Water extrusion in the trap bladders ofUtricularia vulgaris

In the trap bladder ofUtricularia vulgaris, a sudden expansion (convex bladder) by opening of the entrance door upon stimulus was followed by slow decreases in bladder width and internal hydrostatic pressure. The decreases were caused by continuous water outflow from bladder lumen. The bladder reached initial resetting state (concave bladder) in about 30 min. The internal pressure reduced to 0.86 bar. This reduction was inhibited by application of sodium azide in the bladder lumen. The total water outflow for 30 min from a bladder, measured using a glass capillary inserted in the bladder, was 630 nl: the rate was 21 nl/min. This rate was also inhibited by sodium azide. In bladder resetting under paraffin oil, it was observed that water emerges from near the free edge of the trap door. From light and electron microscopic observations of the entrance region, it is concluded that the inlet of water outflow is the bifid trichomes which stand on the inner surface of the bladder near the entrance, and the outlet is the outer and middle zones of the pavement epithelium, or threshold, against which the free edge of the door rests.     

Functional characteristics of traps of aquatic carnivorous Utricularia species

Firing and resetting of traps in aquatic Utricularia species are associated with water flow and trap volume changes. In this study, trap thickness was used as a measure of water flow and was monitored automatically using an electronic position sensor. The basic characteristics of mechanically stimulated firing and resetting were measured in isolated traps from 13 aquatic Utricularia species and in two trap size categories in Utricularia reflexa. This allowed to study the relationship between these trap functions and trap thickness and length (criteria of trap size). Additionally, the characteristics of spontaneous firings (without any mechanical stimulation) were compared for U. reflexa traps fed or denied prey during a 1-day period. On the absolute scale, the 13 Utricularia species differed considerably in their firing and resetting rates. Significant interspecific differences were also found in the magnitude of firing (in total 3.7–4.2 times) and resetting rates (10–24 times) per unit trap thickness or length. Overall, traps of Utricularia australis, Utricularia stellaris and Utricularia inflata showed the greatest firing and resetting rates. The relative magnitude of firing per unit trap thickness or length showed a highly significant negative correlation with both trap thickness and length and the same also held for the relative resetting rates. Smaller and narrower traps are thus relatively more effective at trap firing and resetting than larger traps. Neither firing nor resetting characteristics were significantly different between unfed and prey-fed traps of U. reflexa and this was also true for the occurrence of spontaneous firings. A strict linear resetting rate, without any lag-period, was found during the first 3 min after trap firing in U. reflexa. This suggests that water is pumped out of the trap continuously and probably recirculates. Given the concepts of spontaneous firing and water recirculation, an ecological model based on the literature data has been devised to quantify the daily N and P gain from the ambient water by Utricularia traps devoid of animal prey. The model shows that the total N and P content estimated in the trap fluid is too high to be accumulated from only the ambient water. This implies that the prey-free traps do not take up N or P from the trap fluid but rather exude a quantity of these nutrients to the fluid to support the microbial community. Therefore, the trap microorganisms behave more as parasites than commensals and represent an additional ecological cost for trap maintenance.     

Influence of cell turgor on sucrose partitioning in potato tuber storage tissues

Sucrose uptake and partitioning in potato (Solanum tuberosum L.) tuber discs were examined under a range of mannitol and ethylene-glycol concentrations. Mannitol caused the same changes in turgor over a wide range of incubation periods (90 min-6 h), indicating that it did not penetrate the tissue. In comparison, ethylene glycol reduced turgor losses but did not eliminate them, even after 6 h. Between 100 mM and 300 mM mannitol, turgor fell by 350 kPa, compared with 35 kPa in ethylene glycol. Uptake experiments in mannitol alone showed that total sucrose uptake was strongly correlated with both osmotic potential and with turgor potential. In subsequent experiments sucrose uptake and partitioning were examined after 3 h equilibration in 100 mM and 300 mM concentrations of mannitol and ethylene glycol. Total sucrose uptake and the conversion of sucrose to starch were enhanced greatly only at 300 mM mannitol, indicating an effect of turgor, rather than osmotic potential on sucrose partitioning. The inhibitors p-chloromercuribenzenesulfonic acid and carbonylcyanide m-chlorophenylhydrazone (CCCP) both reduced sucrose uptake, but in quite different ways. p-Chloromercuribenzenesulfonic acid reduced total sucrose uptake but did not affect the partitioning of sucrose to starch. By contrast, CCCP inhibited total uptake and virtually eliminated the conversion of sucrose to starch. Despite this, sucrose uptake in the presence of CCCP continued to increase as the mannitol concentration increased, indicating an increase in passive transport at higher mannitol concentrations. Increased sucrose uptake above 400 mM mannitol was shown to be the result of uptake into the free space. The data show that starch synthesis is optimised at low but positive turgors and the relation between sucrose partitioning and the changing diurnal water relations of the tuber are discussed.Abbreviations CCCP carbonylcyanide m-chlorophenylhydrazone - PCMBS p-chloromercuribenzenesulfonic acid     

