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PubMed1983

Colonic function and fermentation in men consuming high fiber diets.

The relationships between fermentation in the gut and colonic function were studied by using data derived from a human metabolic study. Five healthy men were fed diets that were fiber-free or contained cellulose, xylan, pectin or corn bran. Fermentation was assessed by measuring the excretion of flatus gas, volatile fatty acids (VFA) in feces and fecal pH. Colonic function was assessed by measuring transit time, fecal frequency, fecal output and fecal composition. Fibers that were only marginally fermented included cellulose and corn bran, and these fibers caused large fecal output, frequent defecations and prolonged the residence time of digesta in the gut; feces contained high levels of neutral detergent fiber (NDF); neither diet influenced fecal pH nor flatus gas excretion; and only corn bran increased VFA excretion in feces. Fibers that were mostly fermented in the gut included xylan and pectin, and these fibers did not influence fecal frequency or fecal output, but they did decrease transit time; both diets caused high levels of flatus gas to be excreted; pectin caused higher VFA excretion in feces and lower fecal pH. The excretion of VFA in feces was highly correlated with total fecal output, and high levels of VFA were associated with low flatus gas excretion. Mutagenic activity in feces was negligible for all subjects on all diets as measured by the fluctuation test.

Adult↗
PubMed1988

Effect of hypothyroidism on methylmalonate excretion and hepatic vitamin B-12 levels in rats.

The effect of hypo- and hyperthyroidism on vitamin B-12 metabolism in the rat was studied by measuring methylmalonic acid excretion, B-12 content of liver and oxidation of 2-[14C]histidine. Ten percent pectin was added to increase severity of B-12 deficiency. The addition of thiouracil to a diet containing 10% pectin decreased the excretion of methylmalonic acid suggesting an amelioration of the B-12 deficiency. It was found that part of this decreased methylmalonic acid excretion was due to a decreased food consumption with a correspondingly decreased intake of branched-chain amino acids which are precursors of methylmalonic acid. When attempts were made to increase the protein intake of animals receiving thiouracil so their amino acid intake was equal to that of the control animals, methylmalonic acid excretion was still lower than that of the controls. It was also found that the vitamin B-12 content of the liver was higher in the animals receiving thiouracil than in the controls. Thyroidectomy had the same effect as feeding thiouracil. Liver B-12 levels are rapidly depleted on a B-12 deficient diet containing 10% pectin. It appears that hypothyroidism, induced either by thyroidectomy or by feeding thiouracil, slows the rate of depletion of hepatic B-12 which in turn facilitates the metabolism of methylmalonic acid and decreases its excretion in the urine.

Animals↗
PubMed1988

Long-term effects of fermentable fibers on rat colonic pH and epithelial cell cycle.

The long-term effects of fermentable fibers on colonic luminal pH and the epithelial cell cycle were compared in 50 male Sprague-Dawley rats fed either a defined basal fiber-free diet or the basal diet supplemented with 10% pectin, cellulose or guar or with 20% oat bran. After 8 mo, in vivo pH measurements revealed that acidification of luminal contents occurred in the cecum and in mid and distal colons of rats fed fiber-supplemented diets when compared with the fiber-free controls (P less than 0.05). Pectin and guar produced the greatest acidification of luminal contents, the largest increase in cecal surface area and the highest percentage of colonic cells in S-phase, as measured by flow cytometry. In the proximal colon of the pectin group 9.2 +/- 0.5% of cells were in S-phase (6.3 +/- 0.8% with the fiber-free group) (P less than 0.05) and in the distal colon of the guar group 10.9 +/- 1.4% were in S-phase (7.1 +/- 0.5% with the fiber-free group) (P less than 0.05). Even though the most fermentable fibers produced the greatest mitogenic response, there was no site-specific correlation between pH and mucosal cell growth except in the cecum. This suggests that fibers may act as colon cell growth factors by some mechanism other than extracellular pH changes.

Animals↗
PubMed1989

Differential changes in the urinary excretion of two orally administered polyethylene glycol markers (PEG 900 and PEG 4000) in rats after feeding various carbohydrate gelling agents.

