Cytopathology of Mature Ovaries from Lettuce Plants Infected by Lettuce Mosaic Potyvirus

The location of lettuce mosaic potyvirus (LMV) in mature ovaries of lettuce plants ( Lactuca sativa ) was studied by conventional thin-section electron microscopy and immunogold cytochemistry. Flexuous filamentous particles and inclusion bodies characteristic of LMV infection were observed in the integumentary tapetum, integument and ovary wall of the mature ovary but not in the embryo sac.     

生菜矿质养分特性的品种差异比较研究

为了探明生菜不同品种类型之间的矿质养分特性差异,本实验采用深水栽培方式,比较研究了玻璃生菜、油麦菜和意大利生菜3个品种在不同生长时期地上部Fe、Zn、Ca含量的差异,以及根际缺氧处理对3个品种地上部Fe、Zn、Ca含量的影响.结果表明,随着植株的生长,3个品种地上部的Fe、Zn、Ca含量均呈上升趋势,到出苗后50 d达到最高水平,随后稍有下降.3个品种地上部3种矿质养分含量由高到低的顺序依次是：意大利生菜、玻璃生莱、油麦菜.但3个品种地上部的生长速率的大小顺序却相反.根际缺氧处理（以正常通气栽培植株作对照）均使3个品种地上部的Fe、Zn、Ca含量下降,其中意大利生菜所受的影响最大,其地上部的Fe、Zn、Ca含量分别比对照降低18.04%、12.70%、17.56%;油麦菜的影响最小,其地上部Fe、Zn、Ca含量的降低率不及意大利生菜的一半;玻璃生菜地上部Fe、Ca含量受影响比较大,分别比对照降低10.54%和14.79%,但Zn含量的影响比较小.     

Recent amplification of triose phosphate isomerase related sequences in lettuce.

A random cDNA clone was identified as distinguishing near-isogenic lines for downy mildew resistance in lettuce. The clone detected multiple restriction fragments in genomic Southern blots of lettuce. Restriction fragment length polymorphisms (RFLPs) detected by this clone mapped to separate clusters of resistance genes; therefore, these sequences were studied in a greater detail. Sequence analysis indicated that the cDNA encoded the glycolytic enzyme triose phosphate isomerase (TPI). The lettuce clone shares 85% sequence similarity at the amino acid level with TPI from maize. TPI-related sequences were mapped in lettuce using three crosses. Ten loci were distributed in six linkage groups. Possible mechanisms of amplification and dispersion were investigated. Retrotransposition was excluded, since intron five is retained in all TPI-related genomic sequences. Large scale chromosomal rearrangements were not involved, as RFLP markers flanking TPI loci were not duplicated. A high level of genomic variability was detected by the TPI clone; 37 different restriction fragments were detected in Southern hybridizations to 64 populations of lettuce including 47 cultivars of Lactuca sativa and five wild species. Species distantly related to L. sativa had few TPI loci, indicating that their amplification and dispersion were recent and had occurred after the emergence of the L. serriola complex.     

Interactions between hydrogen cyanide, gibberellin, abscisic acid and red light in germination of lettuce seeds

Germination of lettuce ( Lactuce sativa L. cy. Grand Rapids) seeds was promoted by red light and by pulse treatments with gibbercllie acid (GA₃) or hydrogen cyanide, whereas it was inhibited by short exposure of seeds to absusic acid (ABA). The eflects of unsalLirating red light and of 10 μ M GA₃ on lettuce germination were completely reversed the effect of ABA (100 μ M ). In contrast, hydrogen cyanide did not reverse the effect of 100 μ M ABA and only partly eliminated the effect of 10μ M ABA, independently of the sequence of treatments. Possible interactions between HCN GA₃, ABA and red light were discussed. It was concluded thai light GA₃ and HCN affect different mechanisms involved in lettuce germination: ABA counteracts the stimulatory action of all these faclors. being the most effective against cvanide Additional key words - Lactuca sativa, pholodormancy, phylohormoncs.     

莴苣叶绿体psbA基因序列

1　Ｓｏｕｒｃｅ　ＴｈｅｓｅｑｕｅｎｃｅｗａｓｄｅｔｅｒｍｉｎｅｄｆｒｏｍａＰＣＲｐｒｏｄｕｃｔｏｆｃｈｌｏｒｏｐｌａｓｔｇｅｎｏｍｉｃＤＮＡｏｆＬａｃｔｕｃａｓａｔｉｖａ (ｌｅｔｔｕｃｅ) .2　Ｎａｍｅａｎｄｄｅｓｃｒｉｐｔｉｏｎ　Ｔｈｅｃｏｄｏｎｓｅｑｕ     

Isolation and identification of a potent allelopathic substance in rice root exudates

