Pollen Lipid Research Articles

Quantitative comparison of lipids in some pollens and their phagostimulatory effects in honey bees

SUMMARYLipid extraction in honey bee collected corbiculum pollen from seven plant host species showed distinct differences in amounts of lipid within preferred/non-preferred honey bee pollens. Mean amounts of lipid in highly preferred pollens such as Brassica campestris var. Toria, Cosmos bipinnatus and Raphanus sativum were 20.3%, 19.4% and 17.8%, respectively, and in least preferred pollens such as Helianthus annuus and Petunia hybrida were 11.9% and 11.6%, respectively. The cumulative flabellogustatory responses further demonstrated a significant linear increase in stimulatory effects to B. campestris pollen lipid extracts, whereas the response repertoire with P. hybrida was of reverse order. The bee responses to an identical lipid concentration of B. campestris, Dahlia sp., H. annuus and P. hybrida manifested clear evidence for inhibitory effects of H. annuus lipids to Apis mellifera and A. dorsata suggesting that pollen lipids play a considerable role in honey bee preference for pollen collection.

Quantitative analysis of lipids and protein from the pollen of Brassica napus L.

Brassica napus L. pollen lipids and proteins are divided into two spatially distinct domains by the plasma membrane of the vegetative cell. The extracellular lipid and protein fractions can be separated from the internal cytoplasmic fractions by differential solvent and buffer extraction because the pollen grain wall and plasma membrane act as barriers to both lipid and protein extraction. Mature pollen is composed of 25.4% lipids and 26.0% protein (dry weight). The extracellular pollen-coat is estimated to contain 27.1% of the total lipids and between 9.6 and 19.6% of total protein depending upon the extraction method. We conclude that for assured determination of pollen grain lipid and protein content, the pollen should be fractured during extraction.

Maize pollen lipids

The chloroform extractives of four wild selections of Zea mays pollen were separated quantitatively into chemical classes and the components of each class were identified. Alkanes, alkenes, fatty acids, triterpene esters and triglycerides were found as the main constituents of the lipid extracts. The two hydrocarbon classes were found in a ratio close to 1:1; pentacosane, heptacosane and nonacosane were dominating in the alkanes, whilst alkenes showed major homologues two carbon atoms longer. Free fatty acids, 8–22% of the total, contained predominantly palmitic (16:0), stearic (18:0), oleic (18:1), linoleic (18:2) and lower amounts of palmitoleic (16:1) and linolenic (18:3) acids. Triglycerides and triterpene esters accounted for 17–31 % and 5–34%, respectively. The former class comprised three homologous series, the latter contained tetracyclic and pentacyclic triterpenes esterified with C 16 and C 18 fatty acids. Free triterpenols and linear esters were also found in pollen lipids. These data are discussed in relation to pollen biochemistry and in regard to the natural functions of the lipid classes found.

Correlations between gametophytic (pollen) and sporophytic (seed) generations for polyunsaturated fatty acids in oilseed rape Brassica napus L.

Lipids were extracted from the diploid seed and haploid pollen of Brassica napus L. Two fractions of pollen lipids, namely the diploid-specified pollen-coat and the haploid-specified internal cytoplasmic lipids were obtained. Significant correlations exist between pollen and seed generations for linoleic (18∶2) and linolenic (18∶3) acids. In pollen internal storage lipids, the level of 18∶3 is positively correlated and the level of 18∶2 is negatively correlated with the level of 18∶3 in seed lipids. Evidence is presented that strongly supports the hypothesis that lipid biosynthesis occurs within the pollen and that synthesis is specified by haploid genes. These data support the concept of pollen selection, so that selecting among living pollen grains for superior individuals has potential as a new plant breeding tool for improving seed oil quality.

