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PubMed2003

Isolation and structural characterization of a water-soluble germination inhibitor from Scotch thistle (Onopordum acanthium) cypselas.

Cypsela dormancy in Scotch thistle (Onopordum acanthium) may be affected by the presence of chemical inhibitors. To investigate this phenomenon, a leachate from O. acanthium cypselas was tested for its ability to inhibit germination of the cypselas from which it was derived (i.e., autoinhibition). Leachates varied in their degree of autoinhibition, depending on the cypsela population from which they were prepared. Overall, removal of leachate from a group of O. acanthium cypselas increased their germinability. Using lettuce (Lactuca sativa) cypselas as an indicator species, bioactivity-guided fractionation was used to isolate a water-soluble, para-substituted benzamide from O. acanthium cypselas, which caused germination inhibition. Various chromatographic, spectroscopic, and spectrometric techniques were applied to the characterization of the bioactive compound.

Biological Assay↗
PubMed2005

Host-associated populations in the lettuce root aphid, Pemphigus bursarius (L.).

Pemphigus bursarius is a host-alternating aphid in which annual rounds of sexual reproduction on its primary host, Populus nigra, are interspersed with parthenogenesis on a range of secondary hosts. Evidence was sought for the existence of genetically distinct populations, associated with different secondary hosts, in P. bursarius. Microsatellite markers revealed that genetically distinct populations were present on three different secondary host species. Microsatellites were also used, in conjunction with mitochondrial DNA sequence variation, to investigate the relationships between aphids on Populus, following sexual reproduction, and those on the secondary hosts. Evidence was found for a distinct, cyclically parthenogenetic population that exploited Lactuca sativa as its secondary host. In contrast, populations associated with Matricaria inodora appeared to be largely composed of obligate parthenogens or may even have been another species of Pemphigus. Populations on Lapsana communis appeared to be a mixture of cyclical and obligate parthenogens and were more genetically heterogeneous than those on other secondary hosts, possibly due to founder effects. Experiments to measure the performance of P. bursarius clones on different secondary hosts were inconclusive, failing to demonstrate either the presence or absence of adaptations to secondary hosts.

Animals↗
PubMed2001

One ring or two? Determination of ring number in carotenoids by lycopene epsilon-cyclases.

Carotenoids in the photosynthetic membranes of plants typically contain two beta-rings (e.g., beta-carotene and zeaxanthin) or one epsilon- and one beta-ring (e.g., lutein). Carotenoids with two epsilon-rings are uncommon. We reported earlier that the Arabidopsis thaliana lycopene epsilon-cyclase (LCYe) adds one epsilon-ring to the symmetrical linear substrate lycopene, whereas the structurally related lycopene beta-cyclase (LCYb) adds two beta-rings. Here we describe a cDNA encoding LCYe in romaine lettuce (Lactuca sativa var. romaine), one of the few plant species known to accumulate substantial quantities of a carotenoid with two epsilon-rings: lactucaxanthin. The product of the lettuce cDNA, similar in sequence to the Arabidopsis LCYe (77% amino acid identity), efficiently converted lycopene into the bicyclic epsilon-carotene in a heterologous Escherichia coli system. Regions of the lettuce and Arabidopsis epsilon-cyclases involved in the determination of ring number were mapped by analysis of chimeric epsilon-cyclases constructed by using an inverse PCR approach. A single amino acid was found to act as a molecular switch: lettuce LCYe mutant H457L added only one epsilon-ring to lycopene, whereas the complementary Arabidopsis LCYe mutant, L448H, added two epsilon-rings. An R residue in this position also yields a bi-epsilon-cyclase for both the lettuce and Arabidopsis enzymes. Construction and analysis of chimera of related enzymes with differing catalytic activities provide an informative approach that may be of particular utility for studying membrane-associated enzymes that cannot easily be crystallized or modeled to existing crystal structures.

Amino Acid Sequence↗
PubMed2003

Effect of hypobaric conditions on ethylene evolution and growth of lettuce and wheat.

