AtMYB41 acts as a dual-function transcription factor that regulates the formation of lipids in an organ- and development-dependent manner

The plant cuticle controls non-stomatal water loss and can serve as a barrier against biotic agents, whereas the heteropolymer suberin and its associated waxes are deposited constitutively at specific cell wall locations. While several transcription factors controlling cuticle formation have been identified, those involved in the transcriptional regulation of suberin biosynthesis remain poorly characterized. The major goal of this study was to further analyse the function of the R2R3-Myeloblastosis (MYB) transcription factor AtMYB41 in formation of the cuticle, suberin, and suberin-associated waxes throughout plant development. For functional analysis, the organ-specific expression pattern of AtMYB41 was analysed and Atmyb41ge alleles were generated using the CRISPR/Cas9 system. These were investigated for root growth and water permeability upon stress. In addition, the fatty acid, wax, cutin, and suberin monomer composition of different organs was evaluated by gas chromatography. The characterization of Atmyb41ge mutants revealed that AtMYB41 negatively regulates the production of cuticular lipids and fatty acid biosynthesis in leaves and seeds, respectively. Remarkably, biochemical analyses indicate that AtMYB41 also positively regulates the formation of cuticular waxes in stems of Arabidopsis thaliana. Overall, these results suggest that the AtMYB41 acts as a negative regulator of cuticle and fatty acid biosynthesis in leaves and seeds, respectively, but also as a positive regulator of wax production in A. thaliana stems.

Wound-induced triacylglycerol biosynthesis is jasmonoy-l-isoleucin and abscisic acid independent

Triacylglycerol (TAG) plays a significant role during plant stress - it maintains lipid homeostasis. Upon wounding plants accumulate TAG, likely as a storage form of fatty acids (FAs) that originate from damaged membranes. This study asked if this process depends on the two phytohormones jasmonoyl-isoleucine (JA-Ile) and abscisic acid (ABA), which are involved in wound signalling. To analyse regulation of wound-induced TAG accumulation, we used mutants deficient in JA-Ile, with reduced ABA and the myb96 mutant, which is deficient in an ABA-dependent transcription factor. The expression of genes involved in TAG biosynthesis, and TAG content after wounding were analysed via LC-MS and GC-FID, plastidial lipid content in all mentioned mutant lines was also determined. The localization of newly synthesized TAG was investigated using lipid droplet staining. TAG accumulation upon wounding was confirmed as well as the fact that the newly synthesized TAG are mostly composed of polyunsaturated fatty acids. Nevertheless, all tested mutant lines were able to accumulate TAG similar to the WT. We observed differences in reduction of plastidial lipids - in WT plants this was higher than in mutant lines. Newly synthesized TAGs were stored in lipid droplets at and around the wounded area. Our results show that TAG accumulation upon wounding is not dependent on JA-Ile or ABA. The newly synthesized TAG species are composed of unsaturated fatty acids of membrane origin, and most likely serves as a transient energy store.

Altered regulation of lipid biosynthesis in a mutant of Arabidopsis deficient in chloroplast glycerol-3-phosphate acyltransferase activity

The leaf membrane lipids of many plant species, including Arabidopsis thaliana (L.) Heynh., are synthesized by two complementary pathways that are associated with the chloroplast and the endoplasmic reticulum. By screening directly for alterations in lipid acyl-group composition, we have identified several mutants of Arabidopsis that lack the plastid pathway because of a deficiency in activity of the first enzyme in the plastid pathway of glycerolipid synthesis, acyl-ACP:sn-glycerol-3-phosphate acyltransferase (EC 2.3.1.15) (where ACP is acyl carrier protein). The lesion results in an increased synthesis of lipids by the cytoplasmic pathway that largely compensates for the loss of the plastid pathway and provides nearly normal amounts of all the lipids required for chloroplast biogenesis. However, the fatty acid composition of the leaf membrane lipids of the mutants is altered because the acyltransferases associated with the two pathways normally exhibit different substrate specificities. The remarkable flexibility of the system provides an insight into the nature of the regulatory mechanisms that allocate lipids for membrane biogenesis.

