University of California, Davis

PLB 112

Outline & Announcements – Tuesday 05/28/19 VI. ROOT DEVELOPMENT // D. GENETIC CONTROL OF RAM ORGANIZATION ANNOUNCEMENTS • Discussion Section this week – GMO Discussion • Homework #5 due next Tuesday • Videos Due Tomorrow, Wednesday @ 11:59 pm • The Video Presentation Schedule has been posted • Final Exam Friday, 6/7 @ 1:00 pm – Study Questions for Final are on Canvas Plant Biology 112 Spring 2019 Phyllotaxy Model Based on Polar Auxin Transport • Auxin maximum develops at P0 • Auxin induces PIN1 gene expression • PIN1 becomes oriented to funnel auxin to center of primordium • PIN1 becomes oriented to funnel auxin from center of primordium down into internal tissues • Leaf primordium becomes an auxin sink due to arrangement of PIN1 • Auxin sink activity of primoridia create new auxin maximum • New P0 forms at auxin maximum Progression of Organ Positioning and Outgrowth During the Phyllotactic Cycle (viewed from top) Reinhardt 2005 Auxin gradient – red (only auxin in L1 is shown) Auxin flow – arrows Shoot Root Vegetative Development From Taiz and Zeiger Dolan et al. 1993 Taiz and Zeiger apicalbasal Root Tip is Divided Into Four Developmental Zones Along its Apical-Basal Axis Apical–Basal and Radial Organization of the Root Tip apicalbasal radial Taiz and Zeiger Organization of the Root Apical Meristem Taiz and Zeiger Stem Cells in the Shoot and Root Apical Meristems From Vernoux & Benfey 2005 Stem Cells (blue) Organizing Center (red) Organization of the Root Apical Meristem Taiz and Zeiger Cortex/Endoderm Initial Daughter Cell Endoderm Cortex Generation of Two Tissue Types from a Single Initial Cell with Two Successive Asymmetric Divisions Asymmetric Division Asymmetric Division Pulianmackal et al. 2014 Laser ablation of QC cells Laser Ablation of All Quiescent Center Cells Regeneration of the RAM Following Laser Ablation of All Quiescent Center Cells QC S Col i S S S Si Si Si Si QC Col i Col i Col i QC Former Si Cells S Col i S S S Si Si Si Former S Cells Si Col i Col i Col i QC Former Si Cells Dead QC S Col i S S S Si Si Si Si Col i Col i Col i Dead QC Laser Ablation Regeneration