Elevated levels of ethylene occur in enclosed crop production systems and in spaceflight environments, leading to adverse plant growth and sterility. There are engineering advantages in growing plants at hypobaric (reduced atmospheric pressure) conditions in biomass production for extraterrestrial base or spaceflight environments. Objectives of this research were to characterize the influence of hypobaria on growth and ethylene evolution of lettuce (Lactuca sativa) and wheat (Triticum aestivum). Plants were grown under variable total gas pressures [from 30 to 101 kPa (ambient)]. In one study, lettuce and wheat were direct seeded, germinated and grown in the same chambers for 28 d at 50 or 101 kPa. Hypobaria increased plant growth and did not alter germination rate. During a 10-day study, 28-day-old lettuce and 40-day-old wheat seedlings were transplanted together in the same low and ambient pressure chambers; ethylene accumulated in the chambers, but the rate of production by both lettuce and wheat was reduced more than 65% under 30 kPa compared with ambient pressure (101 kPa). Low O2 concentrations [partial pressure of O2 (pO2) = 6.2 kPa] inhibited ethylene production by lettuce under both low (30 kPa) and ambient pressure, whereas ethylene production by wheat was inhibited at low pressure but not low O2 concentration. There was a negative linear correlation between increasing ethylene concentration and decreasing chlorophyll content of lettuce and wheat. Lettuce had higher production of ethylene and showed greater sensitivity to ethylene than wheat. The hypobaric effect on reduced ethylene production was greater than that of just hypoxia (low oxygen).

Atmospheric Pressure↗
PubMed2004

Cadmium, lead and mercury in fresh and boiled leafy vegetables grown in Lagos, Nigeria.

Vegetables, eaten fresh or boiled, are an important diet relished in many local Nigerian cuisines and delicacies. Increasing their production has therefore become a prime focus of governments in Nigeria. In the process of production, metals capable of impairing the health of consumers are inadvertently picked up. Studies were therefore conducted to determine the presence of cadmium (Cd), lead (Pb) and mercury (Hg) in fresh and boiled leafy vegetables grown in farms close (proximal) to highways (PS) and those distant from highways (DS). Composite samples of fresh lettuce (Lactuca sativa), fresh Amaranthus (Amaranthus speciosa), boiled A. speciosa, soil, irrigation water, and manure from farms located at the two sites were analyzed by Atomic Absorption Spectrophotometry (AAS). The results show that the fresh vegetables grown on sites close to highways (PS) had higher levels of Cd and Pb (0.313 microg g(-1), 16.933 microg g(-1) for Cd and Pb respectively in fresh Amaranthus, and 0.877 microg g(-1), 16.833 microg g(-1) for Cd and Pb respectively in Raw Lettuce) than those from DS farms (0.20 microg g(-1), 8.33 microg g(-1) for Cd and Pb respectively in fresh Amaranthus and 0.266 microg g(-1), 8.00 microg g(-1) for Cd and Pb respectively in Raw Lettuce). The irrigation water at the PS farms contained more Pb but similar levels of Cd and Hg. Soil from the PS was slightly more acidic (pH = 6.32 + 0.08) than those from the DS (pH = 6.49 + 0.02). Soils of PS farms gave very high Pb levels (4.13 microg g(-1)). Boiling had an effect on the levels of Cd and Pb but not Hg in Amaranthus, irrespective of the site of production. Cadmium (Cd) increased from 0.2 microg g(-1) to 1.036 microg g(-1) before and after boiling respectively in DS samples, while it increased from 0.3131 microg g(-1) to 1.037 microg g(-1) in samples from PS farms before and after boiling respectively. The level followed similar trend. Pb increased from 8.33 microg g(-1) to 5.667 microg g(-1) before and after boiling respectively in samples from DS whereas it decreased from 16.933 microg g(-1) to 14.20 microg g(-1) before and after boiling respectively in samples from the PS.

Agriculture↗
PubMed2005

Effects of several applications of digested sewage sludge on soil and plants.

