Sequence of the Mitochondrial Genome of Lactuca virosa Suggests an Unexpected Role in Lactuca sativa’s Evolution

The involvement of the different Lactuca species in the domestication and diversification of cultivated lettuce is not totally understood. Lactuca serriola is considered as the direct ancestor and the closest relative to Lactuca sativa, while the other wild species that can be crossed with L. sativa, Lactuca virosa, and Lactuca saligna, would have just contributed to the latter diversification of cultivated typologies. To contribute to the study of Lactuca evolution, we assembled the mtDNA genomes of nine Lactuca spp. accessions, among them three from L. virosa, whose mtDNA had not been studied so far. Our results unveiled little to no intraspecies variation among Lactuca species, with the exception of L. serriola where the accessions we sequenced diverge significantly from the mtDNA of a L. serriola accession already reported. Furthermore, we found a remarkable phylogenetic closeness between the mtDNA of L. sativa and the mtDNA of L. virosa, contrasting to the L. serriola origin of the nuclear and plastidial genomes. These results suggest that a cross between L. virosa and the ancestor of cultivated lettuce is at the origin of the actual mitochondrial genome of L. sativa.

In-Vivo and In-Vitro Anti-Inflammatory Activities of the Aqueous Extract of Di-Herbal Formulation (Euphorbia hirta and lactuca virosa)

Euphorbia hirta and Lactuca virosa are medicinal plants that have been used in the cure and treatment of various diseases and for health care. This study aims at evaluating the anti-inflammatory activities of the aqueous extracts of Euphorbia hirta and Lactuca virosa plants. Albumin and histamine induced inflammation in mice and xylene induced ear edema were used for the in-vivo anti-inflammatory studies. Erythrocyte membrane stabilization and inhibition of protein denaturation assays were used for the in-vitro anti-inflammatory studies. Combined doses of 100 mg/kg Euphorbia hirta and 50 mg/kg Lactuca virosa, 100 mg/kg Euphorbia hirta and 100 mg/kg Lactuca virosa, 100 mg/kg Lactuca virosa only and 10 mg/kg diclofenac significantly reduced inflamed paw in mice (P<0.05) compared to control in albumin and histamine induced inflammatory test. Combined doses of 50 mg/kg Euphorbia hirta and 100 mg/kg Lactuca virosa,100 mg/kg Euphorbia hirta, 100mg/kg Lactuca virosa significantly reduced xylene induced inflammation (P<0.001) compared to control. The extracts at 1 mg/ml, 2 mg/ml and 3 mg/ml significantly inhibited protein denaturation (P<0.001) and heat induced hemolysis of erythrocytes (P<0.0001). The plant extract of Euphorbia hirta and lactuca virosa possesses in-vivo and in-vivo anti-inflammatory effects. Keywords: Euphorbia hirta, Lactuca virosa, anti-inflammatory, protein denaturation

Effect of pectinase on the production of sesquiterpene lactones in the hairy root culture of Lactuca virosa L.

Direct addition of pectinase as an elicitor to the hairy root culture of <em>Lactuca virosa</em> L. transformed with <em>Agrobacterium rhizogenes</em> stimulates the accumulation of constitutive sesquiterpene lactones - lactuside A and crepidiaside B. The highest amounts of lactuside A (80% above the control level) and crepidiaside B (39% above the control level) have been found 24 and 48 hours, respectively, after pectinase treatment.

Effect of methyl jasmonate on the production of sesquiterpene lactones in the hairy root culture of Lactuca virosa L.

Hairy roots of <em>Lactuca virosa</em> L. transformed with <em>Agrobacterium rhizogenes</em> and treated with methyl jasmonate, are capable of producing sesquiterpene lactones - crepidiaside B and lactuside A in amounts higher than in untreated roots. An HPLC analysis showed the highest content of crepidiaside B after 24 hours of methyl jasmonate treatment (60% above the control). The increase in the content of lactuside A was relatively small and reached 27% after 48 hours of the treatment, in comparison with the control.

Accumulation of ixerin F and activities of some terpenoid bisynthetic enzymes in a cell suspension culture of Lactuca virosa L.

A cell suspension culture of <em>Lactuca virosa</em> L. (<em>Asteraceae</em>, tribe <em>Lactuceae</em>) is capable of synthesizing sesquiterpene lactones of which ixerin F is the main compound. The culture was characterized on growth (by dissimilation rates), on ixerin F accumulation (by RP-HPLC) and on some enzyme activities involved in early steps of terpenoid biosynthesis. Acetoacetyl-coenzyme A thiolase (AACT, E.C. 2.3.1.9) and 3S-hydroxy-3-methylglutaryl-coenzyme A synthase (HMGS, E.C. 4.13.5) activities of the cells were assayed spectrophotometrically. HMGS activity increased during the culture period and reached a maximum during the stationary phase (190 pkat/mg protein), while AACT showed relatively high level of activity throughout the growth cycle, with transient decrease at the logarithmic growth phase and the beginning of stationary phase. Ixerin F accumulated inside the cells and the maximum concentration of 0.08% (on dry weight basis) was found in the early stationary phase of the growth cycle of the culture.

