How do plants develop as integrated organisms?
Zea
Germination
(qt)
Coleus
gravitropism
(qt)
Plants-In-Motion
Roger Hangarter
Indiana University
Cell Theory
Schleiden (1838) and Schwann (1839)
All living things are made of cells
“Omnis cellula e cellula”
“All cells only arise from pre-existing cells”
Rudolph Virchow 1858
Modern Cell Theory:
1. All known living things are made up of cells.
2. The cell is the structural & functional unit of all
living things.
3. All cells come from pre-existing cells by division.
4. All cells contains hereditary information which is
passed from cell to cell during cell division.
5. All cells are basically the same in chemical
composition.
6. All energy flow (metabolism & biochemistry) of
life occurs within cells.
Organismal Theory
“The plant forms cells, not cells the plant”
Anton deBary 1879
Consensus is development of zygote
into embryo is a progressive
process
in which the action of
many genes together is required.
What regulates master control switches that
control changes in morphology of embryos?
During Animal embryogenesis, cells can
migrate past one another
tainano.com/chin/Molecular%20Biology%20Glossa...
Plant cells do not migrated past one another
because the rigidity of the extracellular matrix
Prevents this.
Fundamental plan of body is laid down
so that all organs and tissues are present
at least in rudimentary form in animal embryos
Two distinct regions at opposite poles are
established in plant embryogenensis
(Root and Shoot Apical Meristems)
Internal tissue meristems are established
during plant embryogenesis
(Protodermis, Procambium, Ground Meristem)
Primary plant body subsequently develops via
activity of these meristems.
Number of organs (roots, stems, leaves)
are indeterminate
Since all plant organs basically consist of the same
three tissues, the very nature of plant organs is
different from animal organs.
Functional integrity of
plant organ systems
maintained via
continuous
differentiation of tissue
systems in recognizable
shapes and patterns
Mastery of contemporary plant development
requires bridging classical plant
anatomy/morphology and physiology to modern
molecular techniques
Can development ever be explained mechanistically?
What are the principles of pattern formation?
What roles do cell lineage and positional information
play in plant development?
Challenges for the future
Understanding nature of signal transduction cascades
and internal/external stimuli that direct
activation/repression of transcription factors that
result in pattern formation.
How do cells communicate?
Between meristematic and differentiating regions?
Between different tissue areas?
Between different organ systems?
What are the dynamic relationships between:
Cell division
Planes of cell division
Cell expansion
Direction of cell expansion
Cell differentiation
Genetic regulatory networks
Within and between the different tissue/organ
systems?
Dynamics of cell division, cell expansion and cell behavior at the boundary
region of SAMs. The three-dimensional time lapse series of an SAM
expressing 35S::YFP29-1 was acquired approximately every 2 hours and 30
minutes for a total duration of 65 hours. Twenty-four observations are
animated at 10 frames/second. The movie loops after each cycle. The red
open arrow indicates cells that form the boundary region. The red closed
arrow indicates cells in a primordium. The white arrow indicates cells in the
PZ, dividing along their axis of expansion. The yellow arrow indicates a cell in
the CZ dividing along its short axis. Other cells in the CZ show proportional
expansion in all directions.
Real-time lineage analysis reveals oriented cell divisions associated with
morphogenesis at the shoot apex of Arabidopsis thaliana
Development 2007 Reddy et al. 131: 4225
Fibonacci spiral phyllotaxis simulation
Smith et al. 10.1073/pnas.0510457103. 2006