Figure 4.

Stomatal Development in Grasses.

(A) Schematic diagram of stomatal development in grasses. (1) During early epidermal development in grasses, stomatal and nonstomatal cell files are specified, and cell division polarity is established in the stomatal cell file. This polarity will ensure that the one-cell spacing rule is maintained. (2) Os MUTE controls a single asymmetric division toward the leaf apex in the stomatal cell file, which creates GMCs (blue). Neighboring cell files (SMC; pink gradient) receive a signal via putative receptor PAN1 (magenta), which localizes at the area of GMC contact and polarize in preparation for division. (3) SMCs divide asymmetrically toward PAN1 to form SCs (pink), which will act as ion reservoirs for the operation of mature stomata. (4) GMCs divide once symmetrically to form GCs (light green). (5) Finally, GC and SC terminally differentiate, forming mature dumbbell-shaped stomata (dark green). Os FAMA is required for the differentiation of GCs, though not their symmetric division.

(B) Leaf epidermal peel from the wild type (left) and pan1 mutant maize (right). GC and SC are stained in blue and pink, respectively. Unlike the wild type, the pan1 mutant occasionally fails to produce proper asymmetric divisions that give rise to SC, resulting in abnormal SC patterning. Images kindly provided by Laurie Smith (University of California, San Diego).