Oleic,Linoleic and Linolenic Acids Increase ROS Production by Fibroblasts via NADPH Oxidase Activation

The effect of oleic, linoleic and γ-linolenic acids on ROS production by 3T3 Swiss and Rat 1 fibroblasts was investigated. Using lucigenin-amplified chemiluminescence, a dose-dependent increase in extracellular superoxide levels was observed during the treatment of fibroblasts with oleic, linoleic and γ-linolenic acids. ROS production was dependent on the addition of β-NADH or NADPH to the medium. Diphenyleneiodonium inhibited the effect of oleic, linoleic and γ-linolenic acids on fibroblast superoxide release by 79%, 92% and 82%, respectively. Increased levels of p47^phox phosphorylation due to fatty acid treatment were detected by Western blotting analyses of fibroblast proteins. Increased p47^phox mRNA expression was observed using real-time PCR. The rank order for the fatty acid stimulation of the fibroblast oxidative burst was as follows: γ-linolenic > linoleic > oleic. In conclusion, oleic, linoleic and γ-linolenic acids stimulated ROS production via activation of the NADPH oxidase enzyme complex in fibroblasts.     

A Combined Transcriptomics and Lipidomics Analysis of Subcutaneous,Epididymal and Mesenteric Adipose Tissue Reveals Marked Functional Differences

Depot-dependent differences in adipose tissue physiology may reflect specialized functions and local interactions between adipocytes and surrounding tissues. We combined time-resolved microarray analyses of mesenteric- (MWAT), subcutaneous- (SWAT) and epididymal adipose tissue (EWAT) during high-fat feeding of male transgenic ApoE3Leiden mice with histology, targeted lipidomics and biochemical analyses of metabolic pathways to identify differentially regulated processes and site-specific functions. EWAT was found to exhibit physiological zonation. De novo lipogenesis in fat proximal to epididymis was stably low, whereas de novo lipogenesis distal to epididymis and at other locations was down-regulated in response to high-fat diet. The contents of linoleic acid and α-linolenic acid in EWAT were increased compared to other depots. Expression of the androgen receptor (Ar) was higher in EWAT than in MWAT and SWAT. We suggest that Ar may mediate depot-dependent differences in de novo lipogenesis rate and propose that accumulation of linoleic acid and α-linolenic acid in EWAT is favored by testosterone-mediated inhibition of de novo lipogenesis and may promote further elongation and desaturation of these polyunsaturated fatty acids during spermatogenesis.     

Lipid Composition of Pea and Bean Leaves during Chloroplast Development

The changes in composition of the complex lipids were followed during the greening of dark-grown pea (Pisum sativum) and bean (Phaseolus vulgaris) seedlings. No significant changes in glycerolipid concentrations in the leaves were observed during the early stages of greening (0-8 hour for peas and 0-12 hour for beans). On further greening, there was an increase in the proportion of galactolipids and a decrease in the phospholipids. The fatty acid composition of the galactolipids remained constant during 24 hours of greening, but there was a slight increase in α-linolenic acid at 72 hours in the bean. The percentage of α-linolenic acid in the phospholipids and in sulfolipid showed a marked increase between 24 and 72 hours in the bean. Trans-δ³-hexadecenoic acid was the major fatty acid of phosphatidyl glycerol in bean leaves at 72 hours, but it was barely detectable at 24 hours. The lipid composition of greening leaves is discussed in relation to the fine structure and photochemical activity of the developing plastids.     

Bifidobacterium breve with α-Linolenic Acid and Linoleic Acid Alters Fatty Acid Metabolism in the Maternal Separation Model of Irritable Bowel Syndrome

