Transcript ch 35 tissue organ

Plant Structure, Growth, and
Development
• Plant hierarchy:
– Cells
– Tissue: group of similar cells with similar
function: Dermal, Ground, Vascular
– Organs: multiple kinds of tissue, very diverse
function
– Organ systems
– Organism
35.1
Roots
Roots
– an organ that anchors a vascular plant.
– Absorbs water & inorganic nutrients
– Storage of nutrients
• Types of roots
– Taproot Systems
• Consist of one main vertical root
– Gives rise to lateral roots (like branches)
» Taproots store organic nutrients used in flowering and fruit production.
– Fibrous Root System – a mat of roots that spread out below the soil
– Root Hair – an extension of a root that gathers nutrients
Root cap covers root tip (apical meristem): primary growth site
epidermis, ground and vascular tissue.
Mycorrhizae: mutualistic fungi and plant roots.
Roots Cont.
http://belizebreeze.com/images/lamanai_tree_roots_rev_lowres.jpg
http://quorumsensing.ifas.ufl.edu/HCS200/images/stems&roots/korni.jpg
Stems
• an organ consisting of an altering system of:
– nodes: point where leaves are attached
– internodes: stem segments between nodes
• Axillary bud – a structure that potentially forms a
lateral shoot otherwise known as a branch
– At the end of this branch is a terminal end which develops
leaves.
• Apical Dominance
– A phenomenon where the proximity of the terminal bud inhibits
the growth of an axillary bud
• This is an evolutionary adaption where resources are concentrated
toward elongation; it also increases the plant’s exposure to light.
– If one is removed then the bud stimulates the growth of an axillary
bud which produces more shoots.
» That is why pinching back a plant makes it bushier.
Apical Dominance
Stems Cont.
http://www.infovisual.info/01/015_en.html
Xylem and phloem
Sieve cells
Leaves
• the main photosynthetic organ
of vascular plants
– Leaves usually consist of:
• blade
• petiole – Joins the leave to a
node on the stem
• veins – vascular tissues of
the leaves
– Veins are how monocots and
dicots differ
• Monocots have parallel veins
• Dicots are multi branched
• There are many different types
of modified leaves
– Spines, tendrils, storage,
bracts (poinsettias),
reproductive (succulents)
http://photos.somd.com/data/500/LEAF.jpg
http://academic.kellogg.cc.mi.us/herbrandsonc/bio111/images/stems/stems.4.jpg
Three Types of Tissue:
Dermal, Vascular, and Ground
Tissue system – one or more tissues organized into a functional unit
Dermal Tissue System
– Outer protective covering (like skin)
• Non woody plants – single layer of epidermis
• Cuticle – A waxy coating on the leaves and the stems that helps prevent
water loss.
• Woody plants – periderm replaces epidermis
Vascular Tissue System
– Carries out long distance transport between root and shoot.
• Two vascular tissues
– Xylem – conveys water and dissolved mineral up to shoots
– Phloem – transports organic nutrients to where they are needed.
• Vascular tissue of a root = stele
Ground Tissue System
– Tissues that are neither dermal nor vascular
Tissue System
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/leafstru.gif
Plant Cells
Type of cells found in plants:
– Parenchyma Cells – a relatively unspecialized plant cell type that
carries out most of the metabolism, synthesizes and stores organic
products, and develops into a more differentiated cell type.
– Guard cells
– Sieve tube cells
– Tracheoid cells
– Palisade mesophyll: Photosynthesis
– Spongy mesophyll: spaces allow the exchange of gases
35.2 - 35.4
Meristems generate cells for new
organs
• Apical meristems elongate
shoots and roots through
primary growth
• With the process of primary
growth it also allows roots to
extend throughout the soil and
for shoots to increase there
exposure to light and CO2
• Lateral meristems add girth to
woody plants through
secondary growth.
• Root cap: secretes a mucus
that allows tip growth through
soil
Primary Growth Roots
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Primary growth produces the primary
plant body.