The urinary excretion of two orally administered polyethylene glycol markers (PEG 900 and PEG 4000) was measured in rats after feeding various carbohydrate gelling agents. Pectin, guaran, methylcellulose, and carrageenan were added (20% wt/wt) to a fiber-free control diet and were fed for 4 wk prior to the experiment. Excretion of 3H-PEG 900 and 14C-PEG 4000 was measured over a period of 96 h after administration of the markers in the drinking water. In general, the ratio of PEG 4000 to PEG 900 in the urine increased after fiber feeding: from 0.20 in the controls to 0.31, 0.37, 0.29, or 0.27 (medians) in the pectin-, guaran-, methylcellulose-, or carrageenan-fed group, respectively. The pattern of excretion of the two PEG markers in rats fed the fiber-free diet differed from that in the polysaccharide-fed rats. Pectin and guaran, two polysaccharides readily fermented by intestinal bacteria, led to a higher excretion of PEG 4000 but an unaltered excretion of PEG 900, whereas methylcellulose and carrageenan, two polysaccharides more inert against microbial degradation, were associated with a lower excretion of PEG 900 with unchanged excretion of PEG 4000. The study shows that polysaccharides, which may be representative of the soluble portion of dietary fiber, can influence the intestinal permeability of larger molecules. The microbiologically degradable polysaccharides in particular may lead to an increased absorption of larger molecules.

Animals↗
PubMed1997

Dietary fat and fiber modulate the effect of carcinogen on colonic protein kinase C lambda expression in rats.

To elucidate the mechanisms by which dietary factors influence the risk of colon cancer, we investigated the effect of select dietary fats and fibers on atypical protein kinase C (PKC) lambda expression. Azoxymethane- and saline (control)-injected rats were fed diets containing either corn oil or fish oil (15 g/100 g) and either cellulose or pectin (6 g/100 g) and killed at two time points (15 and 37 wk) in a 2 x 2 x 2 x 2 factorial design. Colonic PKC lambda protein and mRNA levels were determined using immunoblotting and relative competitive polymerase chain reaction, respectively. Azoxymethane suppressed cytosolic PKC lambda protein levels compared with the saline controls at both time points, and this suppression was partially blocked by fish oil feeding at 15 wk and pectin at 37 wk. Also, at 15 wk, azoxymethane-injected rats fed corn oil had higher levels of membrane PKC lambda relative to the other treatment groups. Overall, expression of PKC lambda mRNA was not correlated with differences in the respective isozyme protein levels. Therefore, the chemopreventive effects of dietary fish oil and pectin are associated with the blockage of azoxymethane-induced alterations in colonic PKC lambda protein expression.

Animals↗
PubMed1999

Hamsters and guinea pigs differ in their plasma lipoprotein cholesterol distribution when fed diets varying in animal protein, soluble fiber, or cholesterol content.

There were two objectives to these studies: 1) to compare the lipoprotein cholesterol distribution in two animal models in response to different dietary treatments and 2) to assess whether the hypercholesterolemia induced by high cholesterol intake could be reversed by consumption of vegetable-protein and/or dietary fiber. Guinea pigs, which carry the majority of plasma cholesterol in LDL, and hamsters, with a higher distribution of cholesterol in HDL, were evaluated in three different studies. In Study 1, animals were fed semi-purified diets for 4 wk with proportions of 60:40, 20:80 or 0:100 (w/w) of casein/ soybean protein. Hamsters and guinea pigs that consumed 100% soybean protein had lower plasma total cholesterol (TC) than those fed diets containing casein (P < 0.01). In Study 2, three doses of dietary pectin (2.7, 5.4, or 10.7 g/100g) added in place of cellulose were tested. Intake of 10.7 g/100 g pectin resulted in the lowest plasma TC concentrations for both species (P < 0.01). Although the TC lowering was similar in studies 1 and 2, the lipoprotein cholesterol distribution differed. Whereas the differences in plasma cholesterol were in LDL in guinea pigs, hamsters exhibited differences in both non-HDL and HDL cholesterol. In study 3, animals were fed 100% soybean protein, 10.7 g/100 g pectin, and three doses of dietary cholesterol: 0.04, 0.08, or 0.16 g/100 g, which is equivalent to 300, 600, or 1,200 mg/d in humans. Guinea pigs and hamsters had the highest plasma LDL and hepatic cholesterol concentrations when they consumed 0.16 g/100 g of cholesterol (P < 0.01). However, intake of 0.08 g/100 g of cholesterol resulted in lower plasma LDL cholesterol concentrations than did consuming high animal protein (60:40 casein/ soy) or low soluble fiber (2.7 g/100 g). Relatively high levels of dietary cholesterol combined with vegetable protein and soluble fiber resulted in desirable lipoprotein profiles in animal models that significantly differ in their lipoprotein cholesterol distribution.

