to tracer exchange between sieve elements and companion cells, the mass average velocity of tracer in the sieve tubes was probably closer to 86% of the maximum velocity, a figure which agreed with a predicted velocity distribution based on calculated sieve tube conductivities and the size distribution of functional sieve tubes.

     

Distorted phytochrome action spectra in green plants

An evaluation was made of the extent which a Münch-type pressure flow mechanism (i.e., osmotically-generated pressure flow) might contribute to phloem transport in soybean. Estimates of sucrose concentrations in source (leaf) and sink (root) sieve tubes were obtained by a negativestaining procedure. Water potential measurements of the leaf and of the nutrient solution allowed calculation of the turgor pressures in source and sink sieve tubes. The turgor difference between source and sink sieve tubes was compared to that required to drive translocation at the observed velocity between the source and sink, as measured by [¹⁴C] photosynthate movement. Sieve-tube conductivity was calculated from the sieve-tube dimensions, assuming an essentially unobstructed pathway. In three experiments, the sucrose concentration was consistently higher in source sieve tubes (an average of 11.5%) than in sink sieve tubes (an average of 5.3%). The ratio of these values (2.3:1) agreed reasonably well with an earlier ratio for source/sink sieve tube concentrations of 1.8:1, obtained by quantitative microautoradiography. The resulting calculated turgor difference (an average of 4.1 bars) was adequate to drive a pressure flow mechanism at the observed translocation velocities (calculated to require a turgor difference of 1.2 to 4.6 bars). No other force need be presumed to be involved.This work was presented in part at a joint U.S.-Australian Conference on Transport and Transfer Processes in Plants, Canberra, Australia, December 15–20, 1975; see Fisher (1976)     

Dynamics of photoassimilated carbon in douglas fir seedlings

The relations between CO₂ uptake, translocation, and carbon accumulation in several vegetative components of Douglas fir seedlings (Pseudotsuga menziesii [Mirb.] Franco) have been quantified using ¹⁴CO₂. Seedlings were exposed to a constant specific radioactivity of ¹⁴CO₂ and a repeating daily pattern of temperature and light for 4 consecutive days. Results of ¹⁴C analysis, which indicated a transitory pattern of photoassimilated carbon movement, were extrapolated to a “steady rate” using a compartment analysis. Accumulation rates of photoassimilated carbon, relative to tissue carbon, were new needles, 0.94%/day, old needles, 1.14%/day, new shoots 0.38%/day, stem, 0.16%/day, and roots, 0.50%/day. Therefore, the source of carbon, the needles, is also the strongest sink.     

Ethylene-induced microtubule reorientations: mediation by helical arrays

Pruned source-sink transport systems from predarkened plants of Amaranthus caudatus L. and Gomphrena globosa L. were used to study the localization of ¹⁴C-labeled photosynthate imported into experimentally induced sink leaves by microautoradiography. During a 6-h (Amaranthus) or a 4-h (Gomphrena) transport period, ¹⁴C-assimilates were translocated acropetally from a mature source leaf provided with ¹⁴CO₂, into a younger induced sink leaf (dark/-CO₂). In addition, a young still-expanding source leaf exposed to ¹⁴CO₂ exported ¹⁴C-assimilates basipetally into a mature induced sink leaf (dark/-CO₂). Microautoradiographs showed that imported ¹⁴C-photosynthate was strongly accumulated in the sieve element/companion cell complexes of midveins, secondary veins, and minor veins of both the mature and the expanding sink leaf. Some label was also present in the vascular parenchyma and bundlesheath cells. In petioles, ¹⁴C-label was concentrated in the sieve element/companion cell complexes of all bundles indicating that assimilates were imported and distributed via the phloem. Moreover, a considerable amount of radioactivity unloaded from the sieve element/companion cell complexes of petiolar bundles, was densely located at sites of secondary wall thickenings of differen-tiating metaxylem vessels, and at sites of chloroplasts of the vascular parenchyma and bundle-sheath cells. These observations were more striking in petioles of Gomphrena than Amaranthus.Abbreviation se/cc sieve element/companion cell     

