Presence of polygodial and drimenol in Drimys populations from Chile

Drimys winteri (Winteraceae) is a tree with medicinal properties native to Chile. Its bark contains polygodial and drimenol in unknown quantities, with antimicrobial and antinociceptive activity. The purpose of the present study was to quantify polygodial and drimenol concentrations in leaves of five populations of D. winteri and one of Drimys andina from different regions of Chile, by GC analysis of the hexane extract. The concentration of these compounds was also determined in the bark of one of the D. winteri populations. In dried leaves mean concentrations of 0.99% for polygodial and 0.011% for drimenol could be observed, both differing significantly among the studied populations. It is concluded that polygodial and drimenol are present in the leaves and the bark of D. winteri and in D. andina leaves, this being the first report of the presence of these compounds in the latter species.     

Molecular cloning and characterization of drimenol synthase from valerian plant (Valeriana officinalis)

Drimenol, a sesquiterpene alcohol, and its derivatives display diverse bio-activities in nature. However, a drimenol synthase gene has yet to be identified. We identified a new sesquiterpene synthase cDNA (VoTPS3) in valerian plant (Valeriana officinalis). Purification and NMR analyses of the VoTPS3-produced terpene, and characterization of the VoTPS3 enzyme confirmed that VoTPS3 synthesizes (−)-drimenol. In feeding assays, possible reaction intermediates, farnesol and drimenyl diphosphate, could not be converted to drimenol, suggesting that the intermediate remains tightly bound to VoTPS3 during catalysis. A mechanistic consideration of (−)-drimenol synthesis suggests that drimenol synthase is likely to use a protonation-initiated cyclization, which is rare for sesquiterpene synthases. VoTPS3 can be used to produce (−)-drimenol, from which useful drimane-type terpenes can be synthesized.     

Highly Enantioselective Production of Chiral Secondary Alcohols with Candida zeylanoides as a New Whole Cell Biocatalyst

The increasing demand for biocatalysts in synthesizing enantiomerically pure chiral alcohols results from the outstanding characteristics of biocatalysts in reaction, economic, and ecological issues. Herein, fifteen yeast strains belonging to three food originated yeast species Candida zeylanoides, Pichia fermentans, and Saccharomyces uvarum were tested for their capability for asymmetric reduction of acetophenone to 1‐phenylethanol as biocatalysts. Of these strains, C. zeylanoides P1 showed an effective asymmetric reduction ability. Under optimized conditions, substituted acetophenones were converted to corresponding optically active secondary alcohols in up to 99% enantiomeric excess and at high yields. The preparative scale asymmetric bioreduction of 4‐nitroacetophenone ( 1m ) by C. zeylanoides P1 gave (S)‐1‐(4‐nitrophenyl)ethanol ( 2m ) with 89% yield and > 99% enantiomeric excess. Compound 2m has been obtained in an enantiomerically pure and inexpensive form. Additionally, these results indicate that C. zeylanoides P1 is a promising biocatalyst for the synthesis of chiral alcohols in industry.     

Whole‐cell‐based CYP153A6‐catalyzed (S)‐limonene hydroxylation efficiency depends on host background and profits from monoterpene uptake via AlkL