The aim of this study was to compare the impact of dietary supplementation with a Bifidobacterium breve strain together with linoleic acid & α-linolenic acid, for 7 weeks, on colonic sensitivity and fatty acid metabolism in rats. Maternally separated and non-maternally separated Sprague Dawley rats (n = 15) were orally gavaged with either B. breve DPC6330 (10⁹ microorganisms/day) alone or in combination with 0.5% (w/w) linoleic acid & 0.5% (w/w) α-linolenic acid, daily for 7 weeks and compared with trehalose and bovine serum albumin. Tissue fatty acid composition was assessed by gas-liquid chromatography and visceral hypersensitivity was assessed by colorectal distension. Significant differences in the fatty acid profiles of the non-separated controls and maternally separated controls were observed for α-linolenic acid and arachidonic acid in the liver, oleic acid and eicosenoic acid (c11) in adipose tissue, and for palmitoleic acid and docosahexaenoic acid in serum (p<0.05). Administration of B. breve DPC6330 to MS rats significantly increased palmitoleic acid, arachidonic acid and docosahexaenoic acid in the liver, eicosenoic acid (c11) in adipose tissue and palmitoleic acid in the prefrontal cortex (p<0.05), whereas feeding B. breve DPC6330 to non separated rats significantly increased eicosapentaenoic acid and docosapentaenoic acid in serum (p<0.05) compared with the NS un-supplemented controls. Administration of B. breve DPC6330 in combination with linoleic acid and α-linolenic acid to maternally separated rats significantly increased docosapentaenoic acid in the serum (p<0.01) and α-linolenic acid in adipose tissue (p<0.001), whereas feeding B. breve DPC6330 with fatty acid supplementation to non-separated rats significantly increased liver and serum docosapentaenoic acid (p<0.05), and α-linolenic acid in adipose tissue (p<0.001). B. breve DPC6330 influenced host fatty acid metabolism. Administration of B. breve DPC6330 to maternally separated rats significantly modified the palmitoleic acid, arachidonic acid and docosahexaenoic acid contents in tissues. The effect was not observed in non-separated animals.     

Polyunsaturated Fatty Acid Biosynthesis in Cotyledons from Germinating and Developing Cucumis sativus L. Seedlings

Etiolated Cucumis sativus L. cotyledons preferentially catabolized exogenous [1-¹⁴C]oleic acid and [1-¹⁴C]linoleic acid with relatively little incorporation into complex lipids or desaturation of the ¹⁴C-labeled fatty acids. Following a 16-hour exposure to light, the greening cotyledons efficiently desaturated the exogenous ¹⁴C-labeled fatty acids. A small amount of oleate desaturation to linoleate was observed in etiolated tissue, but hardly any linoleate desaturation to α-linolenate was detected. Both oleate and linoleate desaturation showed diurnal variations with maxima at the end of light periods and minima at the end of dark periods. Illumination of etiolated tissue by flashing light, as opposed to continuous light, failed to stimulate either chlorophyll or α-linolenic acid biosynthesis, and both processes could be halted or reversed by 10 micrograms per milliliter cycloheximide. Production of polyunsaturated fatty acids from [1-¹⁴C]acetate, [1-¹⁴C]oleic acid, and [1-¹⁴C]linoleic acid, by greening cucumber cotyledons, was markedly affected by tissue integrity with finely chopped cotyledons having very little capacity for their synthesis and intact seedlings showing the highest rates.     

The ABC Transporter PXA1 and Peroxisomal β-Oxidation Are Vital for Metabolism in Mature Leaves of Arabidopsis during Extended Darkness

Fatty acid β-oxidation is essential for seedling establishment of oilseed plants, but little is known about its role in leaf metabolism of adult plants. Arabidopsis thaliana plants with loss-of-function mutations in the peroxisomal ABC-transporter1 (PXA1) or the core β-oxidation enzyme keto-acyl-thiolase 2 (KAT2) have impaired peroxisomal β-oxidation. pxa1 and kat2 plants developed severe leaf necrosis, bleached rapidly when returned to light, and died after extended dark treatment, whereas the wild type was unaffected. Dark-treated pxa1 plants showed a decrease in photosystem II efficiency early on and accumulation of free fatty acids, mostly α-linolenic acid [18:3(n-3)] and pheophorbide a, a phototoxic chlorophyll catabolite causing the rapid bleaching. Isolated wild-type and pxa1 chloroplasts challenged with comparable α-linolenic acid concentrations both showed an 80% reduction in photosynthetic electron transport, whereas intact pxa1 plants were more susceptible to the toxic effects of α-linolenic acid than the wild type. Furthermore, starch-free mutants with impaired PXA1 function showed the phenotype more quickly, indicating a link between energy metabolism and β-oxidation. We conclude that the accumulation of free polyunsaturated fatty acids causes membrane damage in pxa1 and kat2 plants and propose a model in which fatty acid respiration via peroxisomal β-oxidation plays a major role in dark-treated plants after depletion of starch reserves.     

