Transcript Root system

24
The Plant Body
Figure 24.1 Vegetative Plant Organs and Systems
Concept 24.1 The Plant Body Is Organized
and Constructed in a Distinctive Way
Two systems of plant vegetative organs:
Root system—anchors plant, absorbs water and
minerals, stores products of photosynthesis. Branching
increases surface area.
Shoot system
• Leaves—main photosynthetic organs
• Stems—hold leaves up in the sunlight; connect roots
and leaves
Figure 24.10 Vascular Bundles in Stems (Part 1)
Figure 24.10 Vascular Bundles in Stems (Part 2)
Figure 24.8 Products of the Root’s Primary Meristems (Part 1)
Dicot aka
Figure 24.8 Products of the Root’s Primary Meristems (Part 2)
Concept 24.2 Meristems Build Roots, Stems, and
Leaves
Angiosperm roots begin to grow as a radicle, which
develops into the primary root (taproot) in eudicots.
Taproots often store nutrients (e.g., carrots, beets,
sweet potato).
Monocots form a fibrous root system; roots are equal in
diameter (e.g., grasses, leeks). Also called
adventitious roots.
Some monocots have prop roots to support the shoot
(e.g., corn, banyan trees).
Concept 24.2 Meristems Build Roots, Stems, and
Leaves
Apical meristems can divide indefinitely, so growth of
roots and shoots is indeterminate.
Apical meristems produce primary meristems.
Concept 24.1 The Plant Body Is Organized
and Constructed in a Distinctive Way
Plant development is influenced by three unique
properties:
• Apical meristems
• Cell walls
• Totipotency of most cells.
Apical meristems are always embryonic, producing new
tissues throughout the plant’s life.
Concept 24.1 The Plant Body Is Organized
and Constructed in a Distinctive Way
Cell walls are a rigid extracellular matrix.
Plant morphogenesis occurs through changes in the
plane of cell division at cytokinesis.
This changes the direction of tissue growth.
Cytokinesis can be uneven; location of the cell plate is
determined by differentiation signals early in mitosis.
Figure 24.5 Three Tissue Systems Extend throughout the Plant
Body
Figure 24.4 Plant Embryogenesis
Concept 24.1 The Plant Body Is Organized
and Constructed in a Distinctive Way
In eudicots, the cotyledons begin to grow, and a shoot
apical meristem forms between them.
At the other end of the embryo, a root apical meristem
forms.
Concept 24.1 The Plant Body Is Organized
and Constructed in a Distinctive Way
Three tissue systems are established during
embryogensis:
1. Dermal—forms epidermis, usually one cell layer.
Some cells differentiate:
• Stomata—pores for gas exchange
• Trichomes—leaf hairs, protect from herbivores and
damaging solar radiation
• Root hairs—increase root surface area
Concept 24.1 The Plant Body Is Organized
and Constructed in a Distinctive Way
Aboveground epidermal cells secrete a waxy cuticle.
Limits water loss, reflects damaging solar radiation,
barrier against pathogens.
Concept 24.1 The Plant Body Is Organized
and Constructed in a Distinctive Way
2. Ground tissue—between dermal and vascular tissue;
Three cell types:
• Parenchyma cells
• Collenchyma cells
• Sclerenchyma cells
Concept 24.1 The Plant Body Is Organized
and Constructed in a Distinctive Way
Parenchyma cells
• most abundant
• large vacuoles and thin cell walls
• do photosynthesis
• store protein and starch
In-Text Art, Ch. 24, p. 510 (1)
Concept 24.1 The Plant Body Is Organized
and Constructed in a Distinctive Way
Collenchyma cells
• elongated
• thick cell walls
• provide support
In-Text Art, Ch. 24, p. 510 (2)
Concept 24.1 The Plant Body Is Organized
and Constructed in a Distinctive Way
Sclerenchyma cells
• very thick walls reinforced with lignin
• undergo programmed cell death
• cell walls remain to provide support
In-Text Art, Ch. 24, p. 510 (4)
Concept 24.1 The Plant Body Is Organized
and Constructed in a Distinctive Way
3. Vascular tissue—the transport system
Xylem carries water and minerals from roots to rest of
plant.
Concept 24.1 The Plant Body Is Organized
and Constructed in a Distinctive Way
Phloem
• living cells moves carbohydrates from production
sites to sites where they are used or stored
Concept 24.2 Meristems Build Roots, Stems, and
Leaves
Primary growth—lengthening of shoots and roots;
branching.
Results in nonwoody tissues—herbaceous
Secondary growth—increase in thickness
Woody plants have a secondary plant body consisting
of wood and bark.
Concept 24.2 Meristems Build Roots, Stems, and
Leaves
When cells divide in meristem tissue, one daughter cell
can differentiate, the other remains undifferentiated.
Apical meristems result in primary growth; cell division
followed by cell elongation
Lateral meristems result in secondary growth
Figure 24.6 Apical and Lateral Meristems
Figure 24.6 Apical and Lateral Meristems (Part 2)
Figure 24.6 Apical and Lateral Meristems (Part 3)
Concept 24.2 Meristems Build Roots, Stems, and
Leaves
Root apical meristems
Daughter cells on the root tip form the root cap —
protects root as it pushes through soil.
Root cap cells detect gravity and control downward
growth of the root.
Above the root cap, three zones result as cells divide and
mature.
Figure 24.7 Tissues and Regions of the Root Tip
Concept 24.2 Meristems Build Roots, Stems, and
Leaves
Root primary meristems give rise to root tissues:
• Protoderm produces the epidermis; many epidermal
cells have root hairs.
• Ground meristem produces the cortex, consisting of
parenchyma cells and the endodermis.
