Lecture+14+slides

Plant Physiology Overview

Lecture 14: Introduction

• Focus on plant physiology, including aspects of plant organization, growth, organs, responses, and defenses.

Lecture Plan

• Topics to be covered today:

  • Plant organization & growth

  • Plant organs

  • Plant response & defense

Lecture Outcomes

By the end of this lecture, you should be able to:

1. State the basic levels of plant organization.

2. Describe major plant organs, their anatomy and function.

3. Identify specialized structures in each organ system.

4. Differentiate between monocot and dicot plants based on stem cross sections, venation, and leaf cross sections.

5. Name and describe various factors that plants sense and respond to.

6. Describe plant defense mechanisms with examples.

Tip: Key terms are in bold!

Part 1: Plant Organization & Growth

Hierarchical Organization

• Plants have a hierarchical structure, similar to animals:

  • Organs composed of various tissues

  • Tissues are groups of cells that work together for specific functions

• Organs consist of multiple tissue types for collaboration in functions.

Structure & Function

• Leaves provide surface area for sunlight absorption and gas exchange.

• Stems support and elevate leaves for maximizing photosynthesis.

• Roots anchor plants and absorb water and minerals.

Types of Tissues

• Dermal Tissue: protects the plant's organs.

• Vascular Tissue: supports and transports resources (xylem carries water and minerals, phloem conducts sugars).

• Ground Tissue: involved in photosynthesis and storage.

Growth Patterns

• Determinate Growth: Maximum growth as determined by genetics (common in animals).

• Indeterminate Growth: Plants continue to grow throughout their lifespan.

Origin of Plant Growth

• Growth originates from apical meristems which differentiate into various tissues.

Plant Life Cycles

1. Annuals: Complete lifecycle in one season, often herbaceous; mainly consist of primary tissues.

2. Perennials: Live for multiple years, usually woody; include both primary and secondary tissues.

Types of Plant Bodies

• Primary Plant Body: From apical meristems, consists of primary tissues (herbaceous).

• Secondary Plant Body: In woody plants, includes secondary tissues (wood and bark) from lateral meristems.

Secondary Growth

• Secondary growth involves the vascular cambium and cork cambium in woody species, leading to additional tissue production in stems and roots.

Benefits and Costs of Wood Production

• Advantages: Increased height, better nutrient/water transport, greater conducting capacity.

• Disadvantages: Requires more resources for structural defenses and can delay reproduction.

Part 2: Plant Organs

Basic Organ Types

• Plants have three basic organs:

  • Roots: Take up water and nutrients from the soil.

  • Stems: Support leaves and reproductive structures; raise them to sunlight.

  • Leaves: Main photosynthetic organs, facilitate gas exchange, and dissipate heat.

Function of Roots

• Roots anchor plants, absorb water and minerals, and store carbohydrates.

• **Types of Root Systems:

  • Taproot System:** One large vertical root with lateral roots (common in dicots/gymnosperms).

  • Fibrous Root System: Thin roots spread out (common in monocots).

Stems Structure

• Stems consist of nodes (leaf attachment points) and internodes (spaces between nodes).

• Apical Bud: Leader shoot tip contributing to elongation.

• Axillary Bud: Potential for lateral growth (branches or flowers).

Leaf Structure

• Leaves are designed for various functions:

  • Photosynthesis, gas exchange, heat dissipation.

  • Usually consist of a blade and a petiole (stalk), with specific anatomy for different leaf types (simple vs. compound).

Leaf Venation Patterns

• Dicots: Netted or reticulate venation.

• Monocots: Parallel venation.

Specialized Leaf Types

• Modifications include:

  • Thorns: Modified stems for protection.

  • Tendrils: Aid in climbing.

  • Insect-Trapping: Examples include pitcher plants and sundews.

Part 3: Plant Response & Defense

Environmental Responses

Plants respond to various factors, including:

• Heat/cold stress

• Light

• Internal chemical signals

• Day length

• Hormones

• Gravity

• Touch

• Wounding

• Infection

• Water availability (drought/flooding)

Defense Mechanisms

Constitutive Defenses

• Passive, always present:

  • Physical Armor: Waxy cuticle, thorns, spines to deter herbivores.

  • Chemical Armor: Synthesis of toxic compounds (e.g., alkaloids).

Induced Defenses

• Active defenses triggered by stimuli:

  • Hypersensitive Response leading to programmed cell death to limit pathogen spread.

Hypersensitive Response Process

1. Pathogens enter through wounds.

2. Pathogen's avr gene products interact with host R gene products.

3. Successful interaction triggers defense mechanisms.

Systemic Acquired Resistance (SAR)

• Activated through hypersensitive responses, spread signals to uninfected tissues to prepare defenses.

Communication with Other Plants

• Damage to one plant can trigger defenses in neighboring plants through volatile signals, attracting more effective biological defenses.