The distribution of 14C-arachidonic acid in hamster lungs is sensitive to quinacrine

Isolated hamster lungs were labelled with ¹⁴C-arachidonic acid. When the lungs were ventillated with a respirator only a small amount of radioactivity was released to the perfusion effluent. This release was not changed significantly by pulmonary infusion of quicacrine (0.5 mM), a known inhibitor of phospholipase A₂. After the perfusion about 75% of the radioactivity in the lungs was in phospholipids, mainly in phosphatidylcholine, phosphatidylethanolamine and phosphatidylinostil and to a lesser degree in phosphatidylserine and phosphatidic acid. About one fourth of the radioactivity was in neutral lipids (tri- and diacylglycerols) and as free unmetabolized ¹⁴C-arachiodonic acid. Pulmonary infusion of quinacrine increased the amount of radioactivity in diacylglycerols and phosphatidylinositol but had no effect on that in phosphatidylcholine, phosphatidylserine, phosphatidic acid and triacylglycerols. The amount of radioactivity in phosphatidylethanolamine was decreased by quinacrine and increased in the vicinity of an unidentified phospholipid-quinacrine complex. The present study indicates that the distribution of ¹⁴C-arachidonic acid in hamster lung lipids is sensitive to quinacrine. The detected changes can, however, not be explained by an overall inhibition of phospholipase A₂ activities.     

The distribution of C-arachidonic acid in hamster lungs is sensitive to quinacrine

Isolated hamster lungs were labelled with ¹⁴C-arachidonic acid. When the lungs were ventillated with a respirator only a small amount of radioactivity was released to the perfusion effluent. This release was not changed significantly by pulmonary infusion of quicacrine (0.5 mM), a known inhibitor of phospholipase A₂. After the perfusion about 75% of the radioactivity in the lungs was in phospholipids, mainly in phosphatidylcholine, phosphatidylethanolamine and phosphatidylinostil and to a lesser degree in phosphatidylserine and phosphatidic acid. About one fourth of the radioactivity was in neutral lipids (tri- and diacylglycerols) and as free unmetabolized ¹⁴C-arachiodonic acid. Pulmonary infusion of quinacrine increased the amount of radioactivity in diacylglycerols and phosphatidylinositol but had no effect on that in phosphatidylcholine, phosphatidylserine, phosphatidic acid and triacylglycerols. The amount of radioactivity in phosphatidylethanolamine was decreased by quinacrine and increased in the vicinity of an unidentified phospholipid-quinacrine complex. The present study indicates that the distribution of ¹⁴C-arachidonic acid in hamster lung lipids is sensitive to quinacrine. The detected changes can, however, not be explained by an overall inhibition of phospholipase A₂ activities.     

Induction of globin mRNA accumulation by hemin in cultured erythroleukemic cells

The role of heme in erythroid development is investigated in erythroleukemic (Friend) cells. Exogenous hemin induces the accumulation of globin mRNA and globin protein in T3-Cl2 erythroleukemia cells to levels comparable to those induced by polar solvents, such as dimethylsulfoxide (DMSO). The hemin concentration required for maximal induction (10^?4 M) is the same as that which stimulates globin message translation in reticulocytes or cell-free reticulocyte lysates. Hemin and DMSO together cause T3-Cl2 cells to accumulate 8–9 fold more globin mRNA than either inducer individually. The kinetics of globin mRNA induction in hemin as compared to DMSO are very different: globin message accumulation begins 4 hr after hemin addition, but not until 30–40 hr after DMSO addition. Biliverdin induces 20–40 fold less hemoglobin than hemin; delta-aminolevulinic acid and porphobilinogen do not induce.     