[Word patterns in the LIM (Life-line Interview Method) / life story]

In this exploratory study, life story data on the word patterns in the LIM (Life-line Interview Method) are reported for 98 men and women, almost equally divided over a younger (18-30), a middle-aged (31-55) and an older (56-84) age group. All respondents tell about their past in great detail, but have a short view of the future. In terms of word frequency are memories (past) and expectations (future) in the proportion of about five to one. As expected, older persons need more words for telling their past story than younger people; word counts of the future life story, however, do not yield in any difference between young, middle-aged and older men and women. In general, the word frequency for memories of negative and positive life events is in the proportion of about three to two. The significance of the LIM word patterns for practical interventions (reminiscence, life-review) is discussed briefly.

Biosynthesis and secretion of plant cuticular wax

The cuticle covers the aerial portions of land plants. It consists of amorphous intracuticular wax embedded in cutin polymer, and epicuticular wax crystalloids that coat the outer plant surface and impart a whitish appearance. Cuticular wax is mainly composed of long-chain aliphatic compounds derived from very long chain fatty acids. Wax biosynthesis begins with fatty acid synthesis in the plastid. Here we focus on fatty acid elongation (FAE) to very long chains (C24-C34), and the subsequent processing of these elongated products into alkanes, secondary alcohols, ketones, primary alcohols and wax esters. The identity of the gene products involved in these processes is starting to emerge. Other areas of this field remain enigmatic. For example, it is not known how the hydrophobic wax components are moved intracellularly, how they are exported out of the cell, or translocated through the hydrophilic cell wall. Two hypotheses are presented for intracellular wax transport: direct transfer of lipids from the endoplasmic reticulum to the plasma membrane, and Golgi mediated exocytosis. The potential roles of ABC transporters and non-specific lipid transfer proteins in wax export are also discussed. Biochemical-genetic and genomic approaches in Arabidopsis thaliana promise to be particularly useful in identifying and characterizing gene products involved in wax biosynthesis, secretion and function. The current review will, therefore, focus on Arabidopsis as a model for studying these processes.

Biosynthesis and secretion of plant cuticular wax

The cuticle covers the aerial portions of land plants. It consists of amorphous intracuticular wax embedded in cutin polymer, and epicuticular wax crystalloids that coat the outer plant surface and impart a whitish appearance. Cuticular wax is mainly composed of long-chain aliphatic compounds derived from very long chain fatty acids. Wax biosynthesis begins with fatty acid synthesis in the plastid. Here we focus on fatty acid elongation (FAE) to very long chains (C24-C34), and the subsequent processing of these elongated products into alkanes, secondary alcohols, ketones, primary alcohols and wax esters. The identity of the gene products involved in these processes is starting to emerge. Other areas of this field remain enigmatic. For example, it is not known how the hydrophobic wax components are moved intracellularly, how they are exported out of the cell, or translocated through the hydrophilic cell wall. Two hypotheses are presented for intracellular wax transport: direct transfer of lipids from the endoplasmic reticulum to the plasma membrane, and Golgi mediated exocytosis. The potential roles of ABC transporters and non-specific lipid transfer proteins in wax export are also discussed. Biochemical-genetic and genomic approaches in Arabidopsis thaliana promise to be particularly useful in identifying and characterizing gene products involved in wax biosynthesis, secretion and function. The current review will, therefore, focus on Arabidopsis as a model for studying these processes.

Biosynthesis and secretion of plant cuticular wax

The cuticle covers the aerial portions of land plants. It consists of amorphous intracuticular wax embedded in cutin polymer, and epicuticular wax crystalloids that coat the outer plant surface and impart a whitish appearance. Cuticular wax is mainly composed of long-chain aliphatic compounds derived from very long chain fatty acids. Wax biosynthesis begins with fatty acid synthesis in the plastid. Here we focus on fatty acid elongation (FAE) to very long chains (C24-C34), and the subsequent processing of these elongated products into alkanes, secondary alcohols, ketones, primary alcohols and wax esters. The identity of the gene products involved in these processes is starting to emerge. Other areas of this field remain enigmatic. For example, it is not known how the hydrophobic wax components are moved intracellularly, how they are exported out of the cell, or translocated through the hydrophilic cell wall. Two hypotheses are presented for intracellular wax transport: direct transfer of lipids from the endoplasmic reticulum to the plasma membrane, and Golgi mediated exocytosis. The potential roles of ABC transporters and non-specific lipid transfer proteins in wax export are also discussed. Biochemical-genetic and genomic approaches in Arabidopsis thaliana promise to be particularly useful in identifying and characterizing gene products involved in wax biosynthesis, secretion and function. The current review will, therefore, focus on Arabidopsis as a model for studying these processes.

