Fat Metabolism in the West African Oil Palm (Elaeis guineensis)

During germination in the light, the endosperm, containing ahigh proportion of reserve fat (composed largely of shorter-chain(C₈ to C₁₄ saturated fatty acids), is slowly invaded by theexpanding haustorium (cotyledon). Free fatty acids accumulatein the endosperm, preferential hydrolysis of longer-chain saturatedacids (C₁₄ to C₁₈ occurring under conditions of slow growth.Lipids are absorbed by the haustorium, the process being superficiallysimilar in certain respects to intestinal fat absorption. Whencomplicating factors are removed, absorption is found to beunselective during disappearance of 75 per cent, of the endospermlipids. Amounts of lipid in the haustorium are low compared with thehigh concentration in the surrounding endosperm and, beforephotosynthesis starts, losses through respiration account fora large part of the reserves which disappear. No free fattyacids are present in the haustorium. Breakdown of fatty acids is relatively unspecific, althoughthe acids characteristic of the haustorium (C₁₆ C₁₈, oleic andlinoleic acids) are metabolized some what less rapidly thanthe shorter-chain saturated acids (C₈ to C₁₄ characteristicof the endosperm fat. Both root and shoot have a low fat content. The fatty-acid compositionof the former changes little during growth, but in the shootlinolenic acid increases proportionately during leaf expansionin the light.     

Midday Closure of Stomata in the Oil Palm Elaeis guineensis. Jacq.

Under natural climatic conditions in West Africa, midday closureof stomata in 3–6-year-old oil palms occurs only in thelatter half of the dry season, when soil moisture is low andair temperatures are high. Using an infiltration method, attempts were made to determinethe climatic factors which affect stomatal closure. The extentof midday closure is related closely to air temperature andshade temperature under the palm, agreeing closely with thefindings of Meidner and Heath (1959) on onion, but the aperture-temperaturecurves are different for watered and unwatered palms in thedry season, the difference being greater at higher temperatures.Watering reduces closure by changing the aperture-temperaturerelationship. Under natural conditions this effect is usuallyobscured because of lower temperatures in the dry season followingrain. During Harmattan weather, with very low relative humidities,the aperture-temperature relationship broke down. The results are discussed in relation to current views on middayclosure of stomata.     

Viability and Storage of Pollen of the Oil Palm, Elaeis guineensis Jacq

The effects of drying pollen of the oil palm, Elaeis guineensis,and storage under various conditions, on its viability havebeen examined. Viability was based on the ability of pollento germinate on a sucrose medium with and without added boricacid, and on its capacity to set fruit when applied to receptivefemale flowers. Oven-drying at 37 °C for 2–8 h followedby storage in a deep freezer proved to be the best method ofstoring the pollen. Pollen treated in this way and stored for12 months was capable of producing fruits which were equal inweight and appearance to those produced by fresh pollen. Elaeis guineensis, oil palm, pollen, storage, viability     

Cell Separation and Anatomy of Abscission in the Oil Palm, Elaeis guineensis Jacq.

Shedding of the fruit of the oil palm takes place in two co-ordinatedstages. The first, a cell separation event at a pre-defined,positionally differentiated abscission zone at the base of thefruit, is followed by further cell separation in peripheraltissue at the junction with the rudimentary androecial ringand the tepals. The position of the second separation is determinedby the age and ripeness of the fruit and the degree of pressureto which it is subjected; it is also dependent upon completionof the first stage. Implications of this unusual two stage separationprocess are discussed. Key words: Abscission, cell separation, anatomy, oil palm, Elaeis guineensis     

Composition, Degradation and Utilization of Endosperm During Germination in the Oil Palm (Elaeis guineensis Jacq.)

