Wednesday, June 25, 2014

Some more cedar literature

Couple of recent scientific papers from our colleagues at Simon Fraser University

Identification of Genes in Thuja plicata Foliar Terpenoid Defenses

Adam J. Foster, Dawn E. Hall, Leanne Mortimer, Shelley Abercromby, Regine Gries, Gerhard Gries, Jörg Bohlmann, John Russell, and Jim Mattsson


Thuja plicata (western redcedar) is a long-lived conifer species whose foliage is rarely affected by disease or insect pests, but can be severely damaged by ungulate browsing. Deterrence to browsing correlates with high foliar levels of terpenoids, in particular the monoterpenoid a-thujone. Here, we set out to identify genes whose products may be involved in the production of a-thujone and other terpenoids in this species. First, we generated a foliar transcriptome database from which to draw candidate genes. Second, we mapped the storage of thujones and other terpenoids to foliar glands. Third, we used global expression profiling to identify more than 600 genes that are expressed at high levels in foliage with glands, but can either not be detected or are expressed at low levels in a natural variant lacking foliar glands. Fourth, we used in situ RNA hybridization to map the expression of a putative monoterpene synthase to the epithelium of glands and used enzyme assays with recombinant protein of the same gene to show that it produces sabinene, the monoterpene precursor of a-thujone. Finally, we identified candidate genes with predicted enzymatic functions for the conversion of sabinene to a-thujone. Taken together, this approach generated both general resources and detailed functional characterization in the identification of genes of foliar terpenoid biosynthesis in T. plicata.

Transfusion tracheids in the conifer leaves of Thuja plicata (Cupressaceae) are derived from parenchyma and their differentiation is induced by auxin

Roni Aloni, Adam Foster and Jim Mattsson


Premise of the study: Conifer leaves are characterized by the differentiation of transfusion tracheids either adjacent to the vascular bundle or away from bundles. Toward uncovering the mechanism regulating this differentiation, we tested the hypotheses that transfusion tracheids differentiate from parenchyma rather than from procambium and that auxin acts as an inducer of this process.
Methods: Transfusion tracheids were studied at different developmental stages in both dissected and cleared juvenile and mature leaves. Auxin accumulation was induced by application of either auxin to juvenile leaves or of auxin transport inhibitors in lanolin to stems.
Key results: Transfusion tracheids originate from parenchyma cells during late stages of leaf development, after the activity of the procambium has ceased. Transfusion tracheids differentiate also in the leaf tip, a region in which there are no procambial cells. Application of either auxin or auxin transport inhibitors resulted in a signifi cant increase in transfusion tracheids in leaves. Disruption of the leaf vascular bundle combined with auxin application resulted in direct differentiation of transfusion tracheids from parenchyma cells; the regeneration of a vascular bundle around the disruption was polar and supports both hypotheses.
Conclusions: The results provide experimental support for a parenchymatic origin of the transfusion tracheids in a conifer leaf and for auxin acting as an inducer of these cells. Our results suggest a new model in which auxin production in the leaf apex continues after primary tracheids and parenchyma cells have differentiated, and this late auxin fl ow induces transfusion tracheids from parenchyma cells.

No comments:

Post a Comment