A condensing enzyme from the seeds of Lesquerella fendleri that specifically elongates hydroxy fatty acids

Lesquerella fendleri seed oil contains up to 60% hydroxy fatty acids, nearly all of which is the 20-carbon hydroxy fatty acid lesquerolic acid (D-14-hydroxyeicos-cis-11-enoic acid). Previous work suggested that lesquerolic acid in L. fendleri was formed by the elongation of the 18-carbon hydroxy fatty acid, ricinoleic acid. To identify a gene encoding the enzyme involved in hydroxy fatty acid elongation, an L. fendleri genomic DNA library was screened using the coding region of the Arabidopsis Fatty Acid Elongation1 gene as a probe. A gene, LfKCS3, with a high sequence similarity to known very long-chain fatty acid condensing enzymes, was isolated. LfKCS3 has a 2,062-bp open reading frame interrupted by two introns, which encodes a polypeptide of 496 amino acids. LfKCS3 transcripts accumulated only in the embryos of L. fendleri and first appeared in the early stages of development. Fusion of the LfKCS3 promoter to the uidA reporter gene and expression in transgenic Arabidopsis resulted in a high level of beta-glucuronidase activity exclusively in developing embryos. Seeds of Arabidopsis plants transformed with LfKCS3 showed no change in their very long-chain fatty acid content. However, when these Arabidopsis plants were crossed with the transgenic plants expressing the castor oleate 12-hydroxylase, significant amounts of 20-carbon hydroxy fatty acids accumulated in the seed, indicating that the LfKCS3 condensing enzyme specifically catalyzes elongation of 18-carbon hydroxy fatty acids.

Expression of the FAE1 gene and FAE1 promoter activity in developing seeds of Arabidopsis thaliana

Plant fatty acid elongase which catalyzes very-long-chain fatty acid (VLCFA) biosynthesis is a membrane-bound multienzyme complex. It is composed of four enzymes, a 3-ketoacyl-CoA synthase (condensing enzyme), a 3-ketoacyl-CoA reductase, a 3-hydroxyacyl-CoA dehydrase, and an enoyl-CoA reductase required for completion of each step of 2-carbon elongation of fatty acids. To improve our understanding of the overall regulation of the fatty acid elongase, we investigated the spatial and temporal expression of its key component, the FAE1-condensing enzyme, and examined the activity of the promoter of the FAE1 gene in Arabidopsis. In situ hybridization results revealed that FAE1 transcripts were found exclusively in the embryo. RNA blot analysis and histochemical analysis of GUS activity in pFAE1::GUS transgenic Arabidopsis lines demonstrated that the FAE1 gene was already transcribed in the early torpedo stage embryos 4-5 days after flowering, with transcription reaching its peak 9-11 days after flowering. VLCFA deposition closely paralleled FAE1 transcript accumulation. FAE1 promoter was highly active and embryo-specific. Because its timing coincides with the period of major storage lipid accumulation, and because its in vivo activity in Arabidopsis is superior to the napin promoter, FAE1 promoter may be ideal for genetic engineering of seed oil composition.

Expression of the wax-specific condensing enzyme CUT1 in Arabidopsis

The Arabidopsis thaliana gene CUT1 encodes a very-long-chain fatty acid-condensing enzyme required for the production of epicuticular wax in bolting stems. We have examined the expression pattern of CUT1 in Arabidopsis at different developmental stages and under different environmental conditions. RNA blot analysis showed that CUT1 was highly expressed in shoots, but not in roots. CUT1 expression was detectable throughout development. Light was required for CUT1 expression, and expression was increased by salt and drought treatments. The promoter region of the CUT1 gene was cloned, and 1.2 kb of the sequence 5' to the translation start codon was used to direct beta-glucuronidase (GUS) expression in transgenic plants. Histochemical and fluorometric (quantitative) GUS assays confirmed that the CUT1 promoter directed epidermal-specific expression and was highly active in Arabidopsis and in tobacco. A construct using the CUT1 promoter to drive CUT1 expression (CUT1p-CUT1) was used to transform Arabidopsis. Transgenic plants which had somewhat increased (overexpression) or greatly reduced (co-suppression) wax loads were recovered. Thus, the CUT1 promoter should be useful for genetic engineering applications that require epidermis-specific expression of genes.

