Introduction to Plant Development
Keep a green tree in your heart and perhaps the singing bird will come.
...Chinese proverb
Plant Biology and Related Fields
Plant BiologyPlant Biology
AgricultureAgriculture
PharmaceuticalsPharmaceuticals
Basic BiologyBasic Biology
GeneticsGenetics
MolecularCellular Biology
MolecularCellular Biology BiotechnologyBiotechnology
EcologyEcology
EvolutionSystematics
EvolutionSystematics
Already
• What are the major organ systems that make up the plant body?
– what are the major functions of these organs?
• What are the three major tissues that make up plant organs?
– which cell types comprise these tissues? – what are some functions of these cells?
• What cellular structures or cellular processes are unique to plants (or at least highly unusual compared with animals)?
Today and Monday
• How do plant organs, tissues and cells develop?
– Examine Plant Growth,
• the irreversible increase in size that (in plants) almost always results from both cell division and cell enlargement,
– Examine Plant Cell Differentiation,
• the process by which a cell acquires metabolic, structural and functional properties distinct from those of its progenitor,
• Development,
– the sum total of events that contribute to the progressive elaboration of the body of an organism.
Developmental Programs
• Indeterminate growth/development,
– capacity for g/d over an extended period of time,
• vegetative growth and flowering,
– g/d is not genetically limited and can* continue as long as environmental conditions and resources permit.
• Determinate growth/development
– g/d is genetically limited.
Plants display great phenotypic plasticity due to a life-style of indeterminate growth and development.
*plants have genetically limited life spans.
(Toti)potency
…the potential of a single cell to become a progenitor for an entire organism (organ, tissue, or cell type),
– growth and development are genetically and epigenetically controlled in all organisms,
• epigenetics: DNA methylation, chromatin remodeling, etc.
- in contrast with most animals, plants retain the capacity to initiate developmental programs throughout their lives,
- nucleated plant cells are (all) totipotent.
Stem Cells
totipotent
Blastocyst
pluripotent
animal development
multipotent
initials initials
derivatives initials
derivatives
plant development
…all nucleated plant cells are totipotent.
initials
Zygote ---> Several Div.
Apical Meristems
• cells that remain in the meristem are termed initials,
• cells that are displaced from the meristem and later differentiate, are called derivatives.
Shoot Apical Meristem
(SAM)
Root Apical Meristem
(RAM)
initials initials
derivatives initials
derivatives
plant development
…all nucleated plant cells are totipotent.
initials
Totipotency
Primary Meristems
• Derive from apical meristems and produce primary growth (apical-basal),
– Protoderm: dermal meristem,
– Procambium: vascular meristem,
– Ground meristem.
Apoplast / Symplast
Symplast
The interconnected protoplasts and their
plasmodesmata.
Apoplast
The cell wall continuum of a plant.
“Outside of the symplast.”
Plant Structure
SAMShoot Apical Meristem
Distal: away from the point of reference,Proximal: situated near the point of reference (the main body),Central/Peripheral: “girth”, also termed lateral,Adaxial/Abaxial: ad (toward), ab (away).
Leaf Development
• Tunica cells differentiate into a leaf founder cell,
– divide more rapidly and form the leaf primordium, a meristem with determinate growth,
• Sub-organ domains develop, i.e. upper leaf, lower leaf, mesophyll, vasculature, etc.
• L1 (epidermis), L2 (ground tissue) and L3 (vasculature).
Phyllotaxy
• The number and order in which leaf primordia form is genetically determined and is generally
characteristic of species.
Root Morphology
The Root Cap
To reduce friction from growth in soil
The root cap secretes mucilage
The root cap sloughs cells
The Zone of Mitosis(Meristematic)
Makes new cells by Mitosis
Meristematic Cells Divide by Mitosis
The Zone of Elongation
Cells Grow in Size
Vacuole Appears and Grows
Mature Organelles are Produced
More Root Morphology
Casparian Strip:
…suberin (fatty) band around the endodermis.
Endodermis:
...innermost layer of the cortex.
Stele:
…central cylinder within roots and stems of dicots.
Primary Root Morphology
Lateral roots form primary meristems in mature regions of roots,
• form new roots (organs).
Pericycle
…outermost layer of the stele in roots, the source of nascent meristematic cells that gives rise to lateral roots,
…root primordia form,
…protoderm, ground meristem and procambium form,
…root cap forms, pushes through the cortex,
…vasculature forms between stele and differentiating derivatives of the root primordium.
Patterns of Development
ZygoteZygote EmbryoEmbryoCotyledonsHypocotyl
Root
CotyledonsHypocotyl
Root
SAMSAM
RAMRAM
apical/basal, axial
embryogenesis
primarygrowth
SAMSAM Cell Differentiation
Cell Differentiation
Leaf Primordia
Leaf Primordia
Stem Tissues
Stem Tissues
1o Growth1o Growth
primarygrowth
RAMRAM RootTissues
RootTissues
? ? ?
Structure/Function
?
?
1o Growth1o Growth
2o Growth2o Growth
2o Growth2o Growth