Sewage sludge production has significantly increased during the last years in European Union (EU) countries, being primarily used for agricultural purposes. In this study, digested sewage sludge was applied to greenhouse soil over a three-year period (2001--2003), with three sludge treatments in the first two years (2, 4, and 6 kg m(-2)) and three more applications using a greater quantity in the last year (6, 8, and 10 kg m(-2)). The effects of sewage sludge application on soil and on a leafy crop (Lactuca sativa L.) were studied. Mineral elements, organic matter, pH, and heavy metals were measured in soil and plant tissues. Pathogen and indicator microorganism dynamics in soil were also determined after each sludge application. Results showed that sewage sludge applications increased organic matter, P, and N Ca content in soil. Furthermore, Zn, Pb, Ni, and Cu content increased in soils, primarily after high doses of sludge. The highest yield value was obtained in the second-year harvest, since the last sludge application did not increase yield. Fecal coliform numbers decreased significantly one month after sludge application. However, total coliforms, Clostridium sulphite-reducers and Salmonella, were present in soils three months after sludge application.

Agriculture↗
PubMed2004

Environmental and potential health effects of growing leafy vegetables on soil irrigated using sewage sludge and effluent: a case of Zn and Cu.

The use of sewage sludge and effluent as a source of nutrients and water for crop production is increasing worldwide. A study was conducted in 2001 at Pension farm (near Harare) to determine the effect of long term (>30 yrs) application of sewage sludge and effluent on Zn and Cu accumulation in top soil, uptake of these metals by lettuce (Lactuca sativa L.) and mustard rape (Brassica juncea L.), and dry matter yield. Application of sewage sludge/effluent significantly (p<0.001) increased total Zn (13.7-1563.9 mg kg(-1)) and Cu (2.5-133.3 mg kg(-1)) in the top soil (0-20 cm depth) compared to the control. Sewage sludge/effluent addition significantly (p<0.001) increased Zn uptake by both test crops, while Cu uptake was significant in the first crop of lettuce and the second crop of mustard rape. Based on the dietary patterns of poor urban households in Zimbabwe, the maximum possible intake of Cu will only constitute 40% the Maximum Daily Intake (MDI). The toxicological implications for Zn will however be more severe, exceeding the MDI by 77% through exposure by lettuce consumption and by 251% consumption of mustard rape. It was concluded that long-term addition of sewage sludge/effluent to soil at Pension farm had increased the concentration of Zn and Cu in top soil to levels that pose environmental concern. The consumption of leafy vegetables produced on these soils pose a health risk to poor communities that reside around the study site, especially children, through possible Zn toxicity.

Copper↗
PubMed2004

Stomatal conductance of lettuce grown under or exposed to different light qualities.

BACKGROUND AND AIMS: The objective of this research was to examine the effects of differences in light spectrum on the stomatal conductance (Gs) and dry matter production of lettuce plants grown under a day/night cycle with different spectra, and also the effects on Gs of short-term exposure to different spectra. METHODS: Lettuce (Lactuca sativa) plants were grown with 6 h dark and 18 h light under four different spectra, red-blue (RB), red-blue-green (RBG), green (GF) and white (CWF), and Gs and plant growth were measured. KEY RESULTS AND CONCLUSIONS: Conductance of plants grown for 23 d under CWF rose rapidly on illumination to a maximum in the middle of the light period, then decreased again before the dark period when it was minimal. However, the maximum was smaller in plants grown under RB, RGB and GF. This demonstrates that spectral quality during growth affects the diurnal pattern of stomatal conductance. Although Gs was smaller in plants grown under RGB than CWF, dry mass accumulation was greater, suggesting that Gs did not limit carbon assimilation under these spectral conditions. Temporarily changing the spectral quality of the plants grown for 23 d under CWF, affected stomatal responses reversibly, confirming studies on epidermal strips. This study provides new information showing that Gs is responsive to spectral quality during growth and, in the short-term, is not directly coupled to dry matter accumulation.

Culture Media↗
PubMed2000

Abscisic acid and hypoxic induction of anoxia tolerance in roots of lettuce seedlings.

