Heslop-Harrison Plant development and meristems BS1003
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Transcript of Heslop-Harrison Plant development and meristems BS1003
Cell and Developmental BiologyModule BS1003
Plant Cell and Developmental Biology
Pat Heslop-Harrison [email protected]#BS1003 on Google+
Plant Development and Meristems
From Jim Haseloff / Gerd Jürgens, Tübingen
FernsGymnospermsAmborellaWaterliliesBasal Magnoliids
Monocots
Eudicots
Seed plant Tree of LifeSearch APGIII
http://www.mobot.org/mobot/research/apweb/
Where does a multicellular organism come from?
• Single-celled embryo
• Plant: usually a seed
• What to study?– Model species: principles are
universal• Comparative analysis
Embryogenesis in Arabidopsis
A. Asymmetric first division B-D. Cells have different FATES Suspensor > transverse divisionsEmbryo > precise cell divisions D. OCTANT: suspensor & embryo lineagesE-F. GLOBULAR: protoderm forms> future epidermis;G. HEART: cotyledons initiated& root meristemH. TORPEDO: axis extension > future hypocotylI. COTYLEDONARY: cotyledon greening, vascular tissues
A D E F
GH I
B C
SKILL: Drawing, emphasizing theimportant parts, not artistic quality!TERMINOLOGY:
Zygote
• From Chun-Ming Liu via biology.kenyon.edu http://tinyurl.com/embryogenesis Arabidopsis Embryogenesis
From Jim Haseloff / Gerd Jürgens, Tübingenhttp://www.plantsci.cam.ac.uk/Haseloff/teaching/PlantSci2_index/notes/notes.html
http://tinyurl.com/Haseloff Lectures 1 and 3 and http://tinyurl.com/embryogenesis
Disturbed apical basal polarity & No bilateral symmetryEarliest defect at first division of zygote > symmetrical
divisionDivision symmetry linked to a change in cell fateSupports hypothesis of asymmetric distribution of cell
fate determinants
wt
gnomgnom
wt
Early embryo development in gnom
gnomForms ball-like embryos
without apical/basal organs
Lacks ability to establish polarity & morphogenesis
GNOM GENE INVOLVED IN EMBRYO DEVELOPMENT (POLARITY)
Mutants are useful tools to understand development
Gerd Jürgens, Tübingen
Summary: Two components of embryogenesis1. PATTERN FORMATION Embryo must establish Polarity (apical-basal &
radial) > Control of cell divisionEmbryo must achieve correct shape
(morphogenesis)> Control of cell division & expansion
2. DIFFERENTIATION(Cells in different regions become specialized
Eg. Chloroplast differentiation in cotyledons/vascular tissues in hypocotyl, radicle & cotyledons)
> Control of Cell Fate???
Building the plant bodyplan…….Complex processes repeated with great precision in
every developing embryoControl mechanisms must also be very carefully co-
ordinated.
Is plant cell fate controlled by:
(1) Segregation (or inheritance) of determinants at each division?
(2) Positional information?
By the end of this lecture you will:
1. Use four ways to understand and study developmental processes
2. Understand pattern formation and plant embryogenesis
3. Know about the structure and development of plant meristems
4. Know about totipotency and cell development
5. Have insight into cell function and communication
Meristems & Organogenesis
Does form reflect function?
What is growth? How is growth
controlled? Where do the major
organ systems of the plant
originate?
How are they generated?
Brooker Chapters 35 & 36
Campbell & Reece Section 6
Raven section VI Chapters 36 & 42
Questions…
Evidence for the role of positional information in specifying cell fate
PLANT TISSUE CULTURES
Cells within differentiated tissues, such as leaf tissue can be induced to REDIFFERENTIATE into a completely new embryo or plant, containing the FULL RANGE OF CELL TYPES
ie Change the relative position (local signals) of cells in the leaf
totipotency!Haberlandt (Austria): The results of attempts to culture isolated vegetative cells from higher plants in simple nutrient should give insight to the properties and potentialities which the cell as an elementary organism possesses … “I am not making too bold a prediction if I point to the possibility that, in this way, one should successfully cultivate artificial embryos from vegetative cells” (1902)
PLANT TISSUE CULTURE
Single cell regeneration demonstrates totipotency PLANT CLONING
Herbert Street (Leicester), Ted Cocking/Mike Davey (Nottingham), Nitsch, Steward, Maheshwari, Skoog: defining nutritional and developmental aspects of cultured plant cells: early 1970s
What does this mean for plants?
