Storage Lipid Accumulation Research Articles

Accumulation and mobilization of storage lipids by Rhodococcus opacus PD630 and Rhodococcus ruber NCIMB 40126.

The time course of the accumulation of triacylglycerols (TAGs) in Rhodococcus opacus PD630 or of TAGs plus polyhydroxyalkanoates (PHA) in Rhodococcus ruber NCIMB 40126 with gluconate or glucose as carbon source, respectively, was studied. In addition, we examined the mobilization of these storage compounds in the absence of a carbon source. R. opacus accumulated TAGs only after the exhaustion of ammonium in the medium, and, with a fixed concentration of the carbon source, the amounts of TAGs in the cells increased with decreasing concentrations of ammonium in the medium. When these cells were incubated in the absence of an additional carbon source, about 90% of these TAGs were mobilized and used as endogenous carbon source, particularly if ammonium was available. R. ruber accumulated a copolyester consisting of 3-hydroxybutyrate and 3-hydroxyvalerate already during the early exponential growth phase, whereas TAGs were synthesized and accumulated mainly during the late exponential and stationary growth phases. In the stationary growth phase, synthesis of TAGs continued, whereas PHA was partially mobilized. In the absence of an additional carbon source but in the presence of ammonium, mobilization of TAGs started first and was then paralleled by the mobilization of PHA, resulting in an approximately 90% and 80% decrease of these storage compounds, respectively. During the accumulation phase, interesting shifts in the composition of the two storage compounds occurred, indicating that the substrates of the PHA synthase and the TAG synthesizing enzymes were provided to varying extents, depending on whether the cells were in the early or late exponential or in the stationary growth phase.

A hypocotyl-derived somatic embryogenic system in Brassica juncea Czern & Coss and its manipulation for enhanced storage lipid accumulation

A simple and reproducible protocol for induction, growth and development of somatic embryos from hypocotyl explants of Indian mustard (Brassica juncea L. Czern & Coss) var. RLM 198 is reported. The HDSE (Hypocotyl-derived somatic embryos) were fleshy globular to torpedo structures that were maintained by regular subculturing every three weeks. These embryos developed non-synchronously into the heart shaped-stage while some were matured into a green cotyledon-stage bearing embryos in the same medium. The HDSE accumulated as much as 50.2% lipid content on a dry weight basis at 14 DAC (days after culture) using a culture medium supplemented with 10% PEG (Polyethylene glycol 6000) in comparison to less than 15% lipid content in 2% sucrose (control) or 20 μM ABA (abscisic acid). An increase in total soluble sugar content was observed with 2.5% PEG and increasing PEG concentration caused a decrease in their contents in HDSE. The activities of invertase, acetyl CoA carboxylase and 1-14C-acetate incorporation into lipids in HDSE were enhanced significantly in the culture medium containing 10% PEG. The content of triacylglycerols in HDSE was maximum with 10% PEG supplemented culture medium. The wax content in HDSE increased progressively with an increase of PEG concentration in the culture medium. The ABA and PEG supplementation increased the content of membrane lipids when the data was expressed on a 100 g dry weight basis. The proportion of palmitate and erucate decreased and that of oleate, linoleate and linolenate increased at 14 DAC in HDSE in 10% PEG supplemented culture medium. Thus, the manipulation of culture conditions significantly altered total lipid content, membrane lipid composition and the quality of storage lipids.

Increased flow of fatty acids toward beta-oxidation in developing seeds of Arabidopsis deficient in diacylglycerol acyltransferase activity or synthesizing medium-chain-length fatty acids.

Synthesis of polyhydroxyalkanoates (PHAs) from intermediates of fatty acid beta-oxidation was used as a tool to study fatty acid degradation in developing seeds of Arabidopsis. Transgenic plants expressing a peroxisomal PHA synthase under the control of a napin promoter accumulated PHA in developing seeds to a final level of 0. 06 mg g(-1) dry weight. In plants co-expressing a plastidial acyl-acyl carrier protein thioesterase from Cuphea lanceolata and a peroxisomal PHA synthase, approximately 18-fold more PHA accumulated in developing seeds. The proportion of 3-hydroxydecanoic acid monomer in the PHA was strongly increased, indicating a large flow of capric acid toward beta-oxidation. Furthermore, expression of the peroxisomal PHA synthase in an Arabidopsis mutant deficient in the enzyme diacylglycerol acyltransferase resulted in a 10-fold increase in PHA accumulation in developing seeds. These data indicate that plants can respond to the inadequate incorporation of fatty acids into triacylglycerides by recycling the fatty acids via beta-oxidation and that a considerable flow toward beta-oxidation can occur even in a plant tissue primarily devoted to the accumulation of storage lipids.