Excess Linoleic Acid Increases Collagen I/III Ratio and “Stiffens” the Heart Muscle Following High Fat Diets

Controversy exists on the benefits versus harms of n-6 polyunsaturated fatty acids (n-6 PUFA). Although n-6 PUFA demonstrates anti-atherosclerotic properties, survival following cardiac remodeling may be compromised. We hypothesized that n-6 PUFA like linoleic acid (LA) or other downstream PUFAs like γ-linolenic acid or arachidonic acid alter the transforming growth factor-β (TGFβ)-collagen axis in the heart. Excess dietary LA increased the collagen I/III ratio in the mouse myocardium, leading to cardiac “stiffening” characterized by impaired transmitral flow indicative of early diastolic dysfunction within 5 weeks. In vitro, LA under TGFβ1 stimulation increased collagen I and lysyl oxidase (LOX), the enzyme that cross-links soluble collagen resulting in deposited collagen. Overexpression of fatty acid desaturase 2 (fads2), which metabolizes LA to downstream PUFAs, reduced collagen deposits, LOX maturation, and activity with LA, whereas overexpressing fads1, unrelated to LA desaturation, did not. Furthermore, fads2 knockdown by RNAi elevated LOX activity and collagen deposits in fibroblasts with LA but not oleic acid, implying a buildup of LA for aggravating such pro-fibrotic effects. As direct incubation with γ-linolenic acid or arachidonic acid also attenuated collagen deposits and LOX activity, we concluded that LA itself, independent of other downstream PUFAs, promotes the pro-fibrotic effects of n-6 PUFA. Overall, these results attempt to reconcile opposing views of n-6 PUFA on the cardiovascular system and present evidence supporting a cardiac muscle-specific effect of n-6 PUFAs. Therefore, aggravation of the collagen I/III ratio and cardiac stiffening by excess n-6 PUFA represent a novel pathway of cardiac lipotoxicity caused by high n-6 PUFA diets.     

Effects of CO(2) Concentration during Growth on Fatty Acid Composition in Microalgae

The degree of unsaturation of fatty acids was higher in Chlorella vulgaris 11h cells grown with air (low-CO₂ cells) than in the cells grown with air enriched with 2% CO₂ (high-CO₂ cells). The change in the ratio of linoleic acid to α-linolenic acid was particularly significant. This change of the ratio was observed in four major lipids (monogalactosyldiacylglycerol, digalactosyldiacylglycerol, phosphatidylcholine, and phosphatidylethanolamine). The relative contents of lipid classes were essentially the same both in high-CO₂ and low-CO₂ cells. After high-CO₂ cells were transferred to low CO₂ condition, total amount of fatty acids remained constant but the relative content of α-linolenic acid increased during a 6-hour lag phase in growth with concomitant decreases in linoleic and oleic acids. When low-CO₂ cells were transferred to high CO₂ condition, total amount of fatty acids and relative content of oleic acid increased significantly. The amount of α-linolenic acid remained almost constant, while the amounts of palmitic, oleic, and linoleic acids increased. Similar, but smaller, changes in fatty acid compositions were observed in two species of green algae Chlamydomonas reinhardtii and Dunaliella tertiolecta. However, no difference was found in Euglena gracilis, Porphyridium cruentum, Anabaena variabilis, and Anacystis nidulans.     

Characterization of Transgenic Tobacco with an Increased α-Linolenic Acid Level

Microsomal ω-3 fatty acid desaturase catalyzes the conversion of 18:2 (linoleic acid) to 18:3 (α-linolenic acid) in phospholipids, which are the main constituents of extrachloroplast membranes. Transgenic tobacco (Nicotiana tabacum) plants with increased 18:3 contents (designated SIIn plants) were produced through the introduction of a construct with the tobacco microsomal ω-3 fatty acid desaturase gene under the control of the highly efficient promoter containing the E12Ω sequence. 18:3 contents in the SIIn plants were increased by about 40% in roots and by about 10% in leaves compared with the control plants. With regard to growth at 15°C and 25°C and the ability to tolerate chilling at 1°C and 5°C, there were no discernible differences between the SIIn and the control plants. Freezing tolerance in leaves and roots, which was assessed by electrolyte leakage, was almost the same between the SIIn and the control plants. The fluidity of plasma membrane from the SIIn plants was almost the same as that of the control plants. These results indicate that an increase in the 18:3 level in phospholipids is not directly involved in compensation for the diminishment in growth or membrane properties observed under low temperatures.     

