Variation of sesquiterpene lactones in Lactuca aculeata natural populations from Israel,Jordan and Turkey

A comparative phytochemical study of seven sesquiterpene lactones in natural populations of the wild lettuce Lactuca aculeata Boiss. (Asteraceae) was performed, based on 23 accessions derived from eight, two, and single localities from Israel, Jordan, and Turkey, respectively. The compounds were profiled and quantified in leaves and roots of the plants, grown from achenes (cypselas) in a greenhouse under controlled conditions, using reverse phase HPLC with on-line photodiode array detector. In the present study, L. aculeata was confirmed as a taxon strongly characterized by four dominant sesquiterpene lactones: 8-deoxylactucin, jacquinelin, crepidiaside B and lactuside A. An analysis of quantitative results of these four constituents led to the following conclusions: (i) the sesquiterpene lactone contents varied significantly, mainly within the populations; however, for two variables (crepidiaside B and lactuside A in root samples) the contents varied mostly between populations, (ii) these differences are likely to be genetically controlled since all accessions were grown under standardized glasshouse conditions. Accessions containing high levels of some sesquiterpene lactones were found in several populations. These traits should be conserved in situ and ex situ and utilized in further research and lettuce improvement.     

Metabolite profiling of sesquiterpene lactones from Lactuca species. Major latex components are novel oxalate and sulfate conjugates of lactucin and its derivatives

Wounding leaves or stems of Lactuca species releases a milky latex onto the plant surface. We have examined the constituents of latex from Lactuca sativa (lettuce) cv. Diana. The major components were shown to be novel 15-oxalyl and 8-sulfate conjugates of the guaianolide sesquiterpene lactones, lactucin, deoxylactucin, and lactucopicrin. The oxalates were unstable, reverting to the parent sesquiterpene lactone on hydrolysis. Oxalyl derivatives have been reported rarely from natural sources. The sulfates were stable and are the first reported sesquiterpene sulfates from plants. Unusual tannins based on 4-hydroxyphenylacetyl conjugates of glucose were also identified. Significant qualitative and quantitative variation was found in sesquiterpene lactone profiles in different lettuce varieties and in other Lactuca spp. The proportions of each conjugate in latex also changed depending on the stage of plant development. A similar profile was found in chicory, in which oxalyl conjugates were identified, but the 8-sulfate conjugates were notably absent. The presence of the constitutive sesquiterpene lactones was not correlated with resistance to pathogens but may have a significant bearing on the molecular basis of the bitter taste of lettuce and related species. The induced sesquiterpene lactone phytoalexin, lettucenin A, was found in the Lactuca spp. but not in chicory.     

Systematic implications of sesquiterpene lactones in Lactuca species

A chemosystematic study of eleven species from the genus Lactuca (Asteraceae) was performed, based on the distributional data for eight sesquiterpene lactones as diagnostic characters. The lactones were identified in leaf and root extracts by comparison of their HPLC retention times and on-line UV spectra with those of reference compounds. Our results support the status of the section Lactuca, subsection Lactuca as a recognizable group within the genus, although Lactuca aculeata is a distinct species. Moreover, sesquiterpene lactone patterns of Lactuca perennis, Lactuca tatarica, Lactuca indica and Lactuca capensis are also given. It is worth noting that the sesquiterpene lactones are absent from Lactuca tenerrima. The chemosystematic impact of lactucin-type guaianolides and the germacranolide lactuside A is discussed briefly.     

Sesquiterpene lactones from Sonchus macrocarpus

Eight sesquiterpene lactones were isolated from the roots of Sonchus macrocarpus. The eudesmanolides 15-hydroxy-4β, 15-dihydroreynosin and 15-hydroxy-4β, 15, 11β, 13-tetrahydroreynosin were isolated for the first time.     

Antiviral activity of extracts of transgenic chicory and lettuce plants with the human interferon α2b gene

This paper studies the biological activity of protein extracts of the Cichorium intybus L. and Lactuca sativa L. transgenic plants with the human interferon ??2b gene againsf vesicular stomatitis virus. Extracts from transgenic lettuce and chicory roots, which were obtained after A. rhizogenes-mediated transformation, had antiviral activity in the range 1620?C5400 IU/g of weight; extracts from leaves of chicory plants transformed by A. tumefaciens, up to 9375 IU/g. The dependence of the antiviral activity of plant extracts from roots or leaves on the vector used for plant transformation is shown. The extracts of plant roots obtained by A. rhizogenes-mediated transformation had antiviral activity; at the same time, such activity was absent in the extracts from leaves.     