A search for growth inhibitors in rice root exudates was undertaken in order to clarify the allelopathic system in rice ( Oryza sativa L.). Rice seedlings inhibited the growth of cress ( Lepidium sativum L.) and lettuce ( Lactuca sativa L.) seedlings when the cress and lettuce were grown with rice seedlings. The putative compound causing the inhibitory effect of rice seedlings was isolated from their culture solution, and the chemical structure of the inhibitor was determined by spectral data as momilactone B. Momilactone B inhibited the growth of cress and lettuce seedlings at concentrations greater than 3 and 30 µ M , respectively. The concentration of momilactone B was 3.4 and 1.1 nmol per seedling in the culture solutions of husked and non-husked rice seedlings, respectively. These results suggest that rice seedlings may release momilactone B into the environment and the stress caused by the husk-treatment may increase the amount of momilactone B released. Thus, momilactone B may play an important role in rice allelopathy.     

Genotype-independent transformation of lettuce using Agrobacterium tumefaciens

The genetic manipulation of lettuce (Lactuca sativa) necessitatesa reliable and efficient, genotype-independent method of transformation.Thirteen lettuce cultivars have been assessed for their amenabilityto Agrobacterrum-mediated gene transfer linked to their tissueculture responsiveness, including callus induction and shootregeneration. A reliable protocol has been developed for theroutine production of transgenic plants for all 13 cultivarsinvestigated. Key words: Agrobacterium-mediated transformation, Lactuca sativa genotypes, lettuce     

Classical and biochemical endpoints in the evaluation of phytotoxic effects caused by the herbicide trichloroacetate

Three terrestrial plant species, oat (Avena sativa ), Chinese cabbage (Brassica campestris cv. chinensis) and lettuce (Lactuca sativa), were exposed to different concentrations of herbicide TCA (sodium trichloroacetate) in a growth test according to guideline OECD # 208. Classical (i.e. germination and biomass) and biochemical (i.e., antioxydant enzyme activities) endpoints were investigated. Germination rate decreased significantly at 3.9 mg TCA kg dry soil(-1) (for oat and lettuce) and 62.5 mg TCA kg dry soil(-1) (for Chinese cabbage). Biomass decreased significantly only at 1.9 mg TCA kg dry soil(-1) (for oat and lettuce) and 15.6 mg TCA kg dry soil(-1) (for Chinese cabbage). The activities of superoxide dismutase (EC 1.15.1.1), catalase (EC 1.11.1.6), peroxidase (EC 1.11.1.7) and glutathione reductase (EC 1.6.4.2) increased significantly at the lowest concentration of TCA tested, i.e. 0.03 mg TCA kg dry soil(-1) (for oat and lettuce) and 0.48 mg TCA kg dry soil(-1) (for Chinese cabbage). Our results showed a ranking of sensitivity among the different endpoints for the three plant species: enzyme activities>biomass>germination rate. The increase in antioxidant enzyme activities observed in this study ensured the detoxification of increased levels of active oxygen species, and presumably prevented the plants from undergoing oxidative stress damage. Thus, the use of enzyme activities will permit the detection of early injury in plant growth testing.     

Evidence of an antilisterial factor induced by wounding of iceberg lettuce tissues

AIMS: To examine the influence of wound-associated reactions in cut iceberg lettuce (Lactuca sativa L.) tissues on the fate of Listeria monocytogenes. METHODS AND RESULTS: Aqueous extracts prepared from shredded iceberg lettuce before and after storage in high oxygen permeability film were inoculated with L. monocytogenes. Listeria monocytogenes grew in extracts prepared from fresh lettuce. In contrast, inhibition ranging from arrested growth to a decline in cell viability was observed in extracts prepared from samples stored for 1-3 days. Similar behaviour was evident in lettuce shreds inoculated with 10(5) CFU g(-1)L. monocytogenes immediately after processing or after 3 days in storage. Heat treatment of the cut tissues at 47 degrees C for 3 min before storage diminished the inhibitory effect. CONCLUSIONS: The results provided evidence that an antilisterial factor or factors are released by wounded iceberg lettuce tissues. Antilisterial activity was mitigated by heat treatment of the lettuce. SIGNIFICANCE AND IMPACT OF STUDY: This study indicates that intrinsic factors associated with plant metabolism could play a significant role in the ecology of human pathogens in packaged horticultural products.     

Sidedness studies of thylakoid phosphatidylglycerol in higher plants.