Efflux of sucrose from minor veins of tobacco leaves

Mature leaves import limited amounts of nutrient when darkened for prolonged periods. We tested the hypothesis that import is restricted by the apoplast-phloem loading mechanism, ie., as sucrose exits the phloem of minor veins it is retrieved by the same tissue, thus depriving the mesophyll of nutrient. When single, attached, mature leaves of tobacco (Nicotiana tabacum L.) plants were darkened, starch disappeared from the mesophyll cells, indicating that the supply of solute to the mesophyll was limited. Starch was synthesized in mesophyll cells of darkened tissue when sucrose was applied to the apoplast at 0.1–0.3 mM concentration. Efflux from minor veins was studied by incubating leaf discs on [¹⁴C]sucrose to load the minor veins and then measuring subsequent ¹⁴C release. Efflux was rapid for the first hour and continued at a gradually decreasing rate for over 13 h. Net efflux increased when loading was inhibited by p-chloromercuribenzene-sulfonic acid, anoxia, isotope-trapping, or reduction of the pH gradient. Neither light nor potassium had a significant effect on the rate of labeled sucrose release. The site of labeled sucrose release was investigated by measuring efflux from discs in which sucrose had previously been loaded preferentially by either the minor veins or mesophyll cells. Efflux occurred primarily from minor veins.Abbreviations Mes 2(N-morpholino)ethanesulfonic acid - Mops 3(N-morpholino)propanesulfonic acid - PCMBS p-chloromercuribenzenesulfonic acid - SE-CC sieve element-companion cell complex     

Root culturing ofFaidherbia=Acacia albida as a source of explants for shoot regeneration

Root culture ofFaidherbia=Acacia albida (Del.) A. Chev. can be maintained over several months by successively subculturing excised roots in modified Bonner and Devirian medium, which was found to be the best of the three media compositions tested. Adding auxins had an inhibiting effect on root growth characteristics. Mesoinositol at 0.05 mM slightly enhanced the overall elongation rate, and sucrose at 59 mM significantly increased root elongation. The effect of sucrose could not be replaced by glucose. Subcultured roots showed progressively less elongation in successive transfers. Shoots were regenerated in vitro from root segments beginning with the first passage on 1/5 strength MS medium.The large variability in the root elongation rate indicates that this technique provides an effective way to select clones with good potential for tap root growth.     

Sucrose stimulates branching morphogenesis of embryonic mouse lung in vitro: a problem of osmotic balance between lumen fluid and culture medium

In organ cultures of lung rudiments from 11-day mouse embryos, it was found that addition of sucrose to the culture medium stimulated branching morphogenesis and reduced lumen distension. Two possible roles of sucrose were postulated: one as a nutrient and another as a generator of osmotic pressure inducing osmosis of water from the lumen fluid to the culture medium across a simple columnar epithelial cell layer. To assess which was the case, branching morphogenesis was investigated in lung rudiments cultured in medium in which osmotic pressure was increased by the addition of lactose or NaCl rather than sucrose: similar acceleration of branching was observed in both. In another experiment, lumen fluid of cultured lung rudiments was mechanically drained each day, and significantly stimulated branching morphogenesis was observed even when sucrose was not added to the culture medium. Heparin is known to induce abnormal lumen distension and inhibits branching morphogenesis. Heparin-induced abnormal morphogenesis was prevented either by the addition of sucrose to the culture medium or by the mechanical drainage of lumen fluid. These results suggest that lumen distension caused by the accumulation of lumen fluid disrupts lung branching morphogenesis in vitro, even when the mechanism of branching morphogenesis is intact.     

