Reinhardt et al. (2003). Regulation of phyllotaxis by polar auxin transport. Nature 426: 255-260.

Kuhlemeier C. (2007). Phyllotaxis. Trends in Plant Sci. 12: 143-50.


1) Is there any adaptive significance relating to phyllotactic patterning? Name three possible reasons spiral phyllotaxis may be so common.

2) Describe the various historical theories for the spiral arrangement of lateral organs: “first available space”, inhibition, biophysical, chemical. Are these hypotheses mutually exclusive?

3) What are some special properties of the L1 layer and why is it so important with respect to lateral organ initiation?

4) Name four types of phyllotactic patterns. Are there genetic mutants that transform one pattern to another (akin to homeotic mutations)?

5) What’s a parastichy?

6) Why did people turn to quantitative modeling to describe phyllotaxis? Why wasn’t genetics alone sufficient?

7) Models of the inhibitory hypothesis are sufficient to recreate phyllotactic patterns. Discuss the implications of this with respect to distinguishing the validity of different phyllotactic mechanisms (ie, inhibition, biophysical, chemical, etc.).

8) When model stability is increased using non-linear functions instead of linear, or “factor X” is included in a model, is there meaning to these model additions without empirical evidence? Which would you believe more: a more stable model with undiscovered empirical factors, or a less-stable, empirically verified model?

9) Explain “top-down” vs. “bottom-up” phyllotactic patterning. That is, L1-derived signaling vs. signaling from underlying layers and/or vasculature.

10) Name three other developmental/patterning events auxin is important for besides phyllotaxis/leaf initiation.

11) Name and discuss four major assumptions of phyllotactic models.

12) What is canalization?

13) Describe I3/I2/I1/P1/P2/P3 nomenclature. Hint: P1/P2/P3 are successively older, visible leaf primordia. Are leaves specified before they are physically visible? Where would the “next leaf to be,” ie the incipient leaf, be located relative to older leaf primordia?