Cortical actin filaments in guard cells respond differently to abscisic acid in wild-type and abi1-1 mutant Arabidopsis

Cortical actin filaments in guard cells of Commelina communis L. show signa l-specific organization during stomatal movements [S.-O. Fun and Y. Lee (19 97) Plant Physiol 115: 1491-1498; S.-O. fun and Y. Lee (2000) Planta 210: 1 014-1017]. To study the roles of actin in signal transduction, it is advant ageous to use Arabidopsis thaliana (L.) Heynh., an excellent model plant wi th numerous well-characterized mutants. Using an immunolocalization techniq ue, we found that actin deployments in guard cells of A. thaliana were basi cally identical to those in C. communis: actin proteins were assembled into radial filaments under illumination, and were disassembled by ABA. In addi tion, we examined actin organization in an ABA-insensitive mutant (abil-1) to test the involvement of protein phosphatase 2C (PP2C) in the control of actin structure. A clear difference was observed after ABA treatment, namel y, neither stomatal closing nor depolymerization of actin filaments was obs erved in guard cells of the mutant. Our results indicate that PP2C particip ates in ABA-induced actin changes in guard cells.