Studies on ectomycorrhiza

Summary Plants ofPicea abies (L.) Karst were grown in mycorrhizal association withTelephora terrestris (Pers. ex Fr.) andPisolithus tinctorius (Mich. ex Pers.) Coker and Couch on sphagnum peat in petri dishes or Perspex chambers. After 1 yearT. terrestris had formed prominent rhizomorphs which were characterized by light microscopy and investigated for³²P-orthophosphate uptake. The absorbed phosphate was transported to sinks throughout the rhizomorphal system as well as into the plant. The calculated translocation velocity and flux rate in the rhizomorph were in the range of 1–3 cm/h and 0.5–4.0 × 10^-10 mol cm^-2 s^-1, respectively. Label was observed to accumulate in the needles 2–3 days after application. Feeding a non-mycorrhized root with³²P-orthophosphate led to an accumulation of label in needles within 1 h, but no radioactivity appeared in the associatedT. terrestris rhizomorphs. The rhizomorphs ofP. tinctorius revealed a higher structural differentiation than those ofT. terrestris. Translocation of labelled phosphorus through rhizomorphs ofP. tinctorius into spruce needles was also demonstrated.     

Feeding in Euchlanis dilatata lucksiana Hauer on filamentous cyanobacteria and a prochlorophyte

Ingestion and assimilation rates of Euchlanis dilatata lucksiana Hauer, isolated from Lake Loosdrecht (The Netherlands) and cultured on lake water (seston < 33 µm), were measured in the laboratory using the ¹⁴C-tracer technique. The five taxa used as tracer foods, together with 6–7 mg C l^–1 of lake seston in each case, included four species of filamentous cyanobacteria (Oscillatoria redekei, O. limnetica, Aphanizomenon flos-aquae, Anabaena PCC 7120) and a prochlorophyte (Prochlorothrix hollandica). Except Anabaena, they are all commonly encountered in eutrophic Loosdrecht lakes, including Lake Loosdrecht, and their dimensions ranged between 150 and 250 µm in length and 2 and 3.5 µm in width. The small and large Euchlanis used as experimental animals had mean lengths of 217–223 µm and 276–305 µm, respectively. Euchlanis fed on all the taxa offered as food. Clearance rates ranged from 51 to 99 µl ind^–1 d^–1 for the large animals and from 22 to 41 µl ind^–1 d^–1 for the small animals. The highest ingestion rate observed, 1.7 µg ind^–1 d^–1, was for the large animals feeding on Aphanizomenon. The daily ration for both size classes far exceeded 100% of body weight, reaching up to 690% for the small animals feeding on Aphanizomenon. The small animals generally appeared to assimilate the ingested food more efficiently (assimilation efficiencies: 37–100%) than the large animals (34–77%). Compared with an earlier study in which only lake seston (<33 µm) was used as food, the specific clearance rates of Euchlanis on the cyanobacteria and Prochlorothrix were generally somewhat lower.     

Feeding kinetics of Brachionus plicatilis fed Isochrysis galbana

Clearance and ingestion rates of Brachionus plicatilis were measured using ¹⁴C-labeled Isochrysis galbana Tahiti. Experiments were conducted at 20–22 °C, 20 ppt salinity, and algal concentrations ranging from 0.13–64 mg C 1^–1. Clearance rates were constant and maximal at concentrations <2 mg C 1^–1, with maximum rates ranging from 3.4–6.9 µl ind.^–1 hr^–1. The ingestion rate varied with food concentration, and was described by a rectilinear model. The maximum ingestion rate varied considerably, and was dependent on the growth rate of the rotifers. Depending on the pre-conditions, B. plicatilis ingested about 0.5 to 2 times its body carbon per day at saturating food concentrations.     