Living microbial cells are considered to be the catalyst of choice for selective terpene functionalization. However, such processes often suffer from side product formation and poor substrate mass transfer into cells. For the hydroxylation of (S)‐limonene to (S)‐perillyl alcohol by Pseudomonas putida KT2440 (pGEc47ΔB)(pCom8‐PFR1500), containing the cytochrome P450 monooxygenase CYP153A6, the side products perillyl aldehyde and perillic acid constituted up to 26% of the total amount of oxidized terpenes. In this study, it is shown that the reaction rate is substrate‐limited in the two‐liquid phase system used and that host intrinsic dehydrogenases and not CYP153A6 are responsible for the formation of the undesired side products. In contrast to P. putida KT2440, E. coli W3110 was found to catalyze perillyl aldehyde reduction to the alcohol and no oxidation to the acid. Furthermore, E. coli W3110 harboring CYP153A6 showed high limonene hydroxylation activities (7.1 U g). The outer membrane protein AlkL was found to enhance hydroxylation activities of E. coli twofold in aqueous single‐phase and fivefold in two‐liquid phase biotransformations. In the latter system, E. coli harboring CYP153A6 and AlkL produced up to 39.2 mmol (S)‐perillyl alcohol L within 26 h, whereas no perillic acid and minor amounts of perillyl aldehyde (8% of the total products) were formed. In conclusion, undesired perillyl alcohol oxidation was reduced by choosing E. coli's enzymatic background as a reaction environment and co‐expression of the alkL gene in E. coli represents a promising strategy to enhance terpene bioconversion rates. Biotechnol. Bioeng. 2013; 110: 1282–1292. © 2012 Wiley Periodicals, Inc.     

Arabidopsis acyl‐CoA‐binding protein ACBP1 participates in the regulation of seed germination and seedling development

A family of six genes encoding acyl‐CoA‐binding proteins (ACBPs), ACBP1–ACBP6, has been characterized in Arabidopsis thaliana. In this study, we demonstrate that ACBP1 promotes abscisic acid (ABA) signaling during germination and seedling development. ACBP1 was induced by ABA, and transgenic Arabidopsis ACBP1‐over‐expressors showed increased sensitivity to ABA during germination and seedling development, whereas the acbp1 mutant showed decreased ABA sensitivity during these processes. Subsequent RNA assays showed that ACBP1 over‐production in 12‐day‐old seedlings up‐regulated the expression of PHOSPHOLIPASE Dα1 (PLDα1) and three ABA/stress‐responsive genes: ABA‐RESPONSIVE ELEMENT BINDING PROTEIN1 (AREB1), RESPONSE TO DESICCATION29A (RD29A) and bHLH‐TRANSCRIPTION FACTOR MYC2 (MYC2). The expression of AREB1 and PLDα1 was suppressed in the acbp1 mutant in comparison with the wild type following ABA treatment. PLDα1 has been reported to promote ABA signal transduction by producing phosphatidic acid, an important lipid messenger in ABA signaling. Using lipid profiling, seeds and 12‐day‐old seedlings of ACBP1‐over‐expressing lines were shown to accumulate more phosphatidic acid after ABA treatment, in contrast to lower phosphatidic acid in the acbp1 mutant. Bimolecular fluorescence complementation assays indicated that ACBP1 interacts with PLDα1 at the plasma membrane. Their interaction was further confirmed by yeast two‐hybrid analysis. As recombinant ACBP1 binds phosphatidic acid and phosphatidylcholine, ACBP1 probably promotes PLDα1 action. Taken together, these results suggest that ACBP1 participates in ABA‐mediated seed germination and seedling development.     

Jasmonoyl‐l‐isoleucine hydrolase 1 (JIH1) regulates jasmonoyl‐l‐isoleucine levels and attenuates plant defenses against herbivores

For most plant hormones, biological activity is suppressed by reversible conjugation to sugars, amino acids and other small molecules. In contrast, the conjugation of jasmonic acid (JA) to isoleucine (Ile) is known to enhance the activity of JA. Whereas hydroxylation and carboxylation of JA‐Ile permanently inactivates JA‐Ile‐mediated signaling in plants, the alternative deactivation pathway of JA‐Ile by its direct hydrolysis to JA remains unstudied. We show that Nicotiana attenuata jasmonoyl‐l ‐isoleucine hydrolase 1 (JIH1), a close homologue of previously characterized indoleacetic acid alanine resistant 3 (IAR3) gene in Arabidopsis, hydrolyzes both JA‐Ile and IAA‐Ala in vitro. When the herbivory‐inducible NaJIH1 gene was silenced by RNA interference, JA‐Ile levels increased dramatically after simulated herbivory in irJIH1, compared with wild‐type (WT) plants. When specialist (Manduca sexta) or generalist (Spodoptera littoralis) herbivores fed on irJIH1 plants they gained significantly less mass compared with those feeding on wild‐type (WT) plants. The poor larval performance was strongly correlated with the higher accumulation of several JA‐Ile‐dependent direct defense metabolites in irJIH1 plants. In the field, irJIH1 plants attracted substantially more Geocoris predators to the experimentally attached M. sexta eggs on their leaves, compared with empty vector plants, which correlated with higher herbivory‐elicited emissions of volatiles known to function as indirect defenses. We conclude that NaJIH1 encodes a new homeostatic step in JA metabolism that, together with JA and JA‐Ile‐hydroxylation and carboxylation of JA‐Ile, rapidly attenuates the JA‐Ile burst, allowing plants to tailor the expression of direct and indirect defenses against herbivore attack in nature.     