Allelopathic potential of two sesquiterpene lactones from Magnolia grandiflora L.

The allelopathic effects of the two sesquiterpene lactones, costunolide and parthenolide, isolated from the leaves of Magnolia grandiflora L. were evaluated on the wheat (Triticum aestivum L.), lettuce (Lactuca sativa L.), radish (Raphanus sativus L.) and onion (Allium cepa L.). Seed germination of the test species was significantly reduced at 500 μg/ml by both compounds. Both sesquiterpenes showed pronounced inhibition of root length of the test species and the inhibitory effect was concentration-dependent. In addition, shoot growth of the four species was significantly inhibited at all the concentrations tested (10–500 μg/ml). Parthenolide reduced germination and inhibited seedling growth more than costunolide. Inhibition of root growth was generally greater than that of shoot growth. The results encourage the use of these sesquiterpenes as models for development of new herbicides.     

Sesquiterpene lactones of Podanthus mitiqui

Ovatifolin and two new sesquiterpene lactones, deacetylovatifolin and arturin (1β-hydroxy-8β-angeloyloxy-eudesmane-4(15),11(13)-diene-6α,12-olide, have been isolated from stems and leaves of Podanthus mitiqui. Two of these compounds showed cytotoxic activity.     

Cloning and expression of sesquiterpene synthase genes from lettuce (Lactuca sativa L.)

Sesquiterpenoid lactones (SLs) from lettuce (Lactuca sativa L.) include constitutive components of latex such as lactucin and the induced phytoalexin, lettucenin A. A redundant primer strategy was used to recover two full length cDNA clones (LTC1 and LTC2) encoding sesquiterpene synthases from a cDNA library derived from seedlings with the red spot disorder, which accumulate phytoalexins. Recombinant enzymes produced from LTC1 and LTC2 in Escherichia coli catalysed the cyclisation of farnesyl diphosphate to germacrene A, potentially an early step in the biosynthesis of SLs. RT-PCR analysis showed LTC1 and LTC2 were expressed constitutively in roots, hypocotyls and true leaves but not in cotyledons. Expression in cotyledons was induced by challenge with the downy mildew pathogen Bremia lactucae in the disease resistant cultivar Diana. Southern hybridisation experiments showed that LTC1 and LTC2 were not part of a multigene family. The germacrene A synthases provide targets for modified expression to generate beneficial modifications to the SL profile in lettuce.     

Construction of transplastomic lettuce (Lactuca sativa) dominantly producing astaxanthin fatty acid esters and detailed chemical analysis of generated carotenoids

The plastid genome of lettuce (Lactuca sativa L.) cv. Berkeley was site-specifically modified with the addition of three transgenes, which encoded β,β-carotenoid 3,3′-hydroxylase (CrtZ) and β,β-carotenoid 4,4′-ketolase (4,4′-oxygenase; CrtW) from a marine bacterium Brevundimonas sp. strain SD212, and isopentenyl diphosphate isomerase from a marine bacterium Paracoccus sp. strain N81106. Constructed transplastomic lettuce plants were able to grow on soil at a growth rate similar to that of non-transformed lettuce cv. Berkeley and generate flowers and seeds. The germination ratio of the lettuce transformants (T₀) (98.8 %) was higher than that of non-transformed lettuce (93.1 %). The transplastomic lettuce (T₁) leaves produced the astaxanthin fatty acid (myristate or palmitate) diester (49.2 % of total carotenoids), astaxanthin monoester (18.2 %), and the free forms of astaxanthin (10.0 %) and the other ketocarotenoids (17.5 %), which indicated that artificial ketocarotenoids corresponded to 94.9 % of total carotenoids (230 μg/g fresh weight). Native carotenoids were there lactucaxanthin (3.8 %) and lutein (1.3 %) only. This is the first report to structurally identify the astaxanthin esters biosynthesized in transgenic or transplastomic plants producing astaxanthin. The singlet oxygen-quenching activity of the total carotenoids extracted from the transplastomic leaves was similar to that of astaxanthin (mostly esterified) from the green algae Haematococcus pluvialis.     