Analysis of Variance↗
PubMed2006

Protein phosphatases 1 and 2A and the regulation of calcium uptake and pollen tube development in Picea wilsonii.

To investigate the roles of protein phosphatases 1 and 2A in the development of pollen tubes of Picea wilsonii Mast., pollen grains were cultured in standard medium in the presence and absence of the protein phosphatase inhibitors okadaic acid and calyculin A. At nanomolar concentrations, these compounds blocked pollen tube growth, causing abnormal morphologies of the pollen tubes. Studies with Fluo-3 revealed that the inhibitors reduced the pollen-tube tip-to-base cytoplasmic calcium (Ca(2+)) gradient and arrested extracellular Ca(2+) uptake. The transmission electron microscope observations indicated that the fusion of paramural bodies with plasma membranes occurred frequently in the tip and sub-tip regions of control pollen tubes, but fusion rarely occurred in inhibitor-treated pollen tubes. Staining with aniline blue showed that callose accumulated in the tip regions of inhibitor-treated pollen tubes. Immunolabeling of pollen tubes revealed that acidic pectin epitopes recognized by the monoclonal antibody JIM5 were present in the tip region and on the flanks of the sub-tip in normal pollen tubes. In inhibitor-treated pollen tubes, these epitopes existed only in the extreme tip region and at higher concentrations than in control pollen tubes. The esterified pectin recognized by JIM7 was located preferentially at the extreme tip region in normal pollen tubes, but at basal sites in inhibitor-treated tubes. Fourier transform infrared (FTIR) analysis further confirmed the changes in acidic and esterified pectin distributions and their relative contents. These results suggest that protein phosphatase 1 or 2A, or both, are involved in the regulation of Ca(2+) uptake across the plasma membrane, in exocytotic activity and in the biosynthesis of cell wall components, all processes that occur in the tip region of pollen tubes and that control pollen tube development.

Biological Transport↗
PubMed2001

Colletotrichum gloeosporioides pelB is an important virulence factor in avocado fruit-fungus interaction.

Colletotrichum gloeosporioides is an important pathogen of tropical and subtropical fruits. The C. gloeosporioides pelB gene was disrupted in the fungus via homologous recombination. Three independent isolates, GD-14, GD-23, and GD-29, did not produce or secrete pectate lyase B (PLB) and exhibited 25% lower pectate lyase (PL) and pectin lyase (PNL) activities and 15% higher polygalacturonase (PG) activity than the wild type. The PLB mutants exhibited no growth reduction on glucose, Na polypectate, or pectin as the sole carbon source at pH 3.8 or 6.0, except for a 15% reduction on pectin at pH 6.0. When pelB mutants were inoculated onto avocado fruits, however, a 36 to 45% reduction in estimated decay diameter was observed compared with the two controls, the wild type and undisrupted transformed isolate. In addition, these pelB mutants induced a significantly higher host phenylalanine ammonia lyase activity as well as the antifungal diene, which is indicative of higher host resistance. These results suggest that PLB is an important factor in the attack of C. gloeosporioides on avocado fruit, probably as a result of its virulence factor and role in the induction of host defense mechanisms.

Colletotrichum↗
PubMed1987

Effect of dietary fiber on pancreatic lipase activity in vitro.

Lipase activity was measured in buffer solutions and in human duodenal juice after incubation with wheat bran, psyllium, pectin, lignin, guar gum, and cellulose. In the presence of wheat bran and pectin, activity of both enzymes was inhibited, whereas psyllium reduced only lipase activity in duodenal juice. The influence was relatively small, it measured between 12.0 and 34.8% if 12.5 g/L of dietary fiber were tested. Maximal effect required about 60 min of incubation. Inhibitory activity was destroyed after 30-min treatment with hydrochloric acid (pH 1.5) or cooking (95 degrees C). Inhibitors in pectin were more heat-resistant. It is concluded that dietary fibers exert inhibitory actions on pancreatic lipase; in man unfavorable effects could occur in exocrine pancreatic insufficiency.

Animals↗
PubMed1996

Regulatory systems modulating the transcription of the pectinase genes of Erwinia chrysanthemi are conserved in Escherichia coli.