The transmembrane distribution of phosphatidylglycerol was determined in thylakoids from barley (Hordeum vulgare), lettuce (Lactuca sativa) and pea (Pisum sativum) chloroplasts. Phospholipase A2 and phospholipase D digestion and chemical-labelling methods were used. Phosphatidylglycerol was preferentially localized in the outer (stromal) leaflet. The proportion of the phospholipid in this leaflet ranged from about 66% in pea to about 75% for barley and lettuce thylakoids. One of the main fatty acids, trans-delta 3-hexadecenoic acid, was exclusively located in the outer leaflet in all three plant types. The data are discussed in relation to suggested roles for phosphatidylglycerol in thylakoid function.     

Interveinal Yellowing Caused by Tomato infectious chlorosis virus in Lettuce and Escarole in Southern Italy

In 2005 and 2006, a severe disease of lettuce and escarole, characterized by interveinal yellowing of the leaves, was observed in the Calabria region (Southern Italy). Samples collected were positive in RT‐PCR assay when specific primers for Crinivirus were used. The identity of the virus was determined by using Tomato infectious chlorosis virus (TICV)‐specific primers and probe. An amplicon of the same size (501 bp) as that from TICV‐infected tomato controls, corresponding to the partial Hsp70 viral gene, was obtained from 36 of 40 lettuce samples and from 19 of 24 escarole samples tested in 2005. The sequences obtained had 99–100% nucleotide sequence identity with other TICV sequences. In an extensive survey carried out in 2006 with TICV‐specific probe, 92% of symptomatic lettuce and 89% of escarole samples were infected with TICV. Adults of Trialeurodes vaporariorum, harvested from symptomatic lettuce and escarole plants, transmitted the virus to healthy plants of the same species. This is the first evidence of a disease caused by TICV in lettuce in Italy and the first record of TICV infection in escarole.     

Synthesis and assembly of Escherichia coli heat-labile enterotoxin B subunit in transgenic lettuce (Lactuca sativa)

Escherichia coli heat-labile enterotoxin B subunit (LTB) strongly induces immune responses and can be used as an adjuvant for co-administered antigens. Synthetic LTB (sLTB) based on optimal codon usage by plants was introduced into lettuce cells (Lactuca sativa) by Agrobacterium tumefaciens-mediated transformation methods. The sLTB gene was detected in the genomic DNA of transgenic lettuce leaf cells by PCR DNA amplification. Synthesis and assembly of the sLTB protein into oligomeric structures of pentameric size was observed in transgenic plant extracts using Western blot analysis. The binding of sLTB pentamers to intestinal epithelial cell membrane glycolipid receptors was confirmed by G(M1)-ganglioside enzyme-linked immunosorbent assay (G(M1)-ELISA). Based on the results of ELISA, sLTB protein comprised approximately 1.0-2.0% of total soluble protein in transgenic lettuce leaf tissues. The synthesis and assembly of sLTB monomers into biologically active oligomers in transgenic lettuce leaf tissues demonstrates the feasibility of the use of edible plant-based vaccines consumed in the form of raw plant materials to induce mucosal immunity.     

Rearing history affects behaviour and performance of two virulent Nasonovia ribisnigri populations on two lettuce cultivars

Many aphid species have become virulent to host‐plant resistance, which limits the sustainability of insect resistance breeding. However, when this adaptation to resistant plants is associated with fitness costs for the aphids, virulence can be lost in the absence of resistant plants. For two populations of the lettuce aphid, Nasonovia ribisnigri (Mosely) (Hemiptera: Aphididae), we evaluated whether virulence to Nr‐gene‐based resistance was lost on a susceptible lettuce, Lactuca sativa L. (Asteraceae), and assessed possible costs of virulence. The feeding behaviour and performance of these aphids, reared and tested on susceptible and resistant lettuce, were investigated. The rearing plant affected feeding behaviour and performance of the aphids. Temporary reduction and long‐term loss of virulence were found. The total duration of phloem intake was shorter after being reared on susceptible lettuce and tested on resistant lettuce. In addition, one population had a lower survival on resistant lettuce after being reared on susceptible lettuce. There were also indications of fitness costs of the virulence in both populations.     

Photomorphogenetic responses to UV radiation and short-term red light in lettuce seedlings

Effects of red light (R), far-red light (FR) and UV radiation on growth and greening of lettuce seedlings (Latuca sativa L., cv. Berlinskii) have been investigated. UV-B and UV-C inhibited hypocotyl elongation and stimulated cotyledonary growth. R in combination with UV-B and UV-C partly eliminated these effects, but FR increased those and reversed the R effect. Chlorophyll accumulation was inhibited by UV-B and UV-C. In comparison with cotyledonary growth, R strengthened the UV inhibitory effect, and FR reversed this effect of R. Thus, UV and phytochrome system modify the effects of each other on hypocotyl and leaf growth in lettuce seedlings depending on the level of active phytochrome formed.     