Transgenic resistance to Mirafiori lettuce virus in lettuce carrying inverted repeats of the viral coat protein gene

Mirafiori lettuce virus (MiLV), a plant RNA virus belonging to the genus Ophiovirus, is considered to be a causal agent of lettuce big-vein disease. In this study, inverted repeats of a fragment of the coat protein (CP) gene of MiLV in a binary vector pBI121 were transferred via Agrobacterium tumefaciens-mediated transformation into lettuce (Lactuca sativa L.) in order to generate MiLV-resistant lettuce. Forty T₁ lines were analyzed for resistance to MiLV by detecting MiLV in leaves, and two lines (lines 408 and 495) were selected as resistant to MiLV. Both lines were susceptible to Lettuce big-vein associated virus (LBVaV), and line 495 showed higher resistance to MiLV than line 408. Further analysis indicated that line 495 showed resistance to big-vein symptoms expression. Small interfering RNA (siRNA) molecules derived from the transgene were detected in plants of line 495. MiLV was detected in roots but not in leaves of line 495 plants after MiLV inoculation, suggesting that resistance to MiLV is less effective in roots than in leaves.     

Features of lettuce transgenic plants with ifn-alpha2b gene regenerated after Agrobacterium rhizogenes-mediated transformation

"Hairy" roots of lettuce Lactuca sativa and regenerated plants with interferon-alpha2b gene had been obtained via Agrobacterium rhizogenes-mediated transformation. According to the results of PCR and rt-PCR analyses the studied plants had ifn-alpha2b gene. The regenerated plants differed from the plants of wild type by elongated internodes, early flower-bearing stem formation and purple coloration of leaves in artificial illumination conditions.     

New sesquiterpene lactones from Inula oculus-christi L.

Investigation of the aerial parts of Inula oculus-christi L. led to the identification of four new sesquiterpene lactones: an eudesmanolide (4α,15α-epoxypulchellin E) and three guaianolides (2α-acetoxy-4α,9β-dihydroxy-1β-guaia-11(13),10(14)-dien-12,8α-olide, 9β,10β-epoxygaillardin, 9α,10α-epoxy-2-epi-gaillardin), in addition to the known gaillardin, pulchellin E, pulchellin C and 3-O-palmitates of 16β-hydroxylupeol, 16β-hydroxy-β-amyrin, and faradiol. The structures of all compounds have been elucidated on the basis of their spectral data.     

A melampolide from Melampodium heterophyllum

The sesquiterpene lactones melampodin and llβ,13-dihydromelampodin have been isolated from Melampodium heterophyllum.     

Identification and comparison of natural rubber from two Lactuca species

Renewed interest in the identification of alternative sources of natural rubber to Hevea brasiliensis has focused on the Compositae family. In our search for Compositae models for rubber synthesis, we extracted latex from stems of two lettuce species: Lactuca serriola, prickly lettuce, and Lactuca sativa cv. Salinas, crisphead lettuce. Both species contained cis-1,4-polyisoprene rubber in the dichloromethane-soluble portions of their latex, and sesquiterpene lactones in their acetone-soluble portions. The rubber from both species and their progeny had molecular weights in excess of 1,000,000g/mol, and polydispersity values of 1.1. Rubber transferase activity was detected across a range of farnesyl diphosphate initiator concentrations, with decreased activity as initiator concentrations exceeded putative saturation. These results add lettuce to the short list of plant species that produce high molecular weight rubber in their latex. Due to the genomic and agronomic resources available in lettuce species, they provide the opportunity for further dissection of natural rubber biosynthesis in plants.     

Trichoderma spp. alleviate phytotoxicity in lettuce plants (Lactuca sativa L.) irrigated with arsenic-contaminated water

The influence of two strains of Trichoderma (T. harzianum strain T22 and T. atroviride strain P1) on the growth of lettuce plants (Lactuca sativa L.) irrigated with As-contaminated water, and their effect on the uptake and accumulation of the contaminant in the plant roots and leaves, were studied. Accumulation of this non-essential element occurred mainly into the root system and reduced both biomass development and net photosynthesis rate (while altering the plant P status). Plant growth-promoting fungi (PGPF) of both Trichoderma species alleviated, at least in part, the phytotoxicity of As, essentially by decreasing its accumulation in the tissues and enhancing plant growth, P status and net photosynthesis rate. Our results indicate that inoculation of lettuce with selected Trichoderma strains may be helpful, beside the classical biocontrol application, in alleviating abiotic stresses such as that caused by irrigation with As-contaminated water, and in reducing the concentration of this metalloid in the edible part of the plant.     