Metabolism of [14C]indole-3-acetic acid by the cortical and stelar tissues of Zea mays L. roots

Reverse-phase high-performance liquid chromatography was used to analyse ¹⁴C-labelled metabolites of indole-3-acetic acid (IAA) formed in the cortical and stelar tissues of Zea mays roots. After a 2-h incubation in [¹⁴C]IAA, stelar segments had metabolised between 1–6% of the methanol-extractable radioactivity compared with 91–92% by the cortical segments. The pattern of metabolites produced by cortical segments was similar to that produced by intact segments bathed in aqueous solutions of [¹⁴C]IAA. In contrast, when IAA was supplied in agar blocks to stelar tissue protruding from the basal ends of segments, negligible metabolism was evident. On the basis of its retention characteristics both before and after methylation, the major metabolite of [¹⁴C]IAA in Zea mays root segments was tentatively identified by high-performance liquid chromatography as oxindole-3-acetic acid.Abbreviations HPLC High-performance liquid chromatography - IAA Indole-3-acetic acid     

PHYSIOLOGICAL INVESTIGATIONS ON ALARIA ESCULENTA (LAMINARIALES,PHAEOPHYCEAE). II. ROLE OF TRANSLOCATION IN BLADE GROWTH1,2

Laboratory studies on blade growth in Alaria esculenta (L.) Grev. showed 3 periods of rapid blade elongation during the year: October–November, February–April and late June. The first two periods are characteristic of many Laminariales; the unique June peak may reflect local nutrient conditions. While the distal blade functions as a source, supplying organic matter to the blade meristem, the stipe can be a source during periods of rapid growth or a sink during late summer when blade growth is slow. Maximum enhancement of elongation rate of blade meristems was observed in 40–50 cm blades; longer blades showed no further increase in growth rate. This blade length-growth promotion relationship may be independent of seasonal variations in meristematic activity. ¹⁴C tracer experiments suggested that separate growth promotion effects by distal blade, sporophylls and stipe were not additive in the intact thallus. The preferential source of assimilate for blade meristem growth was the distal blade. Secondary sources: sporophylls, which were activated following excision of the primary source; and stipe, which began to translocate assimilate when both sources were removed. The role of secondary sources in nature is discussed. Profiles of radioactivity in alcohol-soluble organic matter in blades are evaluated in relation to tracer profiles in higher plants and mechanisms of translocation.     

Bioturbation experiments in the Venice Lagoon

Short experiments (14–21 days) were carried out during autumn 1998 and spring 1999 at one selected site of the Venice Lagoon to measure bioturbation activities and mixing rates, as well as to obtain quantitative information on benthos functionality. Fluorescent sediment particles (luminophores, 63–350 m) were introduced as pulse inputs at the sediment surface. The concentration–depth profiles of the tracer were simulated with a new advection–diffusion–non local model applied under non-steady state conditions. This allowed the quantification of the mixing parameters associated with different mechanisms: biodiffusion (D _b), bioadvection (W) and non-local mixing (Ke, z₁, z₂). A parameter RS (removed sediment) was also calculated to account for the flux of sediment due to non-local transport. Results show that bioturbation was dominated by biodiffusion in autumn and by bioadvection in spring. Mean mixing parameters Db, W, and RS changed from 3.09 to 0.87 cm² y^–1, from 0.93 to 15.50 y^–1 and from 5.85 to 7.79 g cm^–2 y^–1, respectively.     

Evidence for thiol-induced enhanced in situ translocation of 14C-sucrose from source to sink in Brassica juncea

The translocation of ¹⁴C-sucrose to the different parts of the mustard (Brassica juncea) crop has been evaluated in the context of understanding the source to sink relationship in the thiol-induced enhanced crop yield. The foliar application of thiols like TU, TGA and DTT to the plant gave maximum sucrose phosphate synthase activity, which was found to have direct correlation with the movement of sucrose. The distribution pattern of ¹⁴C-sucrose follows the path from internode and node to pod via leaf. The translocation of ¹⁴C-sucrose was found to be a light dependent process. Among the nucleotides ATP and GTP, only ATP was able to promote the translocation and GTP was ineffective. In this unique in situ tracer experiment using ¹⁴C-sucrose, we could establish that thiols are able to enhance the translocation of sucrose from source to sink.     