Laboratory assessment of the antifouling potential of a soluble-matrix paint laced with the natural compound polygodial

Polygodial is a potent and selective inhibitor of ascidian metamorphosis that shows promise for controlling fouling by ascidians in bivalve aquaculture. The current study examined the potency of, and associated effects of seawater exposure on, a rosin-based soluble-matrix paint laced with 0.08–160?ng?polygodial?g^?1 wet paint matrix. Paint-coated surfaces were soaked in seawater for 0, 2, 4 or 12?weeks prior to screening for antifouling activity using a bioassay based on the nuisance ascidian Ciona savignyi Herdman. Mortality was greater (mean 50% lethal concentration: 5?±?2?ng?g^?1; mean 75% lethal concentration: 17?±?4?ng?g^?1) and metamorphosis was inhibited (mean 50% anti-metamorphic concentration: 2?±?0.4?ng?g^?1; mean 75% anti-metamorphic concentration: 15?±?10?ng?g^?1) in C. savignyi larvae exposed to polygodial-laced soluble-matrix paints, relative to control paints without polygodial. Soaking in seawater prior to testing reduced the efficacy of the formulation up to nearly 12-fold, but even after soaking for 12?weeks paints laced with polygodial at 160?ng?g^?1 wet paint matrix prevented ?90% of the larvae of C. savignyi from completing metamorphosis. The outcome of this experiment provides a positive first step in evaluating the suitability of polygodial-laced soluble-matrix paints for use in aquaculture.     

Genetic interactions reveal the antagonistic roles of FT/TSF and TFL1 in the determination of inflorescence meristem identity in Arabidopsis

During the transition to the reproductive phase, the shoot apical meristem switches from the developmental program that generates vegetative organs to instead produce flowers. In this study, we examined the genetic interactions of FLOWERING LOCUS T (FT)/TWIN SISTER OF FT (TSF) and TERMINAL FLOWER 1 (TFL1) in the determination of inflorescence meristem identity in Arabidopsis thaliana. The ft‐10 tsf‐1 mutants produced a compact inflorescence surrounded by serrated leaves (hyper‐vegetative shoot) at the early bolting stage, as did plants overexpressing TFL1. Plants overexpressing FT or TSF (or both FT and TFL1) generated a terminal flower, as did tfl1‐20 mutants. The terminal flower formed in tfl1‐20 mutants converted to a hyper‐vegetative shoot in ft‐10 tsf‐1 mutants. Grafting ft‐10 tsf‐1 or ft‐10 tsf‐1 tfl1‐20 mutant scions to 35S::FT rootstock plants produced a normal inflorescence and a terminal flower in the scion plants, respectively, although both scions showed similar early flowering. Misexpression of FT in the vasculature and in the shoot apex in wild‐type plants generated a normal inflorescence and a terminal flower, respectively. By contrast, in ft‐10 tsf‐1 mutants the vasculature‐specific misexpression of FT converted the hyper‐vegetative shoot to a normal inflorescence, and in the ft‐10 tsf‐1 tfl1‐20 mutants converted the shoot to a terminal flower. TFL1 levels did not affect the inflorescence morphology caused by FT/TSF overexpression at the early bolting stage. Taking these results together, we proposed that FT/TSF and TFL1 play antagonistic roles in the determination of inflorescence meristem identity, and that FT/TSF are more important than TFL1 in this process.     

