Dr.A+-+Lecture+4+-+%5Bdermal+and+ground+tissues%5D

Tissues and Growth in Vascular Plants

I. Introduction to Plant Development

• Focus on growth, differentiation, and development.

• Understanding basic morphology of vascular plants, including cell types and tissues.

II. Basic Morphology of Vascular Plants

• Overview of the structure and function of vascular plants.

III. Plant Cell Basics

• Fundamental understanding of plant cells including their roles and characteristics.

IV. Tissues, Cell Types, Meristems, and Secondary Growth

• Study of primary and secondary tissues in plants:

  • Primary tissue systems in typical dicots:

    • Dermal

    • Ground

    • Vascular

    • In roots and leaves

Dermal Tissue System

I. Overview

• Outermost layer of cells in plants.

• Functions:

  • Controls movement in and out of plant cells.

  • Provides protection from the environment.

  • Often covered by a hydrophobic waxy cuticle.

The Cuticle

I. Function and Importance

• Role of cuticle in preventing water loss.

• The 'lotus effect':

  • Water, wax crystals, and debris affecting surface interaction.

  • Epidermal cell microstructures enhance water repellency.

II. Distinction from Other Effects

• The 'locust effect' confused with the lotus effect, emphasizing clarity in terminology.

Unique Features of Plant Structures

I. Fun Fact by Dagmar Voigt et al.

• Wrinkles in bugs facilitate attachment and movement.

Determining Cell Types

I. Five Criteria for Classification

1. Cell shape.

2. Status at maturity: living or dead?

3. Cytoplasm conditions: dense or vacuolated?

4. Distribution within plant: which organ and tissue it belongs to.

5. Cell wall characteristics: primary, secondary, pits, etc.

Dermal Tissue Cell Types

I. Types in Leaves and Stems

• Unspecialized "Pavement" Epidermal Cells:

  • General protection and structural support.

  • Typically lack chloroplasts, indicating no photosynthesis.

II. Trichomes

• Provides fuzzy texture to leaves and stems.

• Functions:

  • Insect protection.

  • Reduces water loss.

  • Reflects sunlight, aiding in temperature regulation.

  • Secretion of chemicals for defense or attraction.

III. Types of Trichomes

• Unicellular Trichomes:

  • Papillary, Filiform, Branched, Stellate.

• Pluricellular Trichomes:

  • Various forms including filiform, branched, and glandular.

Epidermal Guard Cells

I. Functionality

• Form stomata, regulating gas exchange in leaves.

• Respond to environmental changes via guard cell turgor pressure changes.

• Contain chloroplasts, allowing them to photosynthesize.

II. Structure

• Often accompanied by subsidiary cells that assist in turgor regulation.

Root Epidermis

I. Structure and Function

• Contains trichoblasts (hair cells) for water and nutrient absorption and atrichoblasts for spacing between hairs.

Periderm

I. Secondary Epidermis Characteristics

• Arises from cork cambium as a protective layer.

• Controls water loss and facilitates gas exchange.

Ground Tissue System

I. Structural Role

• Fills space between epidermis and vascular systems.

  • In Stems: Contains cortex and pith.

  • In Leaves: Comprises mesophyll.

  • In Roots: Features cortex and pith in monocots.

II. Types of Ground Tissues

• Parenchyma: Involved in storage, secretion, and photosynthesis.

• Collenchyma: Provides flexible support through non-uniform wall thickening.

• Sclerenchyma: Rigid support structure, details to be discussed in later lectures.

Parenchyma Cells

I. Functions and Examples

1. Storage: Starch, protein, water, etc.

2. Secretion: Surrounding ducts.

3. Photosynthesis: Especially in leaf mesophyll cells.

II. Examples of Parenchyma

• Starch storage in amyloplasts.

• Secretory parenchyma active in resin secretion.

Collenchyma Tissues

I. Characteristics

• Non-uniform cell wall thickness for flexible support in young stems and leaves.

• Composition rich in pectin for compressibility.

II. Lab Examples

• Observations of collenchyma in celery petioles and other specimens.