Effect of carbohydrate on age-related feeding behaviors and longevity in adult black cutworm,Agrotis ipsilon (Lepidoptera: Noctuidae)

Age-related consumption and longevity were monitored in the laboratory for adultA. ipsilon fed either a 1M sucrose solution or water. An additional group was completely starved. Adults consumed sucrose solution and water just after eclosion; the percentage feeding daily and the mean daily consumption for females and males fed sucrose solution declined with time, whereas the percentage feeding daily and the mean daily consumption of those fed water increased with time. Total consumption was significantly higher for those fed sucrose solution (P<0.01) because they lived longer, but consumption per day averaged over the entire adult stage was not significantly different between those fed sucrose solution and those fed water (P>0.05). Mean longevity was significantly extended for females and males fed sucrose solution over those fed water or starved (P<0.01). Moreover, consumption of either fluid was significantly correlated with extended longevity in all groups (P<0.05). These data on fluid consumption by adultA. ipsilon are discussed relative to posteclosion migratory activities.     

Accumulation of peonidin 3-glucoside enhanced by osmotic stress in grape (Vitis vinifera L.) cell suspension

Cell cultures of grapes, Vitis vinifera L. cv Gamay Fréaux were grown under different conditions of external osmotic potential induced by an increase of sucrose concentration or by the addition of mannitol to the culture medium. Addition of 82 mM mannitol or increasing sucrose concentration to 132 mM had similar effects on repressing growth. Cyanidin 3-glucoside, peonidin 3-glucoside and peonidin 3-p-coumaroylglucoside are three main anthocyanins of Vitis cells. Increasing osmotic potential from –0.43 MPa to –0.8 MPa in the medium resulted in a significant intracellular accumulation of anthocyanin especially peonidin 3-glucoside in the pigmented cells. High osmotic potential appears to stimulate the methylation of anthocyanins. Osmotic potential is an important culture factor and may be useful in the controlling of anthocyanin production and composition.     

Paraquat-induced Oxidative Stress in Drosophila melanogaster: Effects of Melatonin, Glutathione, Serotonin, Minocycline, Lipoic Acid and Ascorbic Acid

The efficacy of melatonin, glutathione, serotonin, minocycline, lipoic acid and ascorbic acid in counteracting the toxicity of paraquat in Drosophila melanogaster was examined. Male Oregon wild strain flies were fed for 5 days with control food or food containing the test substance. They were transferred in groups of five to vials containing only filter paper soaked with 20 mM paraquat in 5% sucrose solution. Survival was determined 24 and 48 h later. All the substances assayed increased the survival of D. melanogaster. At equimolar concentrations (0.43 mM) melatonin was more effective than serotonin, lipoic acid and ascorbic acid. However, lower concentrations of glutathione (0.22 mM) and minocycline (0.05 mM) were as efficient as melatonin. The highest survival rate (38.6%) after 48 h of paraquat treatment was found with 2.15 mM of lipoic acid. No synergistic effect of melatonin with glutathione, serotonin, minocycline, lipoic acid and ascorbic acid was detected.     

Sucrose partitioning between vascular bundles and storage parenchyma in the sugarcane stem: a potential role for the ShSUT1 sucrose transporter

A transporter with homology to the SUT/SUC family of plant sucrose transporters was isolated from a sugarcane (Saccharum hybrid) stem cDNA library. The gene, designated ShSUT1, encodes a protein of 517 amino acids, including 12 predicted membrane-spanning domains and a large central cytoplasmic loop. ShSUT1 was demonstrated to be a functional sucrose transporter by expression in yeast. The estimated K_m for sucrose of the ShSUT1 transporter was 2 mM at pH 5.5. ShSUT1 was expressed predominantly in mature leaves of sugarcane that were exporting sucrose and in stem internodes that were actively accumulating sucrose. Immunolocalization with a ShSUT1-specific antiserum identified the protein in cells at the periphery of the vascular bundles in the stem. These cells became lignified and suberized as stem development proceeded, forming a barrier to apoplasmic solute movement. However, the movement of the tracer dye, carboxyfluorescein from phloem to storage parenchyma cells suggested that symplasmic connections are present. ShSUT1 may have a role in partitioning of sucrose between the vascular tissue and sites of storage in the parenchyma cells of sugarcane stem internodes.     

Metabolism of maltose and sucrose by microspores isolated from barley (Hordeum vulgare L.)

