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


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 significant 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 flow induces transfusion tracheids from parenchyma cells.
Department of Molecular Biology and Ecology of Plants, Tel Aviv University, Tel Aviv 69978, Israel.
Roni
R
Aloni
Adam
A
Foster
Jim
J
Mattsson
D001692:Biological Transport / Q000187:drug effects; D007210:Indoleacetic Acids / Q000494:pharmacology*; D038081:Organogenesis / Q000187:drug effects*; D018515:Plant Leaves / Q000033:anatomy & histology* / Q000187:drug effects / Q000254:growth & development*; D012038:Regeneration / Q000187:drug effects; D029783:Thuja / Q000033:anatomy & histology* / Q000187:drug effects / Q000254:growth & development*; D052584:Xylem / Q000033:anatomy & histology / Q000187:drug effects
D007210:Indoleacetic Acids
Cupressaceae; Thuja plicata; auxin; auxin transport inhibitors; conifer leaves; resin glands; transfusion tracheids; western redcedar; xylem differentiation; xylem regeneration