To depolymerize plant pectin, the phytopathogenic enterobacterium Erwinia chrysanthemi produces five isoenzymes of pectate lyases encoded by the five genes pelA, pelB, pelC, pelD and pelE. In Er. chrysanthemi, all genes involved in pectin degradation are specifically controlled by the KdgR repressor and are induced in the presence of a pectin catabolic product, 2-keto-3-deoxygluconate (KDG). transcription of the pectinase genes is dependent on many environmental conditions. Transcriptional fusions present on low-copy-number plasmids were used to study the regulation of the pel genes in a heterologous host, Escherichia coli. Some physiological regulations that take place in Er. chrysanthemi are conserved in E. coli. The five pel fusions in E. coli are affected by growth phase, catabolite repression and anaerobic growth conditions and are induced in the presence of galacturonate, a sugar whose catabolism leads to the formation of KDG, the inducer of pel transcription in Er. chrysanthemi. Expression of pelE increased with the osmolarity of the culture medium. In contrast, the regulation of pel expression by temperature or nitrogen starvation, observed in Er. chrysanthemi, was not conserved in E. coli, suggesting that the mechanisms responsible for these regulations are specific to Er. chrysanthemi. Analysis of different E. coli mutants allowed some regulators affecting the transcription of the pel genes to be identified. In E. coli, the growth-phase regulation of the pel genes is not dependent on the RpoS sigma factor and the fnr gene is not involved in the increase of pel expression in oxygen-limited conditions. The gene hns, involved in the regulation of numerous genes, appears to affect pel expression but the effects of E. coli hns mutations are not related to osmoregulation. In contrast, this analysis clearly demonstrates the interchangeability of two regulatory systems of E. coli and Er. chrysanthemi: the global control exerted by the catabolite activator protein CAP and the specific regulation mediated by the KdgR repressor.

Anaerobiosis↗
PubMed2004

The biosynthesis of UDP-galacturonic acid in plants. Functional cloning and characterization of Arabidopsis UDP-D-glucuronic acid 4-epimerase.

UDP-GlcA 4-epimerase (UGlcAE) catalyzes the epimerization of UDP-alpha-D-glucuronic acid (UDP-GlcA) to UDP-alpha-D-galacturonic acid (UDP-GalA). UDP-GalA is a precursor for the synthesis of numerous cell-surface polysaccharides in bacteria and plants. Using a biochemical screen, a gene encoding AtUGlcAE1 in Arabidopsis (Arabidopsis thaliana) was identified and the recombinant enzyme biochemically characterized. The gene belongs to a small gene family composed of six isoforms. All members of the UGlcAE gene family encode a putative type-II membrane protein and have two domains: a variable N-terminal region approximately 120 amino acids long composed of a predicted cytosolic, transmembrane, and stem domain, followed by a large conserved C-terminal catalytic region approximately 300 amino acids long composed of a highly conserved catalytic domain found in a large protein family of epimerase/dehydratases. The recombinant epimerase has a predicted molecular mass of approximately 43 kD, although size-exclusion chromatography suggests that it may exist as a dimer (approximately 88 kD). AtUGlcAE1 forms UDP-GalA with an equilibrium constant value of approximately 1.9 and has an apparent K(m) value of 720 microm for UDP-GlcA. The enzyme has maximum activity at pH 7.5 and is active between 20 degrees C and 55 degrees C. Arabidopsis AtUGlcAE1 is not inhibited by UDP-Glc, UDP-Gal, or UMP. However, the enzyme is inhibited by UDP-Xyl and UDP-Ara, suggesting that these nucleotide sugars have a role in regulating the synthesis of pectin. The cloning of the AtUGlcAE1 gene will increase our ability to investigate the molecular factors that regulate pectin biosynthesis in plants. The availability of a functional recombinant UDP-GlcA 4-epimerase will be of considerable value for the facile generation of UDP-d-GalA in the amounts required for detailed studies of pectin biosynthesis.

Amino Acid Sequence↗
PubMed2006

Response of the leaf cell wall to desiccation in the resurrection plant Myrothamnus flabellifolius.

The Myrothamnus flabellifolius leaf cell wall and its response to desiccation were investigated using electron microscopic, biochemical, and immunocytochemical techniques. Electron microscopy revealed desiccation-induced cell wall folding in the majority of mesophyll and epidermal cells. Thick-walled vascular tissue and sclerenchymous ribs did not fold and supported the surrounding tissue, thereby limiting the extent of leaf shrinkage and allowing leaf morphology to be rapidly regained upon rehydration. Isolated cell walls from hydrated and desiccated M. flabellifolius leaves were fractionated into their constituent polymers and the resulting fractions were analyzed for monosaccharide content. Significant differences between hydrated and desiccated states were observed in the water-soluble buffer extract, pectin fractions, and the arabinogalactan protein-rich extract. A marked increase in galacturonic acid was found in the alkali-insoluble pectic fraction. Xyloglucan structure was analyzed and shown to be of the standard dicotyledonous pattern. Immunocytochemical analysis determined the cellular location of the various epitopes associated with cell wall components, including pectin, xyloglucan, and arabinogalactan proteins, in hydrated and desiccated leaf tissue. The most striking observation was a constitutively present high concentration of arabinose, which was associated with pectin, presumably in the form of arabinan polymers. We propose that the arabinan-rich leaf cell wall of M. flabellifolius possesses the necessary structural properties to be able to undergo repeated periods of desiccation and rehydration.

