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PubMed2005

Arabidopsis thaliana: a new test species for phytotoxic bioassays.

Lettuce seeds (Lactuca sativa L.) and other crop species are often used in phytotoxic bioassays that are designed to detect allelochemicals. The seeds of these species are considered ideal because they are readily available, germinate rapidly and uniformly, and are routinely used in laboratories around the world. Despite their common use, however, the seeds of these species are often not as sensitive or responsive to some phytotoxic chemicals as are the seeds of other species. While searching for a more sensitive test species for phytotoxic bioassays, the Columbia ecotype of Arabidopsis thaliana exhibited greater sensitivity to seven potent allelochemicals than did lettuce seeds, which, in some cases, did not respond at all to those substances. Sensitivity satisfies one of the criteria for selecting a test species for bioassays. We now report on the results of our study and offer additional reasons for using A. thaliana seeds.

Arabidopsis↗
PubMed2005

Hydroxamic acid content and toxicity of rye at selected growth stages.

Rye (Secale cereale L.) is an important cover crop that provides many benefits to cropping systems including weed and pest suppression resulting from allelopathic substances. Hydroxamic acids have been identified as allelopathic compounds in rye. This research was conducted to improve the methodology for quantifying hydroxamic acids and to determine the relationship between hydroxamic acid content and phytotoxicity of extracts of rye root and shoot tissue harvested at selected growth stages. Detection limits for an LC/MS-MS method for analysis of hydroxamic acids from crude aqueous extracts were better than have been reported previously. (2R)-2-beta-D-Glucopyranosyloxy-4-hydroxy-(2H)-1,4-benzoxazin-3(4H)-one (DIBOA-G), 2,4-dihydroxy-(2H)-1,4-benzoxazin-3(4H)-one (DIBOA), benzoxazolin-2(3H)-one (BOA), and the methoxy-substituted form of these compounds, (2R)-2-beta-D-glucopyranosyloxy-4-hydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one (DIMBOA glucose), 2,4-hydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one (DIMBOA), and 6-methoxy-benzoxazolin-2(3H)-one (MBOA), were all detected in rye tissue. DIBOA and BOA were prevalent in shoot tissue, whereas the methoxy-substituted compounds, DIMBOA glucose and MBOA, were prevalent in root tissue. Total hydroxamic acid concentration in rye tissue generally declined with age. Aqueous crude extracts of rye shoot tissue were more toxic than extracts of root tissue to lettuce (Lactuca sativa L.) and tomato (Lycopersicon esculentum Mill.) root length. Extracts of rye seedlings (Feekes growth stage 2) were most phytotoxic, but there was no pattern to the phytotoxicity of extracts of rye sampled at growth stages 4 to 10.5.4, and no correlation of hydroxamic acid content and phytotoxicity (I50 values). Analysis of dose-response model slope coefficients indicated a lack of parallelism among models for rye extracts from different growth stages, suggesting that phytotoxicity may be attributed to compounds with different modes of action at different stages. Hydroxamic acids may account for the phytoxicity of extracts derived from rye at early growth stages, but other compounds are probably responsible in later growth stages.

Herbicides↗
PubMed1981

Effects of prolonged exposure to space flight factors for 175 days on lettuce seeds.

We have studied the effects of prolonged (up to 175 days) exposure of Lactuca sativa seeds to space flight factors, including primary cosmic radiation heavy ions. The data obtained evidence a significant fourfold increase of spontaneous mutagenesis in seeds both with regard to the total number of aberrant cells as well as the formation of single cells with multiple aberrations. Comparison of the present experiment with earlier works shows that the frequency of such aberrations increases with the duration of the flight.

Chromosome Aberrations↗
PubMed1989

Biological effects of galactic radiation HZE particles in experiments on the orbital station Salyut 7.

Lettuce (Lactuca sativa) seeds were flown on-board the orbital station Salyut 7 for 66-457 days. It was found that a single heavy charged particle (HZE) hitting a seed only slightly affects the subsequent plant growth. However, morphological anomalies of varying type in primordial leaves and roots were observed that show good correlation with the location of the particle track. The most severe damage detected by light and an electron microscopy were "channels" in dry and soaked seeds. The appearance of "channels" seems to be related to the LET of the incident particle. This finding is of considerable importance for assessment of space flight radiation hazard.