Lettuce (Lactuca sativa L.) seedlings were subjected to anoxic stress after ABA-pretreatment (ABA-PT) or hypoxic-pretreatment (H-PT). The H-PT increased the survivability of the anoxia in roots of the seedlings by 5.2-fold compared to that of non-pretreated (N-PT) seedlings. ABA-PT also increased the survivability at concentrations greater than 1 microM, and the survivability increased with increasing ABA doses. At 100 microM ABA, the survivability was 4.5-fold greater than that of N-PT seedlings. During pretreatment periods, alcohol dehydrogenase (ADH, EC 1.1.1.1) activity in the roots became 3.1- and 3.4-fold greater than that of N-PT seedlings following 100 microM ABA-PT and H-PT seedlings, respectively. After the onset of anoxic stress, ADH activities in all roots increased, but the activities in H-PT and ABA-PT roots remained much greater than that in N-PT roots, and the average ethanol production rate for the initial 6 h was 5.3, 4.0 and 1.4 micromol g(-1) FW h(-1) for H-PT, ABA-PT and N-PT roots, respectively. Roots of the seedlings lost ATP rapidly under anoxic stress; however, the decrease in ATP was much slower in the ABA-PT and H-PT seedlings than in the N-PT seedlings. These results suggest that the ABA-PT and H-PT may maintain ATP levels due to activation of ethanolic fermentation, which may be one of the causes of the increasing anoxia tolerance in the seedling roots. Measurement of endogenous ABA levels, however, showed that ABA levels did not increase during the H-PT, suggesting that the H-PT does not increase tolerance through an increase in ABA levels.

Abscisic Acid↗
PubMed2004

Abscisic acid in the thermoinhibition of lettuce seed germination and enhancement of its catabolism by gibberellin.

Germination of lettuce (Lactuca sativa L. cv. 'Grand Rapids') seeds was inhibited at high temperatures (thermoinhibition). Thermoinhibition at 28 degrees C was prevented by the application of fluridone, an inhibitor of abscisic acid (ABA) biosynthesis. At 33 degrees C, the sensitivity of the seeds to ABA increased, and fluridone on its own was no longer effective. However, a combined application of fluridone and gibberellic acid (GA3) was able to restore the germination. Exogenous GA3 lowered endogenous ABA content in the seeds, enhancing catabolism of ABA and export of the catabolites from the intact seeds. The fluridone application also decreased the ABA content. Consequently, the combined application of fluridone and GA3 decreased the ABA content to a sufficiently low level to allow germination at 33 degrees C. There was no significant temperature-dependent change in endogenous GA1 contents. It is concluded that ABA is an important factor in the regulation of thermoinhibition of lettuce seed germination, and that GA affects the temperature responsiveness of the seeds through ABA metabolism.

Abscisic Acid↗
PubMed2000

Identification of multi-gene families encoding isopentenyl diphosphate isomerase in plants by heterologous complementation in Escherichia coli.

Two cDNAs encoding isopentenyl diphosphate isomerase (IPI) in Adonis aestivalis, Arabidopsis thaliana, and Lactuca sativa, and single examples from Oryza sativa and Tagetes erecta were identified. An analysis of these and other ipi leads us to suggest a separate origin for green algal and plant genes and propose that a single gene encodes plastid and cytosolic IPI in plants.

Amino Acid Sequence↗
PubMed1999

A plant-derived edible vaccine against hepatitis B virus.

The infectious hepatitis B virus represents 42 nm spherical double-shelled particles. However, analysis of blood from hepatitis B virus carriers revealed the presence of smaller 22 nm particles consisting of a viral envelope surface protein. These particles are highly immunogenic and have been used in the design of hepatitis B virus vaccine produced in yeast. Upon expression in yeast, these proteins form virus-like particles that are used for parenteral immunization. Therefore, the DNA fragment encoding hepatitis B virus surface antigen was introduced into Agrobacterium tumerifacience LBA4404 and used to obtain transgenic lupin (Lupinus luteus L.) and lettuce (Lactuca sativa L.) cv. Burpee Bibb expressing envelope surface protein. Mice that were fed the transgenic lupin tissue developed significant levels of hepatitis B virus-specific antibodies. Human volunteers, fed with transgenic lettuce plants expressing hepatitis B virus surface antigen, developed specific serum-IgG response to plant produced protein.