Production of hydroxy fatty acids in the seeds of Arabidopsis thaliana

Seed-specific expression in Arabidopsis thaliana of oleate hydroxylase enzymes from castor bean and Lesquerella fendleri resulted in the accumulation of hydroxy fatty acids in the seed oil. By using various Arabidopsis mutant lines it was shown that the endoplasmic reticulum (ER) n-3 desaturase (FAD3) and the FAE1 condensing enzyme are involved in the synthesis of polyunsaturated and very-long-chain hydroxy fatty acids, respectively. In Arabidopsis plants with an active ER Delta12-oleate desaturase the presence of hydroxy fatty acids corresponded to an increase in the levels of 18:1 and a decrease in 18:2 levels. Expression in yeast indicates that the castor hydroxylase also has a low level of desaturase activity.

All fatty acids are not equal: discrimination in plant membrane lipids

Plant membrane lipids are primarily composed of 16-carbon and 18-carbon fatty acids containing up to three double bonds. By contrast, the seed oils of many plant species contain fatty acids with significantly different structures. These unusual fatty acids sometimes accumulate to >90% of the total fatty acid content in the seed triacylglycerols, but are generally excluded from the membrane lipids of the plant, including those of the seed. The reasons for their exclusion and the mechanisms by which this is achieved are not completely understood. Here we discuss recent research that has given new insights into how plants prevent the accumulation of unusual fatty acids in membrane lipids, and how strict this censorship of membrane composition is. We also describe a transgenic experiment that resulted in an excessive buildup of unusual fatty acids in cellular membranes, and clearly illustrated that the control of membrane lipid composition is essential for normal plant growth and development.

The natural genetic variation of the fatty-acyl composition of seed oils in different ecotypes of Arabidopsis thaliana

The fatty-acyl composition of the seed oil was determined for 100 ecotypes of Arabidopsis thaliana. Despite coming from diverse geographical locations, seed fatty-acyl profiles of all ecotypes were remarkably similar. They contained identical fatty acids, including the characteristic C20 and C22 very-long-chain fatty acids (VLCFAs). The total proportions of seed VLCFA varied between 22% and 35% w/w of the total seed fatty acid content.

CUT1, an Arabidopsis gene required for cuticular wax biosynthesis and pollen fertility, encodes a very-long-chain fatty acid condensing enzyme

Land plants secrete a layer of wax onto their aerial surfaces that is essential for survival in a terrestrial environment. This wax is composed of long-chain, aliphatic hydrocarbons derived from very-long-chain fatty acids (VLCFAs). Using the Arabidopsis expressed sequence tag database, we have identified a gene, designated CUT1, that encodes a VLCFA condensing enzyme required for cuticular wax production. Sense suppression of CUT1 in transgenic Arabidopsis plants results in waxless (eceriferum) stems and siliques as well as conditional male sterility. Scanning electron microscopy revealed that this was a severe waxless phenotype, because stems of CUT1-suppressed plants were completely devoid of wax crystals. Furthermore, chemical analyses of waxless plants demonstrated that the stem wax load was reduced to 6 to 7% of wild-type levels. This value is lower than that reported for any of the known eceriferum mutants. The severe waxless phenotype resulted from the downregulation of both the decarbonylation and acyl reduction wax biosynthetic pathways. This result indicates that CUT1 is involved in the production of VLCFA precursors used for the synthesis of all stem wax components in Arabidopsis. In CUT1-suppressed plants, the C24 chain-length wax components predominate, suggesting that CUT1 is required for elongation of C24 VLCFAs. The unique wax composition of CUT1-suppressed plants together with the fact that the location of CUT1 on the genetic map did not coincide with any of the known ECERIFERUM loci suggest that we have identified a novel gene involved in wax biosynthesis. CUT1 is currently the only known gene with a clearly established function in wax production.