Cosmic Radiation↗
PubMed1989

Effects of prolonged exposure of lettuce seeds to HZE particles on orbital stations.

In a study of the biological effects of cosmic HZE particles, lettuce (Lactuca sativa) seeds were flown on the orbital stations Salyut 6 and 7 for varying periods of time (from 40 to 457 days). The dependence of the biological damage on flight duration, physical parameters and the fact of passage of an HZE particle through the seed was estimated using the criterion of the frequency of aberrant cells. The arrangement of the flight biological container Biobloc made it possible to trace the location of tracks of individual HZE particles with Z > or = 6 and LET 200 keV/um. In seeds hit by HZE particles, for all exposure times, a statistically significant much higher yield of aberrant cells and also of cells containing multiple chromosome aberrations was observed than in the control material. The frequency of aberrant cells is markedly higher (by a factor of 1,5) in seeds hit than in non-hit ones. The changes of the yield of aberrant cells as a function of the absorbed dose (3.2-63.4 mGy) and the fluence (4.8-44.2 particles/cm2) are linear for the exposure duration ranging from 40 to 457 days.

Chromosome Aberrations↗
PubMed1994

Analysis of remote reflection spectroscopy to monitor plant health.

Remote non-contact reflection spectroscopy is examined as a method for detecting stress in Controlled Ecological Life Support System CELSS type crops. Lettuce (Lactuca [correction of Latuca] Sativa L. cv. Waldmans Green) and wheat (Triticum Aestivum L. cv. Yecora Rojo) were grown hydroponically. Copper and zinc treatments provided toxic conditions. Nitrogen, phosphorous, and potassium treatments were used for deficiency conditions. Water stress was also induced in test plants. Reflectance spectra were obtained in the visible and near infrared (400nm to 2600nm) wavebands. Numerous effects of stress conditions can be observed in the collected spectra and this technique appears to have promise as a remote monitor of plant health, but significant research remains to be conducted to realize the promise.

Algorithms↗
PubMed1996

Proximate composition of CELSS crops grown in NASA's Biomass Production Chamber.

Edible biomass from four crops of wheat (Triticum aestivum L.), four crops of lettuce (Lactuca sativa L.), four crops of potato (Solanum tuberosum L.), and three crops of soybean (Glycine max (L.) Merr.) grown in NASA's CELSS Biomass Production Chamber were analyzed for proximate composition. All plants were grown using recirculating nutrient (hydroponic) film culture with pH and electrical conductivity automatically controlled. Temperature and humidity were controlled to near optimal levels for each species and atmospheric carbon dioxide partial pressures were maintained near 100 Pa during the light cycles. Soybean seed contained the highest percentage of protein and fat, potato tubers and wheat seed contained the highest levels of carbohydrate, and lettuce leaves contained the highest level of ash. Analyses showed values close to data published for field-grown plants with several exceptions: In comparison with field-grown plants, wheat seed had higher protein levels; soybean seed had higher ash and crude fiber levels; and potato tubers and lettuce leaves had higher protein and ash levels. The higher ash and protein levels may have been a result of the continuous supply of nutrients (e.g., potassium and nitrogen) to the plants by the recirculating hydroponic culture.

Biomass↗
PubMed1996

Effect of CO2 levels on nutrient content of lettuce and radish.