Endodermal cells have waterproof suberin in the cell
walls and can control movement of water and mineral
ions into the vascular system.
Concept 24.2 Meristems Build Roots, Stems, and
Leaves
• Procambium produces the vascular cylinder (stele),
made up of pericycle, xylem, phloem.
Pericycle has 3 functions:
• Tissue within which lateral roots arise.
• Contributes to secondary growth by giving rise to lateral
meristems.
• Membrane transport proteins export nutrient ions into
the xylem.
Figure 24.9 Root Systems of Eudicots and Monocots (Part 1)
Figure 24.9 Root Systems of Eudicots and Monocots (Part 2)
Figure 24.9 Root Systems of Eudicots and Monocots (Part 3)
Concept 24.2 Meristems Build Roots, Stems, and
Leaves
Shoots are composed of repeating modules (phytomers).
Each has a node with attached leaves, internode (stem
section), and one or more axillary buds.
Shoots grow by adding more phytomers.
Concept 24.2 Meristems Build Roots, Stems, and
Leaves
Shoot apical meristem also produces three primary
meristems, which give rise to shoot tissue systems.
Stems have vascular bundles with xylem, phloem, and
fibers.
The bundles have different arrangements in eudicots
and monocots.
Concept 24.2 Meristems Build Roots, Stems, and
Leaves
Stem modifications
Potato tubers are underground stems; the “eyes” are
axillary buds.
Many desert plants have enlarged stems that store
water.
Strawberry plant runners are horizontal stems from which
roots grow. If the runners break, new plants develop on
either side (asexual reproduction).
Figure 24.11 Modified Stems (Part 1)
Figure 24.11 Modified Stems (Part 2)
Figure 24.11 Modified Stems (Part 3)
Concept 24.2 Meristems Build Roots, Stems, and
Leaves
Growth of leaves is determinate: they stop growing once
they reach a predetermined mature size.
Leaves consist of a blade, attached to the plant stem by
a petiole.
Leaves are often oriented perpendicular to the sun’s
rays, to maximize the amount of light for
photosynthesis.
Concept 24.2 Meristems Build Roots, Stems, and
Leaves
Leaf anatomy is well adapted to:
• Carry out photosynthesis
• Exchange O2 and CO2 with the environment
• Limit evaporative water loss
• Export products of photosynthesis to the rest of the
plant
Concept 24.2 Meristems Build Roots, Stems, and
Leaves
Leaf mesophyll has two zones of photosynthetic
parenchyma tissue.
A network of air spaces allows CO2 to diffuse to
photosynthetic cells.
Vascular bundles form veins that extend to within a few
diameters of all cells—to ensure transport of water and
minerals in and carbohydrates out.
Figure 24.12 Eudicot Leaf Anatomy
Concept 24.2 Meristems Build Roots, Stems, and
Leaves
Leaf surfaces are covered with nonphotosynthetic
epidermal cells.
They secrete the waterproof cuticle.
Water and gases are exchanged through pores called
stomata.
Concept 24.2 Meristems Build Roots, Stems, and
Leaves
Leaves can also be modified for other functions:
• Nutrient storage (e.g., onion bulbs)
• Water storage (e.g., in succulent plants)
• Protection (e.g., cacti have spines that are modified
leaves)
• Tendrils that wrap around structures to support
climbing plants (e.g., peas)
Concept 24.2 Meristems Build Roots, Stems, and
Leaves
Many eudicot stems and roots have secondary growth:
Wood and bark are derived by secondary growth from
the two lateral meristems:
• Vascular cambium produces secondary xylem (wood)
and secondary phloem (inner bark).
• Cork cambium produces waxy-walled protective cells;
some become the outer bark.
Figure 24.13 A Woody Twig Has Both Primary and Secondary Tissues
Figure 24.13 A Woody Twig Has Both Primary and Secondary Tissues (Part 2)
Figure 24.13 A Woody Twig Has Both Primary and Secondary Tissues (Part 3)
Concept 24.2 Meristems Build Roots, Stems, and
Leaves
A stem or root increases in diameter when cells of the
vascular cambium divide, producing secondary xylem
cells toward the inside and secondary phloem cells
toward the outside.
Some cells of the secondary phloem divide and form a
cork cambium, which produces layers of protective
cork.
The cork soon becomes the outermost tissue of the stem
or root.
Concept 24.2 Meristems Build Roots, Stems, and
Leaves
Cork cambium produces cells to the inside, forming the
phelloderm.
Periderm—secondary dermal tissue composed of cork
cambium, cork, and phelloderm
Bark—periderm plus secondary phloem
Concept 24.2 Meristems Build Roots, Stems, and
Leaves
In temperate zones, annual rings form in the wood.
In spring, tracheids or vessel elements tend to be large in
diameter and thin-walled.
In summer, thick-walled, narrow cells are produced.
Figure 24.14 Annual Rings
Concept 24.3 Domestication Has Altered Plant Form
Humans domesticate crop plants by artificial selection for
phenotypes best suited for agriculture.
Corn was domesticated from the wild grass teosinte,
which still grows in Mexico.
Teosinte is highly branched; corn has a single shoot.
Branching is controlled by a single gene that regulates
axillary buds.
Figure 24.15 Corn Was Domesticated from the Wild Grass Teosinte
Concept 24.3 Domestication Has Altered Plant Form
Brassica oleracea (wild mustard) is the ancestor of
several morphologically diverse crops: kale, broccoli,
brussels sprouts, cabbage.
Starting with diverse populations of wild mustard,
humans selected and planted seeds from variants with
traits they found desirable.
Figure 15.4 Many Vegetables from One Species