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BIO2202 Plant Physiology 1 Water Relations Lecture 5

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Appeared during the Devonian period 390 mill. years ago. ... erection of a diffusion barrier, e.g. leaf abscission sites and wound sealing. ... – PowerPoint PPT presentation

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Title: BIO2202 Plant Physiology 1 Water Relations Lecture 5


1
BIO2202 Plant Physiology 1 Water Relations -
Lecture 5
  • Stomata and the Leaf Epidermis

2
Occurence
  • Appeared during the Devonian period 390 mill.
    years ago.
  • Co-evolved with cuticle and vascular system.
  • Occur in all higher plants above Bryophytes.
  • Mainly on leaves green stems. Also flowers,
    fruits, pods.
  • In dicots scattered randomly across the
    epidermis.
  • In monocots and Gymnosperms typically in rows
    along long axis of leaf

3
Anatomy of the Epidermis
  • The shoot system of vascular plants is covered by
    a waxy cuticle. What is its function?
  • Reduces water loss
  • Repels entry by hydrophillic substances
  • Important deterent to pathogenic attack
  • Thickness is responsive to environmental
    conditions

4
Hydrophobic Structural Components of Plants
  • Cutin
  • Makes up the bulk of the cuticular material.
  • Long chain (16-18C) saturated hydroxy fatty
    acids.
  • Esterified to each other to form a 3-D network.
  • Waxes
  • Long single chain alkanes and saturated fatty
    acid esters.
  • Not cross-linked.

5
T Z Figure 13.1
6
Hydrophobic Structural Components of Plants
  • Suberin
  • polymer, contains dicarboxylic acids,
  • components have longer chain lengths than in
    cutin and some phenolic groups (esp.ferulic
    acid).
  • Generally not found in the cuticle, but a major
    component of the surface layer of underground
    plant parts, the periderm of bark, the Casparian
    strip of the root endodermis.
  • Suberin formation is a frequent response to
    stress or physiological factors which require
    erection of a diffusion barrier, e.g. leaf
    abscission sites and wound sealing.

7
TZ Fig 13.2
8
Cell Types of the Leaf Surface
  • Epidermal cells
  • Typically large and highly vacuolated, /-
    chloroplasts.
  • Often contain crystals of calcium oxalate.
  • Cuticularised outer walls prevent water loss and
    act as a barrier to resist attack by insects and
    pathogens.

9
Cell Types of the Leaf Surface
  • Trichomes
  • Single or multicelled adaptations of epidermal
    tissue.
  • Form hairs, scales, secretory glands.
  • May ? H2O loss by ? boundary layer resistance.
  • May excrete unwanted products e.g. salt in
    halophytes.
  • Frequently exhibit high metabolic activity.

10
Cell Types of the Leaf Surface
  • Subsidiary (accessory) cells
  • Smaller, specialised epidermal cells lying
    adjacent to stomatal guard cells.
  • Usually contain a dense cytoplasm with many
    organelles.
  • Usually without chloroplasts or crystalline
    inclusions.
  • Are involved in the stomatal mechanism.

11
Cell Types of the Leaf Surface
  • Guard cells
  • Complex cells which occur in pairs either side of
    the stomatal pore.
  • Have a high metabolic activity, contain high
    numbers of mitochondria, but few chloroplasts.
  • Two anatomic forms of stomata those with
    kidney-shaped guard cells and elliptical
    pores(dicots) and those with dumbbell-shaped
    guard cells (grasses).
  • Appear to have few or no plasmodesmata, thus are
    isolated from the symplast of surrounding cells.

12
T Z Figure 4.16 (A) Dicot stoma (B) Monocot
stoma
13
The Importance of Guard Cell Microfibrils
  • The pattern and direction of cellulose
    microfibril deposition determines the shape of
    the guard cells and the directions in which they
    expand and contract

14
T Z Figure 4.16 (A) Dicot stoma (B) Monocot
stoma
15
TZ Fig. 4.15
16
Opening and Closing of Stomates
  • Stomata open due to an influx of water into the
    guard cells which causes them to swell
  • Water enters the guard cells because there is a
    reduction in the osmotic potential of the guard
    cells
  • This drop in osmotic potential ( and hence total
    water potential) is a result of the accumulation
    of solutes in the guard cells, in particular K.

17
From Willmer, C.W. (1983) Stomata. Longman,
London.
18
From Willmer, C.W. (1983) Stomata. Longman,
London.
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