(−)-3β-Acetoxydrimenin from the leaves of Drimys winteri

A new natural product, 3β-acetoxydrimenin was isolated from the petrol extract of the leaves of Drimys winteri which also contains the known compounds safrol, drimenol and polygodial. The structure of the new compound was determined by chemical and spectroscopic methods.     

Stereoselective Synthesis of a Promising Flower-Inducing KODA Analog, (9R,12S,13R,15Z)-9-Hydroxy-12,13-methylene-10-oxooctadec-15-enoic Acid

Stereoselective synthesis of a promising flower-inducing 9,10-ketol octadecadienoic acid (KODA) analog, (9R,12S,13R,15Z)-9-hydroxy-12,13-methylene-10-oxooctadec-15-enoic acid, was designed to obtain the desired stereoisomer via coupling between chiral sulfone and aldehyde segments. A known chiral cyclopropane derivative was converted to the sulfone segment via carbon-chain elongation and sulfonylation. Dec-9-en-1-ol was converted to the aldehyde segment, whose C-9 configuration was introduced by Sharpless asymmetric dihydroxylation. Coupling of the both segments and subsequent assembly gave the desired (9R,12S,13R,15Z)-analog. The (9S,12S,13R,15Z)-analog was also synthesized by using the enatiomeric aldehyde segment. This strategy made it possible to synthesize the remaining stereoisomeric analogs.     

Schistosomicidal Activity of Dihydrobenzofuran Neolignans

We have evaluated the antischistosomal activity of synthetic dihydrobenzofuran neolignans (DBNs) derived from (±)‐trans‐dehydrodicoumaric acid dimethyl ester ( 1 ) and (±)‐trans‐dehydrodiferulic acid dimethyl ester ( 2 ) against adult Schistosoma mansoni worms in vitro. Compound 4 ((±)‐trans‐4‐O‐acetyldehydrodiferulic acid dimethyl ester) displayed the most promising activity; at 200 μm , it kills 100 ± 0% of worms after 24 h, which resembles the result achieved with praziquantel (positive control) at 1.56 μm . The hydrogenation of the double bond between C7′ and C8′, the introduction of an additional methyl group at C3′, and a double bond between C7 and C8 decreased the schistosomicidal activity of DBNs. On the other hand, the presence of the acetoxy group at C4 played an interesting role in this activity. These results demonstrated the interesting schistosomicidal potential of DBNs, which could be further exploited.     

Antifeedant and toxic effects of drimanes on Colorado potato beetle larvae

Among the drimane compounds tested, the dialdehydes polygodial and warburganal were the most active as antifeedants against Colorado potato beetle larvae, Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae), in a dual-choice assay with potato, Solanum tuberosum L., leaf discs. Lactones were less effective. Direct observations showed that decreased feeding on leaf discs treated with polygodial and warburganal was accompanied by increased locomotry activity. Topical application of these two compounds on the insect's cuticle decreased food intake of untreated leaf discs, indicating that besides deterrent effects, toxic properties of these molecules influence feeding behaviour.     

Anaerobic C–H Oxyfunctionalization: Coupling of Nitrate Reduction and Quinoline Hydroxylation in Recombinant Pseudomonas putida