The aim of this work was to discover why barley (Hordeum vulgare L.) microspores die when cultured on media containing 40 mM sucrose but undergo embryogenesis on 40 mM maltose. Freshly isolated microspores were cultured for 6–24 h on media containing either [U-¹⁴C]maltose or [U-¹⁴C]sucrose at 40 mM, and the detailed distribution of ¹⁴C was determined. The amounts of glycolytic intermediates, ATP, ADP and AMP, in microspores were also measured. Cultures on sucrose differed from those on maltose in that the initial rate of metabolism was faster but declined rapidly, less ¹⁴C was recovered in polymers and more in alanine, there was extensive leakage of assimilated carbon, significant accumulation of ethanol and a lower adenylate energy charge. It is argued that microspores cultured on 40 mM sucrose die because they metabolize the sugar rapidly, become hypoxic and, as a result, accumulate large quantities of ethanol within the cells. Metabolism of maltose is slower and there is sufficient oxygen available to allow cells to survive in culture. Consequently some of the cultured cells undergo embryogenesis.P.S. thanks the Science and Engineering Research Council and Shell Research Ltd., Sittingbourne, for a Cooperative Award in Science and Engineering studentship.     

The cellular pathway of sucrose transport in developing cotyledons ofVicia faba L. andPhaseolus vulgaris L.: a physiological assessment

The cellular pathway of sugar uptake in developing cotyledons of Vicia faba L. and Phaseolus vulgaris L. seed was evaluated using a physiological approach. The cotyledon interface with the seed coat is characterised by a specialised dermal cell complex. In the case of Vicia faba cotyledons, the epidermal component of the dermal cell complex is composed of transfer cells. Sucrose is the major sugar presented to the outer surface of both cotyledons and it is taken up from the apoplasm unaltered. Estimated sucrose concentrations within the apparent free space of Vicia and Phaseolus cotyledons were 105 and 113 mM respectively. Rates of in-vitro uptake of [¹⁴C]sucrose by cotyledon segments or by whole cotyledons following physical removal or porter inactivation of the outer cells demonstrated that, for both Vicia and Phaseolus cotyledons, the dermal cell complexes are the most intense sites of sucrose uptake. Accumulation of [¹⁴C]sucrose in the storage parenchyma of whole cotyledons was directly affected by experimental manipulation of uptake by the outer cell layers and plasmolytic disruption of the interconnecting plasmodesmata. These findings indicated that sucrose accumulated by the dermal cell complexes is transported symplasmically to the storage parenchyma. Overall, it is concluded that the dermal cell complexes of the developing legume embryo, irrespective of the presence or absence of wall ingrowths, are the major sites for the uptake of sucrose released from the maternal tissues to the seed apoplasm. Thereafter, the accumulated sucrose is transported radially inward through the symplast to the storage parenchyma.Abbreviations AFS apparent free space - CF 5-(6)-carboxyfluorescein - CFDA 5-(6)-carboxyfluorescein diacetate - Mes 2-(N-morpholino)ethanesulfonic acid - PCMBS p-chloromercuribenzenesulfonic acid - SRG sulphorhodamine G The investigation was supported by funds from the Research Management Committee, The University of Newcastle and the Australian Research Council. One of us, R. McDonald, gratefully acknowledges the support of an Australian Postgraduate Research Award. We are grateful to Stella Savoury for preparing the photomicrographs.     

Sucrose level influences micropropagation and gene delivery into leaves from in vitro propagated highbush blueberry shoots

In an effort to increase in vitro blueberry (Vaccinium corymbosum L.) shoot production without negatively impacting subsequent genetic engineering experiments, studies were conducted to examine the effects of sucrose concentration in the propagation medium on shoot proliferation and on the transfer of an intron-containing -glucuronidase (GUS) gene into leaf explants from the propagated shoots. Numbers of axillary shoots >0.5 cm in length did not significantly increase for `Bluecrop' when sucrose levels were increased from 15 mM to either 29, 44 or 58 mM. The number of axillary shoots increased significantly for Duke ' and `Georgiagem' when sucrose concentrations were increased from 15 to 44 mM, and from 15 to 58 mM, respectively. Four-days of cocultivation with Agrobacterium tumefaciens strain EHA105 yielded highest GUS-expressing leaf zones on leaf explants from shoots cultured on either 15 or 29 mM sucrose. The number of GUS-expressing leaf zones was significantly lower on leaf explants derived from shoots grown on 58 mM sucrose than from those grown on 15 mM sucrose for all three cultivars, and was significantly lower on 44 mM compared to 15 mM for cultivars Duke and Georgiagem. These studies indicate shoot pretreatment conditions for optimizing subsequent blueberry genetic engineering experiments. Thus, a blueberry shoot proliferation medium containing 15–29 mM sucrose is recommended for explants later used for genetic transformation.     