The role of malic enzyme in the regulation of lipid accumulation in filamentous fungi.

The hypothesis is advanced that NADP(+)-malic enzyme (ME; EC 1.1.1.40) is an important activity in regulating the extent of lipid accumulation in filamentous fungi. In Mucor circinelloides, a fungus capable of accumulating only 25% (w/w, dry wt) lipid, even under the most propitious conditions, ME disappears 15-20 h after nitrogen exhaustion, coincident with the cessation of lipid accumulation. In contrast, ME in Mortierella alpina, a fungus capable of accumulating 50% (w/w, dry wt) lipid, remains active for over 60 h after N-exhaustion during which time lipid accumulation continues. No other enzyme activity studied, including the lipogenic enzymes acetyl-CoA carboxylase, fatty acid synthase, diacyglycerol acyltransferase, ATP: citrate lyase and the NADPH-generating enzymes glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and NADP+:isocitrate dehydrogenase, demonstrated any correlation with the accumulation of storage lipid in either fungus. Full activity of ME is restored in Mr. circinelloides within 4 h by adding NH4+ to the cultures, but this is prevented by adding cycloheximide as an inhibitor of protein synthesis. This suggests that the decrease in ME activity occurs due to down-regulation of the ME gene.

Does dietary fat influence insulin action?

What is clear from the research thus far is that dietary fat intake does influence insulin action. However, whether the effect is good, bad, or indifferent is strongly related to the fatty acid profile of that dietary fat. The evidence has taken many forms, including in vitro evidence of differences in insulin binding and glucose transport in cells grown with different types of fat in the incubation medium, in vivo results in animals fed different fats, relationships demonstrated between the membrane structural lipid fatty acid profile and insulin resistance in humans, and finally epidemiological evidence linking particularly high saturated fat intake with hyperinsulinemia and increased risk of diabetes. This contrasts with the lack of relationship, or even possible protective effect, of polyunsaturated fats. In particular, habitual increased n-3 polyunsaturated dietary fat intake (as fish fats) would appear to be protective against the development of glucose intolerance. It is reassuring that the patterns of dietary fatty acids that appear beneficial for insulin action and energy balance are also the patterns that would seem appropriate in the fight against thrombosis and cardiovascular disease. Mechanisms, though, still need to be defined. However, there are strong indicators that defining the ways in which changes in the fatty acid profile of membrane structural lipids are achieved, and in turn influence relevant transport events, plus understanding the processes that control accumulation and availability of storage lipid in muscle may be fruitful avenues for future research. One of the problems of moving the knowledge gained from research at the cellular level through to the individual and on to populations is the need for more accommodating research designs. In vitro studies may provide in-depth insights into intricate mechanisms, but they do not give the "big picture" for practical recommendations. On the other hand, correlational studies tend to be fairly blunt instruments, requiring large numbers that are very often not feasible if a greater depth of understanding of the biological processes is to be incorporated. There may be benefit in turning to the clinical case study as a framework for a more comprehensive analysis of the links between dietary fats and insulin action. The real challenge is to keep the depth of analysis rigorous enough to be able to explain and accommodate individual variation (i.e., the diversity of both environmental and genetic backgrounds) while at the same time satisfying the cultural need to provide appropriate overall dietary guidelines. Finally, David Kritchevsky brought to our attention a delightful quote from Mark Twain: "There is something fascinating about science. One gets such a wholesale return of conjecture for such a trifling investment of fact." In the field of dietary fats and the Metabolic Syndrome, this quotation is, unfortunately, apt. Much more research is necessary to define how dietary fats really work to affect insulin action. Well designed, long-term studies in "free range" humans must be undertaken if dietary guidelines for the Metabolic Syndrome are to be based on anything more than a "trifling" amount of "fact."