Evidence for thiol-induced enhanced in situ translocation of 14C-sucrose from source to sink in Brassica juncea

The translocation of ¹⁴C-sucrose to the different parts of the mustard (Brassica juncea) crop has been evaluated in the context of understanding the source to sink relationship in the thiol-induced enhanced crop yield. The foliar application of thiols like TU, TGA and DTT to the plant gave maximum sucrose phosphate synthase activity, which was found to have direct correlation with the movement of sucrose. The distribution pattern of ¹⁴C-sucrose follows the path from internode and node to pod via leaf. The translocation of ¹⁴C-sucrose was found to be a light dependent process. Among the nucleotides ATP and GTP, only ATP was able to promote the translocation and GTP was ineffective. In this unique in situ tracer experiment using ¹⁴C-sucrose, we could establish that thiols are able to enhance the translocation of sucrose from source to sink.     

TRANSLOCATION OF 14C IN MACROCYSTIS INTEGRIFOLIA (PHAEOPHYCEAE)1,2

Translocation patterns in the giant kelp, Macrocystis integrifolia Bory, were investigated in situ using ¹⁴C tracer; sources and sinks were identified. Export was first detected after 4 h of labeling; experiments were routinely 24 h continuous ¹⁴C application. Mature blades exported ¹⁴C to young blades on the same frond and on younger fronds, as well as to sporophylls and frond initials at the bases of the fronds. Blades <0.3 m from the apex imported and did not export; this distance did not change seasonally. In spring export from blades 0.3–1.25 m from the apex was exclusively upwards; older blades also exported downwards. In fall downward export began 0.5 m from the apex, and blades >2 m from the apex exported exclusively downwards. Carbon imported by frond initials, young fronds, and sporophylls in fall may partly be stored for growth in early spring. No translocation was seen in very young plants until one blade (secondary frond initial) bad been freed from the apical blade; this blade exported to the apical blade for a time, but imported when it began to develop into a frond. The second and third formed blades on the primary fronds (sporophylls also exported when <0.3 m from the apex, and later stopped. Frond initials and sporophylls on later-formed fronds did not export at all. The translocation pattern in M. integrifolia differs from that previously reported in M. pyrifera in seasonal change and in distances from the apex at which the changes take place.     

Source pool kinetics for C-photosynthate translocation in morning glory and soybean

The kinetic behavior of translocation profiles indicates that their shape is determined largely by the rate at which tracer enters the sieve tubes in the source leaf. Confirmation of this relationship was sought by investigating the kinetics of ¹⁴C in the immediate source pool for translocated sucrose in soybean (Glycine max L., cv. Bragg) and morning glory (Ipomea nil Roth, cv. Scarlet O'Hara) leaves. Quantitative microautoradiography was used to follow the water-soluble ¹⁴C contents of the companion cells in minor veins after pulse-labeling with ¹⁴CO₂. In both morning glory and soybean, the observed kinetics in the companion cells matched reasonably well those expected from the shape of the translocation profiles.

Marked compartmentation of sucrose was evident in soybean leaves in that the specific radioactivity of total leaf sucrose was greatest immediately after labeling and quickly declined, whereas labeling in the companion cells was low at first and did not reach a maximum for about 35 minutes. In morning glory leaves, the kinetics of sucrose specific radioactivity and of companion cell-labeling more closely paralleled one another.