Taraxacoside,a type of acylated γ-butyrolactone glycoside from taraxacum officinale

In addition to the four new sesquiterpene lactones previously identified, a new acylated γ-butyrolactone glucoside, taraxacoside, was isolated from the roots of Taraxacum officinale. Its structure was elucidated mainly by ¹H and ¹³C NMR studies as β-O-[4-O-(p-hydroxyphenylacetyl]β-D-glucopyranosyl]-β-hydroxy-γ-butyrolactone. This seems to be the first instance of the detection of a monocyclic five-membered, saturated lactone O-glycoside. Additionally, p-hydroxyphenylacetic acid was identified for the first time as an acylating acid in a sugar ester.     

Root-shoot ratio in irrigated plants

Relationship between roots and shoots ofPimpinella saxifraga L.,Petroselinum hortense Hoffm.,Lactuca sativa L., andBeta vulgaris subsp.esculenta (Salisbury) Gürke var.altissima Roessig was studied in irrigated and non-irrigated plants. It was found that the irrigation water did not influence distinctly the root-shoot ratio of the experimental plants. From the statical point of view, this relationship could be expressed by the following quantitative ratios for irrigated and non-irrigated plants: 3∶1 forPimpinella saxifraga L., 2∶1 forPetroselinum hortense Hoffm., 9∶1 forLactuca sativa L., and 1∶1 for beetroot. From the dynamic point of view it is possible to state that this ratio changes in the course of individual development. With plants cultivated for their aerial parts, it increased with age, while with plants cultivated for their roots, it decreased with age. The irrigation water produced much greater morphological changes (the shape and the surface area) in the root and shoot system of experimental plants.     

Sesquiterpene lactones from dicoria canescens

Dicoria canescens from Baja California, Mexico afforded the known monoterpene glucoside, (?)-cis-chrysanthenol O-β-d-glucopyranoside, ivalbatin, a xanthanolide and two new sesquiterpene lactones, 4-dihydroivalbatin (dicorin) and 11β, 13-tetrahydrovalbatin (dihydrocorin).     

Bidirectional backcrosses between wild and cultivated lettuce identify loci involved in nonhost resistance to downy mildew

Key message

The nonhost resistance of wild lettuce to lettuce downy mildew seems explained by four components of a putative set of epistatic genes.

Abstract

The commonplace observation that plants are immune to most potential pathogens is known as nonhost resistance (NHR). The genetic basis of NHR is poorly understood. Inheritance studies of NHR require crosses of nonhost species with a host, but these crosses are usually unsuccessful. The plant-pathosystem of lettuce and downy mildew, Bremia lactucae, provides a rare opportunity to study the inheritance of NHR, because the nonhost wild lettuce species Lactuca saligna is sufficiently cross-compatible with the cultivated host Lactuca sativa. Our previous studies on NHR in one L. saligna accession led to the hypothesis that multi-locus epistatic interactions might explain NHR. Here, we studied NHR at the species level in nine accessions. Besides the commonly used approach of studying a target trait from a wild donor species in a cultivar genetic background, we also explored the opposite, complementary approach of cultivar introgression in a wild species background. This bidirectional approach encompassed (1) nonhost into host introgression: identification of L. saligna derived chromosome regions that were overrepresented in highly resistant BC1 plants (F1?×?L. sativa), (2) host into nonhost introgression: identification of L. sativa derived chromosome regions that were overrepresented in BC1 inbred lines (F1?×?L. saligna) with relatively high infection levels. We demonstrated that NHR is based on resistance factors from L. saligna and the genetic dose for NHR differs between accessions. NHR seemed explained by combinations of epistatic genes on three or four chromosome segments, of which one chromosome segment was validated by the host into nonhost approach.

     

Sesquiterpene lactones,flavonoids and anthraquinones from Asphodeline globifera and Asphodeline Damascena

The known compounds chrysoeriol, apigenin, luteolin, acacetin, scutellarein, 6-methoxyluteolin, apigenin 7-glucoside, luteolin 7-glucoside, esculetin, chrysophanol, asphodeline, mircocarpin, sitosterol, 1-β-acetoxyeudesman-4(15),7(11)dien-2α,12-olide and 1-β-acetoxy-8β-hydroxyeudesman-4(15),7(11)-dien-8α,12-olide were isolated from Asphodeline globifera and A. damascena. A new sesquiterpene lactone 1-β-acetoxy-8β-ethoxyeudesman-4(15),7(11)dien-8α, 12-olide was also characterized. These are the first reports of sesquiterpene lactones in Asphodeline and in the Liliaceae.