Chemical Characterization of a Shriveled Seed Trait in Peanut

Seed morphology mutations affecting the major seed components in pea (Pisum sativum L.) and maize (Zea mays L.) opened specialty markets for these crops. Peanut (Arachis hypogaea L.) is an important oil and food crop of the world. Genetic alteration of seed composition may be useful in expanding markets for this crop. Some lines from the University of Florida peanut breeding program showed seed shriveling characteristic even when harvested mature. In the present study, three shriveled lines (529B, 563A, and 647A) were chemically characterized and compared with a normal‐seeded cultivar, Sunrunner. They were found to have only one third to two thirds the amount of storage lipid and double the amount of sucrose as normal peanuts. Differences were also observed for seed protein concentration, when expressed on a defatted meal basis. Higher relative proportions of phospholipid to triacylglycerol may indicate a block in the biochemical pathway for the conversion of sucrose into triacylglycerol in the shriveled seed mutants. Sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE) patterns revealed that there were differences in the levels of various proteins between normal seed and shriveled seed phenotypes. Differences were identified in the level of accumulation of storage lipid and also in the various proteins during the development of the shriveled seed.

Accumulation of storage lipids in species of Rhodococcus and Nocardia and effect of inhibitors and polyethylene glycol

AbstractMembers of the genera Rhodococcus and Nocardia corallina were investigated for their capability to accumulate storage lipids that occur in the cytoplasm during cultivation of the cells under nitrogen‐limiting conditions in the absence or presence of various effectors. All bacteria were able to accumulate triacylglycerols (TAG) as main compounds plus minor amounts of diacylglycerols and wax esters. In addition to neutral lipids, R. fascians, R. erythropolis, and R. opacus MR22 accumulated small amounts of polyhydroxybutyrate (PHB), and N. corallina and R. ruber accumulated significant amounts of polyhydroxyalkanoates (PHA) consisting of 3‐hydroxybutyrate (3HB) and 3‐hydroxyvalerate (3HV) from glucose or valerate. Alloxan or 3‐nitropropionate, which are inhibitors of the citric acid cycle, caused a decrease in the content of odd‐numbered fatty acids in the TAG accumulated from acetate by R. opacus PD630. Cerulenin, an inhibitor of the fatty acid de novo synthesis, completely inhibited accumulation of TAG from glucose or gluconate but not from hexadecane in all bacteria investigated. In addition, cerulenin caused an increase of the PHA content and resulted in an increase of the relative amounts of 3HB units in the PHA in R. ruber and N. corallina. Acrylic acid, an inhibitor of fatty acid β‐oxidation, completely or partially inhibited accumulation of TAG from hexadecane or valerate, respectively, in R. opacus PD630. In R. ruber, acrylic acid completely inhibited accumulations of TAG from valerate; under these conditions the content of PHA increased twofold, and the polyester consisted exclusively of 3HV. PEG‐200 (0.2 to 5%, w/v) caused a decrease in the PHA content, but stimulated the incorporation of 3HV units into the PHA in R. ruber. Therefore, the relative amounts and compositions of both storage lipids can be affected by various compounds in these Gram‐positive bacteria.

Changes in lipid composition during in vitro encystation and fatty acid desaturase activity of Giardia lamblia

Lipids of axenically-cultured Giardia lamblia trophozoites were compared with those of cells undergoing in vitro encystation. Although the lipid composition of the organisms grossly resembled those of low-bile or high-bile culture media, differences were clearly detected. Encysting trophozoites incubated in a high-bile medium for 24 h had a higher concentration of unsaturated fatty acids in the total cellular lipids than did nonencysting trophozoites. The organism, but not the medium, contained linoleate and linolenate, suggesting that G. lamblia desaturates oleate. The presence of a fatty acid desaturase activity in the organism was demonstrated by the conversion of a radiolabeled monounsaturated fatty acid (oleate) to radiolabeled polyunsaturated fatty acids. Triglycerides, a common form of storage lipids, were unusually low in G. lamblia, but steryl esters (which can also serve as reserves) were abundant. Steryl esters increased during encystation of G. lamblia. The changes observed in G. lamblia lipids (increased fatty acid unsaturation and the accumulation of storage lipids) are consistent with parasite differentiation into a cyst stage that is able to survive outside the host at reduced temperatures and reduced available nutrient resources. This study also demonstrated that G. lamblia not only has the capacity to de novo synthesize isoprenoid lipids (ubiquinone, prenylated proteins), but it can also metabolize fatty acids by the addition of double bonds.