The insoluble carbohydrate and lipid fractions, and -D-galactosidase,ß-D-mannosidase and isocitrate lyase activities werestudied in the various tissues of oil palm (Elaeis guineensisJacq.) kernels prior to and during germination. In ungerminatedkernels insoluble carbohydrate and lipid constituted 36 and47% of endosperm dry weight respectively. During germinationthe thick endosperm cell walls became markedly thinner, concurrentwith a significant decrease in the percentage of insoluble carbohydrateand an increase in -galactosidase and ß-mannosidaseactivity in both degraded and residual endosperm. The proportionof lipid in degraded endosperm also increased significantly.The insoluble carbohydrate appears to be a galactomannan locatedin the secondary walls of the endosperm. No galactomannan wasdetected in oil palm embryos or haustoria. Isocitrate lyasewas present in, and confined to, tissues of the haustorium ofgerminating kernels. The enzyme was not active in endospermat any stage of germination, nor was it active in embryos beforeor at the end of imbibition. The results suggest that galactomannan is the second largestcomponent of oil palm endosperm and that it is utilized morerapidly than lipid during the early stages of germination. Thefact that isocitrate lyase activity is confined to the haustoriumsuggests that in Elaeis gluconeogenesis, the conversion of triglycerideto carbohydrate, takes place entirely within the cotyledon ofthe seed. Elaeis guineensis, galactomannan, galactosidase, germination, isocitrate lyase, mannosidase, oil palm     

Identification of p.Methoxyallybenzene in the Pollen of the Oil Palm Elaeis guineensis Jacq.

The lipid extract prepared from the pollen of the West African,oil palm, Elaeis guineensis, was found to contain p-methoxyallylbenzenein substantial amount. The pure substance after isolation bymeans of preparative gas-liquid chromatography and steam distillationwas characterized by using a combination of g.l.c.-mass spectrometry,infrared spectrometry, and chemical reactions. Mass spectrometrygave a spectrum with a parent ion at m/e 148 corresponding tothe molecular weight and fragmentation ions at m/e 133, 121,117, 105, 91, and 77. The structure was further confirmed bymeans of the infrared spectrum which showed major peaks at 1250,920, and 815 cm^–1 corresponding to a CH₃O group, a 1,4-substitutedaromatic ring, and a RCH=CH₂ group respectively. Its chemicaland physical properties (hydrogenation, oxidation, etc.) werefound to be similar to those of its positional isomer, p-methoxy--phenylpropene.The physiological and economic importance of the compound arediscussed.     

Chilling-induced Lipid Hydrolysis in the Oil Palm (Elaeis guineensis) Mesocarp

Oil palm fruits exposed to temperatures of 15 °C and belowshowed a significant increase in free fatty acid (FFA) contentin the mesocarp. This effect was most pronounced in fruits exposedto 5 °C when FFA levels exceeding 70% of the total oil wereobserved. The increase in FFA was accompanied by an increasein lipid-soluble phosphorus levels and a decrease in carotenecontent. Chilling did not have an effect on palm kernel oil.The results suggest the activation of a lipase in the mesocarpby low temperature stress. Key words: Lipase, oil palm, free fatty acid     

High-temperature Pre-treatment and the Germination of Seed of the Oil Palm, Elaeis guineensis (Jacq.)

Germination experiments have shown that oil palm seeds requireheattreatment before they germinate. The heat-treatment is insome ways analogous to low-temperature stratification of temperateseed, as it may be applied as a pretreatment, even at a moisturecontent too low for germination to occur. Following the heatpre-treatment, seed brought to the optimum moisture contentgerminates rapidly, after an initial lag period, at ambienttemperature. Below a critical seed moisture content, heat-treatmentis ineffective although seed viability is largely unimpaired.The high-temperature reaction has a Q₁₀ between 3.5 and 5.0and is apparently irreversible. Heat-treatment may be effectivelyapplied to stored, as well as fresh, seed. A reinvestigationof the optimum temperature for the high-temperature reactionshowed that dry heat-treatment is effective at 42.0°C.,the duration of the treatment necessary being only 60 days comparedwith the previously accepted value of 80 days at 39.5°C.necessary for seed heat-treated at optimum moisture content.A temperature of 44.5°C. is rapidly fatal. These resultsare discussed in relation to the alternation of dry and wetseasons in West Africa, and in relation to practical aspectsof oil palm cultivation.     

