Dr.A+-+Lecture+3-+%5Bcells%2C+tissues%5D
Academic Integrity
Reminder to complete the academic integrity tutorial if not yet done.
Plant Cell Basics
I. Introduction and Growth
Focus on growth, differentiation, and development of plant cells.
II. Basic Morphology of Vascular Plants
Explore the structure and arrangement of various parts of vascular plants.
III. Plant Cell Basics
Understand the fundamental components of plant cells.
IV. Tissues, Cell Types, and Growth
Study plant tissues, different cell types, meristems, and secondary growth processes.
Movement of Cellulose Synthase
Scientific Date: June 9, 2006
Publication: Science, Vol. 312, Issue 5779, pp. 1491-1495
Focus on cellulose synthase enzymes within the plasma membrane.
Utilize confocal microscopy to observe cellulose synthase tagged with Yellow Fluorescent Protein.
Confocal Microscopy Observations
Cellulose Synthase Movement
Movement along microtubules is illustrated using fluorescence.
Merged images show cellulose synthase and microtubules both tagged for visualization.
Plasmodesmata
Definition: Holes in the cell wall allowing intercellular movement of substances.
Cells interconnected through plasmodesmata form a symplasm.
May close as differentiation occurs; not visible with light microscopes, requiring Electron Microscopy (EM).
Structure:
PM (Plasma Membrane)
CW (Cell Wall)
Middle Lamella
Primary Pit Fields
Characteristics:
Thin regions in the primary wall, enriched in plasmodesmata.
Contributes to intercellular communication.
Cell Wall Types
Secondary Cell Walls:
Characteristics: Thicker and more rigid, providing additional support.
Formation of Secondary Walls
Form after the primary wall is established, created by cellulose synthase.
Location: Just inside the primary wall, adjacent to the plasma membrane.
Structure and Composition:
High lignin content (10-25%) adds strength and waterproofing.
Typically lacks pectin and structural proteins present in primary walls.
Often has three layers (S1, S2, S3) with varied orientations of cellulose microfibrils for added fortification.
Functions of Secondary Walls
Structural Support: Rigid structure allowing growth and stress resistance.
Protection: Thick walls protect against pathogens and environmental stress.
Waterproofing: Hydrophobic lignin retains water within vascular systems.
Water Transport: Facilitates efficient conduction in tracheary elements.
Primary vs. Secondary Cell Walls
Primary Cell Walls:
Present in all plant cells, formed during expansion, thin and flexible, no lignin.
Secondary Cell Walls:
Not found in all cells, formed post-expansion, thick and rigid, contain lignin, hydrophobic.
Pits in Cell Walls
Location: Form at primary pit fields where secondary walls do not deposit, leaving thin areas.
Pit Membrane: Result of primary pit fields forming the thin membrane between cells.
Example: Sclereids from Pear Fruit
Images showing the structure of sclereids in pear fruit, approximately 25 µm.
Pits in Xylem Vessel Elements
Visual examples of pits towards rays in xylem elements, typically 100 µm in size.
Preparing Microscopy Slides
Steps in preparing microscope slides:
Fix specimen
Dehydrate with ethanol
Embed in paraffin or resin
Section using microtome
Mount on slide
Stain
Add coverslip and seal for observation.
Plant Anatomy and Development Overview
I. Introduction and Development
Focus on growth, differentiation, and cell morphology.
II. Plant Tissue Systems
Dermal, Ground, and Vascular tissue systems.
Primary vs Secondary Tissues
Primary Tissues:
Formed by primary growth, increasing organ length, found in herbaceous plants.
Secondary Tissues:
Formed by secondary growth, increasing organ width, typical in woody plants.
Summary of Primary Tissue Systems in Dicot Plants
Breakdown of dermal, stem, ground, vascular, root, and leaf systems.
Next Lecture
Focus on the Dermal Tissue System.