Accumulation of very-long-chain fatty acids in membrane glycerolipids is associated with dramatic alterations in plant morphology

Transgenic Arabidopsis plants overexpressing the Arabidopsis FATTY ACID ELONGATION1 gene under the control of the 35S promoter from cauliflower mosaic virus accumulated very-long-chain fatty acids (VLCFAs) throughout the plant. In some transformants, C20 and C22 VLCFAs accounted for >30% of the total fatty acids, accumulating at the expense of C16 and C18 fatty acids. These C20 and C22 fatty acids were incorporated into all of the major membrane glycerolipid classes. Plants with a high VLCFA content displayed a dramatically altered morphology, which included the failure of flowering shoots to elongate, a modified spatial pattern of siliques, an altered floral phenotype, and a large accumulation of anthocyanins. In addition, these plants also exhibited a unique alteration of the chloroplast membrane structure. We discuss a possible role for VLCFAs in establishing the shape/curvature of the membranes, which in turn may affect the shape of the cell and ultimately that of the whole plant.

Very-long-chain fatty acid biosynthesis is controlled through the expression and specificity of the condensing enzyme

The Arabidopsis FATTY ACID ELONGATION1 (FAE1) gene encodes a putative seed-specific condensing enzyme. It is the first of four enzyme activities that comprise the microsomal fatty acid elongase (FAE) involved in the biosynthesis of very-long-chain fatty acids (VLCFAs). FAE1 has been expressed in yeast and in tissues of Arabidopsis and tobacco, where significant quantities of VLCFAs are not found. The introduction of FAE1 alone in these systems is sufficient for the production of VLCFAs, for wherever FAE1 was expressed, VLCFAs accumulated. These results indicate that FAE1 is the rate-limiting enzyme for VLCFA biosynthesis in Arabidopsis seed, because introduction of extra copies of FAE1 resulted in higher levels of the VLCFAs. Furthermore, the condensing enzyme is the activity of the elongase that determines the acyl chain length of the VLCFAs produced. In contrast, it appears that the other three enzyme activities of the elongase are found ubiquitously throughout the plant, are not rate-limiting and play no role in the control of VLCFA synthesis. The ability of yeast containing FAE1 to synthesize VLCFAs suggests that the expression and the acyl chain length specificity of the condensing enzyme, along with the apparent broad specificities of the other three FAE activities, may be a universal eukaryotic mechanism for regulating the amounts and acyl chain length of VLCFAs synthesized.

Alteration of seed fatty acid composition by an ethyl methanesulfonate-induced mutation in Arabidopsis thaliana affecting diacylglycerol acyltransferase activity

In characterizing the enzymes involved in the formation of very long-chain fatty acids (VLCFAs) in the Brassicaceae, we have generated a series of mutants of Arabidopsis thaliana that have reduced VLCFA content. Here we report the characterization of a seed lipid mutant, AS11, which, in comparison to wild type (WT), has reduced levels of 20:1 and 18:1 and accumulates 18:3 as the major fatty acid in triacylglycerols. Proportions of 18:2 remain similar to WT. Genetic analyses indicate that the fatty acid phenotype is caused by a semidominant mutation in a single nuclear gene, designated TAG1, located on chromosome 2. Biochemical analyses have shown that the AS11 phenotype is not due to a deficiency in the capacity to elongate 18:1 or to an increase in the relative delta 15 or delta 12 desaturase activities. Indeed, the ratio of desaturase/elongase activities measured in vitro is virtually identical in developing WT and AS11 seed homogenates. Rather, the fatty acid phenotype of AS11 is the result of reduced diacylglycerol acyltransferase activity throughout development, such that triacylglycerol biosynthesis is reduced. This leads to a reduction in 20:1 biosynthesis during seed development, leaving more 18:1 available for desaturation. Thus, we have demonstrated that changes to triacylglycerol biosynthesis can result in dramatic changes in fatty acid composition and, in particular, in the accumulation of VLCFAs in seed storage lipids.