Secondary structure of peptides. 4: 13C-Nmr CP/MAS investigation of solid oligo- and poly(L-alanines)

Primary and tertiary amine-initiated polymerizations of L -alanine-N-carboxyanhydride (L -Ala-NCA) were conducted at 20 or 100°C in a variety of solvents. The 75.5-MHz ¹³C-nmr CP/MAS spectra of the resulting poly(L -alanines) revealed that all samples contain both α-helix and pleated-sheet structures. Depending on the reaction conditions the α-helix content varied between ca. 1 and 99%. Reprecipitation from aprotic nonsolvents does not change the α-helix/β-sheet ratio, indicating that this ratio is thermodynamically controlled. Since relatively large amounts of oligopeptides of degree of polymerization (DP ) 4–6 can be extracted by means of acetic acid, it is concluded that (a) most poly(L -alanines) possess a bimodal molecular weight distribution, (b) the oligopeptide fraction with DP ? 11 is responsible for the β-sheet fraction of all samples, and (c) the two-stage crystal growth proposed by Komoto and Kawai is not correct. Solubilizing initiators such as poly(ethylene oxide) NH₂ prevent the precipitation of oligoalanine and, thus, the formation of a β-sheet structure. ¹³C-nmr CP/MAS measurements also show that tri- and tetra-L -alanines form insoluble β-sheet structures.     

Auxin transport in roots

Summary The net uptake and movement of radioactivity by 12-mm root segments of Zea mays have been studied as a function of time at 5, 15 and 25° C. Segments were supplied with an agar donor block containing 1 M IAA-1-¹⁴C or IAA-2-¹⁴C continuously or for a limited period of time (pulse-labelling). In the latter case the original donor block was replaced either by a plain agar block or by one containing 1 M unlabelled IAA. Receiver blocks were placed at the other end of the segments.The net uptake of radioactivity from the donor block at 15° C was greater at the basal end than at the apical end of the segment. At 5 and 15° C, the net uptake from a basal donor was virtually linear with time but at 25° C the rate of net accumulation decreased after about 10 h. Decarboxylation of IAA undoubtedly occurred at 15 and 25° C when the concentration in the tissue attained a high value.An acropetally polarised movement of radioactivity into the receiver blocks occurred regardless of whether the results were based on the actual amounts of radioactivity in the receiver block, or on the amounts in the receiver block expressed as a percentage of the net total radioactivity accumulated from the donor block. Only one radioactive substance was present in the receiver block and it ran to the same R_f as IAA in the isopropanol: ammonium: water solvent system.The amounts of radioactivity moving into that part of the root segment at least 6 mm distant from the end in contact with either an apical or a basal donor block were assessed. An acropetal polarity in the movement of radioactivity was observed on the basis of the actual amounts of radioactivity in these distal parts of the segments, but no such polarity was evident when the amounts of radioactivity were expressed as a percentage of the net total accumulated from the donor block. At least 3 radioactive substances were present in the tissue in addition to the substance running to the same R_f as IAA. The distribution of radioactivity in the segment cannot therefore be used to assess the distribution of IAA.Acropetal movement of radioactivity into an apical receiver block is not dependent upon the continued uptake of IAA at the basal end of the segment. No distinct pulses of radioactivity were detected moving through the root segments.Only a small part of the radioactivity in the root segment appears to be located in the polar transport system, while the bulk is not. The polarity found in the movement of the bulk radioactivity within the segment seems to be related to the polarity in IAA uptake from the donor blocks.     

Carbon Assimilation in Photoheterotrophic Cells of Peanut (Arachis hypogaea L.) Grown in Still Nutrient Medium

The relative transport of photosynthetic and dark carboxylation products in photoheterotrophic cells of Arachis hypogaea L. var. TMV-3 at varied phases of growth were determined. Despite the presence of an equally competent photosynthetic apparatus as determined from ¹⁴CO₂ incorporation rates in the dark and light, pulse-chase experiments revealed little or no change in the radioactivity of the C₃ intermediates but rapid disappearance of label from the dark carbon assimilates (malate and other tricarboxylic acid cycle intermediates) with a simultaneous increase in the aminoacid pool in early log-phase (10 days old) cells. However, significant flow of carbon through the photosynthetic intermediates resulting in the accumulation of sugars occurred in the late log-phase (34 days old) cells. Limitation of exogenous sugar in the nutrient milieu and depletion of reserve carbohydrates stored in starch of the chloroplasts of the cells were considered as the decisive factors in promoting transport of C₃ cycle intermediates through the reductive pentose phosphate pathway in photoheterotrophic cells. The observed drain of radioactivity even from the small amounts of tricarboxylic acid cycle intermediates synthesized during photosynthesis into glutamate indicated that the transport of carbon through the nonautotrophic pathway is not controlled by these factors.     

