How do plants develop as integrated organisms? Zea Germination (qt) Coleus gravitropism (qt) Plants-In-Motion Roger Hangarter Indiana University

“Omnis cellula e cellula” “All cells only arise from pre-existing cells” Rudolph Virchow 1858 Cell Theory Schleiden (1838) and Schwann (1839) All living things are made of cells

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?

tainano.com/chin/Molecular%20Biology%20Glossa... During Animal embryogenesis, cells can migrate past one another

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 /pnas