Atmospheric carbon-dioxide enrichment is known to affect the yield of lettuce and radish grown in controlled environments, but little is known about CO2 enrichment effects on the chemical composition of lettuce and radish. These crops are useful model systems for a Controlled Ecological Life-Support System (CELSS), largely because of their relatively short production cycles. Lettuce (Lactuca sativa L.) cultivar 'Waldmann's Green' and radish (Raphanus sativus L.) cultivar 'Giant White Globe' were grown both in the field and in controlled environments, where hydroponic nutrient solution, light, and temperature were regulated, and where CO2 levels were controlled at 400, 1000, 5000, or 10,000 ppm. Plants were harvested at maturity, dried, and analyzed for proximate composition (protein, fat, ash, and carbohydrate), total nitrogen (N), nitrate N, free sugars, starch, total dietary fiber, and minerals. Total N, protein N, nonprotein N (NPN), and nitrate N generally increased for radish roots and lettuce leaves when grown under growth chamber conditions compared to field conditions. The nitrate-N level of lettuce leaves, as a percentage of total NPN, decreased with increasing levels of CO2 enrichment. The ash content of radish roots and of radish and lettuce leaves decreased with increasing levels of CO2 enrichment. The levels of certain minerals differed between field- and chamber-grown materials, including changes in the calcium (Ca) and phosphorus (P) contents of radish and lettuce leaves, resulting in reduced Ca/P ratio for chamber-grown materials. The free-sugar contents were similar between the field and chamber-grown lettuce leaves, but total dietary fiber content was much higher in the field-grown plant material. The starch content of growth-chamber lettuce increased with CO2 level.

Atmosphere↗
PubMed1989

Effects of incandescent radiation on photosynthesis, growth rate and yield of 'Waldmann's Green' leaf lettuce.

Effects of different ratios incandescent (ln) to fluorescent (Fl) radiation were tested on growth of 'Waldmann's Green' leaf lettuce (Lactuca sativa L.) in a controlled environment. After 4 days of treatment, dry weight, leaf area, relative growth rate (RGR), net assimilation rate (NAR), leaf area ratio (LAR) and photosynthetic rate (Pn) were greater for plants grown at 84 rather than 16% of total irradiance (82 W m-2) from ln lamps. Although leaf dry weight and area were 12-17% greater at 84% ln after the first 8 days of treatment, there were no differences in RGR or Pn between treatments during the last 4 days. If 84% ln was compared with 50% ln, all cumulative growth parameters, RGR, NAR and Pn were greater for 84% ln during the first 4 days of treatment. However, during the second 4 days, RGR was greater for the 50% ln treatment, resulting in no net difference in leaf dry weight or area between treatments. Shifting from 84 to 50% ln radiation between the first and second 4 days of treatment increased plant dry weight, leaf area, RGR and NAR relative to those under 84% ln for 8 days continuously.

Biomass↗
PubMed1988

Growth and yield characteristics of 'Waldmann's Green' leaf lettuce under different photon fluxes from metal halide or incandescent + fluorescent radiation.

'Waldmann's Green' leaf lettuce (Lactuca sativa L.) was grown either under 84% irradiance from incandescent (In) + 16% from fluorescence (Fl) lamps, or 100% from metal halide (MH) lamps, both at 392 micromoles s-1 m-2 of photosynthetically active radiation (400-700 nm) from 11 to 19 days after seeding. No differences in leaf dry weight, leaf area, relative growth rate (RGR) or photosynthesis (Pn) occurred after 8 days of exposure to these radiation treatments for 20 h day-1. However, a 23% reduction in root dry weight, a 123% increase in stem length and a 61% increase in stem dry weight were found with In + Fl relative to MH radiation. A photosynthetic photon flux (PPF) of 920 micromoles s-1 m-2 from the In + Fl source increased leaf dry weight by 13% and RGR by 21% relative to those at 460 micromoles s-1 m-2 from the same source. From 4 to 8 days of treatment, high PPF did not lower shoot dry gain, but did lower RGR. Photosynthesis and net assimilation rate were lower while leaf area ratio was higher at 460 than at 920 micromoles s-1 m-2 over the 8-day treatment period. When PPF from MH lamps was 400 micromoles s-1 m-2, leaf dry weight was 20% greater than if PPF was 805 micromoles s-1 m-2 after 4 days of treatment, but no differences were detected after 8 days. Relative growth rate increased by 11% during the first 4 days, but declined by 12% during the second 4 days under high- relative to low-PPF MH radiation. Lettuce productivity was stimulated by high PPF from either lamp type from Day 11 to Day 14, but not from Day 15 to Day 19 after seeding.