The activity of acetyl-CoA carboxylase is not correlated with the rate of lipid synthesis during development of oilseed rape (Brassica napus L.) embryos

Acetyl-CoA carboxylase (ACCase; EC 6.4.1.2) activity has been determined in seed tissues of oilseed rape (Brassica napus L.), pea (Pisum sativum L.) and castor bean (Ricinus communis L.). A new method is described which leads to significantly higher measurable activities of the enzyme in tissue homogenates than previously reported. This method does not involve either Triton X-100 or centrifugation treatments which have been used previously in the study of the enzyme. In the case of oilseed rape the activity was also increased by removal of the testa from the seed. The activity of ACCase was determined throughout the development of oilseed rape embryos. Enzyme activity increased 3.5-fold as the embryo fresh weight increased from 0.3 to 2.0 mg and then reached a plateau at 1.1 nmol malonyl-CoA-min−1 · embryo−1. The main period of lipid accumulation commenced at an embryo fresh weight of 2.3 mg, which was after the plateau in ACCase activity had been reached. Activity of the enzyme declined after an embryo fresh weight of 3.5 mg, which was before lipid accumulation in the embryo had been completed. Comparison of the activity of ACCase and the apparent in-vivo rate of lipid synthesis on an embryo-fresh-weight basis (i.e. nmol malonyl-CoA formed or utilized·min−1·mg−1 fresh weight) revealed that ACCase activity declines relative to the rate of lipid synthesis throughout development. The negative correlation between these two rates is discussed in relation to the role of ACCase in the regulation of accumulation of storage lipid during embryo development.

Embryogenesis in Higher Plants: An Overview.

The sporophytic generation of higher plants is initiated with the double fertilization event that results in the formation of a single-celled zygote and a progenitor cell of the endosperm. Embryogenesis describes the subsequent period of development, during which the zygote undergoes a complex series of morphological and cellular changes resulting in the formation of a developmentally arrested mature embryo comprised of an embryonic axis with shoot and root poles and cotyledon(s), which often contains high levels of storage macromolecules such as proteins and lipids. Thus, the events that occur during embryonic development establish the organization of the plant body and prepare the embryo for both dormancy and germination. Higher plant embryogenesis has been studied intensively during the past century. Studies using light and electron microscopy have provided detailed descriptions of the morphological and anatomical changes that characterize embryonic development (Maheshwari, 1950; Wardlaw, 1955; Natesh and Rau, 1984; Raghavan, 1986). Cellular differentiation has been studied largely in relationship to the biosynthesis and accumulation of storage proteins, lipids, and starch, macromolecular reserves that ultimately serve as nutrients for postgerminative seedlings (Jenner, 1982; Slack and Browse, 1984; Casey et al., 1986; Shotwell and Larkins, 1989). The focus of attention on these reserves reflects their agricultura1 importance and the fact that the abundance of these macromolecules facilitates studies of their accumulation. By contrast, much less is known about the processes that underlie embryo morphogenesis, although increasing attention is being devoted to this area. In this review, we will provide an overview of the processes that occur during embryonic development, focusing primarily on dicotyledonous plants. Additionally, we will discuss some of the critical processes involved in embryo formation, about which relatively little is known. This review is meant to provide a conceptual summary of embryonic development rather than to cover all aspects of embryogenesis in detail or to describe events that occur in all species of plants. Readers are referred to other reviews on embryogenesis for additional coverage of the topic (Natesh and Rau, 1984; Dure, 1985; Raghavan, 1986; Crouch, 1987; Goldberg et al., 1989; Meinke, 1991a; De Jong et al., 1993; Lindsey and Topping, 1993).

