A model for leaf initiation: determination of phyllotaxis by waves in the generative circle.
A biophysical model is proposed for how leaf primordia are positioned on the shoot apical:  meristem in both spiral and whorl phyllotaxes. Primordia are initiated by signals that propagate:  in the epidermis in both azimuthal directions away from the cotyledons or the most recently:  specified primordia. The signals are linear waves as inferred from the spatial periodicity of the:  divergence angle and a temporal periodicity. The periods of the waves, which represent actively:  transported auxin, are much smaller than the plastochron interval. Where oppositely directed:  waves meet at one or more angular positions on the periphery of the generative circle, auxin:  concentration builds and as in most models this stimulates local movement of auxin to:  underlying cells, where it promotes polarized cell division and expansion. For higher order:  spirals the wave model requires asymmetric function of auxin transport; that is, opposite wave:  speeds differ. An algorithm for determination of the angular positions of leaves in common leaf:  phyllotaxic configurations is proposed. The number of turns in a pattern repeat, number of leaves:  per level and per pattern repeat, and divergence angle are related to speed of auxin transport and:  radius of the generative circle. The rule for composition of Fibonacci or Lucas numbers:  associated with some phyllotaxes is discussed. A subcellular model suggests how the shoot:  meristem might specify either symmetric or asymmetric transport of auxin away from the:  forming primordia that produce it. Biological tests that could make or break the mathematical:  and molecular hypotheses are proposed.
Department of Electrical and Systems Engineering, and Gladys Levis Allen Laboratory of Plant Sensory Physiology, Washington University, St. Louis, MO, USA. bas@wustl.edu
Barbara
B
Abraham-Shrauner
Barbara G
BG
Pickard
D000465:Algorithms; D007210:Indoleacetic Acids / Q000378:metabolism*; D018519:Meristem / Q000254:growth & development*; D008954:Models, Biological; D018515:Plant Leaves / Q000254:growth & development*; D015398:Signal Transduction
D007210:Indoleacetic Acids