Download Chapter 35: Plant Structure, Growth, and Development

Chapter 35: Plant Structure, Growth, and Development
I.
II.
Plant organization levels:
A.
Organs
1.
Root System – roots
a.
Monocots – fibrous roots
b.
Dicots – taproot system
c.
Root hairs – increase surface area for water absorption
2.
Shoot System – stems and leaves
a.
Nodes – point at which leaves are attached
b.
Axillary bud – potential to form lateral shoot
c.
Terminal bud – at shoot apex (tip)
d.
Apical dominance – inhibit growth of axillary buds
B.
Tissues
1.
Dermal
a.
Epidermis – single layer of cells on the outer surface of plant
b.
Periderm – in woody species only, replaces old epidermal cells
c.
Cuticle – waxy substance produced by epidermal cells for protection
from water loss and pathogen invasion
2.
Vascular
a.
Xylem and Phloem
b.
In root or stem, vascular tissues collectively called the stele
c.
Root – organized into vascular cylinder
d.
Stem/leaves – organized into vascular bundles
3.
Ground
a.
Used for storage, photosynthesis, and general support
b.
Internal to vascular tissue: Pith
c.
External to vascular tissue: Cortex
C.
Cells
1.
Protoplast – cell contents exclusive of cell walls
2.
Parenchyma – thin, flexible primary walls, no secondary walls
a.
example would be fleshy part of the fruit
b.
least specialized cell type, still able to differentiate
3.
Collenchyma –grouped in strands, uneven thickness of primary walls, no
secondary walls
a.
mature: living and flexible, used for support
b.
example would be celery strings
4.
Sclerenchyma – thick secondary walls filled with lignin for hardness
a.
cannot elongate after maturity
b.
because they are dead at functional maturity
c.
sclereids (gritty part of pears) and fibers
5.
Water-conducting xylem
a.
Tracheids
i.
secondary walls interrupted by pits (sections missing secondary
wall) – used for lateral transport
ii.
long and dead at functional maturity
b.
Vessel Elements
i.
shorter, wider, less tapered, and thinner walled than tracheids
ii.
characterized by perforations at end walls for water transport
6.
Sugar-conducting phloem
a.
alive at functional maturity
b.
need companion cell for metabolic needs
c.
sieve-tube members conduct phloem, separated by sieve-plates
d.
sieve-plates resemble strainers
Meristems
A.
III.
IV.
Three primary growth root meristems (all apical meristem)
1.
Protoderm – source of dermal tissue (outermost)
2.
Procambium – source of vascular tissue (innermost)
3.
Ground meristem – source of ground tissue (middle)
B.
Lateral Growth (woody plants only)
1.
Lateral meristems
2.
Vascular cambium
a.
Phloem to the outside
b.
Xylem to the inside
c.
Order of tissue from center of woody plant to the outside:
i.
primary xylem, secondary xylem, vascular cambium, secondary
phloem, primary phloem
ii.
Periderm made up of Cork and Cork Cambium
Leaf Anatomy
A.
Top to Bottom list of tissues:
1.
Upper epidermis
2.
Palisade mesophyll
3.
Vein (Vascular bundles)
4.
Spongy mesophyll
5.
Lower epidermis with guard cells and stomata
Plant Growth and Development
A.
Cytoskeleton determines where the preprophase microtubule bands form
B.
These bands determine which way the cell will divide and expand
C.
Morphogenesis is the result of controlled cell growth and differentiation
D.
Morphology determined by gene expression
E.
Gene expression determined by transcription factors
F.
Positional information used to determine how the cell differentiates
1.
Example: glabra-2 gene (when expressed, turns epidermal cells into root
hairs)
a. When the cell is in contact with one cortical cell, no glabra-2, no
root hair formation
b. When the cell is in contact with two cortical cells, glabra-2 is
expressed, root hair formation ensues
G.
Transcription factors at work:
1.
ABC model of plant part formation:
a.
gene A – sepals and petals
b.
gene B – petals and stamens
c.
gene C – stamens and carpels
2.
Take Home Message: petals and stamens require expression of 2 genes,
sepals and carpels each need only the expression of 1 gene