Production of Dihomo-γ-Linolenic Acid by a Δ5-Desaturase-Defective Mutant of Mortierella alpina 1S-4

A mutant, which has low Δ5-desaturase activity, of an arachidonic acid-producing fungus, Mortierella alpina 1S-4, was shown to be a novel potent producer of dihomo-γ-linolenic acid (DHGA). On submerged culture under optimal conditions for 6 days at 28°C in a 10-liter fermentor, the mutant produced 3.2 g of DHGA per liter of culture broth (123 mg/g of dry mycelia), which accounted for 23.4% of the total mycelial fatty acids. Mycelial arachidonic acid amounted to only 19 mg/g of dry mycelia (0.5 g/liter of culture broth), which accounted for 3.7% of the total mycelial fatty acids. The other major mycelial fatty acids were palmitic acid (11.0%), stearic acid (12.8%), oleic acid (22.7%), linoleic acid (8.9%), γ-linolenic acid (6.5%), and lignoceric acid (7.8%). More than 97 mol% of the DHGA produced was found in the triglyceride fraction irrespective of the growth temperature employed (12 to 28°C).     

Overproduction of gamma-Linolenic and Eicosapentaenoic Acids by Algae

The pharmaceutical interest and limited availability of γ-linolenic acid (GLA) and eicosapentaenoic acid (EPA) prompted the search for genetic means for increasing the production of these fatty acids from algal sources. Cell lines of Spirulina platensis and Porphyridium cruentum resistant to the growth inhibition of the herbicide Sandoz 9785 were selected by serial transfers of the culture in the presence of increasing concentrations of the herbicide. The resistant cell lines of S. platensis overproduced GLA and those of P. cruentum overproduced EPA and were stable for at least 50 generations in the absence of the inhibitor.     

NADPH–Cytochrome P450 Reductase Mediates the Fatty Acid Desaturation of ω3 and ω6 Desaturases from Mortierella alpina

Fatty acid desaturases play an important role in maintaining the appropriate structure and function of biological membranes. The biochemical characterization of integral membrane desaturases, particularly ω3 and ω6 desaturases, has been limited by technical difficulties relating to the acquisition of large quantities of purified proteins, and by the fact that functional activities of these proteins were only tested in an NADH-initiated reaction system. The main aim of this study was to reconstitute an NADPH-dependent reaction system in vitro and investigate the kinetic properties of Mortierella alpina ω3 and ω6 desaturases in this system. After expression and purification of the soluble catalytic domain of NADPH–cytochrome P450 reductase, the NADPH-dependent fatty acid desaturation was reconstituted for the first time in a system containing NADPH, NADPH–cytochrome P450 reductase, cytochrome b5, M. alpina ω3 and ω6 desaturase and detergent. In this system, the maximum activity of ω3 and ω6 desaturase was 213.4 ± 9.0 nmol min⁻¹ mg⁻¹ and 10.0 ± 0.5 nmol min⁻¹ mg⁻¹, respectively. The highest k_cat/K_m value of ω3 and ω6 desaturase was 0.41 µM⁻¹ min⁻¹ and 0.09 µM⁻¹ min⁻¹ when using linoleoyl CoA (18:2 ω6) and oleoyl CoA (18:1 ω9) as substrates, respectively. M. alpina ω3 and ω6 desaturases were capable of using NADPH as reductant when mediated by NADPH–cytochrome P450 reductase; although, their efficiency is distinguishable from NADH-dependent desaturation. These results provide insights into the mechanisms underlying ω3 and ω6 fatty acid desaturation and may facilitate the production of important fatty acids in M. alpina.     

The biohydrogenation of α-linoleic acid and oleic acid by rumen micro-organisms

1. α-[U-¹⁴C]Linolenic acid was incubated with the rumen contents of sheep and the metabolic products were characterized by thin-layer chromatography, gas–liquid chromatography and absorption spectroscopy in the ultraviolet and infrared. 2. A tentative scheme for the biohydrogenation route to stearic acid is presented. The main pathway is through diconjugated cis–cis–cis-octadecatrienoic acid, non-conjugated trans–cis (cis–trans)-octadecadienoic acid and trans-octadecenoic acid, but other pathways are apparent. 3. Washed rumen micro-organisms possessed only a limited capacity to hydrogenate α-linolenic acid and oleic acid but the rate was greatly stimulated by a factor(s) present in the supernatant rumen liquor. 4. Pure cultures of Clostridium perfringens, Streptococcus faecalis, Escherichia coli and a coliform organism isolated from sheep faeces possessed negligible ability to hydrogenate unsaturated fatty acids compared with a mixed population of rumen micro-organisms. Butyrivibrio fibrisolvens slowly converted linoleic acid into octadecenoic acid.     