ROOTS the root tip is covered by a
thimble-like cap which protects the
vulnerable apical meristem as the root
pushed through the soil.
GROWTH occurs just behind the root
tip, zone of cell division, elongation,
and maturation.
The zone of cell division: produced in
the apical meristem
The zone of elongation, root cells
elongate and new cell are added
allowing the root to dive further into the
soil.
The zone of Maturation, cells
complete their differentiation and
become functionally mature.
Primary Growth of Shoots
• The apical meristem
of a shoot is a dome
shaped mass which is
located in the terminal
bud, where it gives
rise to a repetiton of
internodes and leaf
bearing nodes.
The Vascular Cambium and
secondary Vascular tissue
• The vascular cambium
develops from parenchyma
cells into a meristematic
cylinder that produces
secondary xylem to the inside
and secondary phloem to the
outside.
• Older layers of secondary
xylem (heartwood) eventually
become inactive.
• Younger layers (sapwood) still
conduct water.
• Only the youngest secondary
phloem is active.
Cork Cambia and the Production of
Periderm
• The cork cambia is a
lateral meristem:
• Makes dermal tissue or
periderm.
• The bark on the other
hand consists of all the
tissues external to the
vascular cambium which
include secondary
phloem and periderm.
35.5
Growth, Morphogenesis, and the
Differentiation Produce the Plant Body
• Morphogenesis: The development of body form and organization
Each cell in the plant body contains the same set of genes, exact
copies of the genome present in the fertilized egg.
• Different patterns of gene expression among cells cause the
cellular differentiation that creates a diversity of cell types.
• The three developmental processes of growth, morphogenesis,
and cellular differentiation act in concert to transform the fertilized
egg into a plant.
Growth: Cell Division and Expansion
• Cell division and self-expansion are primary factors for growth
• Plant cells rarely expand in all directions, their greatest expansion
occurs in the plants main axis.
• Growing plant cells expand mainly through water uptake. In a
growing cell, enzymes weaken cross–links in the cell wall, allowing it
to expand as water diffuses into the vacuole by osmosis.
• Orientation of the cytoskeleton also affects direction of cell
elongation by controlling the orientation of cellulose micro fibrils.
Preprophase Band
http://www.nature.com/nrm/journal/v2/n1/images/nrm0101_040a_f1.gif
Differentiation and Pattern Formation
• Development of tissues and organs in specific locations (pattern
formation) depends on cells ability to detect and respond to
positional info.
– Polarity-is the idea that a cell (egg) has diff. concentration of contents
– Homeotic genes often control morphogenesis and also mediate many
of the other events in an individual’s development, such an initiation of
an organ.
• Gene Expression and control of Cellular Differentiation
– Cellular differentiation: selective gene expression
– Cellular differentiation depends on a large extend on positional
information, where a particular cell is located relative to other cells.
Gene Expression
http://www.biosci.ohio-state.edu/~bdinglab/Research/Resear7.jpg
Shifts in Development: Phase Change
• Internal or environmental cues may cause a
plant to switch from one developmental
phase to another.
•
From the development of juvenile leaves
to the development of mature leaves, these
are called phase changes.
Juvenile vs. Adult Leaves
http://upload.wikimedia.org/wikipedia/en/c/ce/Pinus_pinea.jpg
Genetic Control of Flowering
– Research on organ identity genes in developing flowers
provides an important model of pattern formation.
• The ABC model of flower formation identifies how 3 classes of
organ identity genes control the formation of sepals, petals stamens,
and carpel’s.
– The floral organs develop in four circles, or whorls: Sepals form the
fourth (outermost) whorl; petals form the third; stamens form the
second; and carpels form the first (innermost) whorl. Plant biologists
have identified several organ identity genes that regulate the
development of this characteristic floral pattern. Organ identity
genes, also called plant homeotic genes, code for transcription
factors. Positional information determines which organ identity
genes are expressed in a particular floral organ. The result is
development of an emerging leaf into a specific floral organ, such
as a petal or a stamen.