Plant Organ Primordia


Plants are made up of the shoot axis, the root axis and the organs produced by each including leaves, petals, some tendrils, some thorns and lateral roots. These organs are produced throughout the lifespan of the plant, their production involves changes in cell fate, delineating boundaries, patterning the new organ and controlling its outgrowth. Shoot organs are formed in a regular pattern on the flanks of the shoot apical meristem. They lose the indeterminacy of meristem cells. Signals from the meristem pattern the organ, establishing an upper (adaxial) and a lower (abaxial) side. Organs of the root are produced from nonmeristematic cells the peri‚Äźcycle cells which surround the vasculature. If these cells receive the correct signal they start to divide and produce a new indeterminate meristem. This meristem activates as it breaks through the primary root tissues.

Key Concepts:

  • Plant organs form throughout the lifespan of the plant.

  • Shoot organs include leaves, floral organs and some tendrils or thorns.

  • Shoot organs form on the flanks of the shoot apical meristem.

  • Root organs include lateral roots and nodules.

  • Root organs form by the dedifferentiation of pericycle cells and activation of new meristems.

  • Auxin plays a key role in the origin of new organs.

  • Patterning of organs occurs early in their development.

Keywords: meristem; lateral root primordia; leaf primordia; phyllotaxy; auxin; cell division

Figure 1.

(a) The Arabidopsis SAM and developing organ primordia. Organ primordia (flower primordia; numbered from the order of the youngest to the oldest) are constantly generated at the flank of the SAM (inflorescence meristem, IM). Groups of cells on the flank of the meristem, in the peripheral zone, are recruited into organ primordia (I1, I2 and I3; numbered from the order of emergence). The scanning electron micrograph was taken by Laurel Hanson in the Torii laboratory. Bar, 10 μm. (b) A cross‐section of Ranunculus acris primary root. A lateral root primordium initiates from the pericycle cells adjacent to the xylem of the stele, and grows through the cortex.

Figure 2.

Processes and genes involved in organ formation in the shoot (a) and the root (b).

Figure 3.

(PAT) is crucial for the formation of lateral organ primordia. The Arabidopsis pin1 mutant, which lacks PIN1 auxin efflux carrier, failed to form organ primordia at the inflorescence stems. (Close up) Local application of the auxin using wax (coloured in pink) induced the organ primordia. The images are kindly provided by Dr Didier Reinhardt (University of Bern, Switzerland).



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Kidner, Catherine A(Apr 2010) Plant Organ Primordia. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0002055.pub2]