XVI International Botanical Congess

Zeaxanthin (Z), plays a role in the transduction of light and CO2 signals in guard cells (GCs). Stomata from npq1, a Z-less Arabidopsis mutant, lack a blue light (BL) response, and GCs from the facultative CAM, ice plant, lose their BL response and ability to form Z upon CAM induction. The BL response of GCs increases with their Z content, and an inhibitor of Z formation, DTT, blocks BL-dependent opening. At constant light and temperature, Z content in GCs is linearly related to stomatal apertures over a wide range of [CO2]. GC photosynthesis is optimally suited for the coupling of Z concentrations with light/CO2 changes. Spectroscopic studies suggest that Z operates as a pair of blue/green absorbing, interconvertible isomers, with the green absorbing form being physiologically active. Supported by NSF and DOE.