Administration, Oral↗
PubMed2003

The eukaryotic translation initiation factor 4E controls lettuce susceptibility to the Potyvirus Lettuce mosaic virus.

The eIF4E and eIF(iso)4E cDNAs from several genotypes of lettuce (Lactuca sativa) that are susceptible, tolerant, or resistant to infection by Lettuce mosaic virus (LMV; genus Potyvirus) were cloned and sequenced. Although Ls-eIF(iso)4E was monomorphic in sequence, three types of Ls-eIF4E differed by point sequence variations, and a short in-frame deletion in one of them. The amino acid variations specific to Ls-eIF4E(1) and Ls-eIF4E(2) were predicted to be located near the cap recognition pocket in a homology-based tridimensional protein model. In 19 lettuce genotypes, including two near-isogenic pairs, there was a strict correlation between these three allelic types and the presence or absence of the recessive LMV resistance genes mo1(1) and mo1(2). Ls-eIF4E(1) and mo1(1) cosegregated in the progeny of two separate crosses between susceptible genotypes and an mo1(1) genotype. Finally, transient ectopic expression of Ls-eIF4E restored systemic accumulation of a green fluorescent protein-tagged LMV in LMV-resistant mo1(2) plants and a recombinant LMV expressing Ls-eIF4E degrees from its genome, but not Ls-eIF4E(1) or Ls-eIF(iso)4E, accumulated and produced symptoms in mo1(1) or mo1(2) genotypes. Therefore, sequence correlation, tight genetic linkage, and functional complementation strongly suggest that eIF4E plays a role in the LMV cycle in lettuce and that mo1(1) and mo1(2) are alleles coding for forms of eIF4E unable or less effective to fulfill this role. More generally, the isoforms of eIF4E appear to be host factors involved in the cycle of potyviruses in plants, probably through a general mechanism yet to be clarified.

Amino Acid Sequence↗
PubMed1996

Violaxanthin de-epoxidase.

Violaxanthin de-epoxidase catalyzes the de-epoxidation of violaxanthin to antheraxanthin and zeaxanthin in the xanthophyll cycle. Its activity is optimal at approximately pH 5.2 and requires ascorbate. In conjunction with the transthylakoid pH gradient, the formation of antheraxanthin and zeaxanthin reduces the photochemical efficiency of photosystem II by increasing the nonradiative (heat) dissipation of energy in the antennae. Previously, violaxanthin de-epoxidase had been partially purified. Here we report its purification from lettuce (Lactuca sativa var Romaine) to one major polypeptide fraction, detectable by two-dimensional isoelectic focusing/sodium dodecyl sulfate-polyacrylamide gel electrophoresis, using anion-exchange chromatography on Mono Q and a novel lipid-affinity precipitation step with monogalactosyldiacylglyceride. The association of violaxanthin de-epoxidase and monogalactosyldiacyglyceride at pH 5.2 is apparently specific, since little enzyme was precipitated by eight other lipids tested. Violaxanthin de-epoxidase has an isoelectric point of 5.4 and an apparent molecular mass of 43 kD. Partial amino acid sequences of the N terminus and tryptic fragments are reported. The peptide sequences are unique in the GenBank data base and suggest that violaxanthin de-epoxidase is nuclear encoded, similar to other chloroplast proteins localized in the lumen.

Amino Acid Sequence↗
PubMed1998

Phytochrome regulates gibberellin biosynthesis during germination of photoblastic lettuce seeds.