Cell Wall↗
PubMed1994

Aluminum-Induced Rapid Root Inhibition and Changes in Cell-Wall Components of Squash Seedlings.

Growth of squash (Cucurbita maxima Duch.) roots was significantly inhibited by 1 mM AlCl3 as early as 1 h after the treatment. The growth inhibition was confined to the elongating zone (1-6 mm from the root tip). Chemical analysis of cell-wall polysaccharides from roots revealed that aluminum increased pectin, hemi-cellulose, and cellulose contents after 3 h of treatment. The effect of aluminum on pectin content was found in the elongating zone including the root tip, whereas change in cellulose content was confined to only nonelongating zones. Hemicellulose content increased in all of the regions along the root axis. The increase in the pectin fraction was due to the increases in uronic acids, galactose, and arabinose constituents, whereas hemicellulose content changed due to increases in glucose, xylose, galactose, and arabinose. The results clearly indicate that aluminum rapidly reduced squash root growth by inhibiting cell elongation and altering metabolism of cell-wall polysaccharides in the nonelongating zone as well as in the elongating zone.

Journal Article↗
PubMed1997

Localization of Pectic Galactan in Tomato Cell Walls Using a Monoclonal Antibody Specific to (1[->]4)-[beta]-D-Galactan.

To develop antibody probes for the neutral side chains of pectins, antisera were generated to a pectic galactan isolated from tomato (Lycopersicon esculentum) pericarp cell walls and to a (1[->]4)-[beta]-galactotetraose-bovine serum albumin neoglycoprotein. The use of these two antisera in immunochemical assays and immunolocalization studies indicated that they had very similar specificities. A monoclonal antibody (LM5) was isolated and characterized subsequent to immunization with the neoglycoprotein. Hapten inhibition studies revealed that the antibody specifically recognized more than three contiguous units of (1[->]4)-[beta]-galactosyl residues. The antigalactan antibody was used to immunolocalize the galactan side chains of pectin in tomato fruit pericarp and tomato petiole cell walls. Although the LM5 epitope occurs in most cell walls of the tomato fruit, it was absent from both the locular gel and the epidermal and subepidermal cells. Furthermore, in contrast to other anti-pectin antibodies, LM5 did not label the cell wall thickenings of tomato petiole collenchyma.

Journal Article↗
PubMed1997

Molecular Rigidity in Dry and Hydrated Onion Cell Walls.

Solid-state nuclear magnetic resonance relaxation experiments can provide information on the rigidity of individual molecules within a complex structure such as a cell wall, and thus show how each polymer can potentially contribute to the rigidity of the whole structure. We measured the proton magnetic relaxation parameters T2 (spin-spin) and T1p (spin-lattice) through the 13C-nuclear magnetic resonance spectra of dry and hydrated cell walls from onion (Allium cepa L.) bulbs. Dry cell walls behaved as rigid solids. The form of their T2 decay curves varied on a continuum between Gaussian, as in crystalline solids, and exponential, as in more mobile materials. The degree of molecular mobility that could be inferred from the T2 and T1p decay patterns was consistent with a crystalline state for cellulose and a glassy state for dry pectins. The theory of composite materials may be applied to explain the rigidity of dry onion cell walls in terms of their components. Hydration made little difference to the rigidity of cellulose and most of the xyloglucan shared this rigidity, but the pectic fraction became much more mobile. Therefore, the cellulose/xyloglucan microfibrils behaved as solid rods, and the most significant physical distinction within the hydrated cell wall was between the microfibrils and the predominantly pectic matrix. A minor xyloglucan fraction was much more mobile than the microfibrils and probably corresponded to cross-links between them. Away from the microfibrils, pectins expanded upon hydration into a nonhomogeneous, but much softer, almost-liquid gel. These data are consistent with a model for the stress-bearing hydrated cell wall in which pectins provide limited stiffness across the thickness of the wall, whereas the cross-linked microfibril network provides much greater rigidity in other directions.