Separation of alpha and beta chains of rabbit globin using SDS-polyacrylamide gel electrophoresis

A procedure to separate the α and β globin chains of rabbit hemoglobin, denatured with sodium dodecyl sulfate in the presence of mercaptoethanol, on a column of polyacrylamide gel was developed. The identity of the two separated chains was verified by (a) differences in distribution of radioactivity between the chains when the hemoglobin samples were labeled uniformly with various ³H- or ¹⁴C-labeled amino acids; (b) the analysis of the chain distribution of radioactivity in purified hemoglobin isolated from rabbit reticulocytes, pulse-labeled with [³H] leucine; and (c) the separation pattern of a mixture of authentic [α-³H]- and [β-¹⁴C]-labeled globin chains. The globin chains of human hemoglobin A also could be separated in a similar manner. This procedure is particularly useful when only microgram quantities of hemoglobin are available for study.     

Synergistic effect of two β globin gene cluster mutations leading to the hereditary persistence of fetal hemoglobin (HPFH) phenotype

Co-inheritance of gamma and beta globin gene mutations in a compound heterozygous state is rare but of clinical interest as it provides an important data on understanding the HbF expression. Hematological analysis was carried out (Sysmex KX-21). F-cells were enumerated using flow cytometry. Beta globin gene was analysed by CRDB technique and by DNA sequencing. Gamma globin promoter region was sequenced and expression studies were carried out using real time Taqman assay. We report a family, where two inherited defects of the β globin gene cluster segregate. The proband and her sibling were compound heterozygotes for a novel ^Gγ promoter mutation and the 619 bp deletion a common Indian β thalassemia mutation. Molecular characterization revealed that the father (HbA₂ 5.1%, HbF 5.4%), proband (HbA₂ 3.6%, HbF 31.7%) and her brother (HbA₂ 3.9%, HbF 23.6%) were heterozygous for the 619 bp deletion. The mother (HbA₂ 2.1%, HbF 3.4%) had a normal β globin gene. As both the children showed high HbF levels, the γ globin gene work up was carried out. The ^Gγ-globin gene promoter analysis revealed that the mother and the two children were heterozygous for a 5 bp deletion -ATAAG (-533 to -529) that resides in the GATA binding site. These findings suggest that the 5 bp deletion in the ^Gγ globin promoter has a functional role in silencing the γ-globin gene expression in adults by disrupting GATA-1 binding and the associated repressor complex and results in the up-regulation of gamma globin gene expression. When co-inherited with β -thalassemia trait it leads to a phenotype of HPFH.     

Control of ketogenesis from amino acids: III. In vitro and in vivo studies on ketone body formation, lipogenesis and oxidation of tyrosine by rats

