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SUMMARY:Chemical and Physical Signals Interact to Create Pattern in Plant 
 Development - Elliot Meyerowitz\, Sainsbury Lab\, Cambridge University
DTSTART:20121122T130000Z
DTEND:20121122T140000Z
UID:TALK39037@talks.cam.ac.uk
CONTACT:Jill Harrison
DESCRIPTION:One pattern generated by the shoot apical meristem of flowerin
 g plants has held a fascination for generations of biologists and mathemat
 icians.  This is the phyllotactic pattern\, the pattern of leaves and flow
 ers around the stem.  The most common such pattern is the spiral phyllotac
 tic pattern\, which creates the highly recognizable organization of compou
 nd fruits such as pineapples\, of flowers like roses\, and of inflorescenc
 es such as sunflowers.  The model plant Arabidopsis thaliana also has a sp
 iral phyllotaxis\, and we have used genetic\, genomic\, and cell biologica
 l approaches to learn in detail how the cells of the meristem collaborate 
 to generate this pattern. \n\nThe major chemical signal is auxin\, which h
 as a specific transport system\, in which a family of plasma membrane prot
 eins directs the efflux of the hormone from cells\, while both diffusion a
 nd a group of importers directs influx.  The efflux proteins are not unifo
 rmly distributed\, hence they cause efflux directionally\, leading to a ne
 t flow of auxin in complex patterns across the surface of the meristem.  A
 uxin not only induces new primordia of leaves and flowers\, but also chang
 es the physical properties of the cell wall.  These physical changes alter
  the stress pattern in the meristem surface\, which in turn regulates the 
 position of the auxin efflux carrier in anisotropically stressed cells.  T
 he feedback between auxin concentration and physical stress creates the dy
 namic auxin patterns that cause successive auxin peaks at positions approx
 imately 130-140 degrees around the stem\, creating the spiral (and other p
 atterns of) phyllotaxis.  The stress pattern in the meristem may also dete
 rmine aspects of cell wall synthesis\, direction of cell growth\, and plan
 e of cell division.
LOCATION:Sainsbury Laboratory
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