     

Turnover and distribution of root exudates of Zea mays

Decomposition and distribution of root exudates of Zea mays L. were studied by means of ¹⁴CO₂ pulse labeling of shoots on a loamy Haplic Luvisol. Plants were grown in two-compartment pots, where the lower part was separated from the roots by monofilament gauze. Root hairs, but not roots, penetrated through the gauze into the lower part of the soil. The root-free soil in the lower compartment was either sterilized with cycloheximide and streptomycin or remained non-sterile. In order to investigate exudate distribution, 3 days after the ¹⁴C labeling, the lower soil part was frozen and sliced into 15, one-mm thick layers using a microtome. Cumulative ¹⁴CO₂ efflux from the soil during the first 3 days after ¹⁴C pulse labeling did not change during plant growth and amounted to about 13–20% of the total recovered ¹⁴C (41–55% of the carbon translocated below ground). Nighttime rate of total CO₂ efflux was 1.5 times lower than during daytime because of tight coupling of exudation with photosynthesis intensity. The average CO₂ efflux from the soil with Zea mays was about 74 g C g^–1 day^–1 (22 g C m^–2 day^–1), although, the contribution of plant roots to the total CO₂ efflux from the soil was about 78%, and only 22% was respired from the soil organic matter. Zea mays transferred about 4 g m^–2 of carbon under ground during 26 days of growth. Three zones of exudate concentrations were identified from the distribution of the ¹⁴C-activity in rhizosphere profiles after two labeling periods: (1) 1–2 (3) mm (maximal concentration of exudates) 2) 3–5 mm (presence of exudates is caused by their diffusion from the zone 1); (3) 6–10 mm (very insignificant amounts of exudates diffused from the previous zones). At the distance further than 10 mm no exudates were found. The calculated coefficient of exudate diffusion in the soil was 1.9 × 10^–7 cm² s^–1.     

Amino-acid absorption by developing herring eggs

¹⁴C-glycine absorption by eggs of the herringClupea harengus from a 2 µM solution at 15°C depends on the stage of embryonic development. Unidirectional¹⁴C-glycine influx rates are small at early stages: 0.6 ± 0.1 and 0.5 ± 0.1 pmoles egg^–1 h^–1 in embryos 5 h and 28 h after fertilization, respectively. They increase drastically about 51 h after fertilization (prior to blastopore closure) to 3.7 ± 0.9 pmoles egg^–1 h^–1. Glycine uptake steadily continues to increase almost until hatching (maximum values = 18.8 ± 2.7 pmoles egg^–1 h^–1), decreasing slightly prior to hatching. Distribution ratios (radioactivity µl^–1 of egg volume: radioactivity µl^–1 ambient medium) exceed the equilibrium ratio of 1 between 51 h and 78 h after fertilization, reaching values of 4.7 two days prior to hatching, thus suggesting the presence of a transport mechanism capable of transferring the amino acid against the concentration gradient. Curves for concentration-dependent¹⁴C-glycine and¹⁴C--aminoisobutyric acid absorption are very similar; they consist of a linear portion at higher concentrations and a saturable component, indicating a mediated uptake process. Calculations performed by means of aminoacid absorption rates and O₂ uptake data suggest that herring eggs scarcely obtain nutritional benefits from absorption of dissolved amino acids in natural spawning areas.     

Bioregulator enhancement of sink activity in sugar beet

The sink mobilizing abillity is partially determined by sugar uptake rates of storage cells. Two synthetic growth regulators (Pix and BAS 106W) were tested for their effect on sucrose uptake in root tissue discs or glucose uptake in cell cultures of sugar beet. In tissue discs, uptake at the plasmalemma was determined by incubating the discs for 1 h in the presence of 5 mM sucrose and at the tonoplast for 4 h in the presence of 40 mM sucrose. Cell cultures were incubated for 1 h in the presence of 1 mM glucose. Pix (10 mg l^–1) caused a 20% stimulation of active sucrose uptake at the plasmalemma. Active sucrose uptake at the tonoplast was increased 67% by 100 mg l^–1 Pix. No effect of BAS 106W was observed on sucrose uptake in tissue discs. In cell cultures, a 65% enhancement of active glucose uptake was observed with both Pix and BAs 106W. When the bioregulators were applied to the root medium of seedlings, Pix but not BAS 106W resulted in increased root/shoot ratio, translocation of ¹⁴C-assimilates, and allocation of more biomass to the root sink. The data suggested that sugar transport and translocation may be used as biochemical criteria for rapid screening of effective yield enhancing bioregulators.