Osmotic regulation of starch synthesis in potato tubers?

Using potato (Solanum tuberosum L.) tuber discs incubated in a range of mannitol concentrations it has been demonstrated that both sucrose uptake and the conversion of sucrose to starch are sensitive to the osmotic environment of the storage cells. Starch synthesis was optimised at 300 mM but declined sharply at both lower and higher osmotic concentrations. The decline in starch synthesis on either side of optimum was not proportional to the change in mannitol concentration, indicating different inhibitory mechanisms under low and high osmotica. The fraction of the total sucrose converted to starch i.e. the partitioning between sucrose and starch, was also influenced by osmotic environment. The amount of soluble material taken up by the storage cells, but not converted to starch, was maintained under mannitol concentrations (300–400 mM) which inhibited starch synthesis, indicating that sucrose uptake continued during declining starch synthesis. At mannitol concentrations above 400 mM, sucrose uptake was greatly enhanced but no significant change in starch synthesis occurred.     

The effect of pH, sucrose and ammonium sulphate concentrations on the production of bacterial cellulose (Nata-de-coco) by Acetobacter xylinum

The effect of pH, sucrose and ammonium sulphate concentrations on the production of nata-de-coco, a form of bacterial cellulose, by Acetobacter xylinum was studied. Comparisons for physical properties like thickness, wet weight, water-holding capacity (WHC), moisture content and hardness, a textural parameter were done on nata-de-coco grown in tender coconut water medium supplemented with varying concentrations of sucrose and ammonium sulphate at different pH values. The results were analysed by fitting a second-order polynomial regression equation. Response surface methodology was used to study the effect of the three variables. The study showed that A. xylinum could effectively use sucrose as the sole carbon source in coconut water medium and that cellulose production was more dependent on pH than either sucrose or ammonium sulphate concentrations. Maximum thickness of nata was obtained at pH 4.0 with 10% sucrose and 0.5% ammonium sulphate concentrations. These conditions also produced good quality nata-de-coco with a smooth surface and soft chewy texture. The study will enable efficient utilization of coconut water, a hitherto wasted byproduct of coconut industry and will also provide a new product dimension to the aggrieved coconut farmers who are not getting the right price for their product.     

Ion activities in the lateral intercellular spaces of gallbladder epithelium transporting at low external osmolarities

The ion activities in the lateral spaces of the unilateral preparation of the gallbladder of Rana catesbiana were measured by double-barrelled ion-selective microelectrodes. The bladders were bathed in a saline solution with a low osmolarity (62 mOsm) containing, in mM: 27 Na+, 27 Cl-, 2 K+, 1 Ca++, 4 HCO3-. Working at reduced osmolarities had the advantage of an increased volume transport and of widened intercellular spaces. The reference barrel recorded an electrical potential of +2.7 mV in the spaces; they contained a solution similar to the external solution. The electrodes recorded a Na+ concentration of 27 mM, a K+ concentration of 1.7 mM, a Ca++ concentration of 0.69 mM and a Cl- concentration of 28.5 mM. In the spaces there was a lower resistance between the tip of the electrode and the serosal bath than that recorded with the tip in the lumen, and injection of fluorescent dye (11 A diameter) via the electrodes did not stain the cells. The concentrations in the secretion were similar to those in the spaces. The intracellular compartment had an apparent K+ concentration of 95 mM, and the concentrations of Na+ and Cl- were both about 5 mM. These data indicate that when the gallbladder is bathed with hypotonic solutions and is transporting fluid at approximately three or four times the normal rate, there are no significant osmotic gradients between the lumen and the lateral spaces. It is suggested that transcellular transport of water is implemented by a combination of high osmotic permeabilities across both mucosal and serosal cell membranes and low reflection coefficients (for K+ salts) at the serosal cell membranes.     