Biomass↗
PubMed1990

Reliability of trajectory identification for cosmic heavy ions and cytogenetic effects of their passage through plant seeds.

The potentially specific importance of the study of heavy ions from galactic cosmic rays for the understanding of radiation protection in manned spaceflight continues to stimulate spaceflight experiments in order to investigate the radiobiological properties of these ions. Chromosome aberrations as an expression of a direct assault on the genome are of particular interest in view of carcinogenesis as the primary radiation risk for man in space. An essential technical ingredient of such spaceflight experiments is the visual nuclear track detector which permits identification of those biological test organisms which have been affected by cosmic heavy ions. We describe such a technique and report on an analysis of the qualitative and quantitative reliability of this identification of particle trajectories in layers of biological test organisms. The incidence of chromosome aberrations in cells of lettuce seeds, Lactuca sativa, exposed during the Kosmos 1887 mission, was determined for seeds hit by cosmic heavy ions. In those seeds the incidence of both single and multiple chromosome aberrations was enhanced.

Chromosome Aberrations↗
PubMed2005

Structural analysis of xyloglucans in the primary cell walls of plants in the subclass Asteridae.

The structures of xyloglucans from several plants in the subclass Asteridae were examined to determine how their structures vary in different taxonomic orders. Xyloglucans, solubilized from plant cell walls by a sequential (enzymatic and chemical) extraction procedure, were isolated, and their structures were characterized by NMR spectroscopy and mass spectrometry. All campanulids examined, including Lactuca sativa (lettuce, order Asterales), Tenacetum ptarmiciflorum (dusty miller, order Asterales), and Daucus carota (carrot, order Apiales), produce typical xyloglucans that have an XXXG-type branching pattern and contain alpha-d-Xylp-, beta-D-Galp-(1-->2)-alpha-D-Xylp-, and alpha-L-Fucp-(1-->2)-beta-D-Galp-(1-->2)-alpha-D-Xylp- side chains. However, the lamiids produce atypical xyloglucans. For example, previous analyses showed that Capsicum annum (pepper) and Lycopersicon esculentum (tomato), two species in the order Solanales, and Olea europaea (olive, order Lamiales) produce xyloglucans that contain arabinosyl and galactosyl residues, but lack fucosyl residues. The XXGG-type xyloglucans produced by Solanaceous species are less branched than the XXXG-type xyloglucan produced by Olea europaea. This study shows that Ipomoea pupurea (morning glory, order Solanales), Ocimum basilicum (basil, order Lamiales), and Plantago major (plantain, order Lamiales) all produce xyloglucans that lack fucosyl residues and have an unusual XXGGG-type branching pattern in which the basic repeating core contains five glucose subunits in the backbone. Furthermore, Neruim oleander (order Gentianales) produces an XXXG-type xyloglucan that contains arabinosyl, galactosyl, and fucosyl residues. The appearance of this intermediate xyloglucan structure in oleander has implications regarding the evolutionary development of xyloglucan structure and its role in primary plant cell walls.

Alcohols↗
PubMed2004

Photoinduced toxicity of fluoranthene on germination and early development of plant seedling.

The influence of light on phytotoxicity of increased concentration (2, 5, 10 mg/l) of intact fluoranthene (FLT) and photomodified fluoranthene (phFLT) diluted in experimental solutions was investigated. The germination rate of lettuce (Lactuca sativa L.), onion (Allium cepa L.) and tomato (Lycopersicum esculentum L.) seeds and some parameters of seedlings primary growth of these plant species were used as laboratory indicators of phytotoxicity. Among them a length of root and shoot, their dry weight and a content of photosynthetic pigments in shoot were measured. The results demonstrated that the higher concentration (5 and 10 mg/l) of FLT and especially of phFLT significantly inhibited the germination rate of seeds and the length of root and shoot seedlings of all plant species. Decreased production of biomass expressed by dry weight of root and shoot was found in lettuce seedlings under the inhibitory effect of FLT and phFLT. An increased concentration of FLT and phFLT did not exhibit an unambiguous effect on the content of photosynthetic pigments in shoot of experimental plants. Only the highest concentration (10 mg/l) of FLT significantly increased content of chlorophylls a and b in lettuce, onion and tomato plants and content of carotenoids in lettuce and onion. Light intensified a significant inhibitory effect of phFLT in the most testified parameters of germination and seedling growth.

