Phloem loading in the tulip tree. Mechanisms and evolutionary implications. (1/13)

Minor vein ultrastructure and phloem loading were studied in leaves of the tulip tree (Liriodendron tulipifera; Magnoliaceae). Plasmodesmatal frequencies leading into minor vein companion cells are higher than in species known to load via the apoplast. However, these companion cells are not specialized as "intermediary cells" as they are in species in which the best evidence for symplastic phloem loading has been documented. Mesophyll cells plasmolyzed in 600 mM sorbitol, whereas sieve elements and companion cells did not plasmolyze even in 1.2 M sorbitol, indicating that solute accumulates in the phloem against a steep concentration gradient. Both [(14)C]sucrose and (14)C-labeled photo-assimilate accumulated in the minor vein network, as demonstrated by autoradiography. [(14)C]sucrose accumulation was prevented by p-chloromercuribenzenesulfonic acid, an inhibitor of sucrose-proton cotransport from the apoplast. p-Chloromercuribenzenesulfonic acid largely, but not entirely, inhibited exudation of radiolabeled photoassimilate. The evidence is most consistent with the presence of an apoplastic component to phloem loading in this species, contrary to speculation that the more basal members of the angiosperms load by an entirely symplastic mechanism.  (+info)

Initial frequency of alleles conferring resistance to Bacillus thuringiensis poplar in a field population of Chrysomela tremulae. (2/13)

Globally, the estimated total area planted with transgenic plants producing Bacillus thuringiensis (Bt) toxins was 12 million hectares in 2001. The risk of target pests becoming resistant to these toxins has led to the implementation of resistance-management strategies. The efficiency and sustainability of these strategies, including the high-dose plus refuge strategy currently recommended for North American maize, depend on the initial frequency of resistance alleles. In this study, we estimated the initial frequencies of alleles conferring resistance to transgenic Bt poplars producing Cry3A in a natural population of the poplar pest Chrysomela tremulae (Coleoptera: Chrysomelidae). We used the F(2) screen method developed for detecting resistance alleles in natural pest populations. At least three parents of the 270 lines tested were heterozygous for a major Bt resistance allele. We estimated mean resistance-allele frequency for the period 1999-2001 at 0.0037 (95% confidence interval = 0.00045-0.0080) with a detection probability of 90%. These results demonstrate that (i) the F(2) screen method can be used to detect major alleles conferring resistance to Bt-producing plants in insects and (ii) the initial frequency of alleles conferring resistance to Bt toxin can be close to the highest theoretical values that are expected prior to the use of Bt plants if considering fitness costs and typical mutation rates.  (+info)

Complete plastid genome sequences of Drimys, Liriodendron, and Piper: implications for the phylogenetic relationships of magnoliids. (3/13)

BACKGROUND: The magnoliids with four orders, 19 families, and 8,500 species represent one of the largest clades of early diverging angiosperms. Although several recent angiosperm phylogenetic analyses supported the monophyly of magnoliids and suggested relationships among the orders, the limited number of genes examined resulted in only weak support, and these issues remain controversial. Furthermore, considerable incongruence resulted in phylogenetic reconstructions supporting three different sets of relationships among magnoliids and the two large angiosperm clades, monocots and eudicots. We sequenced the plastid genomes of three magnoliids, Drimys (Canellales), Liriodendron (Magnoliales), and Piper (Piperales), and used these data in combination with 32 other angiosperm plastid genomes to assess phylogenetic relationships among magnoliids and to examine patterns of variation of GC content. RESULTS: The Drimys, Liriodendron, and Piper plastid genomes are very similar in size at 160,604, 159,886 bp, and 160,624 bp, respectively. Gene content and order are nearly identical to many other unrearranged angiosperm plastid genomes, including Calycanthus, the other published magnoliid genome. Overall GC content ranges from 34-39%, and coding regions have a substantially higher GC content than non-coding regions. Among protein-coding genes, GC content varies by codon position with 1st codon > 2nd codon > 3rd codon, and it varies by functional group with photosynthetic genes having the highest percentage and NADH genes the lowest. Phylogenetic analyses using parsimony and likelihood methods and sequences of 61 protein-coding genes provided strong support for the monophyly of magnoliids and two strongly supported groups were identified, the Canellales/Piperales and the Laurales/Magnoliales. Strong support is reported for monocots and eudicots as sister clades with magnoliids diverging before the monocot-eudicot split. The trees also provided moderate or strong support for the position of Amborella as sister to a clade including all other angiosperms. CONCLUSION: Evolutionary comparisons of three new magnoliid plastid genome sequences, combined with other published angiosperm genomes, confirm that GC content is unevenly distributed across the genome by location, codon position, and functional group. Furthermore, phylogenetic analyses provide the strongest support so far for the hypothesis that the magnoliids are sister to a large clade that includes both monocots and eudicots.  (+info)

Biodegradation and saccharification of wood chips of Pinus strobus and Liriodendron tulipifera by white rot fungi. (4/13)

Degradation and glucose production from wood chips of white pine (Pinus strobus) and tulip tree (Liriodendron tulipifera) by several white rot fungi were investigated. The highest weight losses from 4 g of wood chips of P. strobus and L. tulipifera by the fungal degradation on yeast extractmalt extract-glucose agar medium were 38% of Irpex lacteus and 93.7% of Trametes versicolor MrP 1 after 90 days, respectively. When 4 g of wood chips of P. strobus and L. tulipifera biodegraded for 30 days were treated with cellulase, glucose was recovered ot the highest values of 106 mg/g degraded wood by I. lacteus and 450 mg/g degraded wood by T. versicolor. The weight loss of 10 g of wood chip of L. tulipifera by T. versicolor on the nutrient non-added agar under the nonsterile conditions was 35% during 7 weeks of incubation, and the cumulative amount of glucose produced during this period was 239 mg without cellulase treatment. The activities of ligninolytic enzymes (lignin peroxidase, manganese peroxidase, and laccase) of fungi tested did not show a high correlation with degradation of the wood chips and subsequent glucose formation. These results suggest that the selection of proper wood species and fungal strain and optimization of glucose recovery are all necessary for the fungal pretreatment of woody biomass as a carbon substrate.  (+info)

Neotype designation and redescription of Toumeyella liriodendri (Gmelin) (Hemiptera: Coccoidea: Coccidae). (5/13)

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Antiplasmodial activity of aporphine alkaloids and sesquiterpene lactones from Liriodendron tulipifera L. (6/13)

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Chloroplast microsatellite markers in Liriodendron tulipifera (Magnoliaceae) and cross-species amplification in L. chinense. (7/13)

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Bio-functional constituents from the stems of Liriodendron tulipifera. (8/13)

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