Whole‐cell biocatalysis for C–H oxyfunctionalization depends on and is often limited by O₂ mass transfer. In contrast to oxygenases, molybdenum hydroxylases use water instead of O₂ as an oxygen donor and thus have the potential to relieve O₂ mass transfer limitations. Molybdenum hydroxylases may even allow anaerobic oxyfunctionalization when coupled to anaerobic respiration. To evaluate this option, the coupling of quinoline hydroxylation to denitrification is tested under anaerobic conditions employing Pseudomonas putida (P. putida) 86, capable of aerobic growth on quinoline. P. putida 86 reduces both nitrate and nitrite, but at low rates, which does not enable significant growth and quinoline hydroxylation. Introduction of the nitrate reductase from Pseudomonas aeruginosa enables considerable specific quinoline hydroxylation activity (6.9 U g_CDW^?1) under anaerobic conditions with nitrate as an electron acceptor and 2‐hydroxyquinoline as the sole product (further metabolization depends on O₂). Hydroxylation‐derived electrons are efficiently directed to nitrate, accounting for 38% of the respiratory activity. This study shows that molybdenum hydroxylase‐based whole‐cell biocatalysts enable completely anaerobic carbon oxyfunctionalization when coupled to alternative respiration schemes such as nitrate respiration.     

Cytotoxic Oleanane‐Type Saponins from the Leaves of Albizia anthelmintica Brongn.

Two new oleanane‐type saponins: β‐d ‐xylopyranosyl‐(1 → 4)‐6‐deoxy‐α‐l ‐mannopyranosyl‐(1 → 2)‐1‐O‐{(3β)‐28‐oxo‐3‐[(2‐O‐β‐d ‐xylopyranosyl‐β‐d ‐glucopyranosyl)oxy]olean‐12‐en‐28‐yl}‐β‐d ‐glucopyranose ( 1 ) and 1‐O‐[(3β)‐28‐oxo‐3‐{[β‐d ‐xylopyranosyl‐(1 → 2)‐α‐l ‐arabinopyranosyl‐(1 → 6)‐2‐acetamido‐2‐deoxy‐β‐d ‐glucopyranosyl]oxy}olean‐12‐en‐28‐yl]β‐d ‐glucopyranose ( 2 ), along with two known saponins: (3β)‐3‐[(β‐d ‐Glucopyranosyl‐(1 → 2)‐β‐d ‐glucopyranosyl)oxy]olean‐12‐en‐28‐oic acid ( 3 ) and (3β)‐3‐{[α‐l ‐arabinopyranosyl‐(1 → 6)‐[β‐d ‐glucopyranosyl‐(1 → 2)]‐β‐d ‐glucopyranosyl]oxy}olean‐12‐en‐28‐oic acid ( 4 ) were isolated from the acetone‐insoluble fraction obtained from the 80% aqueous MeOH extract of Albizia anthelmintica Brongn . leaves. Their structures were identified using different NMR experiments including: ¹H‐ and ¹³C‐NMR, HSQC, HMBC and ¹H,¹H‐COSY, together with HR‐ESI‐MS/MS, as well as by acid hydrolysis. The four isolated saponins and the fractions of the extract exhibited cytotoxic activity against HepG‐2 and HCT‐116 cell lines. Compound 2 showed the most potent cytotoxic activity among the other tested compounds against the HepG2 cell line with an IC₅₀ value of 3.60μm . Whereas, compound 1 showed the most potent cytotoxic effect with an IC₅₀ value of 4.75μm on HCT‐116 cells.     

Pre‐ and post‐ingestive defenses affect larval feeding on a lethal invasive host plant