Ketone body formation from tyrosine was studied in rat liver in vitro with special references to the activities of tyrosine aminotransferase (EC 2.6.1.5) and p-hydroxyphenylpyruvate hydroxylase (EC 1.14.2.2). Liver was obtained from rats which had been given a high protein diet or cortisol to induce various levels of tyrosine aminotransferase. The enzyme activities of the preparations were plotted against the amounts of ketone body formed from tyrosine. It was found that over a low range of tyrosine aminotransferase activities, activity was proportional to the amount of ketone body formed. However, above this range, ketone body formation ceased to increase and p-hydroxyphenylpyruvate started to accumulate. This inhibition of ketone body formation and accumulation of the p-hydroxyphenylpyruvate could be prevented by addition of ascorbate. These results suggest that the primary factor regulating metabolism of tyrosine in vitro is tyrosine aminotransferase and when the activity of this is high so that it is no longer rate limiting, p-hydroxyphenylpyruvate hydroxylase becomes the rate limiting step because its activity is inhibited by the accumulation of p-hydroxyphenylpyruvate.For in vivo studies rats were given a high protein diet or cortisol to induce various levels of tyrosine aminotransferase and then injected with a tracer dose of [U- or 1-¹⁴ C]tyrosine. Then their respiratory ¹⁴CO₂ and the incorporation of ¹⁴C into total lipids of liver were measured. The amounts of radioactivity in CO₂ and lipids were found to be proportional to the tyrosine aminotransferase activity and were not affected by the free tyrosine concentration in the liver. After injection of [U-¹⁴C] acetate the radioactivities in CO₂ and lipids were not proportional to the tyrosine aminotransferase activity. These results indicate that the enzyme activity also regulates tyrosine metabolism in vivo. In vivo studies gave no evidence of the participation of p-hydroxyphenylpyruvate hydroxylase in regulation of tyrosine metabolism.     

Incorporation of 3H-Gibberellin A20 in roots of G2 peas

Following application of ³H-Gibberellin A₂₀ (GA₂₀) to roots of G2 pea seedlings and homogenization of the roots, about 3% of the radioactivity in the tissue could be precipitated from a 30,000 × g supernatant with trichloroacetic acid (TCA) (soluble fraction) while about 5% of the radioactivity pelleted at 30,000 × g (particulate fraction). The radioactivity in the particulate fraction was soluble in sodium dodecyl sulfate (SDS), but was not dialyzable and was insoluble in ethanol. Electrophoresis of the soluble fraction gave only one band of radioactivity, while that of the particulate fraction gave multiple bands. Acid hydrolysis of the soluble fraction released radioactivity that ran coincident with acid-treated GA₂₀ on silicic-acid column chromatography. The particulate fraction gave numerous radioactive peaks following acid hydrolysis, two of which were coincident with GA₂₀ and GA₂₉ (hydroxylation product of GA₂₀) on silicic acid chromatography. Treatment of the particulate and soluble fractions with RNase, DNase, and proteases showed a significant solubilization of radioactivity only with the proteases, suggesting that the GA is bound to a proteinaceous macromolecule. Complete proteolytic hydrolyis followed by thin layer chromatography showed 65% of the radioactivity from the soluble fraction running separately from free GAs or the individual amino acids; the particulate fraction gave mainly (60%) free GAs on enzymatic hydrolysis and much smaller amounts (17%) in a position separate from that of the GAs or amino acids. Binding of ³H-GA to protease-sensitive material was obtained with biologically active ³H-GA₂₀ and ³H-GA₁.     

Evidence that the 5' end of rabbit globin mRNA is hybridized with its 3' end

• 1.1. A radiopolyadenylated rabbit globin mRNA was treated with different concentrations of ribonuclease V₁ from cobra venom.
• 2.2. The enzymatic digests were chromatographed on an aminophenylboronate-agarose column, which specifically captured the cap structure i.e. n⁷G(5') ppp (5') NmP.
• 3.3. When the capture fragment was chromatographed on a Sephadex G-100 column, its size was smaller than the native molecule and also bore radioactivity, i.e. a poly(A) tail.
• 4.4. These results provide evidence that the 5' end (which encompasses the cap structure) of rabbit globin mRNA is hybridized and in close proximity to its 3' end.
• 5.5. We conclude that this conformation is required for messenger translation efficiency.

