Abstract
Leaf temperature provides an indicator of the transpiration of plants, because evaporation of water causes leaf cooling. With a high throughput leaf thermal imaging CO2 screen, we isolated two allelic Arabidopsis mutants (high leaf temperature 1; ht1-1 and ht1-2) altered in their ability to control stomatal movements in response to CO2. The strong allele, ht1-2 exhibits a dramatically impaired CO2 response but functional reactions to blue light and ABA, suggesting a specific role for HT1 in stomatal CO2 signalling. HT1 encodes a protein kinase expressed mainly in guard cells. Phosphorylation assays demonstrate that the activity of the HT1 protein carrying the ht1-1 or ht1-2 mutation is greatly impaired or abolished, respectively. Furthermore, dominant negative HT1:kw transgenic plants which lack HT1 kinase activity show a disrupted CO2 response. Further analysis suggested that the HT1 is a Raf-like protein kinase functioning as CO2 signalling molecule in cytosol.