Analysis of Variance↗
PubMed2005

Phytotoxicity and accumulation of anthracene applied to the foliage and sandy substrate in lettuce and radish plants.

The effects of anthracene (ANT) on the growth of two species of vegetable plants (Lactuca sativa L. and Raphanus sativus L.), which play an important role in the human diet, were studied. ANT was applied to the leaves of these plants by foliar deposition, in aerosol form, and to the sandy substrate in which the plants were grown in a greenhouse. It was found that ANT affected plant biomass, especially root biomass, in the case of both foliar and soil application. Under conditions of induced chemical stress, the dry matter of aboveground parts and roots was lower than that in control plants. The rate of photosynthesis decreased by about 20% in both plant species following foliar ANT application. A lower rate of transpiration was also observed in lettuce plants. After the foliar application of ANT, small quantities of the compound were found in the leaves only (0.06-0.18% of the total dose). ANT translocation to other parts of the plants was not observed. This compound underwent rapid chemical changes on the leaf surface under greenhouse conditions. After the application of ANT to a sandy substrate, this compound was detected in the roots and aboveground parts of plants, which indicates that it was transported throughout the plant. In a sandy substrate, the process of ANT decomposition was much slower-60-70% of the administered dose was measured in the soil after the completion of the experiment.

Anthracenes↗
PubMed2004

Effects of compost and phosphate on plant arsenic accumulation from soils near pressure-treated wood.

Leaching of arsenic (As) from chromated copper arsenate (CCA)-treated wood may elevate soil arsenic levels. Thus, an environmental concern arises regarding accumulation of As in vegetables grown in these soils. In this study, a greenhouse experiment was conducted to evaluate As accumulation by vegetables from the soils adjacent to the CCA-treated utility poles and fences and examine the effects of soil amendments on plant As accumulation. Carrot (Daucus carota L.) and lettuce (Lactuca sativa L.) were grown for ten weeks in the soil with or without compost and phosphate amendments. As expected, elevated As concentrations were observed in the pole soil (43 mg kg(-1)) and in the fence soil (27 mg kg(-1)), resulting in enhanced As accumulation of 44 mg kg(-1) in carrot and 32 mg kg(-1) in lettuce. Addition of phosphate to soils increased As accumulation by 4.56-9.3 times for carrot and 2.45-10.1 for lettuce due to increased soil water-soluble As via replacement of arsenate by phosphate in soil. However, biosolid compost application significantly reduced plant As uptake by 79-86%, relative to the untreated soils. This suppression is possibly because of As adsorbed by biosolid organic mater, which reduced As phytoavailability. Fractionation analysis showed that biosolid decreased As in soil water-soluble, exchangeable, and carbonate fraction by 45%, whereas phosphate increased it up to 2.61 times, compared to the untreated soils. Our results indicate that growing vegetables in soils near CCA-treated wood may pose a risk of As exposure for humans. Compost amendment can reduce such a risk by reducing As accumulation by vegetables and can be an important strategy for remediating CCA-contaminated soils. Caution should be taken for phosphate application since it enhances As accumulation.

Arsenates↗
PubMed2005

Effectiveness of two-sided UV-C treatments in inhibiting natural microflora and extending the shelf-life of minimally processed 'Red Oak Leaf' lettuce.