Evolutionary traps arise when organisms use novel, low‐quality or even lethal resources based on previously reliable cues. Persistence of such maladaptive interactions depends not only on how individuals locate important resources, such as host plants, but also the mechanisms underlying poor performance. Pieris macdunnoughii (Remington) (Lepidoptera: Pieridae) lays eggs on a non‐native mustard, Thlaspi arvense (L.) (Brassicaceae), which is lethal to the larvae. We first tested whether larval feeding behavior was affected before (pre‐) ingestion or following (post‐) ingestion of leaf material, indicating activity of feeding deterrents, toxins, or both in this evolutionary trap. Neonates were less likely to start feeding and eventually fed more slowly on T. arvense than on the native host plant Cardamine cordifolia (Gray) (Brassicaceae) in both laboratory and field. Starvation was a primary cause of mortality, indicating the role of a feeding deterrent. Feeding did not differ between larvae from invaded and uninvaded population. Second, T. arvense defensive chemistry is dominated by the glucosinolate sinigrin (allyl or 2‐propenyl glucosinolate). Adding sinigrin to the leaves of T. arvense and native hosts C. cordifolia and Descurainia incana (Bernhardi ex Fischer & Meyer) (Brassicaceae) delayed the onset of feeding, caused larvae to feed more slowly, and decreased survival on the native hosts. This evolutionary trap may not be driven by a novel deterrent, but rather by a change in the concentration of a deterrent found in native hosts. Many insects have adapted to evolutionary traps posed by invasive plants, incorporating the new plant into their diets. Thlaspi arvense remains lethal to P. macdunnoughii, and pre‐ingestive deterrents such as excess sinigrin may contribute to persistent maladaptation.     

Carbon sequestration in soil in a semi‐natural Miscanthus sinensis grassland and Cryptomeria japonica forest plantation in Aso,Kumamoto, Japan

Although Miscanthus sinensis grasslands (Misc‐GL) and Cryptomeria japonica forest plantations (Cryp‐FP) are proposed bioenergy feedstock systems, their relative capacity to sequester C may be an important factor in determining their potential for sustainable bioenergy production. Therefore, our objective was to quantify changes in soil C sequestration 47 years after a Misc‐GL was converted to a Cryp‐FP. The study was conducted on adjacent Misc‐GL and Cryp‐FP located on Mt. Aso, Kumamoto, Japan. After Cryp‐FP establishment, only the Misc‐GL continued to be managed by annual burning every March. Mass C and N, δ¹³C, and δ¹⁵N at 0–30 cm depth were measured in 5 cm increments. Carbon and N concentrations, C:N ratio, δ¹³C, and δ¹⁵N were measured in litter and/or ash, and rhizomes or roots. Although C input in Misc‐GL by M. sinensis was approximately 36% of that in Cryp‐FP by C. japonica, mean annual soil C sequestration in Misc‐GL (503 kg C ha^?1 yr^?1) was higher than that in Cryp‐FP (284 kg C ha^?1 yr^?1). This was likely the result of larger C input from aboveground litter to soil, C‐quality (C:N ratio and lignin concentration in aboveground litter) and possibly more recalcitrant C (charcoal) inputs by annual burning. The difference in soil δ¹⁵N between sites indicated that organic C with N had greater cycling between heterotrophic microbes and soil and produces more recalcitrant humus in Misc‐GL than in Cryp‐FP. Our data indicate that in terms of soil C sequestration, maintenance of Misc‐GL may be more advantageous than conversion to Cryp‐FP in Aso, Japan.     

Nectar yeasts enhance the interaction between Clematis akebioides and its bumblebee pollinator

• It has been hypothesised that intense metabolism of nectar‐inhabiting yeasts (NIY) may change nectar chemistry, including volatile profile, which may affect pollinator foraging behaviours and consequently plant fitness. However, empirical evidence for the plant–microbe–pollinator interactions remains little known.
• To test this hypothesis, we use a bumblebee‐pollinated vine Clematis akebioides endemic to southwest China as an experimental model plant. To quantify the incidence and density of Metschnikowia reukaufii, a cosmopolitan NIY in floral nectar, a combination of yeast cultivation and microscopic cell‐counting method was used. To examine the effects of NIY on plant–pollinator interactions, we used real flowers filled with artificial nectar with or without yeast cells. Then the volatile metabolites produced in the yeast‐inoculated nectar were analysed with coupled gas chromatography and mass spectrometry (GC‐MS).
• On average 79.3% of the C. akebioides flowers harboured M. reukaufii, and cell density of NIY was high to 7.4 × 10⁴ cells mm^?3. In the field population, the presence of NIY in flowers of C. akebioides increased bumblebee (Bombus friseanus) pollinator visitation rate and consequently seed set per flower. A variety of fatty acid derivatives produced by M. reukaufii may be responsible for the above beneficial interactions.
• The volatiles produced by the metabolism of M. reukaufii may serve as an honest signal to attract bumblebee pollinators and indirectly promote the female reproductive fitness of C. akebioides, forming a potentially tripartite plant–microbe–pollinator mutualism.

