Methods
protein spot identification from broad and narrow pH range two-dimensional (2D) gels, and 2D liquid chromatography-matrix assisted laser desorption/ionization multidimensional protein identification technology. This extensive single-cell-type proteome includes 336 proteins not previously represented in transcriptome analyses of guard cells and 52 proteins classified as signaling proteins by Gene Ontology analysis, of which only two have been previously assessed in the context of guard cell function. THIOGLUCOSIDE GLUCOHYDROLASE1 (TGG1), a myrosinase that catalyzes the production of toxic isothiocyanates from glucosinolates, showed striking abundance in the guard cell proteome. tgg1 mutants were hyposensitive to abscisic acid (ABA) inhibition of guard cell inward K(+) channels and stomatal opening, revealing that the glucosinolate-myrosinase system, previously identified as a defense against biotic invaders, is required for key ABA responses of guard cells. Our