Germination of lettuce (Lactuca sativa L.) seed is regulated by phytochrome. The requirement for red light is circumvented by the application of gibberellin (GA). We have previously shown that the endogenous content of GA1, the main bioactive GA in lettuce seeds, increases after red-light treatment. To clarify which step of GA1 synthesis is regulated by phytochrome, cDNAs encoding GA 20-oxidases (Ls20ox1 and Ls20ox2, for L. sativa GA 20-oxidase) and 3beta-hydroxylases (Ls3h1 and Ls3h2 for L. sativa GA 3beta-hydroxylase) were isolated from lettuce seeds by reverse-transcription polymerase chain reaction. Functional analysis of recombinant proteins expressed in Escherichia coli confirmed that the Ls20ox and Ls3h encode GA 20-oxidases and 3beta-hydroxylases, respectively. Northern-blot analysis showed that Ls3h1 expression was dramatically induced by red-light treatment within 2 h, and that this effect was canceled by a subsequent far-red-light treatment. Ls3h2 mRNA was not detected in seeds that had been allowed to imbibe under any light conditions. Expression of the two Ls20ox genes was induced by initial imbibition alone in the dark. The level of Ls20ox2 mRNA decreased after the red-light treatment, whereas that of Ls20ox1 was unaffected by light. These results suggest that red light promotes GA1 synthesis in lettuce seeds by inducing Ls3h1 expression via phytochrome action.

Amino Acid Sequence↗
PubMed2001

Production of dwarf lettuce by overexpressing a pumpkin gibberellin 20-oxidase gene.

We investigated the effect of overexpressing a pumpkin gibberellin (GA) 20-oxidase gene encoding an enzyme that forms predominantly biologically inactive products on GA biosynthesis and plant morphology in transgenic lettuce (Lactuca sativa cv Vanguard) plants. Lettuce was transformed with the pumpkin GA 20-oxidase gene downstream of a strong constitutive promoter cassette (El2-35S-Omega). The transgenic plants in which the pumpkin gene was detected by polymerase chain reaction were dwarfed in the T(2) generation, whereas transformants with a normal growth phenotype did not contain the transgene. The result of Southern-blot analysis showed that the transgene was integrated as a single copy; the plants segregated three dwarfs to one normal in the T(2) generation, indicating that the transgene was stable and dominant. The endogenous levels of GA(1) and GA(4) were reduced in the dwarfs, whereas large amounts of GA(17) and GA(25), which are inactive products of the pumpkin GA 20-oxidase, accumulated in these lines. These results indicate that a functional pumpkin GA 20-oxidase is expressed in the transgenic lettuce, resulting in a diversion of the normal pathway of GA biosynthesis to inactive products. Furthermore, this technique may be useful for controlling plant stature in other agricultural and horticultural species.

Cucurbitaceae↗
PubMed2001

Overexpression of KNAT1 in lettuce shifts leaf determinate growth to a shoot-like indeterminate growth associated with an accumulation of isopentenyl-type cytokinins.

Leaves are specialized organs characterized by defined developmental destiny and determinate growth. The overexpression of Knotted1-like homeobox genes in different species has been shown to alter leaf shape and development, but a definite role for this class of genes remains to be established. Transgenics that overexpress Knotted1-like genes present some traits that are characteristic of altered cytokinin physiology. Here we show that lettuce (Lactuca sativa) leaves that overexpress KNAT1, an Arabidopsis kn1-like gene, acquire characteristics of indeterminate growth typical of the shoot and that this cell fate change is associated with the accumulation of specific types of cytokinins. The possibility that the phenotypic effects of KNAT1 overexpression may arise primarily from the modulation of local ratios of different cytokinins is discussed.

Arabidopsis Proteins↗
PubMed1985

Salicylhydroxamic acid potentiates germination of 'Waldmann's Green' lettuce seed.

A combination of salicylhydroxamic acid (SHAM) + cyanide (CN) is known to stimulate dark germination of Lactuca sativa L. seeds. Further studies were done to characterize SHAM and CN action in stimulating dark germination of lettuce seed. Germination was stimulated slightly by either SHAM or CN, whereas when SHAM and CN were combined germination was greatly enhanced. Treatment of seeds with SHAM + CN only during the first 8 hours of hydration stimulated germination as much as did treatment for 72 hours. During the first 8 hours of incubation in SHAM + CN, potentiation (i.e. domancy-breaking) of germination occurs. SHAM alone stimulated potentiation nearly to the level of SHAM + CN but inhibited subsequent radicle elongation, thereby decreasing germination when present for 72 hours. Oxygen must be present for SHAM or SHAM + CN to potentiate dark germination. The ability of SHAM and SHAM + CN to potentiate germination is influenced by O2 concentration and the timing of chemical treatment.

Cell Respiration↗