Some Enzymic Activities in the Germinating Oil Palm (Elaeis guineensis) Seedling

In germinating oil palm (Elaeis guineensis var D × P) seedling, an active lipase was present in the shoot but absent from both the kernel and the haustorium. It has an optimum pH of 6.2 and a smaller peak at pH 8.6. The shoot lipase was active against a number of mono-, di-, and triacylglycerols as well as the endogenous lipids present in the shoot, haustorium, and kernel. Activity against related substrates were in the order: trilaurin > dilaurin > monolaurin but monopalmitin > dipalmitin > tripalmitin. The level of the enzyme in the seedling was highest at a relatively early stage of growth (18-21 days) and also higher in dark-grown seedlings. Glyoxylate bypass enzymes (malate synthetase and isocitrate lyase), glutamate-oxaloacetate transaminase, phosphoenolpyruvate carboxykinase and lauroyl-coenzyme A oxidase were located in the haustorium. The levels of the enzymes paralleled seedling development and were slightly higher in light-grown seedlings. Fatty acyl-coenzyme A synthetase activity was very low and was found in both the shoot and haustorium.     

Pollination and Pollen-pistil Interaction in Oil Palm, Elaeis guineensis

Structural and cytochemical aspects of the pistil and detailsof pollination and pollen-pistil interaction were investigatedin the African oil palm (Elaeis guineensis Jacq.), an importantperennial oil crop. The stigma is trilobed, wet and papillate.The branched papillae are confined to a narrow linear zone oneach stigmatic lobe. Each stigmatic lobe harbours a deep stigmaticgroove, which runs adaxially along the surface. The stigmaticgroove is bordered by a well-defined layer of glandular cells,each of which has a pectinaceous cap on the inner tangentialwall. The style is hollow. The canal cells show thickeningson the inner tangential wall. The stigmatic groove and stylarcanal contain an extracellular matrix secreted by the canalcells which is rich in proteins, acidic polysaccharides andpectins. The canal cells at the base of the style are papillateand loosely fill the stylar canal. The stigma becomes receptivewhen the stigmatic lobes separate, and remains so for 24 h.Pollination is mediated by weevils as well as by the wind. Undernatural conditions the pollination efficiency was 100%. Pollinationinduces additional secretion in the stigmatic groove and stylarcanal. During post-pollination secretion, the pectinaceous capsof the cells lining the stigmatic groove are degraded. Pollengrains germinate on the stigmatic papillae and tubes grow onthe surface of the papillae, entering the stigmatic groove andadvancing along it into the stylar canal to eventually gainaccess to the locules. Pollen tubes are seen in the ovules 18–20h after pollination. Copyright 2001 Annals of Botany Company Arecaceae, Elaeis guineensis, African oil palm, pollination, stigmatic grove, stylar canal, Tenera hybrid, weevil     

Observations on Sex Differentiation in the Oil Palm, Elaeis guineensis L.

The morphology and frequency of occurrence of abnormal hermaphroditeinflorescences in the oil palm is described for palms of varyingage. Hermaphrodite inflorescences are manifest during changesof the sex cycle in the normally monoecious species, and grossmorphological differences in the type of hermaphrodite inflorescencesoccurred depending on whether the change of cycle was from maleto female or vice versa. The significance of the occurrenceand morphology of the abnormal inflorescences is discussed inrelation to the accumulation of photo-synthetic reserves andto the maturation process.     

Oil Palm (Elaeis guineensis Jacq.) Clonal Fidelity: Endogenous Cytokinins and Indoleacetic Acid in Embryogenic CallusCultures

Endogenous levels of indole-3-acetic acid (I AA) and cytokininswere measured in the two types of callus of oil palm (ElaeisguineensisJacq.) by an HPLC-ELISA methodology. The Nodular Compact Callus(NCC) is commonly used to establish stableembryoid strains ensuringclonal fidelity(     

Cytokinin Differences in In Vitro Cultures and Inflorescences from Normal and Mantled Oil Palm (Elaeis guineensis Jacq.)