     

Autoradiographic studies with 3H 1,25 dihydroxyvitamin D3 in thyroid and associated tissues of the neck region

Summary Rats and mice fed a vitamin D-deficient or vitamin D-complete diet were injected with ³H 1,25 (OH)₂ vitamin D₃. Autoradiograms prepared from cross sections through the neck region revealed nuclear concentration of radioactivity strongest in parathyroid chief cells, occasionally in thyroid follicular epithelial and interfollicular cells, in the epithelium of tubular remnants of the ultimobranchial body, in epithelium of the esophagus, in chondrocytes of tracheal cartilage, and in myoepithelial cells of tracheal glands. In the thyroid, most of the follicle epithelial cells did not show nuclear concentration of radioactivity which occurred only occasionally and predominantly in follicles located in marginal positions. Thyroglobulin in lumina of thyroid follicles contained varying amounts of radioactivity that correspond to the diameter of the follicles, with relatively high amounts in large follicles and little or no radioactivity in small follicles. Competition with excess of unlabeled 1,25 (OH)₂ vitamin D₃ abolished nuclear radioactivity, but not the radioactivity in the colloid, while 25 (OH) vitamin D₃ did not affect either. When a combination of autoradiography and immunohistochemistry was applied, follicular and parafollicular C-cells positive for calcitonin antibodies, did not show nuclear concentration of radioactivity. Tubular remnants of ultimobranchial bodies, however, showed distinct nuclear labeling, but did not stain, or only weakly stain, with antibodies to calcitonin. When ³H 25 (OH) vitamin D₃ was injected, no nuclear concentration of radioactivity was noted in any of the tissues.The results from these histochemical studies suggest the existence of nuclear receptors and direct genomic effects of 1,25 (OH)₂ vitamin D₃ in heterogeneous tissues of the neck region, which include parathyroid chief cells, myoepithelial cells of tracheal glands, chondrocytes of tracheal cartilage, epithelial cells of esophagus, and certain thyroid follicle epithelial cells. No evidence could be obtained for nuclear receptors in C-cells and cells of striated muscle.     

Metabolism of thromboxane B2 in the cynomolgus monkey

[5,6,8,9,11,12,14,15-³H₈]-Thromboxane B₂ was injected into the saphenous vein of female cynomolgus monkeys, and blood samples were withdrawn from the contralateral saphenous vein. The compound was eliminated from the circulation with a half-life of about 10 min after an initial rapid disappearnace. Some more polar products appeared with time, and also small amounts of material less polar than thromboxane B₂; however, the dominating compound in all blood samples was unconverted thromboxane B₂.About 45% of the given dose of tritium was excreted into urine in 48 hrs. Several metabolites of thromboxane B₂ were found. The major urinary metabolites was identified as dinorthromboxane B₂ (about 32% of urinary radioactivity). Unconverted thromboxane B₂ was also found in considerable amounts (13% of urinary radioactivity).It is concluded that 1) dehydrogenation at C-12 is not a major pathway in the degradation of this compound, in contrast to metabolism at the corresponding C-15 alcohol group of prostaglandins; 2) after having gained access to the circulation, thromboxane B₂ is the main circulating compound; however, assay of thromboxane B₂ in plasma will be complicated or precluded by large artifactual production of the compound by platelets during sample collection.     

Characterization by high performance liquid chromatography of nuclear metabolites of testosterone in the brains of male rhesus monkeys

Testosterone (T) restores the potency of castrated male rhesus monkeys, and our autoradiographic data have demonstrated that ³H-T or its metabolites concentrate in cell nuclei in the corticomedial amygdala, bed nucleus of stria terminalis, preoptic area, and hypothalamus. In rat, ³H-estradiol (³H-E₂) is a major nuclear metabolite of ³H-T in areas of the limbic system, but comparable data are lacking for the primate. We have therefore developed an improved technique using high performance liquid chromatography for investigating metabolites of ³H-T that accumulate in cell nuclei in small amounts of tissue obtained from the brain of the rhesus monkey. Two castrated male rhesus monkeys were injected with 5 mCi of ³H-T and were killed 30 min later. In amygdala, preoptic area-bed nucleus of stria terminalis, and hypothalamus, 48–70% of the nuclear radioactivity was in the form of ³H-E₂ (Type I tissues). In six other brain areas and in pituitary, 35–85% of the nuclear radioactivity was in the form of ³H-T (Type II tissues), whereas in genital tract tissues, 86–99% of the nuclear radioactivity was in the form of ³H-dihydrotestosterone (³H-DHT) (Type III tissues). In plasma and in supernatants from both Type I and Type II tissues, the proportions of ³H-T were high, and ³H-E₂ did not exceed 10% of the total extractable radioactivity. These data suggest that, as in rodents, some of the central actions of T in primates may be mediated by estrogen target neurons.     