In planta transformation of Arabidopsis thaliana

Transformants of Arabidopsis thaliana can be generated without using tissue culture techniques by cutting primary and secondary inflorescence shoots at their bases and inoculating the wound sites with Agrobacterium tumefaciens suspensions. After three successive inoculations, treated plants are grown to maturity, harvested and the progeny screened for transformants on a selective medium. We have investigated the reproducibility and the overall efficiency of this simple in planta transformation procedure. In addition, we determined the T-DNA copy number and inheritance in the transformants and examined whether transformed progeny recovered from the same Agrobacterium-treated plant represent one or several independent transformation events. Our results indicate that in planta transformation is very reproducible and yields stably transformed seeds in 7-8 weeks. Since it does not employ tissue culture, the in planta procedure may be particularly valuable for transformation of A. thaliana ecotypes and mutants recalcitrant to in vitro regeneration. The transformation frequency was variable and was not affected by lower growth temperature, shorter photoperiod or transformation vector. The majority of treated plants gave rise to only one transformant, but up to nine siblings were obtained from a single parental plant. Molecular analysis suggested that some of the siblings originated from a single transformed cell, while others were descended from multiple, independently transformed germ-line cells. More than 90% of the transformed progeny exhibited Mendelian segregation patterns of NPTII and GUS reporter genes. Of those, 60% contained one functional insert, 16% had two T-DNA inserts and 15% segregated for T-DNA inserts at more than two unlinked loci. The remaining transformants displayed non-Mendelian segregation ratios with a very high proportion of sensitive plants among the progeny.(ABSTRACT TRUNCATED AT 250 WORDS)

Testing the usefulness of twin formation theory: the tocopherols and vitamin D

The theoretical and empirical search for biologically and pharmacologically active molecules has long been of interest. In 1965 Revici proposed a class of biologically and pharmacologically active molecules which he described as having twin formations. Twin formations are defined as molecules containing two or more adjacent carbon atoms having the same induced electrical charge. An examination of recently discovered facts about the biological activity of the tocopherol family and of vitamin D lends support to this concept, which if true, could greatly facilitate selection of promising pharmacological substances for testing.

AP2 Gene Determines the Identity of Perianth Organs in Flowers of Arabidopsis thaliana

We have examined the floral morphology and ontogeny of three mutants of Arabidopsis thaliana, Ap2-5, Ap2-6, and Ap2-7, that exhibit homeotic changes of the perianth organs because of single recessive mutations in the AP2 gene. Homeotic conversions observed are: sepals to carpels in all three mutants, petals to stamens in Ap2-5, and petals to carpels in Ap2-6. Our analysis of these mutants suggests that the AP2 gene is required early in floral development to direct primordia of the first and second whorls to develop as perianth rather than as reproductive organs. In addition, our results support one of the two conflicting hypotheses concerning the structures of the calyx and the gynoecium in the Brassicaceae.

AP2 Gene Determines the Identity of Perianth Organs in Flowers of Arabidopsis thaliana

We have examined the floral morphology and ontogeny of three mutants of Arabidopsis thaliana, Ap2-5, Ap2-6, and Ap2-7, that exhibit homeotic changes of the perianth organs because of single recessive mutations in the AP2 gene. Homeotic conversions observed are: sepals to carpels in all three mutants, petals to stamens in Ap2-5, and petals to carpels in Ap2-6. Our analysis of these mutants suggests that the AP2 gene is required early in floral development to direct primordia of the first and second whorls to develop as perianth rather than as reproductive organs. In addition, our results support one of the two conflicting hypotheses concerning the structures of the calyx and the gynoecium in the Brassicaceae.

Enhanced thermal tolerance in a mutant of Arabidopsis deficient in palmitic Acid unsaturation

A mutant of Arabidopsis thaliana, deficient in the activity of a chloroplast omega9 fatty acid desaturase, accumulates high amounts of palmitic acid (16:0), and exhibits an overall reduction in the level of unsaturation of chloroplast lipids. Under standard conditions the altered membrane lipid composition had only minor effects on growth rate of the mutant, net photosynthetic CO(2) fixation, photosynthetic electron transport, or chloroplast ultrastructure. Similarly, fluorescence polarization measurements indicated that the fluidity of the membranes was not significantly different in the mutant and the wild type. However, at temperatures above 28 degrees C, the mutant grew more rapidly than the wild type suggesting that the altered fatty acid composition enhanced the thermal tolerance of the mutant. Similarly, the chloroplast membranes of the mutant were more resistant than wild type to thermal inactivation of photosynthetic electron transport. These observations lend support to previous suggestions that chloroplast membrane lipid composition may be an important component of the thermal acclimation response observed in many plant species which are photosynthetically active during periods of seasonally variable temperature extremes.

