We observed that the stomata under R630BG and R660BG were elliptical with narrow pores; this morphology is associated with normal function (Sha Valli et al., 2003). Stomata have been found to function as hydraulic valves on the surface of aerial plant parts,with the guard cells that surround each pore rapidly adjusting their turgor to optimize photosynthetic CO2 uptake and to minimize transpiration water loss from leaves (Outlaw, 2003). Moreover,Kim et al. (2004a) found that plantlets with a smaller number of larger-sized stomata in leaves showed vigorous growth. Similarly,we found that treatments containing G reduced stomata density but increased stomata size (Table 3, Fig. 4) and thus increased the DM and health index of potato plantlets in vitro compared with other treatments (Table 2).