Acyl carrier proteins from developing seeds of Cuphea lanceolata Ait

The structure of acyl carrier protein (ACP) may determine the fate of the acyl moieties linked to it in the course of de-novo fatty acid synthesis in higher plants. To investigate a possible correlation between the structure of ACP and the synthesis of medium-chain fatty acids, we isolated and characterized ACP from the seeds of Cuphea lanceolata Ait. (subgenus Eucuphea/Section Heterodon), an annual crop that contains up to 90% decanoic (capric) acid in seed triacylglycerols. After a cell-free extract prepared from developing seeds was treated to 65% saturation with ammonium sulfate, two ACP-isoforms (ACP 1 and ACP 2) were identified in the supernatant that could be purified to homogeneity by anion-exchange chromatography and subsequent reversed-phase high-performance liquid chromatography. The molecular mass determined by matrix-assisted ultraviolet-laser desorption ionization mass spectrometry of ACP 1 was 9315 Da, whereas further heterogeneity was observed for ACP 2 with molecular masses of 8598 and 8703 Da. Aminoterminal sequencing was performed showing a high homology in the primary structures of ACP 1 and ACP 2. Both isoforms were present in the embryo, whereas in the chloroplast-containing seed coat ACP 2 was found in minute amounts, if at all. The expression of ACP 2 correlated with the production of capric acid during the phase of storage-lipid accumulation. These data indicate that ACP 2 is part of the machinery for the synthesis of medium-chain fatty acids, whereas ACP 1 appears to be a constitutive protein.

Storage lipid formation in seeds

AbstractThe mechanisms and regulation of storage lipid formation in seeds are reviewed. Seed storage lipids are ultimately derived from simple carbon compounds, such as sucrose, which are imported into seeds from source tissues, such as leaves or pods. The partitioning of this important carbon towards storage lipid, carbohydrate or protein is regulated by a complex interaction between genetically-determined endogenous factors and external environmental influences. Storage lipids are synthesized from fatty acids, derived from acetyl-CoA, and glycerol 3-phosphate. Fatty acid biosynthesis and probably acetyl-CoA formation, occurs within the plastids to produce oleoyl-CoA. Further elaboration of oleoyl-CoA to produce polyunsaturates, hydroxylates or very long chain acyl-CoAs occurs on the endoplasmic reticulum, as does the esterification of acyl-CoAs to glycerol-3-phosphate to produce the final triacylglycerol storage oil. The temporal and hormonal regulation of storage lipid accumulation in seeds is discussed.

A Developmental Analysis of the Enolase Isozymes from Ricinus communis

Enolase activity was measured in clarified homogenates of various tissues during the life cycle of the castor oil plant (Ricinus communis L. cv Baker 296). The proportions of total activity due to the plastid and cytosolic isozymes were determined after separation by ion-exchange chromatography. The contribution of the plastid isozyme varied from more than 30% of the total at the midpoint of endosperm development to less than 1% in mature leaves and roots. During endosperm development, enolase activity increased to a peak coincident with the maximum rate of storage lipid accumulation, then decreased to nearly undetectable levels in the mature seed. Plastid enolase protein, measured using an enzyme-linked immunosorbent assay, increased in parallel with the increase in activity but decreased less rapidly and was still easily detectable in mature seeds.

Biosynthesis of storage lipids in plant cell and embryo cultures.

The biosynthesis of storage lipids in plant cell and embryo cultures is discussed in the light of their significance in the breeding of agriculturally important oil seed crops. After a short introduction to the biosynthesis of storage lipids, i.e. triacylglycerols and wax esters, this review covers the occurrence and biosynthesis of storage lipids in plant cell and embryo cultures. Plant cells in culture generally contain low levels of both unusual fatty acids and triacylglycerols indicating that these cells are quite different from cells of oil storage tissues. There are a few exceptions to this rule which demonstrate that induction of genes involved in the expression of fatty acid modification and triacylglycerol assembly is possible in plant cell cultures. Such biosynthetically active plant cells may be of particular interest in future studies of storage lipid assembly. Both somatic and gametophytic embryos of oil plants exhibit high capacities for storage lipid biosynthesis and accumulation in vitro compared to cultured plant cells. Above all, the microspore-derived embryo system is recommended to both plant breeders and plant biochemists for the selection and multiplication of plants of superior quality.