Hairy root culture of Lactuca virosa L.

A hairy root culture of <i>Lactuca virosa</i> L. (<i>Asteraceae</i>) was initiated by infection of the leaf explants of the aseptic plants with <i>Agrobacterium rhizogenes</i> - strain LBA 9402. One of the obtained clones which showed the most favourable growth rate was used for further investigation. An influence of different nutrient media and sucrose concentrations on the biomass accumulation was studied. The most advantageous for the biomass increment were media: MS and MS containing macronutrients reduced to half concentration, supplemented with 5% sucrose. A preliminary chromatographic analysis of the tissue extract revealed the presence of sesquiterpene lactones characteristic of the roots of the intact plant.

Performance and feeding behaviour of two biotypes of the black currant-lettuce aphid,Nasonovia ribisnigri, on resistant and susceptibleLactuca sativanear-isogenic lines

The black currant-lettuce aphid,Nasonovia ribisnigri, is an important pest of cultivated lettuce,Lactuca sativa.Since 1982, the control of this aphid on lettuce is largely based on host plant resistance, conferred by theNrgene, introgressed fromLactuca virosa. The resistance mechanism remains to be identified.N. ribisnigripopulations virulent on theNr-based resistance in lettuce have emerged in several locations in Europe since 2007. The objective of this study was to investigate the resistance mechanism mediated by theNrgene in lettuce by detailed studies of aphid feeding behaviour and performance. Both avirulent (Nr:0) and virulent (Nr:1) biotypes ofN. ribisnigriwere studied on five resistant and two susceptible near isogenic lines (NILs). In addition, survival and colony development were quantified. Nr:0 aphids showed a strong decrease in sieve element ingestion and took longer to accept a sieve element on resistant NILs compared with susceptible NILs, and no aphids survived on the resistant NIL. Nr:1 aphids fed and performed equally well on the resistant and susceptible NILs. The resistance mechanism against Nr:0 aphids encoded by theNrgene seems to be located in the phloem, although we also observed differences in feeding behaviour during the pathway phase to the phloem. Nr:1 aphids were highly virulent to the resistance conferred by theNrgene. The consequences of the appearance of Nr:1 aphids for control ofN. ribisnigriare discussed.

Resistance to Lettuce Aphid (Nasonovia ribisnigri) Biotype 0 in Wild Lettuce Accessions PI 491093 and PI 274378

The lettuce aphid, Nasonovia ribisnigri Mosley (Hemiptera: Aphididae), is a major insect pest of lettuce, Lactuca sativa L, in many commercial lettuce production areas around the world. Resistance to lettuce aphid biotype 0 (Nr:0) was first reported in Lactuca virosa L. accession IVT 280 and characterized as complete, i.e., virtually no aphids survived, and genetically dominant to partial resistance in L. virosa accession IVT 273. Complete and partial resistances to Nr:0 were conditioned by two alleles, Nr (complete resistance) and nr (partial resistance), but the genetic relationship to susceptibility was not reported. We previously reported two new potential sources of unique genes for resistance to Nr:0 in Lactuca serriola L. accession PI 491093 and L. virosa PI 274378. We report on the genetic and phenotypic nature of resistance to Nr:0 in these two wild lettuce accessions. Resistance to Nr:0 in PI 274378 is complete and allelic to complete resistance in IVT 280. Resistance to Nr:0 in PI 491093 was partial, recessive to complete resistance in ‘Barcelona’ that was derived from IVT 280, but dominant to susceptibility in ‘Salinas’. We propose the revised gene symbols for resistance to Nr:0: Nr:0C for complete resistance and Nr:0P for partial resistance, which was originally designated as nr but may now be regarded as the symbol for susceptibility to all strains of lettuce aphid. The dominance relationships among these three alleles are Nr:0C (in IVT 280, ‘Barcelona’) > Nr:0P (in PI 491093) > nr (in susceptible genotypes). Expression of partial resistance in PI 491093 was variable in controlled infestation tests, but in a naturally infested field test provided a potentially useful level of resistance to Nr:0. Partial resistance, where complete resistance has not been widely deployed, may either alone or as a component of integrated pest management delay or prevent emergence of genotypes that overcome complete resistance controlled by Nr:0C.