The mantled abnormality phenotype of the oil palm affects fruit development and thus jeopardizes oil yield. Cytokinins have been implicated in the development of the mantled phenotype. Endogenous cytokinin levels in the normal and mantled phenotypes were compared to determine whether levels of specific cytokinins are associated with mantling. Endogenous cytokinins were identified and quantified in in vitro cultures and inflorescences from normal and mantled oil palms. Twenty-two isoprenoid cytokinins, comprising the zeatin, dihydrozeatin, and isopentenyladenine types, were quantified. Total cytokinin levels, particularly of trans-zeatin and isopentenyladenine types, increased during the in vitro culture process, with the highest levels detected at the proliferating polyembryoid stages. The cytokinins were present mainly in their inactive 9-glucoside forms during in vitro culture. On the other hand, the predominant trans-zeatin cytokinins in inflorescences were present mainly in their ribotide forms, suggesting a metabolic pool of cytokinins for conversion to biologically active free bases or ribosides. Levels of specific cytokinins were significantly different in tissues at different stages. Mantled developed inflorescences contained higher levels of isopentenyladenine 9-glucoside compared with normal inflorescences. Mantled-derived callus tissues had higher isopentenyladenine levels but significantly lower levels of trans-zeatin 9-glucoside, dihydrozeatin riboside, and dihydrozeatin riboside 5′-monophosphate cytokinins compared with normal-derived callus. It would be of considerable interest to verify these specific cytokinin differences in more callus cultures and clones.     

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.

     

An Analysis of the Factors Controlling the Germination of the Seed of the Oil Palm, Elaeis guineensis (Jacq.)

Under natural conditions in West Africa at the average groundtemperatures of 25-30° C, oil-palm seed germinates sporadicallyover a period of years, but with continuous heat treatment (38-40°C.) 50 per cent, germination of either nuts or extracted kernelsoccurs within a few months. The kernel comprises a small cylindrical embryo embedded ina mass of oily endosperm which in turn is surrounded by a thicktesta. At germination the testa and layer of endosperm coveringthe distal part of the embryo are forced out as a disc-likeoperculum which is already demarcated in the ungerminated kernelby a circular abscission zone in the endosperm cells. The excised embryo is non-dormant and at 30° C. starts toelongate within 24 hours, either on moist filter paper or whilestill in contact with the endosperm. At 30° C. removal of the operculum is followed by sluggishemergence of the embryo in air; emergence at the normal rateoccurs in pure oxygen, or in air if a long period at high temperatureprecedes de-operculation. Fresh intact kernels remain ungerminatedfor at least 6 months at 30° C, either in air or in pureoxygen. At high temperature (40° C.) intact kernels germinate fasterin pure oxygen than in air; at 30° C. the same applies onlyafter previous treatment at high temperature. This acceleratingeffect of oxygen is shown to be dependent upon the progressof slow processes stimulated by high temperature. It is postulated that germination of oil-palm seed is dependentupon a minimal threshold concentration of oxygen in the embryoand that during dormancy this minimal level progressively decreasesat a rate depending on the temperature.     