The use of UV-C radiation treatments to inhibit the microbial growth and extend the shelf-life of minimally processed 'Red Oak Leaf' lettuce was investigated. Initially, UV-C resistance of 20 bacterial strains from different genera often associated with fresh produce (Enterobacter, Erwinia, Escherichia, Leuconostoc, Pantoea, Pseudomonas, Rahnela, Salmonella, Serratia and Yersinia) were tested in vitro. Most of the bacterial strains were inhibited with the minimum dose (30 J m(-2)). Erwinia carotovora, Leuconostoc carnosum, Salmonella typhimurium, and Yersinia aldovae were the most resistant strains requiring a UV-C dose of 85 J m(-2) to completely inhibit growth. An in vivo study consisted of treating minimally processed 'Red Oak Leaf' lettuce (Lactuca sativa) with UV-C at three radiation doses (1.18, 2.37 and 7.11 kJ m(-2)) on each side of the leaves and storing the product under passive MAP conditions at 5 degrees C for up to 10 days. The gas composition inside packages varied significantly among the treatments, with CO2 concentrations positively and O2 concentrations negatively correlating with the radiation dose. All the radiation doses were effective in reducing the natural microflora of the product, although the highest doses showed the greatest microbial inhibitions. Taking into account the microbial limit set by Spanish legislation [Boletín Oficial del Estado (BOE), 2001. Normas de higiene para la elaboración, distribución y comercio de comidas preparadas, Madrid, Spain, Real Decreto 3484/2000, pp. 1435-1441], all UV-C treatments extended the shelf-life of the product. However, the 7.11 kJ m(-2) dose induced tissue softening and browning after 7 days of storage at 5 degrees C. Therefore, the use of two sided UV-C radiation, at the proper dose, is effective in reducing the natural microflora and extending the shelf-life of minimally processed 'Red Oak Leaf' lettuce.

Bacteria↗
PubMed2006

Quantification of contamination of lettuce by GFP-expressing Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium.

The primary objective of this study was to determine the possibility of internalization of GFP-expressing Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium (S. Typhimurium) strains MAE 110 (multi-cellular morphology) and 119 (wild type morphology) into lettuce seedlings (Lactuca sativa cv. Tamburo) grown in an inoculated hydroponic and soil system. The second aim was to quantify the level of contamination with the use of a proper surface sterilization method. Silver nitrate was superior in reducing the number of viable bacteria on leave surfaces compared to sodium hypochlorite and ethanol. With the hydroponic system internal colonization of lettuce only occurred at high densities with S. Typhimurium MAE 119. With the soil system E. coli O157:H7, S. Typhimurium 110 and S. Typhimurium 119 were found at considerable densities in sterilized leaf samples (respectively, 3.95, 2.57 and 2.37 log cfu/g on average) with prevalences of 0.29, 0.23 and 0.15, respectively. No statistical differences were observed between the Salmonella strains. A negative correlation was observed between shoot weight and leaf contamination. The observed presence of the pathogens in lettuce, after thorough surface sterilization, demonstrates the possible presence of human pathogens in locations were they are unlikely to be removed by the actions of consumer washing and therefore pose a serious threat when occurring in field situations.

Anti-Bacterial Agents↗
PubMed2005

Preferential inhibition of the lycopene epsilon-cyclase by the substituted triethylamine compound MPTA in higher plants.

In addition to the usual complement of carotenoids found in the plant leaf tissues, lettuce (Lactuca sativa), unusually, possesses large amounts of the diol lactucaxanthin. This carotenoid possesses two epsilon-end-groups and its presence provides a good model in which to study the effects of the substituted triethylamine compound 2-(4-methylphenoxy)triethylamine (MPTA) on the cyclisation of beta- and epsilon-end-groups during the biosynthesis of carotenoids. Treatment with 10 or 20microM MPTA significantly reduced levels of both beta-carotene and neoxanthin (up to 18-fold), whilst levels of violaxanthin and lutein were less affected (4-fold reduction). In contrast, levels of lactucaxanthin were not reduced even at the highest inhibitor concentration, and at 10microM MPTA levels of this xanthophyll doubled. The pigment stoichiometry of the bulk light-harvesting complex (LHCIIb) isolated from treated plants shows that lactucaxanthin successfully substituted for lutein and neoxanthin in two of the xanthophyll binding sites, namely L2 and N1. Inhibition of cyclisation was accompanied by the accumulation of lycopene and trace amounts of delta-carotene and a number of oxygenated derivatives of these precursors. Two forms of mono-hydroxy lycopene were identified together with mono-epoxy delta-carotene.

Carotenoids↗