Variation in fatty acid composition of <Emphasis Type="BoldItalic">Arthrospira</Emphasis> (Spirulina) strains

A study of the fatty acid composition was made for 35 Arthrospira strains, concentrating on the most abundant fatty acids, the two polyunsaturated C₁₈ acids, linoleic and γ-linolenic acid, and palmitic acid. When grown at 30 ^∘C and low irradiance (10 μmol photon m⁻² s⁻¹), these three acids together formed 88–92% of total fatty acids. There were considerable differences in the composition of the two polyunsaturated acids. Depending on the strain, linoleic acid formed 13.1–31.5% and γ-linolenic acid formed 12.9–29.4% total fatty acids. In contrast, the range for palmitic acid was narrow: 42.3–47.6% of total fatty acids. Repeat experiments on several strains under defined conditions led to closely similar results for any particular environment, suggesting that fatty acid composition can be used as an aid in differentiating between strains. Five additional strains, which had apparently originated from the same original stock cultures as 3 of the 35 in the main study, but from different culture collections, were also assayed. With four strains the results were similar, irrespective of culture source, but with one strain marked differences occurred, especially in the polyunsaturated C₁₈ fatty acid fraction. These differences were independent of the age of the culture. In addition, straight morphotypes derived during repeat subcultures of four strains; each showed a similar fatty acid composition to that of the helical morphotypes of the same strains. A decrease in temperature from 30 to 20 ^∘C, an increase in irradiance (at 30 ^∘C) from 10 to 70 μmol photon m⁻² s⁻¹ and transfer to dark heterotrophy all favoured an increase in polyunsaturated C₁₈ fatty acids. The highest γ-linolenic acid content of any conditions was found for three strains grown heterotrophically on glucose in the dark at 30 ^∘C. A comparative study of six strains of Spirulina confirmed a previous study showing the absence of γ-linolenic acid in all Spirulina strains, thus permitting the separation of these two genera.     

Light-dependent Induction of Polyunsaturated Fatty Acid Biosynthesis in Greening Cucumber Cotyledons

Greening cucumber (Cucumis sativus L.) cotyledons exhibited dramatic increases in the ability to desaturate exogenously added [1-¹⁴C]oleic acid and [1-¹⁴C]linoleic acid within 2 to 3 hours of illumination. These increases were effectively inhibited by 10 micrograms per milliliter cycloheximide. Oleate desaturation remained at a high level in constant light for 5 to 6 days after induction and then declined by about 50%; when returned to the dark, the tissue showed a sharp decrease in conversion of [¹⁴C]oleate to [¹⁴C]linoleate. Linoleate desaturation reached a maximum about 15 hours after induction and declined immediately thereafter while the tissue still was in the light; after induction had peaked return of the tissue to the dark showed a dramatic fall of linoleate desaturation. The changes in desaturation were correlated with the conversion of the principal fatty acid in the etiolated cotyledons, linoleate, to α-linolenate, and with the assembly of the chlorophyll-containing photosynthetic membranes. The incorporation of [1-¹⁴C]acetate into lipids showed no significant light stimulation. The role of light in the regulation of certain aspects of plant metabolism during development is discussed.     

Heterologous Production of Dihomo-γ-Linolenic Acid in Saccharomyces cerevisiae

To make dihomo-γ-linolenic acid (DGLA) (20:3n-6) in Saccharomyces cerevisiae, we introduced Kluyveromyces lactis Δ12 fatty acid desaturase, rat Δ6 fatty acid desaturase, and rat elongase genes. Because Fad2p is able to convert the endogenous oleic acid to linoleic acid, this allowed DGLA biosynthesis without the need to supply exogenous fatty acids on the media. Medium composition, cultivation temperature, and incubation time were examined to improve the yield of DGLA. Fatty acid content was increased by changing the medium from a standard synthetic dropout medium to a nitrogen-limited minimal medium (NSD). Production of DGLA was higher in the cells grown at 15°C than in those grown at 20°C, and no DGLA production was observed in the cells grown at 30°C. In NSD at 15°C, fatty acid content increased up until day 7 and decreased after day 10. When the cells were grown in NSD for 7 days at 15°C, the yield of DGLA reached 2.19 μg/mg of cells (dry weight) and the composition of DGLA to total fatty acids was 2.74%. To our knowledge, this is the first report describing the production of polyunsaturated fatty acids in S. cerevisiae without supplying the exogenous fatty acids.     