     

Isolation and characterization of a novel peroxisomal choline monooxygenase in barley

Glycine betaine (GB) is a compatible solute accumulated by many plants under various abiotic stresses. GB is synthesized in two steps, choline → betaine aldehyde → GB, where a functional choline-oxidizing enzyme has only been reported in Amaranthaceae (a chloroplastic ferredoxin-dependent choline monooxygenase) thus far. Here, we have cloned a cDNA encoding a choline monooxygenase (CMO) from barley (Hordeum vulgare) plants, HvCMO. In barley plants under non-stress condition, GB had accumulated in all the determined organs (leaves, internodes, awn and floret proper), mostly in the leaves. The expression of HvCMO protein was abundant in the leaves, whereas the expression of betaine aldehyde dehydrogenase (BADH) protein was abundant in the awn, floret proper and the youngest internode than in the leaves. The accumulation of HvCMO mRNA was increased by high osmotic and low-temperature environments. Also, the expression of HvCMO protein was increased by the presence of high NaCl. Immunofluorescent labeling of HvCMO protein and subcellular fractionation analysis showed that HvCMO protein was localized to peroxisomes. [¹⁴C]choline was oxidized to betaine aldehyde and GB in spinach (Spinacia oleracea) chloroplasts but not in barley, which indicates that the subcellular localization of choline-oxidizing enzyme is different between two plant species. We investigated the choline-oxidizing reaction using recombinant HvCMO protein expressed in yeast (Saccharomyces cerevisiae). The crude extract of HvCMO-expressing yeast coupled with recombinant BBD2 protein converted [¹⁴C]choline to GB when NADPH was added as a cofactor. These results suggest that choline oxidation in GB synthesis is mediated by a peroxisomal NADPH-dependent choline monooxygenase in barley plants.     

The role of lipid metabolism in the acquisition of desiccation tolerance in Craterostigma plantagineum: a comparative approach

Dehydration leads to different physiological and biochemical responses in plants. We analysed the lipid composition and the expression of genes involved in lipid biosynthesis in the desiccation‐tolerant plant Craterostigma plantagineum. A comparative approach was carried out with Lindernia brevidens (desiccation tolerant) and two desiccation‐sensitive species, Lindernia subracemosa and Arabidopsis thaliana. In C. plantagineum the total lipid content remained constant while the lipid composition underwent major changes during desiccation. The most prominent change was the removal of monogalactosyldiacylglycerol (MGDG) from the thylakoids. Analysis of molecular species composition revealed that around 50% of 36:x (number of carbons in the acyl chains: number of double bonds) MGDG was hydrolysed and diacylglycerol (DAG) used for phospholipid synthesis, while another MGDG fraction was converted into digalactosyldiacylglycerol via the DGD1/DGD2 pathway and subsequently into oligogalactolipids by SFR2. 36:x‐DAG was also employed for the synthesis of triacylglycerol. Phosphatidic acid (PA) increased in C. plantagineum, L. brevidens, and L. subracemosa, in agreement with a role of PA as an intermediate of lipid turnover and of phospholipase D in signalling during desiccation. 34:x‐DAG, presumably derived from de novo assembly, was converted into phosphatidylinositol (PI) in C. plantagineum and L. brevidens, but not in desiccation‐sensitive plants, suggesting that PI is involved in acquisition of desiccation tolerance. The accumulation of oligogalactolipids and PI in the chloroplast and extraplastidial membranes, respectively, increases the concentration of hydroxyl groups and enhances the ratio of bilayer‐ to non‐bilayer‐forming lipids, thus contributing to protein and membrane stabilization.