plant embryognesisplant embryogenesisplant embryogenesisplant embryogenesis.ppt

A Signaling Module Controlling the Stem Cell Niche in Arabidopsis Root Meristems Figure 1. CLE40 Is Expressed in the Embryo and Differentiated Root Cells (A) Diagram illustrating root cell positions from proximal (P1) to distal (D1–D4). Color codes indicate cell fates. Stem cells surrounding the QC are outlined in gray. SI, stele initials; QC, quiescent center; CSC, columella stem cell; CC, columella cell; DM, distal meristem; PM, proximal meristem; LRC, lateral root cap; EP, epidermis; C, cortex; EN, endodermis. Gray dots, starch granules. (B–F) CLE40 expression (purple-blue) in embryos. Arrowheads, root progenitor cells (blue) and stele (yellow). High probe concentrations (F) detect CLE40 expression also in the stele. (G) pCLE40:CLE40-GFP expression (green) in the stele and CC of a lateral root. The scale bars represent 25 mm in (B)–(D) and 50 mm in (E)–(G). Compound leaf formation. (a) Developmental sequence of compound leaf formation. The sites of organ initiation are determined in the meristem (m) by local peaks of auxin response resulting from coordinated cell-to-cell auxin flow mediated by PIN1 proteins [7]. This response leads to the exclusion of KNOXI expression from the lateral organ founder cells and young leaf primordia [8,9]. However, in most compound leafed-species, KNOXI gene expression is rapidly turned-on again during leaf primordium development [14,15,17]. Leaflet primordia are initiated at the sites of high auxin-response [43,44]. Localised NAM/CUC3 expression in the axils of the leaflets [49,50], and the repression of auxin response by the ENTIRE (E) protein in the inter-leaflet regions [44] contribute to proper leaflet separation. The auxin-induced repression of the KNOXI genes [43] allows gibberrellin (GA) signalling to be enhanced, which in turn eventually leads to leaflet growth and differentiation. (b) Developing tomato compound leaf with one distal leaflet and two lateral leaflet primordia that are initiated basipetally (from tip to base).