Metabolism of Cytokinins by Tissue Culture Lines of Oil Palm (Elaeis guineensis Jacq.) Producing Normal and Abnormal Flowering Palms

The metabolism of cytokinins in tissue cultures of two oil palm clones previously known to regenerate palms ultimately manifesting normal and abnormal flowering was studied using radiolabeled benzyladenine and isopentenyladenosine, with particular regard to the kinetics of formation of the cytokinin 9-glucoside. Labeled products were separated by high performance liquid chromatography and identified by comparison of retention times with authentic cytokinin standards run immediately before or after the experimental sample. Using benzyladenine, which is insensitive to cytokinin oxidase, ribotide appeared rapidly and then declined. 6-Benzylaminopurine (BA) 9-glucoside quickly became the major soluble product with some formation of riboside. No other ethanol-soluble products were found. Over an incubation period of 24 h up to 30% of label appeared in the ethanol-insoluble fraction. The uptake of label was consistently faster in the normal than the abnormal clone. Dose-rate and time course experiments produced an in vivo asymptotic dose-response curve for the accumulation of BA 9-glucoside analogous to a Michaelis-Menten first-order reaction with a ~~``V <sub>max</sub>' of 3.5 nmol·g<sup>−1</sup>·h<sup>−1</sup> (on a fresh weight basis) and a ``K _m ' of 0.12 mm. There were no differences between clones in the rate of synthesis. Using isopentenyladenosine, which is susceptible to cytokinin oxidase and cannot be glucosylated without prior deribosylation, a complex pattern of metabolism was seen, with much slower production of 9-glucoside. A number of transient unidentified compounds were seen, together with adenosine and adenine. Comparison of normal and abnormal flowering clones showed striking differences in the kinetics of production of a compound thought to be [9R]Z and in a transient compound eluting at 22 min which accounted for 42% of the radioactivity after a 7-h incubation in the abnormal line. By 17 h there was no difference between normal and abnormal lines in the radioactivity in this compound. Cytokinin uptake was slower in the abnormal than in the normal flowering clone. Received December 17, 1997; accepted August 24, 1998     

Origin of Initial Microflora of Palm Wine from Oil Palm Trees (Elaeis guineensis)

S ummary . In a study of the origin of the initial microflora of palm wine from the oil palm ( Elaeis guineensis ), micro-organisms from parts of the immature spadix, the plant tissues around the point of tapping the tree, the palm leaves and the atmosphere around the palm trees, were isolated and examined. It was shown that the yeasts in fresh palm wine might have originated from those that colonize those parts of the palm which are covered with fluffy hairy outgrowths. These materials which surround the tapping hole are the stalk of the male inflorescence, the leaf petiole, the felt (a fabric-like outgrowth of the frond petiole used to cover the tapping hole) and the cross strips. Another possible source of the yeasts was the xylem stream.     

Histology of Somatic Embryogenesis from Leaf Explants of the Oil Palm Elaeis guineensis

Histological analysis was carried out during the sequence ofevents which lead to the obtaining of somatic embryos of oilpalm. Calluses from the division of perivascular cells formedat the veins of young leaf explants. Subsequent proliferationof histologically similar nodules was by means of a cambium-likezone. Under certain conditions these calluses consisted almostentirely of meristematic cells. They then differentiated rapidly:the cambium-like zone fragmented, leading to protuberance inwhich the cells divide rapidly; epidermal structures were formed,with a network of procambial strands, and synthesis of storagelipids accompanied the formation of these embryo-like structureswhich developed into clumps of true somatic embryos, each witha shoot apex and a root apex. Other structures frequently observedduring in vitro culture are also described and show that alternatepathways do exist. The structure and evolution of somatic embryosare compared to those of zygotic embryos. Storage lipids emergeas an early tracer of the satisfactory development of tissuetowards somatic embryogenesis. Oil palm, Elaeis guineensis, histology, somatic embryogenesis, callogenesis, storage lipids     

The Distribution and Mobility of Boron within the Oil Palm, Elaeis guineensis L.: I. Natural Distribution

Leaf boron concentration is important in determining applicationof this element in oil-palm plantations. Older leaves of oilpalm contain more boron than younger leaves while tips and marginsof leaflets contain the highest levels of boron. Upper rankleaflets contain more boron than lower rank leaflets and upward-pointingleaflets contain more boron than downward-pointing leaflets.Boron concentration in leaves varies diurnally, and also overlonger periods; boron accumulates with time but at times ispunctuated with loss of boron. The significance of these observationsis discussed.