CDNA cloning and expression of Brassica napus enoyl-acyl carrier protein reductase in Escherichia coli

The onset of storage lipid biosynthesis during seed development in the oilseed crop Brassica napus (rape seed) coincides with a drastic qualitative and quantitative change in fatty acid composition. During this phase of storage lipid biosynthesis, the enzyme activities of the individual components of the fatty acid synthase system increase rapidly. We describe a rapid and simple purification procedure for the plastid-localized NADH-dependent enoyl-acyl carrier protein reductase from developing B. napus seed, based on its affinity towards the acyl carrier protein (ACP). The purified protein was N-terminally sequenced and used to raise a potent antibody preparation. Immuno-screening of a seed-specific lambda gt11 cDNA expression library resulted in the isolation of enoyl-ACP reductase cDNA clones. DNA sequence analysis of an apparently full-length cDNA clone revealed that the enoyl-ACP reductase mRNA is translated into a precursor protein with a putative 73 amino acid leader sequence which is removed during the translocation of the protein through the plastid membrane. Expression studies in Escherichia coli demonstrated that the full-length cDNA clone encodes the authentic B. napus NADH-dependent enoyl-ACP reductase. Characterization of the enoyl-ACP reductase genes by Southern blotting shows that the allo-tetraploid B. napus contains two pairs of related enoyl-ACP reductase genes derived from the two distinct genes found in both its ancestors, Brassica oleracea and B. campestris. Northern blot analysis of enoyl-ACP reductase mRNA steady-state levels during seed development suggests that the increase in enzyme activity during the phase of storage lipid accumulation is regulated at the level of gene expression.

Three Classes of Abscisic Acid (ABA)-Insensitive Mutations of Arabidopsis Define Genes that Control Overlapping Subsets of ABA Responses

Wild type and three abscisic acid (ABA)-insensitive mutants of Arabidopsis (ABI1, ABI2, and ABI3) were compared for their ability to respond to ABA for a variety of ABA-inducible responses throughout the life cycle of the plants. The responses tested included effects on seedling growth, proline accumulation in seedlings, ABA-regulated protein synthesis in plantlets, and seed storage protein and lipid synthesis and accumulation. The abi1 and abi2 mutants showed reduced sensitivity to ABA for inhibition of seedling growth, induction of proline accumulation, and alterations in protein synthesis patterns during vegetative growth, but had wild type levels of storage reserves. In contrast, the abi3 mutant had wild type sensitivity for induction of proline accumulation and was only slightly less responsive to ABA with respect to effects on seedling growth and changes in patterns of protein synthesis. The major effects of this mutation were on seed development. Seeds of the abi3 mutant had two-thirds of the wild type level of storage protein and one-third the wild type level of eicosenoic acid, the major fatty acid component of storage lipids in wild type seeds. These results show that none of the abi mutants is insensitive for all ABA-inducible responses and that the abi3 effects are not seed-specific. Comparison of the degree of ABA sensitivity of monogenic mutant lines with that of digenic mutant lines carrying pairwise combinations of the abi mutations suggests that ABA responses in mature seeds are controlled by at least two parallel pathways.

Storage-protein regulation and lipid accumulation in microspore embryos of Brassica napus L.

