Stomatal patterning can be viewed from different perspectives and used as a model system for investigations in developmental biology, morphology, evolution, ecology, and physiology. The function of these specialized pores—and probably their distribution—has played a critical role in plant evolution and the successful exploitation of the terrestrial environment. Stomatal patterns are ordered indicating position complements the internal geometry of the plant organ and its photosynthetic function. Although quantitative aspects of stomatal pattern (degree of order and absolute number of stomata) in extant plants may permit adaptation to changing atmospheric conditions, the mechanism and plasticity of patterning are central in understanding the evolution of land plants.
The critical questions in stomatal patterning today revolve around two issues: the cell cycle and cellular communication. As the evidence presented here indicates, the patterning of stomata in angiosperms is likely coupled to the cell cycle. This connection can be tested directly by altering the cycle dynamics and noting the final stomatal pattern. The second critical question is centered on cellular connections because the molecule that specifies stomatal fate may come from a cell other than the one that will be specified. Knowing which cells are symplastically connected during the time of specification tells us which routes are available for specification. Cells that are symplastically isolated from their neighbors may still receive signals from them, but the mechanics of the process would differ. Knowing the routes of travel provides essential information regarding the possible pathways of signal movement.
The ultimate goal of all developmental biology studies is to understand how undifferentiated cells acquire their fate. Patterning decisions are made throughout plant growth, from the zygote onward. What is learned about distribution of stomata may be applicable to other situations, such as trichomes, root hairs, and crystal distribution, for patterning mechanisms are likely conserved. What is successful in one circumstance is likely successful in another; evolution works with the tools at hand.
1 The author thanks Tsvi Sachs and Fred Sack for stimulating discussions regarding patterning; Kandis Elliot and Claudia Lipke for assistance with illustrations; and M. Christianson for providing constructive comments on an early version of the manuscript.
2 Author for correspondence ([email protected] ).