Germination‐induced changes in acyl lipids and free sterols of olive pollen

SUMMARYThe capacity of Olea europaea L. pollen grains to germinate has been studied. They germinated poorly when incubated in media with a pH higher than 5.55. However, germination was stimulated when a stream of air was passed through the incubation medium. Phosphatidylcholine, diacylglycerols, free fatty acids and triacylglycerols are the most abundant lipids in mature and germinated pollen. The level of diacylglycerol increases during germination while phosphatidylcholine, free fatty acids and triacylglycerols decrease, as compared with mature pollen. Overall, the fatty acid composition of mature pollen lipids is similar to that of germinated pollen. Compared to phospholipids and triacylglycerols, monoacyl‐, diacylglycerols and free fatty acids contain more laurate and myristate fatty acids. In relation to the amount of acyl lipids, free‐sterols are minor constituents of the lipid fraction from mature and germinated pollen, β‐sitosterol being the only significant component. The percentage of stigmasterol is significantly higher in mature than in germinated pollen.

SURVEY OF POLLEN AND POLLENKITT LIPIDS–CHEMICAL CUES TO FLOWER VISITORS?

A chemical survey of pollen lipids was carried out to examine the composition of pollenkitt in relation to that of whole pollen and to evaluate the possible role of pollenkitt as the principal carrier of chemical cues used by flower visitors. Investigated pollen was collected from 69 angiosperm species (28 families) in California. Lipid extracts of pollenkitt and of the internal portion of pollen were analyzed for each species using thin‐layer chromatography. Neutral lipids (energy storage and essential oil constituents) were most diverse in pollenkitt, while polar lipids (mostly membrane constituents) were found almost exclusively in the internal pollen fraction. Patterns in neutral lipid compositions suggest that pollenkitt may provide pollen with species‐specific odors. Yellow pigments were observed in pollen of most species, with carotenoids predominating in pollenkitt and flavonoids in the internal fraction. Phenolic and heterocyclic nitrogen compounds were found in the lipid extracts of several species.

Lipid metabolism during germination of tobacco pollen

The variation of tobacco pollen lipids was studied during a germination time of four hr. During this time pollen grains went through a lag phase of 30 min after which pollen tube growth started. After four hr this growth had extended the area of the plasmamembrane by factors of five to 10. The major lipids were neutral lipids followed by phospholipids, whereas glycolipids represented only a minor fraction. The increase in membrane surface during pollen tube growth was not reflected by a similar increase in lipid content, which increased only slightly during the lag phase. Labelling with radioactive acetate showed a continuous incorporation of precursor into all lipid components from the beginning of germination, whereas labelling by radioactive phosphate commenced later. The data are discussed in terms of membrane assembly and turnover during pollen germination.

A crystalline lipid phase in a dry biological system: evidence from X-ray diffraction analysis of Typha latifolia pollen

The temperature limits for germination in Typha latifolia pollen lie within the range 4–40° C. These limits correlate at the low-temperature end with the ‘crystallization’ of endogenous triacylglycerols and on the high-temperature end with the ‘melting’ of a gel-like lipid component in intact pollen. X-ray diffraction analysis was used to structurally characterize and to trace the latter gel-like lipid from the intact pollen through a range of pollen lipid fractions. We tentatively identify this component as a fatty acyl sterol ester and present evidence that it resides in the exine of the pollen grain. Its thermotropic behavior is insensitive to pollen hydration. The possibility of interpreting a crystalline lipid phase as being membrane-derived when in fact it originates from contaminating non-membranous neutral lipid is discussed. The total lipid content of T. latifolia pollen is 123 mg g dry weight, of which 37% is polar lipid. The neutral lipid consists primarily of triacylglycerols and of the aforementioned sterol ester, which represents 0.34% (w/w) of pollen dry weight. The polar lipid fraction has phosphatidylcholine, phosphatidylethanolamine and phosphatidic acid as major components with lesser amounts of phosphatidylglycerol and phosphatidylinositol. Palmitic (16:0) and linoleic (18:2) acids, in a 1:2 molar ratio, constitute the major fatty acids of both polar and neutral lipid fractions with lesser amounts of linolenic (18:3), oleic (18:1) and stearic (18:0) acid in evidence.

Role of flower and pollen aromas in host-plant recognition by solitary bees.