Dark Respiration during Photosynthesis in Wheat Leaf Slices

The metabolism of [¹⁴C]succinate and acetate was examined in leaf slices of winter wheat (Triticum aestivum L. cv Frederick) in the dark and in the light (1000 micromoles per second per square meter photosynthetically active radiation). In the dark [1,4-¹⁴C]succinate was rapidly taken up and metabolized into other organic acids, amino acids, and CO₂. An accumulation of radioactivity in the tricarboxylic acid cycle intermediates after ¹⁴CO₂ production became constant indicates that organic acid pools outside of the mitochondria were involved in the buildup of radioactivity. The continuous production of ¹⁴CO₂ over 2 hours indicates that, in the dark, the tricarboxylic acid cycle was the major route for succinate metabolism with CO₂ as the chief end product. In the light, under conditions that supported photorespiration, succinate uptake was 80% of the dark rate and large amounts of the label entered the organic and amino acids. While carbon dioxide contained much less radioactivity than in the dark, other products such as sugars, starch, glycerate, glycine, and serine were much more heavily labeled than in darkness. The fact that the same tricarboxylic acid cycle intermediates became labeled in the light in addition to other products which can acquire label by carboxylation reactions indicates that the tricarboxylic acid cycle operated in the light and that CO₂ was being released from the mitochondria and efficiently refixed. The amount of radioactivity accumulating in carboxylation products in the light was about 80% of the ¹⁴CO₂ release in the dark. This indicates that under these conditions, the tricarboxylic acid cycle in wheat leaf slices operates in the light at 80% of the rate occurring in the dark.     

Origin of cholesterol in myelin

We review some of the older literature concerning metabolic turnover of cholesterol in the nervous system. The overall picture is that incorporation of radioactive precursors into brain cholesterol is roughly proportional to the rate of myelination and that, once incorporated, radioactive cholesterol is relatively stable metabolically. We outline a strategy for demonstrating the source (local synthesis or uptake from the circulation) of cholesterol in brain. The experimental design involves determining the rate of accumulation of cholesterol this is calculated as the increasing amounts of sterol in brain at successive time intervals during development. The rate of appearance of newly synthesized cholesterol is determined from incorporation of radioactivity from³H₂O (injected i.p. several hours prior to sacrifice) into cholesterol. The radioactivity associated with the sterol fractions and the specific activity of body water determined from the serum can be used to calculate the absolute amount of sterol newly synthesized during the time when³H₂O was present. The results obtained demonstrated that all of the bulk cholesterol accumulating in brain can be accounted for by newly synthesized cholesterol. None of the radioactive cholesterol came from the circulation, since cholesterol feeding suppressed cholesterol biosynthesis in the liver and specific radioactivity of circulating cholesterol was negligible. Thus, almost all cholesterol accumulating in brain during development is locally synthesized. Special issue dedicated to Dr. Marion R. Smith.     

