The stomatal developmental response to [CO2] involves the HIC signalling pathway

Abstract

Increases in atmospheric carbon dioxide concentration, caused by man¿s activities on earth, have been accompanied by a decrease in stomatal numbers in many plant species. It is not currently known how the developmental fate of epidermal cells is controlled. We have recently identified a gene involved in this pathway that controls stomatal numbers at elevated CO2. In contrast to the usual reduction in stomatal development, the Arabidopsis mutant hic has an approximately 40% increase in stomatal density in response to a doubling of atmospheric CO2. The, HIC gene is expressed specifically in developing guard cells and encodes a putative 3-keto acyl Co-A synthase; an enzyme involved in the synthesis of very long-chain fatty acids. These fatty acids are principal components of the epicuticular wax layer. We propose that knocking out the activity of this wax biosynthesis enzyme results in an altered permeability of the guard cell wax layer. This alteration in guard cell wax permeability may alter the diffusion of an elevated CO2 stimulated signaling molecule that is normally responsible for the repression of stomatal development.