Journal Article↗
PubMed1997

Effect of Antisense Suppression of Endopolygalacturonase Activity on Polyuronide Molecular Weight in Ripening Tomato Fruit and in Fruit Homogenates.

Fruit of tomato (Lycopersicon esculentum Mill.) in which endopolygalacturonase (PG) activity had been suppressed to <1% of wild-type levels were slightly firmer than nontransgenic controls later in ripening. Enzymically inactive cell walls were prepared from these ripening fruit using Tris-buffered phenol. When extracted with chelator followed by Na2CO3, the amounts of pectin solubilized from cell walls of nontransgenic control or from transgenic antisense PG fruit were similar. Size-exclusion chromatography analysis showed that, relative to controls, in antisense PG fruit polyuronide depolymerization was delayed in the chelator-soluble fraction throughout ripening and reduced in the Na2CO3-soluble fraction at the overripe stage. Reduced pectin depolymerization rather than altered extractability thus may have contributed to enhanced fruit firmness. Substantially larger effects of suppressed PG activity were detected in tomato fruit homogenates processed to paste. In control paste the majority of the polyuronide was readily soluble in water and was very highly depolymerized. In antisense PG paste the proportion of polyuronide solubilized by water was reduced, and polyuronides retained a high degree of polymerization. The suppression of fruit PG activity thus has a small effect on polyuronide depolymerization in the fruit but a much larger effect in paste derived from these fruit. This indicates that in the cell wall PG-mediated degradation of polyuronide is normally restricted but that in tissue homogenates or in isolated cell walls this restriction is removed and extensive pectin disassembly results unless PG is inactivated.

Journal Article↗
PubMed1999

Changes in cell wall polysaccharides of green bean pods during development.

The changes in cell wall polysaccharides and selected cell wall-modifying enzymes were studied during the development of green bean (Phaseolus vulgaris L.) pods. An overall increase of cell wall material on a dry-weight basis was observed during pod development. Major changes were detected in the pectic polymers. Young, exponentially growing cell walls contained large amounts of neutral, sugar-rich pectic polymers (rhamnogalacturonan), which were water insoluble and relatively tightly connected to the cell wall. During elongation, more galactose-rich pectic polymers were deposited into the cell wall. In addition, the level of branched rhamnogalacturonan remained constant, while the level of linear homogalacturonan steadily increased. During maturation of the pods, galactose-rich pectic polymers were degraded, while the accumulation of soluble homogalacturonan continued. During senescence there was an increase in the amount of ionically complexed pectins, mainly at the expense of freely soluble pectins. The most abundant of the enzymes tested for was pectin methylesterase. Peroxidase, beta-galactosidase, and alpha-arabinosidase were also detected in appreciable amounts. Polygalacturonase was detected only in very small amounts throughout development. The relationship between endogenous enzyme levels and the properties of cell wall polymers is discussed with respect to cell wall synthesis and degradation.

Carboxylic Ester Hydrolases↗
PubMed1976

Effect of Benzyladenine, 2,4-Dichlorophenoxyacetic Acid, and d-Glucose on myo-Inositol Metabolism in Acer pseudoplatanus L. Cells Grown in Suspension Culture.

Suspension cultures of Acer pseudoplatanus L. cells grown for 15 days in medium (T. Murashige and F. Skoog. 1962. Physiol. Plant. 15: 473-497) contained 3% sucrose, 1 mg/l 6-benzylaminopurine (BA), and 0.1 mg/l 2,4-dichlorophenoxyacetic acid (2,4-D), referred to here as normal media, removed newly added myo-inositol-2-(3)H up to 100 mg/l in 24 hours and utilized up to 20% of this cyclitol for pectin biosynthesis. When the BA content of the growth medium was raised 10-fold, uptake of myo-inositol was drastically reduced and very little was available for pectin biosynthesis. Neither cell growth as measured by packed cell volume or by dry weight, nor monomer composition of pectic polysaccharides was affected by the increased level of cytokinin. Increasing, 2,4-d 10-fold instead of BA had little or no effect on myo-inositol uptake, although it did reduce the amount of myo-inositol utilized for pectin biosynthesis. Cells grown 15 days in normal media failed to remove added myo-inositol if 3% d-glucose was included. The net result was similar to that found in cells grown in the high BA condition. If a trace amount of d-galactose-1-(14)C was supplied to cells after 15 days of growth in normal, high BA, or high 2,4-d media, there was no significant variation in uptake and utilization of label among the three growth conditions.

Journal Article↗