1. Differentiated plant cells are usually NOT irreversibly committed
2. They contain all the genetic information necessary for all aspects of plant development.
3. There is no loss of genetic information during development
4. Their relative ‘position’ is important in signalling to maintain their fate.
A cell is totipotent if it is has the ability to divide and re-differentiate to form a whole
organism
In contrast we easily cannot change the fate of differentiated animal cells without drastic measures
Nuclear transplant > genetic re-programming of udder cell nucleus in enucleated egg cytoplasmI am a clone
Plant Cells > change of position (external signals) sufficient to re-programme the nucleusCloning in plants is comparatively easy
What you need to know:• Pattern formation (embryogenesis)
– Materials and methods• Model species (Arabidopsis, tobacco)• Experimental biology• Mutants• Evolution• DNA sequence analysis
– Growth and development• Essential processes
– From the single-celled zygote to the embryo
• Asymmetrical first division• Pattern formation and polar/radial symmerty
– From the embryo to plant with reiteration of patterns
• Positional information in cell fate– Totipotency and regeneration
MERISTEM A spatially restricted region within an
organ in which cell division for growth
occurs
Leaf primordiumShoot apical meristem
Meristems are vital!All POSTEMBRYONIC development in plants
occurs from meristemsGive rise to all major organ systems > roots, stems, leaves, flowers
Primary meristems
• Shoot Apical Meristem• Root Apical Meristem
• SAM and RAM produce additional meristematic tissue that increases plant length and produces new organs
• Primary meristems produce primary tissues and organs of diverse types
Tissues in plants
D: (Epi-)DermisV: VascularG: Ground
• SAM and RAM both produce– Protoderm – generates dermal tissue– Procambium – produces vascular tissues– Ground meristem – produces ground
tissues defined by location• Plant cell specialization and tissue
development do not depend much on the lineage of a cell or tissue
• Chemical influences are much more important
Stem development and structure• New primary stem tissues arise by the cell
division activities of primary meristems located near the bases of SAMs
• Epidermis develops at the stem surface– Produces a waxy cuticle (reduces water loss,
protects plant) • Cortex – composed of parenchyma tissue
– Composed of only one cell type, parenchyma cells
– Stores starch in plastids • Stem parenchyma also has the ability to
undergo cell division (meristematic capacity) to heal damage
Vegetative growth
• Production of tissues by SAM and RAM and growth of mature plant
• Plant shoots produce vegetative buds – miniature shoots having a dormant SAM
• Under favorable conditions, buds produce new stems and leaves
• Indeterminate growth – SAMs continuously produce new stem tissue and leaves as long as conditions are favorable
Plant growth & morphogenesis
requires co-ordination of 3 key cellular processes which occur within
and around the meristem
RATE of CELL DIVISIONPLANE of CELL DIVISION
DIRECTION of CELL EXPANSION
Fasciation - loss of control of meristem size
How might cell division and expansion be co-ordinated to maintain meristem size and activity?
Positional information might be exchanged between cells
Question…
Are cells in the meristem interconnected?
Communication between meristem cell layers
PlasmodesmataMembranes from adjacent cellsconnect through a pore inthe cell wall
Transmission electron micrograph
Summary
• SAM is the site of organ initiation
• Major activity of the SAM is cell division
• Meristem size/shape must be maintained• Otherwise there would be CHAOS!
• Involves coordinated control of rates and
planes of cell division in different regions
• Communication between different cell
layers via plasmodesmata which traverse
the cell wall
http://www2.mcdaniel.edu/Biology/botf99/tissimages/meristematic.html
Root meristems
ROOT APICAL MERISTEM (RAM) ORGANISATION
SIMPLER IN ORGANIZATION THAN SHOOT APEX
CELLS ARRANGED IN FILES
NO LATERAL ORGANS FORMED
NEAR APEX
ROOT CAP PRESENT
HOW DO CELL FILES ARISE?
Most division in apical regionLess division below the apex A group of cells that divide
infrequently:
QUIESCENT CENTRE
Divisions take place at the PERIPHERY of the QUIESCENT CENTRE
INITIAL OR STEM CELLS
Cells DIFFERENTIATE as they expand.
ROOT BRANCHINGLATERAL ROOTS emerge
further back behind the apical meristem from the PERICYCLE CELL LAYER
Establishment of a NEW MERISTEM
DEVELOPMENTAL RESPONSE TO AN ENVIRONMENTAL SIGNAL water/nutrient suppliesAuxin signalling
EpidermisCortexEndodermisPERICYCLEStele
Other meristems [Allow propagation
via cloning]
KalanchoeMeristems formed at the leaf
marginsGenetically identical progeny
(mitotic divisions)Vegetative reproduction
• Roots, stems and leaves can function in asexual reproduction– Kalanchoe leaves
form plantlets, sucker shoots, potato “eyes”, banana suckers or spears
• Apomixis – fruits and seeds are produced in the absence of fertilization– Meiosis produces
diploid megaspores (no meiosis II)
Meristems & Organogenesis
Where do the major organ
systems of the plant
originate?Meristem: A spatially restricted region within an organ in which cell division for growth occursPOSTEMBRYONIC development in plants occurs from meristemsRoot and Shoot Apical MeristemsRate & Plane of cell division; direction of expansionCell communication