Download Chapter 25 - Napa Valley College

The shoot: Primary structure
and development
Repeated modules
(phytomeres)
Shoot meristem
ü leaves
ü Internodes
ü Flowers
The vegetative shoot apical meristem of most flowering plants has a
tunica-corpus organzation
The vegetative shoot apical meristem of most flowering plants
has a tunica-corpus organzation
Anticlinal divisions:
perpendicular to the surface
of the tissue.
Periclinal divisions: parallel to
the surface of the tissue
Elongation of the stem in monocots is
restricted to the base of the internode
Internodal elongation can occur simultaneously over several
internodes
Removing part of a meristem = regeneration of a complete
meristem.
Removing completely the meristem = incipient meristem (at
the base of the leaf) to develop.
Thus growing meristems inhibit the growth of nearby ones.
Phyllotaxy (from Greek phyllo-,
leaf; -taxis, motion/orientation).
The pattern of leaves on a plant is
controlled by the plant hormone
auxin.
Helical
Helical with
elongated
internodes
(alternatedistichous)
(e) opposite
Opposite
(oppositedecussate)
Whorled
(verticillate).
margin
midrib
vein
Sessile leaves do not possess a petiole.
Trichomes: "growth of hair”
Development of the flower
The development of the flower or inflorescence ends the
meristimatic activity of the vegetative shoot apex.
Reproductive apex
Annuals
Perennials
A typical flower consists of four whorls of organs
1)  Sepals
2)  petals
3)  stamens
4)  carpels
A flower bud of the
outcrossing variety of
Clarkia xantiana ssp.
xantiana.
§ petals (red)
§ large anthers (blue
§ small anthers (purple
§ style/stigma (yellow)
At this stage the bud is
only 1 mm in diameter.
Scanning electron micrograph. John Runions.
Homeotic mutations and genes A,B,C
normal
apetala 2 (ap2)
pistillata (pi)
agamous (ag)
SEPALLATA
OR LEAFY
Sepal (se) class A activity, petal class A and class B activity, stamen (st)
B and class C activity and carpel (ca) C activity. Class E activity is
required for the specification of each organ type
Mesophytes are terrestrial plants which are adapted to neither a particularly
dry nor particularly wet environment.
• Usually have broad, flat and green leaves.
• Epidermis is single layered usually with obvious stomata and large
cortex.
Xerophytes
Limited water
• reduced permeability of the
epidermal layer, stomata and
cuticle
• adaptations of the root system to
acquire water from deep
underground sources or directly
from humid atmospheres
• swollen stems, leaves or root
tissues
Bromelia
Hydrophytes
Aquatic plants
• Thin cuticle
• Increased number of stomata
that are open most of time, they
are on either side of leaves
• guard cells are generally inactive
• A less rigid structure
• Commonly flat leaves
• Air sacs for flotation.
• Smaller roots
• Feathery roots
• Specialized roots able to take in
oxygen.
Stem and leaf modifications
tendril: specialized stem, leaf or petiole with a threadlike shape
Pea tendril modified leaf
Virginia creeper modified
stem
Cladophylls: branches or portions of a stem that resemble leaves and
replace them as the main photosynthetic organs of the plant
1. Ocotillo with spines (modified
leaves)
2. Citrus with thorns (modified
branches or stems)
3. Rose with prickles (extensions of
the cortex and epidermis
Attendance
From your book, page 579, questions
3, 7 and 9