Effects of Polyunsaturated Fatty Acids in Growth Medium on Lipid Composition and on Physicochemical Surface Properties of Lactobacilli

Most probiotic lactobacilli adhere to intestinal surfaces, a phenomenon influenced by free polyunsaturated fatty acids (PUFA). The present study investigated whether free linoleic acid, γ-linolenic acid, arachidonic acid, α-linolenic acid, or docosahexaenoic acid in the growth medium alters the fatty acid composition of lactobacilli and their physical characteristics. The most abundant bacterial fatty acids identified were oleic, vaccenic, and dihydrosterculic acids. PUFA, especially conjugated linoleic acid (CLA) isomers and γ-linolenic, eicosapentaenoic, docosahexaenoic, and α-linolenic acids, also were identified in lactobacilli. When lactobacilli were cultured in MRS broth supplemented with various free PUFA, the incorporation of a given PUFA into bacterial fatty acids was clearly observed. Moreover, PUFA supplementation also resulted in PUFA-dependent changes in the proportions of other fatty acids; major interconversions were seen in octadecanoic acids (18:1), their methylenated derivatives (19:cyc), and CLA. Intermittent changes in eicosapentaenoic acid proportions also were noted. These results were paralleled by minor changes in the hydrophilic or hydrophobic characteristics of lactobacilli, suggesting that PUFA interfere with microbial adhesion to intestinal surfaces through other mechanisms. In conclusion, we have demonstrated that free PUFA in the growth medium induce changes in bacterial fatty acids in relation to the regulation of the degree of fatty acid unsaturation, cyclization, and proportions of CLA and PUFA containing 20 to 22 carbons. The potential role of lactobacilli as regulators of PUFA absorption may represent another means by which probiotics could redirect the delicate balance of inflammatory mediators derived from PUFA within the inflamed intestine.     

Metabolism of Linoleic Acid or Mevalonate and 6-Pentyl-α-Pyrone Biosynthesis by Trichoderma Species

The understanding of the biosynthetic pathway of 6-pentyl-α-pyrone in Trichoderma species was achieved by using labelled linoleic acid or mevalonate as a tracer. Incubation of growing cultures of Trichoderma harzianum and T. viride with [U-¹⁴C]linoleic acid or [5-¹⁴C]sodium mevalonate revealed that both fungal strains were able to incorporate these labelled compounds (50 and 15%, respectively). Most intracellular radioactivity was found in the neutral lipid fraction. At the initial time of incubation, the radioactivity from [¹⁴C]linoleic acid was incorporated into 6-pentyl-α-pyrone more rapidly than that from [¹⁴C]mevalonate. No radioactivity incorporation was detected in 6-pentyl-α-pyrone when fungal cultures were incubated with [1-¹⁴C]linoleic acid. These results suggested that β-oxidation of linoleic acid was a probable main step in the biosynthetic pathway of 6-pentyl-α-pyrone in Trichoderma species.     

Interference in Carotenogenesis as a Mechanism of Action of the Pyridazinone Herbicide Sandoz 6706: Accumulation of C-40 Carotenoid Precursors Inhibition of beta-Carotene Synthesis and Enhancement of Phytoene Epoxidation

The herbicide Sandoz 6706 (4-chloro-5-(dimethylamino)-2-α,α,α, (trifluoro-m-tolyl)-3(2H)-pyridazinone), when applied as a preplant soil treatment at a concentration of 0.05 μg/g reduced the content of β-carotene and chlorophylls in 21-day-old wheat seedlings (Triticum aestivum L.) by 55% and 29%, respectively, without affecting the fresh or dry matter of the seedlings. At 0.8 μg/g, the herbicide reduced the content of β-carotene and chlorophyll by as much as 98%, while the fresh weight of the albino seedlings was reduced by only 24%. The effect of the herbicide on chlorophyll b was much stronger than on chlorophyll a. Time course studies of pigment synthesis in Sandoz 6706-treated seedlings showed that chlorophyll, β-carotene, cyclic xanthophylls, phytoene, phytofluene, and ζ-carotene were accumulating during the first 7 days after sowing. Later on, there was a sharp decline in the content of chlorophyll and β-carotene and a gradual reduction in the content of phytofluene, ζ-carotene, and cyclic xanthophylls; the content of phytoene remained essentially unchanged. Coinciding with the drop in content of β-carotene and chlorophyll, there was a remarkable increase in the content of epoxy phytoene. It is suggested that Sandoz 6706 might act as an inhibitor of the cyclization reaction in the biosynthetic pathway of carotenoids and that other effects, such as the bleaching of chlorophyll, are a consequence of this inhibition.