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Plant bio
Plant development I
| Question | Answer |
|---|---|
| Plant cell walls | - plant cells surrounded by thin but rigid cell wall - adjacent cells held together by middle lamella (prevents cell migration) - development based on division/enlargement - plasmodesmata connects, selective molecules pass through |
| Basic body plan | 3 types of organs: - roots - stems - leaves 3 major tissue systems: - dermal - ground - vascular |
| Dermal tissues | - upper/lower epidermal |
| Ground tissues | - palisade parenchyma - bundle sheath parenchyma - spongy mesophyll |
| Vascular tissues | - xylem - phloem |
| Tissues in stems | - epidermis: dermal - cortex/pith: vascular - xylem/phloem |
| Arabidopsis thaliana life cycle | Germination Vegetative growth Floral transition Flowering Maturing siliques (embryogenesis) |
| Animal embryogenesis | Morphogenic changes confined to a brief embryonic phase • Embryogenesis generates rudimentary miniature scale models of the adult • Lineage and mobility important in determining and maintaining cell fate (cell intrinsic information) |
| Plant embryogenesis | • Establishes radial tissue patterning found in stems and roots • Embryo is determinate whereas subsequent development is indeterminate • Cell fate is determined by position rather than cell lineage (cell extrinsic information) |
| Meristems | - form new plant cells |
| Apical meristems | - found at the tips of roots and shoots. Cell division at the apices is necessary for primary growth - contain stem cells that retain ability to divide and produce new cells in an indeterminate manner - root meristem for primary and lateral roots |
| Similarities in animal/plant development | - requires control of cell proliferation and cell fate Asymmetric cell divisions in the zygote generates cells that undergo distinct development patterns. - cell fate is controlled by transcription factors that then regulate gene expression |
| Cell division plane | Periclincal cell divisions - new cell walls form parallel to the tissue surface. Anticlinal cell divisions - new cell walls at 90o to the tissue surface |
| Morphogens | - form generating substance - Morphogen concentration regulates gene expression differentially |
| Position dependent signalling | 1. A cue that signifies position within the developing structure (morphogen) 2. Individual cells must be able to ‘read’ this positional cue 3. Cells must have the capacity to respond to this information |
| Auxins | - function similarly to morphogens in animals - plant hormones - mutant analysis to find genes involved in embryogenesis |
| Monopteros | - transcription factor (TF) responding to auxin |
| Lateral meristems | - such as the vascular cambium and cork cambium are necessary for secondary growth |
| Shoot apex morphology | - peripheral zone: leaf primordia (earliest development stage) - rib zone: structural cells of the stem |
| Apical initials (stem cells) | - retain capacity to divide |
| The arabidopsis SAM (shoot apical meristem) | - comprised of distinct cellular layers and functional zones (stem cell regions/leaf primordia/central tissues |
| WUSCHEL | WUSCHEL promotes cell division in SAM (mutants do not produce SAM) Wuschel is a homeobox transcription factor; induces transcription of genes necessary for SAM function |
| clavata3 | Clavata3 mutants make a bigger meristem Therefore, the function of clavata3 is to inhibit meristem growth. CLAVATA3 is a small extracellular protein (ligand) - controls WUSCHEL expression |
| CLAVATA1 | Wuschel and clavata3 expression doesn't overlap Another gene involved in meristem maintenance is CLV1 CLV1 necessary to inhibit meristematic growth; same phenotype of enlarged meristem as CLV3 CLV1 is a receptor kinase: CLV3 is a ligand for CLV1 |
| The role of cell-extrinsic information in meristem maintenance | • SAM is in the L1, L2 and L3 layers • WUSCHEL induces transcription of genes required for SAM function • WUSCHEL acts non-cell-autonomously - produced in L3 below the SAM (short range stimulator) |
| The role of cell-extrinsic information in meristem maintenance | • WUSCHEL induces expression of CLV3 in L1 and L2 cells of the SAM. • CLV3 also acts non-cell-autonomously (long range inhibitor). • CLV1 expressing cells can regulate WUSCHEL expression in response to CLV3. |
| The role of cell-extrinsic information in meristem maintenance | • CLV1 expression is confined to a small region of cells where WUS is also expressed. |
| Stem cell automatic feedback loop | 1. stem cell increase promotes transcription of CLV3 2. CLV3 binds to CLV1, suppressing WUSCHEL (needed for stem cell number maintenance) 3. stem cell count decreases, CLV3 decreases, WUSCHEL expressed, stem cells increase |
| Other genes involved in SAM | STM - suppresses cell differentiation (Shoot promeristem does not form in stm) AS1 – promotes leaf development |
| Root apical meristem | Quiescent center (QC) cells are similar to the organizing centre in the shoot apical meristem ▪ Generates the stem cells for different tissues around it ▪ In general, similar idea to the SAM, but protected by a root cap |
| Apical meristem similarities | WOX and WUS promote initials in each meristem • Their zones of expression define ‘organizing centres’ for the establishment and maintenance of each meristem • This is achieved through feedback interactions |
| Apical meristem similarities | In both the RAM and SAM the WOX5 and WUS TFs suppressed by peptide-mediated interactions with extracellular receptor kinase |
| Apical meristem similarities | • Patterning processes that exploit regulatory interactions between small peptides (CLV3 and CLE40) and WOX class TFs (WOX and WUS) |
Created by:
reub8n
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