A mutant of Arabidopsis deficient in desaturation of palmitic Acid in leaf lipids

The overall fatty acid composition of leaf lipids in a mutant of Arabidopsis thaliana was characterized by elevated amounts of palmitic acid and a decreased amount of unsaturated 16-carbon fatty acids as a consequence of a single nuclear mutation. Quantitative analysis of the fatty acid composition of individual lipids suggested that the mutant is deficient in the activity of a chloroplast omega9 fatty acid desaturase which normally introduces a double bond in 16-carbon acyl chains esterified to monogalactosyldiacylglycerol (MGD). The mutant exhibited an increased ratio of 18- to 16-carbon fatty acids in MGD due to a change in the relative contribution of the prokaryotic and eukaryotic pathways of lipid biosynthesis. This appears to be a regulated response to the loss of chloroplast omega9 desaturase and presumably reflects a requirement for polyunsaturated fatty acids for the normal assembly of chloroplast membranes. The reduction in mass of prokaryotic MGD species involved both a reduction in synthesis of MGD by the prokaryotic pathway and increased turnover of MGD molecular species which contain 16:0.

Altered chloroplast structure and function in a mutant of Arabidopsis deficient in plastid glycerol-3-phosphate acyltransferase activity

Mutants of Arabidopsis thaliana deficient in plastid glycerol-3-phosphate acyltransferase activity have altered chloroplast membrane lipid composition. This caused an increase in the number of regions of appressed membrane per chloroplast and a decrease in the average number of thylakoid membranes in the appressed regions. The net effect was a significant decrease in the ratio of appressed to nonappressed membranes. A comparison of 77 K fluorescence emission spectra of thylakoid membranes from the mutant and wild type indicated that the ultrastructural changes were associated with an altered distribution of excitation energy transfer from antenna chlorophyll to photosystem II and photosystem I in the mutant. The changes in leaf lipid composition did not significantly affect growth or development of the mutant under standard conditions. However, at temperatures above 28 degrees C the mutant grew slightly more rapidly than the wild type, and measurements of temperature-induced fluorescence yield enhancement suggested an increased thermal stability of the photosynthetic apparatus of the mutant. These effects are consistent with other evidence suggesting that membrane lipid composition is an important determinant of chloroplast structure but has relatively minor direct effects on the function of the membrane proteins associated with photosynthetic electron transport.

Enhanced thermal tolerance of photosynthesis and altered chloroplast ultrastructure in a mutant of Arabidopsis deficient in lipid desaturation

A mutant of Arabidopsis thaliana, deficient in activity of the chloroplast n-6 desaturase, accumulated high levels of C(16:1) and C(18:1) lipids and had correspondingly reduced levels of polyunsaturated lipids. The altered lipid composition of the mutant had pronounced effects on chloroplast ultrastructure, thylakoid membrane protein and chlorophyll content, electron transport rates, and the thermal stability of the photosynthetic membranes. The change in chloroplast ultrastructure was due to a 48% decrease in the amount of appressed membranes that was not compensated for by an increased amount of nonappressed membrane. This resulted in a net loss of 36% of the thylakoid membrane per chloroplast and a corresponding reduction in chlorophyll and protein content. Electrophoretic analysis of the chlorophyll-protein complexes further revealed a small decrease in the amount of light-harvesting complex. Relative levels of whole chain and protosystem II electron transport rates were also reduced in the mutant. In addition, the mutation resulted in enhanced thermal stability of photosynthetic electron transport. These observations suggest a central role of polyunsaturated lipids in determining chloroplast structure and maintaining normal photosynthetic function and demonstrate that lipid unsaturation directly affects the thermal stability of photosynthetic membranes.

A mutant of Arabidopsis deficient in the chloroplast 16:1/18:1 desaturase

Leaf tissue of a mutant of Arabidopsis thaliana contains reduced levels of both 18-carbon and 16-carbon polyunsaturated fatty acids and increased levels of the 18:1 and cis-16:1 precursors due to a single nuclear mutation at a locus designated fadC. Analysis of the fatty acid compositions of individual lipids and the kinetics of lipid labeling with [(14)C]acetate in vivo indicate that the mutant lacks activity of the chloroplast glycerolipid omega-6 desaturase. As a result, lipids synthesized by the prokaryotic pathway are not desaturated further than 18:1 and 16:1. Lipids derived from the eukaryotic pathway are desaturated-presumably by the endoplasmic reticulum 18:1 phosphatidylcholine desaturase. However, an increase in the level of 18:1 on all the phospholipids derived from the eukaryotic pathway in leaves of the mutant suggests that the mutation does exert an effect on the composition of extrachloroplast membranes. Synthesis of monogalactosyldiacylglycerol (MGD) by the prokaryotic pathway is reduced 30 to 35% in the mutant and there is a corresponding increase in MGD synthesis by the eukaryotic pathway. This shift in metabolism which results in a more unsaturated MGD pool, may reflect the existence of a regulatory mechanism which apportions lipid synthesis between the two pathways in response to alterations in the physical properties of the chloroplast membranes.