Nutrient modifications for improved growth of Brassica nigra cell suspension cultures

Cell pellet yield of two Brassica nigra suspension cultures was stimulated by amino acid supplements in the growth medium. This could confound the interpretation of amino acid feeding studies involved in characterizing amino acid metabolism mutants. The nutritional requirements of one of the Brassica nigra suspension cultures growing in modified Murashige & Skoog medium were therefore reviewed. Sucrose at 2% w/v was growth limiting and amino or organic acid supplements stimulated growth rate and yield. Increasing sucrose to 6% and supplementing with 15 mM sodium succinate increased maximum cell pellet volume by 2.7 times and maximum dry weight by 2.8 times, stimulated cell enlargement and produced similar maximum numbers of cells per culture. The further addition of an amino acid supplement of 4 mM alanine, 4 mM glutamine and 1 mM glutamate produced no further improvement. The revised medium was more strongly buffered, supported cell growth for a longer period and permitted a 30-fold reduction in the minimum cell inoculum. Cells grown in the revised medium are 10-fold more resistant to growth inhibition by the tryptophan analogue 5MT. These advantages recommend the revised medium for amino acid feeding, mutant isolation and similar studies.     

Very high water permeability in vasopressin-induced endocytic vesicles from toad urinary bladder

The regulation of transepithelial water permeability in toad urinary bladder is believed to involve a cycling of endocytic vesicles containing water transporters between an intracellular compartment and the cell luminal membrane. Endocytic vesicles arising from luminal membrane were labeled selectively in the intact toad bladder with the impermeant fluid-phase markers 6-carboxyfluorescein (6CF) or fluorescein-dextran. A microsomal preparation containing labeled endocytic vesicles was prepared by cell scraping, homogenization, and differential centrifugation. Osmotic water permeability was measured by a stopped-flow fluorescence technique in which microsomes containing 50 mM mannitol, 5 mM K phosphate, pH 8.5 were subject to a 60-mM inwardly directed gradient of sucrose; the time course of endosome volume, representing osmotic water transport, was inferred from the time course of fluorescence self-quenching. Endocytic vesicles were prepared from toad bladders with hypoosmotic lumen solution treated with (group A) or without (group B) serosal vasopressin at 23 degrees C, and bladders in which endocytosis was inhibited by treatment with vasopressin at 0-2 degrees C (group C), or with vasopressin plus sodium azide at 23 degrees C (group D). Stopped-flow results in all four groups showed a slow rate of 6CF fluorescence decrease (time constants 1.0-1.7 s for exponential fit) indicating a component of nonendocytic 6CF entrapment into sealed vesicles. However, in vesicles from group A only, there was a very rapid 6CF fluorescence decrease (time constant 9.6 +/- 0.2 ms, SEM, 18 separate preparations) with an osmotic water permeability coefficient (Pf) of greater than 0.1 cm/s (18 degrees C) and activation energy of 3.9 +/- 0.8 kcal/mol (16 kJ/mol). Pf was inhibited reversibly by greater than 60% by 1 mM HgCl2. The rapid fluorescence decrease was absent in vesicles in groups B, C, and D. These results demonstrate the presence of functional water transporters in vasopressin-induced endocytic vesicles from toad bladder, supporting the hypothesis that water channels are cycled to and from the luminal membrane and providing a functional marker for the vasopressin-sensitive water channel. The calculated Pf in the vasopressin-induced endocytic vesicles is the highest Pf reported for any biological or artificial membrane.     

Enhancement of phenylethanoid glycosides biosynthesis in cell cultures of <Emphasis Type="Italic">Cistanche deserticola</Emphasis> by osmotic stress

The effect of osmotic stress on cell growth and phenylethanoid glycosides (PeGs) biosynthesis was investigated in cell suspension cultures of Cistanche deserticola Y. C. Ma, a desert medicinal plant grown in west region of China. Various initial sucrose concentrations significantly affected cell growth and PeGs biosynthesis in the suspension cultures, and the highest dry weight and PeGs accumulation reached 15.9 g l⁻¹-DW and 20.7 mg g⁻¹-DW respectively at the initial osmotic stress of 300 mOsm kg⁻¹ where the sucrose concentration was 175.3 mM. Stoichiometric analysis with different combinations of sucrose and non-metabolic sugar (mannitol) or non-sugar osmotic agents (PEG and NaCl) revealed that osmotic stress itself was an important factor for enhancing PeGs biosynthesis in cell suspension cultures of C. deserticola. The maximum PeGs contents of 26.9 and 23.8 mg g⁻¹-DW were obtained after 21 days at the combinations of 87.6 mM sucrose with 164.7 mM mannitol (303 mOsm kg⁻¹) or 20 mM PEG respectively, which was higher than that of C. deserticola cell cultures grown under an initial sucrose concentration of 175.3 mM after 30 days. The stimulated PeGs accumulation in the cell suspension cultures was correlated to the increase of phenylalanine ammonium lyase (PAL) activity induced by osmotic stress.