The means by which newly emerged pollen-specific (oligolectic) solitary bees locate their appropriate pollen host plant is not clearly understood. To evaluate the role of flower and pollen odors in this recognition process, preference tests were performed on foraging-inexperienced and, for comparison, field-experienced individuals of the solitary bee Colletes fulgidus longiplumosus. The bees were presented with a choice of four plant species, offered in the form of aromas from flowers, whole pollen, pollenkitt, and internal pollen lipids. Observed feeding-attempt response patterns suggest: 1) that bees can distinguish between plant species on the basis of odors from flowers, whole pollen, and pollenkitt, 2) inexperienced bees show a preference for the pollen on which they were reared as larvae, and 3) chemicals eliciting feeding responses to pollen appear to be contained in the pollenkitt. Feeding responses by experienced bees differ from those of inexperienced bees in ways which indicate that the insects' odor-based search image of the host plant becomes modified by foraging experience.

Evidence for the Presence of Neutral Glycerylether Derivatives in Pollen Lipids of Pine Tree Pinus halepensis

The separation and identification of glyceryl ether (G E ) derivatives from pollen neutral lipids of Pine tree Pinus halepensis (Miller) is described. The separation and purification of GE derivatives from the other lipid classes, especially from monoglycerides and diglycerides, was done by thin layer chromatography. The purified GE derivatives were examined by infrared spectrometry analyzed by gas liquid chromatography, and the glycerylether backbones were identified by gas chromatography-mass spectrometry of its isopropylidene derivatives. Fatty acids were detected as esterified constituents after mild alkaline hydrolysis of the GE fraction. The GE derivatives are characterized as 1-O-(di)hydroxyalke(die)nyl-glycerols, the side hydroxyl group(s) of the O-carbonchain being esterified mainly with saturated fatty acids.

Brood Rearing and Food Consumption by Honeybee Colonies Fed Pollen Substitutes Supplemented with Starch-Encapsulated Pollen Extracts

SummaryThe whole lipid fraction of fresh bee-collected pollen was encapsulated in a starch polymer and added to a whey-yeast pollen substitute. Honeybee colonies fed pollen substitute supplemented with 2, 4, 6 or 8% (dry weight) of the lipid reared significantly more brood to the sealed stage than did colonies fed the substitute without lipid. Colonies fed 2 or 4% lipid reared as much brood as colonies fed pollen. Addition of the starch-coated pollen lipid to the pollen substitute also improved its consumption, but not in proportion to the improvement in brood production; thus the pollen lipid may have influenced brood production directly as well as by increasing protein intake.

Mesocarp, seed and pollen lipids of Raphia palms

AbstractThe lipid classes, fatty acids and sterols of the mesocarp, seed and pollen lipids of five species of Raphia palms endemic to Nigeria were analysed. Apart from quantitative differences in the fatty acid compositions, chromatographic analyses demonstrated very little change in the patterns of the characteristic lipids associated with either the mesocarps, seed endosperms or pollens. Mesocarp lipids contained mainly triglycerides, while palmitic, oleic and linoleic acids were the major acids. Contrary to published data for seed lipids, Raphia seed endosperms contained a relatively small amount of triglycerides and a high proportion of polar lipids. Fatty acids associated with this tissue were not only highly unsaturated, but were significantly different from typical fatty acids of seed lipids. Raphia pollens, on the other hand, showed a complex array of lipid types. Triglycerides, sterols and sterol esters constituted the main neutral lipids while phosphatidyl choline, phosphatidyl inositol, phosphatidyl ethanolamine and galactosyl diglycerides represented the polar fraction. Apart from minor trends, palmitic, oleic and linoleic acids constituted the major fatty acids in all species. The biological importance of the steroidal sapogenins found in all organs is discussed.

Reactions of singlet oxygen with pine pollen.

Exposure of pine pollen to single oxygen, generated in an aqueous environment, resulted in a decrease in the relative quantities of unsaturated fatty acids that could be recovered by solvent extraction of surface and near surface pollen lipids. The involvement of excited oxygen was confirmed by substitution of deuterium oxide for water, which led to a twofold greater decrease in the unsaturated acids. The potential environmental and biomedical implications of these observations are discussed in terms of this model system.

Pollen lipids attractive to honeybees

Two substances attractive to honeybees have been isolated from mixed pollens. One is a pigment which was identified as a lutein ester, the other is a free fatty acid which chromatographed was identified as a C(18) straight-chain dienoic or trienoic acid.