Lecture Notes on Stomata and Water Transport in Plants

Overview of Water and CO₂ in Plants

• Transport Mechanisms: Plants uptake, transport, and lose water through various structures.

• Stomatal Function:

  • Stomata regulate gas exchange, allowing CO₂ intake and H₂O loss.
  • Dense stomata on leaves impact photosynthetic efficiency.

• Water Pathway:

  • Water enters roots and navigates through the root architecture into the vascular system (xylem) before reaching leaves.
  • Key components include epidermis, cortex, endodermis, and vascular bundles.

• Root Structure:

  • High surface area root hairs enhance water absorption.

• Aerial Water Loss:

  • Loss occurs primarily through stomata in the leaf's upper epidermis.

• Stomatal Movement Monitoring:

  1. Direct Measurement: Aperture size in micrometers (µm).
  2. Gas Analysis: Using gas exchange data to determine conductance in mmol m² s⁻¹.
  3. Thermal Imaging: Open and closed stomata affect plant temperatures.

• Gas Exchange Balance:

  • Plants strive to balance CO₂ absorption with H₂O loss,
  • Measured by Intrinsic Water Use Efficiency (iWUE): $iWUE = \frac{CO₂ ext{ assimilated}}{H₂O ext{ lost}}$.

• Factors Affecting Stomatal Response Speed:

  • Biochemical Factors: Ion transport, metabolism affecting solute concentration.
  • Structural Factors: Cell wall and cytoskeleton dynamics.

• Stomatal Opening Mechanism:

  • Involves vacuole swelling and cytoskeleton reorganization, allowing guard cells to change shape and open stomata.