Occurrence of the allene oxide cyclase in different organs and tissues of Arabidopsis thaliana

Occurrence of an essential enzyme in jasmonate (JA) biosynthesis, the allene oxide cyclase, (AOC) was analyzed in different developmental stages and various organs of Arabidopsis thaliana plants by immuno blot analysis and immunocytological approaches. Levels of AOC and of the two preceding enzymes in JA biosynthesis increased during seedling development accompanied by increased levels of JA and 12-oxophytodienoic acid levels after 4 and 8 weeks. Most tissues including all vascular bundles and that of flower buds contain AOC protein. Flowers shortly before opening, however, contain AOC protein preferentially in ovules, stigma cells and vascular bundles, whereas in anthers and pollen AOC could not be detected. The putative roles of AOC and JA in development are discussed.     

Characterization of four lectin-like receptor kinases expressed in roots of Medicago truncatula. Structure, location, regulation of expression, and potential role in the symbiosis with Sinorhizobium meliloti

To study the role of LecRK (lectin-like receptor kinase) genes in the legumerhizobia symbiosis, we have characterized the four Medicago truncatula Gaernt. LecRK genes that are most highly expressed in roots. Three of these genes, MtLecRK7;1, MtLecRK7;2, and MtLecRK7;3, encode proteins most closely related to the Class A LecRKs of Arabidopsis, whereas the protein encoded by the fourth gene, MtLecRK1;1, is most similar to a Class B Arabidopsis LecRK. All four genes show a strongly enhanced root expression, and detailed studies on MtLecRK1;1 and MtLecRK7;2 revealed that the levels of their mRNAs are increased by nitrogen starvation and transiently repressed after either rhizobial inoculation or addition of lipochitooligosaccharidic Nod factors. Studies of the MtLecRK1;1 and MtLecRK7;2 proteins, using green fluorescent protein fusions in transgenic M. truncatula roots, revealed that they are located in the plasma membrane and that their central transmembrane-spanning helix is required for correct sorting. Moreover, their lectin-like domains appear to be highly glycosylated. Of the four proteins, only MtLecRK1;1 shows a high conservation of key residues implicated in monosaccharide binding, and molecular modeling revealed that this protein may be capable of interacting with Nod factors. However, no increase in Nod factor binding was found in roots overexpressing a fusion in which the kinase domain of this protein had been replaced with green fluorescent protein. Roots expressing this fusion protein however showed an increase in nodule number, suggesting that expression of MtLecRK1;1 influences nodulation. The potential role of LecRKs in the legume-rhizobia symbiosis is discussed.     

Noma: experiences with a microvascular approach under West African conditions

Noma (cancrum oris) is a serious ulcerating disease that generally begins in the gingival sulcus of children. One of the main areas of prevalence today is West Africa. If noma is survived, it results in disfiguring midfacial defects and intense scarring. Oral incompetence is often combined with trismus resulting from scar formation or bony fusion between the maxilla and the mandible. Reconstructive approaches with pedicled flaps from the head or shoulder area for closure of the outer defects have been prone to donor-site complications or have not properly addressed the trismus, leading to high recurrence rates. During three West African Interplast missions, a single-stage procedure was developed for reconstruction of the inner and outer linings of the oral, nasal, and paranasal cavities, with restoration of jaw function. The procedure consists of radical scar excision, placement of an external distractor for mouth opening, and primary closure of the defect with a folded free parascapular flap for full-thickness coverage. Twenty-three patients with various noma-related defects were treated with this procedure; two cases are described in detail. This combined treatment can be a safe successful procedure for patients with noma, especially those with severe soft-tissue destruction and profound trismus, even under demanding surgical conditions.     

Enzymes of jasmonate biosynthesis occur in tomato sieve elements

The allene oxide cyclase (AOC) is a plastid-located enzyme in the biosynthesis of the signaling compound jasmonic acid (JA). In tomato, AOC occurs specifically in ovules and vascular bundles [Hause et al. (2000) Plant J. 24; 113]. Immunocytological analysis of longitudinal sections of petioles and flower stalks revealed the occurrence of AOC in companion cells (CC) and sieve elements (SE). Electron microscopic analysis led to the conclusion that the AOC-containing structures of SE are plastids. AOC was not detected in SE of 35S::AOCantisense plants. The enzymes preceding AOC in JA biosynthesis, the allene oxide synthase (AOS) and the lipoxygenase, were also detected in SE. In situ hybridization showed that the SE are free of AOC-mRNA suggesting AOC protein traffic from CC to SE via plasmodesmata. A control by in situ hybridization of AOS mRNA coding for a protein with a size above the exclusion limit of plasmodesmata indicated mRNA in CC and SE. The data suggest that SE carry the capacity to form 12-oxo-phytodienoic acid, the unique precursor of JA. Together with preferential generation of JA in vascular bundles [Stenzel et al. (2003) Plant J. 33: 577], the data support a role of JA in systemic wound signaling.     