The effects of reduced amounts of lipid unsaturation on chloroplast ultrastructure and photosynthesis in a mutant of Arabidopsis

A mutant of Arabidopsis thaliana with reduced content of C(18:3) and C(16:3) fatty acids in membrane lipids exhibited a 45% reduction in the cross-sectional area of chloroplasts and had a decrease of similar magnitude in the amount of chloroplast lamellar membranes. The reduction in chloroplast size was partially compensated by a 45% increase in the number of chloroplasts per cell in the mutant. When expressed on a chlorophyll basis the rates of CO(2)-fixation and photosynthetic electron transport were not affected by these changes. Fluorescence polarization measurements indicated that the fluidity of the thylakoid membranes was not significantly altered by the mutation. Similarly, on the basis of temperature-induced fluorescence yield enhancement measurements, there was no significant effect on the thermal stability of chlorophyll-protein complexes in the mutant. These observations suggest that the high content of trienoic fatty acids in chloroplast lipids may be an important factor regulating organelle biogenesis but is not required to support normal levels of the photosynthetic activities associated with the thylakoid membranes.

Quantitative correlative proton and electron microprobe analysis of biological specimens

To investigate the possibility of quantitative correlative proton microprobe (PMP) and electron microprobe (EMP) analysis of biological soft tissue, model specimens were analyzed by both techniques. The specimens consisted of freeze-dried sections of gelatin containing known concentrations of nickel chloride. Both for PMP and for EMP, the signal was expressed as the ratio of the characteristic intensity and the continuum intensity in a peak-free region of the spectrum. With both techniques, calibration curves (signal versus known concentration) obtained, showed a deviation from linearity at high nickel concentrations. However, a linear relation (correlation coefficient 0.996) was obtained in a plot of EMP signal versus PMP signal. This indicates that quantitative correlative PMP and EMP analysis can be carried out by using the same standard for both analytical techniques.

Formation of Tryptophol Galactoside and an Unknown Tryptophol Ester in Euglena gracilis

The unicellular alga Euglena gracilis Klebs ;Z' converted exogenous indole-3-ethanol (trytophol) to two major metabolites: tryptophol galactoside and an unknown compound, and to minor amounts of indole-3-acetic acid, tryptophol acetate, and tryptophol glucoside. The unknown was hydrolyzed to tryptophol by methanolic ammonia and should therefore be a tryptophol ester. The galactoside was identified as 2-(indol-3-yl)ethyl-beta-d-galactopyranoside. This structure was established by comparison with an authentic standard involving chromatographic methods, ultraviolet and mass spectroscopy, enzymic and acid hydrolysis, and identification of the galactose in the hydrolysate. By forming tryptophol galactoside, Euglena differs from the higher plants examined so far, for which the corresponding glucoside is the only sugar conjugate of tryptophol detected.

Do pelvic floor exercises really improve orgasmic potential?

Women with orgasmic difficulties are commonly taught pubococcygeal (PC) muscle exercises which, practiced regularly, are said to have both specific and nonspecific beneficial effects on sexual enjoyment. The hypothesis tested was that women practicing these exercises over a 12-week period, would be more likely to become orgasmic than women practicing relaxation exercises, or than women in an attention-control group. Forty-six women were allocated to one of three groups, PC exercise, relaxation or control. PC muscle tone was measured and questionnaires about sexual response were completed over a 12-week period with a 6-month follow-up assessment. Results indicated that there was no difference in orgasmic outcome for the three groups during the experimental period. This was taken to imply that PC exercises are not of specific value for women with normal muscle tone. It remains possible that women with poor muscle tone are helped by the exercises and further research is considered necessary in this area.