Lactuca saligna,a non-host for lettuce downy mildew ( Bremia lactucae), harbors a new race-specific Dm gene and three QTLs for resistance

Lactuca sativa (lettuce) is susceptible to Bremia lactucae (downy mildew). In cultivated and wild Lactuca species, Dm genes have been identified that confer race-specific resistance. However, these genes were soon rendered ineffective by adaptation of the pathogen. Lactuca saligna (wild lettuce) is resistant to all downy mildew races and can be considered as a non-host. Therefore, L. saligna might be an alternative source for a more-durable resistance to downy mildew in lettuce. In order to analyze this resistance, we have developed an F(2) population based on a resistant L. saligna x susceptible L. sativa cross. This F(2) population was fingerprinted with AFLP markers and tested for resistance to two Bremia races NL14 and NL16. The F(2) population showed a wide and continuous range of resistance levels from completely resistant to completely susceptible. By comparison of disease tests, we observed a quantitative resistance against both Bremia races as well as a race-specific resistance to Bremia race NL16 and not to NL14. QTL mapping revealed a qualitative gene ( R39) involved in the race-specific resistance and three QTLs ( RBQ1, RBQ2 and RBQ3) involved in the quantitative resistance. The qualitative gene R39 is a dominant gene that gives nearly complete resistance to race NL16 in L. saligna CGN 5271 and therefore it showed features similar to Dm genes. The three QTLs explained 51% of the quantitative resistance against NL14, which indicated that probably only the major QTLs have been detected in this F(2) population. The perspectives for breeding for durable resistance are discussed.     

Reduced allelopathic inhibition of lettuce (Lactuca sativa) growth caused by velvet bean (Mucuna pruriens) under 3D-clinorotation.

Allelopathy between Mucuna pruriens (velvet bean) and Lactuca sativa (lettuce) was studied under 3D-clinorotation. Growth of both roots and shoots of lettuce seedlings was suppressed by the presence of velvet bean. The degree of suppression was less on the clinostat compared to the normal static earth gravity. L-DOPA (L-3, 4-dihydroxyphenylalanine) is known to be a major substance in allelopathy of velvet bean. Amount of L-DOPA diffused out from a sintered filter paper into agar medium was compared between clinorotation and control group, and found no significant difference. It was concluded that some factors related to release, transport, and sensing phenomena of allelopathic substances may be responsible to the new findings in this study.     

Microsatellite retrieval in lettuce (Lactuca sativa L.).

By using enriched genomic libraries, microsatellite-containing sequences were isolated from lettuce (Lactuca sativa) with high efficiency. With this approach, a sizeable fraction (up to 55%) of the clones contained a microsatellite. In about half of these clones, primers could be designed for PCR amplification of the microsatellite. This yielded 28 primer sets amplifying unambiguously scorable products, of which 26 showed polymorphisms in a test set of six lettuce varieties. Practically all microsatellite-amplifying primer sets yielded products in lettuce's nearest relative, L. serriola, but only half of the primer sets yielded products in the more distant species L. saligna and L. virosa. An average polymorphism information content (PIC) value of 0.55 and an average number of 3.5 alleles per locus were in the normal range for a self-fertilizing species like lettuce. In addition, the incidental cloning of a microsatellite-containing repeat family, apparently specific for Lactuca, is reported and the implications for the efficient retrieval of single-locus microsatellite sequences are discussed. The microsatellite loci isolated will be useful for distinguishing lettuce cultivars and for screening diversity of genetic resources.     

纳米氢氧化铜暴露对水培生菜生长变化的影响

研究以生菜(Lactuca sativa L.)为考察对象, 探讨纳米氢氧化铜[nano-Cu(OH)₂]不同暴露浓度(0、1和50 mg/L)与时间(7d、14d、21d和28d)对水培生菜生长变化的影响。在生菜叶片涂抹nano-Cu(OH)₂过程中发现, 暴露初期(0—14d)Cu主要富集于生菜的老叶(靶器官)中, 且导致老叶失绿泛黄。同时, 老叶中的Cu会不同程度地向新叶(P<0.05)与根(P>0.05)中转移。在暴露后期(14—28d), nano-Cu(OH)₂胁迫对生菜产生不可逆的损伤致使生菜老叶干枯变黄脱落。虽然老叶的脱落阻断了Cu在生菜体内进一步的富集, 但前期累积在老叶中的Cu会继续向新叶与根中转移。在28d的nano-Cu(OH)₂暴露期间, 生菜主要通过调控体内超氧化物歧化酶(SOD)和过氧化物酶(POD)的含量来抵御Cu的胁迫伤害, 且nano-Cu(OH)₂暴露对生菜生长表现出低浓度促进和高浓度抑制的效应。研究表明, nano-Cu(OH)₂对生菜的主要致毒机理来源于它溶出的Cu离子。