MPB2C,a microtubule-associated plant protein binds to and interferes with cell-to-cell transport of tobacco mosaic virus movement protein

The movement protein of tobacco mosaic virus, MP30, mediates viral cell-to-cell transport via plasmodesmata. The complex MP30 intra- and intercellular distribution pattern includes localization to the endoplasmic reticulum, cytoplasmic bodies, microtubules, and plasmodesmata and likely requires interaction with plant endogenous factors. We have identified and analyzed an MP30-interacting protein, MPB2C, from the host plant Nicotiana tabacum. MPB2C constitutes a previously uncharacterized microtubule-associated protein that binds to and colocalizes with MP30 at microtubules. In vivo studies indicate that MPB2C mediates accumulation of MP30 at microtubules and interferes with MP30 cell-to-cell movement. In contrast, intercellular transport of a functionally enhanced MP30 mutant, which does not accumulate and colocalize with MP30 at microtubules, is not impaired by MPB2C. Together, these data support the concept that MPB2C is not required for MP30 cell-to-cell movement but may act as a negative effector of MP30 cell-to-cell transport activity.     

Repeated freeze–thaw cycles induce embolism in drought stressed conifers (Norway spruce,stone pine)

Freezing and thawing lead to xylem embolism when gas bubbles caused by ice formation expand during the thaw process. However, previous experimental studies indicated that conifers are resistant to freezing-induced embolism, unless xylem pressure becomes very negative during the freezing. In this study, we show that conifers experienced freezing-induced embolism when exposed to repeated freeze-thaw cycles and simultaneously to drought. Simulating conditions at the alpine timberline (128 days with freeze-thaw events and thawing rates of up to 9.5 K h(-1) in the xylem of exposed twigs during winter), young trees of Norway spruce [Picea abies (L.) Karst.] and stone pine (Pinus cembra L.) were exposed to 50 and 100 freeze-thaw cycles. This treatment caused a significant increase in embolism rates in drought-stressed samples. Upon 100 freeze-thaw cycles, vulnerability thresholds (50% loss of conductivity) were shifted 1.8 MPa (Norway spruce) and 0.8 MPa (stone pine) towards less negative water potentials. The results demonstrate that freeze-thaw cycles are a possible reason for winter-embolism in conifers observed in several field studies. Freezing-induced embolism may contribute to the altitudinal limits of conifers.     

Synthesis and conformation of four 16,17-diols in the 3-methoxy-13alpha-estra-1,3,5(10)-triene series

All four diasteromeric 16,17-diols in the 3-methoxy-13alpha-estra-1,3,5(10)-triene series have been synthesized. The trans-diols 1 and 2 can be obtained by hydroborating the 17-enol acetate 6 (61%, ratio 27:73, preferred alpha attack). OsO(4) dihydroxylation of the olefin 7 yielded the cis-diols 3 and 4 (ratio 13:87). The dihydroxylation proceeds with preference for beta attack caused by a C-ring twist-boat form of 7. The conformations of the diols 2 and 4, the 17-benzyl-17-hydroxy compounds 9 and 10 (obtained by Grignard reaction), and the 16alpha-bromo-17beta-hydroxy compound 8 were determined by X-ray analysis and by 1H NMR spectroscopy in solution. Some compounds, in spite of a 17beta-hydroxy group, had a conformation with a ring C chair form (4, 8, 9) caused by intermolecular interaction in the solid state. The rest of the compounds studied here (2, 10) possessed a conformation with a ring C twist-boat form, which has been also found for all 17beta-substituted compounds in solution. The preferred conformation of the D-ring with 17beta-substituents seems to be the 16beta-envelope form or near this form, but the existence of the 16alpha-envelope form (inversion of the ring D) for some compounds showed great variance in the conformation of ring D, which is substituent dependent.     

Diagnosing ancient diphyllobothriasis from Chinchorro mummies

Diphyllobothrium pacificum has been reported as a human parasite from coprolites and skeletons in Peru and Chile. Our analysis of Chinchorro mummies from Chile provides the oldest evidence of D. pacificum directly associated with human mummies. These mummies date between 4,000 and 5,000 years ago. The basis for our diagnosis is presented. We find that the size of the eggs in the mummies is smaller than other discoveries of D. pacificum. We suggest that this is due to the peculiar circumstances of preservation of parasite eggs within mummies and the release of immature eggs into the intestinal tract as the tapeworms decompose after the death of the host. This information is important to consider when making diagnoses from mummies.