Plant feeding site selection on soybean by the facultatively phytophagous predator Orius insidiosus

Experiments were conducted to test whether the facultatively phytophagous predator Orius insidiosus (Say) (Heteroptera: Anthocoridae) ingested phloem, xylem or mesophyll contents from soybean plants (Glycine max L.). Potential uptake of phloem sap was examined by radiolabeling photosynthate with ¹⁴CO₂ and then measuring the accumulation of radiolabeled metabolites in feeding animals. Most O. insidiosus feeding on radiolabeled plants ingested no or very low levels of label; only 3% ingested small amounts of label, indicating the experimental insects fed very little, if at all, on the phloem. In contrast, well known phloem feeding insects used as positive controls accumulated substantial levels of labeled metabolites after feeding on known host plants. O. insidiosus did feed on xylem contents, as shown by ingestion of safranin-labeled xylem fluid. A few of the insects showed signs of feeding on the mesophyll, as indicated by the presence of chloroplasts in the gut. However, the small diameter of the food canal may cause limited passage of chloroplasts, which would contribute to an underestimation of the frequency of mesophyll feeding. Some radiolabeled metabolites remain in the mesophyll so those insects that ingested low levels of radiolabel probably ingested label from the mesophyll, which supports the notion that some level of mesophyll feeding occurred. Feeding site determines the nutrients ingested during phytophagy. These insects obtain water from the xylem, and may ingest small amounts of starches, sugars, and amino acids from the mesophyll. The results suggest that facultative phytophagy by this heteropteran predator primarily provides the insect with water, but also may provide some nutrients that supplement a prey diet and help the predator survive periods when prey are scarce.     

Uptake and metabolism of radioactive gibberellins by barley aleurone layers

Summary When aleurone layers were treated with labeled gibberellin A₁ (³H-GA₁), gibberellin A₅ (³H-GA₅) and the methyl ester of ³H-GA₅ (³H-GA₅-ME), radioactivity was accumulated by the tissue for a period of 20–30 h. After this time, radioactivity was released into the medium. Concomitantly, ribonuclease was also liberated by the tissue. The radioactivity accumulated by aleurone layers was associated with polar metabolites of the respective GAs, and the extent of extent of accumulation was a function of the degree of GA metabolism (GA₅-ME>GA₅>GA₁). Accumulation of radioactivity was inhibited in the cold and by the metabolic poisons NaF and dinitrophenol. This was thought to be due to inbition of GA metabolism. The accumulation of ³H-GA₁ in aleurone tissue did not reach saturation when unlabeled GA₃ up to 10^-2 M was added to the incubation medium.Abbreviations GA gibberellin - GA₅ ME, gibberellin A₅ methyl ester - RNase ribonuclease     

The Metabolism of the Germinating Oil Palm (Elaeis guineensis) Seedling : In Vivo Studies

The metabolism of ¹⁴C-labeled fatty acids and triacylglycerols was followed in intact germinating oil palm seedlings as well as in tissue slices. In the germinating seedling, the shoot contained a normal pattern of membrane fatty acids (mainly C₁₆, C_18:1, C_18:2) but the kernel contained about 68% C₁₂ and C₁₄ fatty acids. Haustorium fatty acids were intermediate between the two. [¹⁴C]Acetate was actively metabolized by shoot and haustorium slices but not so actively by the kernel. Approximately 9% to 17% was converted to water-soluble substances, 4% to 6% to CO₂, and 0.5% to 5.9% to lipids. The fatty acids synthesized in the shoot and haustorium were mainly C₁₆, C₁₈, and C_18:1 fatty acids but in the kernel about 18% to 32% of the ¹⁴C-fatty acids were C₁₂ fatty acids.

[¹⁴C]Lauric acid was absorbed and metabolized by haustorium slices and by the haustorium in intact seedlings; it was partly esterified to triacylglycerols and also converted to water-soluble substances and insoluble tissue material. In contrast, tri-[¹⁴C]laurin was absorbed but not metabolized. The haustorium also absorbed other fatty acids but the longer chain (C₁₆ and C₁₈) fatty acids were not esterified or metabolized further. Preincubation of the haustorium with plant hormones or in the presence of kernel tissue did not alter its inactivity towards tri-[¹⁴C]laurin.

When tri-[¹⁴C]laurin or [¹⁴C]lauric acid were injected into the seed or the shoot, there was no movement or radioactivity to other parts of the seedling. When injected into the shoot, but not into the seed, tri-[¹⁴C] laurin was hydrolyzed and partly metabolized to water-soluble substances.