Embryos derived in vitro from isolated microspores of Brassica napus L. were compared with their zygotic counterparts. Parameters investigated included storage-protein accumulation and gene expression, fattyacid composition, storage-lipid biosynthesis, and the appearance of oil-body proteins. The microspore embryos accumulate storage-protein and show increases in levels of their transcripts during the torpedo stage. These embryos were sensitive to abscisic acid (ABA) with respect to accumulation of storage-protein mRNA and oil-body proteins. Post-transcriptional regulation of cruciferin accumulation is indicated by a disparity between ABA-enhanced transcript accumulation and a less marked effect at the level of protein accumulation. To investigate storage-lipid profiles, two cultivars of Brassica napus, Reston and Topas, were used. The former accumulates major quantities of C20 (11.2%) and C22 (39.9%) fatty acids in its seeds, the latter predominantly C18 fatty acids. The higher-molecular-weight fatty acids (>C18) normally occur only in seeds and were used as biochemical markers for seed-specific metabolism in microspore embryos. Microspore embryos from Reston were found to accumulate C20 (10.6%) and C22 (31.2%) fatty acids after 35 d in culture at levels and proportions comparable to those found in seeds. Similarly, microspore embryos of Topas had a fatty-acid profile similar to that of mature Topas seed. Activities of enzymes involved in the accumulation of storage lipids (erucoyl-CoA synthetase [EC 6.2.1.3], erucoyl-CoA thioesterase [EC 3.1.2.2] and erucoyl-CoA acyltransferase [EC 2.3.1.15 or EC 2.3.1.20]) were detected in torpedostage microspore embryos. Their specific activities were higher than have been reported to date for analogous preparations from zygotic embryos of B. napus. The similarities in storage-lipid and protein composition of these embryos to their zygotic counterparts, along with their sensitivity to ABA, indicate that microspore embryos might be exploited to facilitate studies of biochemistry and gene regulation in oilseeds.

Storage Lipid Accumulation by Zygotic and Somatic Embryos in Culture

Storage Lipid Accumulation by Zygotic and Somatic Embryos in Culture

Accumulation of Storage Materials, Precocious Germination and Development of Desiccation Tolerance During Seed Maturation in Mustard (Sinapis alba L.)

AbstractUnder defined environmental conditions (20°C, continuous light of 15 klx) development of mustard seeds from artificial pollination to maturity takes about 60 d. After surpassing the period of embryo cell division and histodifferentiation (12–14d after pollination = dap), the seed enters into a maturation period. The time courses of various physiological, biochemical, and structural changes of embryo and testa during seed maturation were analyzed in detail (dry and fresh mass changes, osmotic and water potential changes, respiration, DNA amplification by endomitosis, total ribosome and polysome formation, storage protein synthesis and accumulation, storage lipid accumulation). In addition to the final storage products protein and lipid, embryo and testa accumulate transiently large amounts of starch within the chloroplasts during early maturation. Concomitantly with the subsequent total breakdown of the starch, the plastids lose most of their internal structure and chlorophyll and shrink into proplastids, typical for the mature seed. At about 30 dap the seeds shift from a desiccation‐sensitive to a desiccation‐tolerant state and are able then to germinate rapidly upon drying and reimbibition. If isolated from the immature fruit and sown directly on water, the seeds demonstrate precocious germination from about 13 dap onwards. Young seeds (isolated ≦ 38 dap) germinate only after surpassing a lag‐phase of several days (after‐ripening) during which the embryo continues to accumulate storage protein and lipid at the expense of the surrounding seed tissues. We conclude from these results that the maturing seed represents a rather closed developmental system which is able to continue its development up to successful germination without any specific regulatory influence from the mother plant. Immature seeds are able to germinate without a preceding dehydration treatment, which means that partial or full desiccation does not serve as an environmental signal for reprogramming seed development from maturation to germination. Instead, it is argued that the water relations of the seed are a critical element in the control of maturation and germination: during maturation on the mother plant the embryo is subject to a considerable turgor pressure (of the order of 12 bar) accompanied by a low water potential (of the order of −12 bar). This turgor permits maturation growth but is subcritical for germination growth. However, upon imbibition in water, the low water potential provides a driving force for a burst of water uptake overcoming the critical turgor threshold and thereby inducing germination.

Storage and depletion of lipid components in the pyloric caeca and ovaries of the seastarAsterias rubens during its annual reproductive cycle

Detailed information is presented on the changes in lipid-class profiles (polar lipids, total neutral lipids, free sterols, steryl esters, triacylglycerols, neutral ether lipids and free fatty acids), which are manifest during the annual reproductive cycle of the seastarAsterias rubens for both the storage organs (pyloric caeca) and utilizing organs (ovaries). The ovaries appear to accumulate all individual lipid components proportional to progression of vitellogenesis. Pyloric caeca, in contrast, show variable lipid-class levels, probably due to more complex processes in these organs, operating simultaneously: digestion of food, accumulation of storage lipids, mobilization of stored lipids and their release. The results are discussed in terms of current knowledge on the role of lipids in echinoderm reproduction.