Practice question

Stalk cell differentiation in monolayer assays requires DIF-1 plus elevation of cytosolic calcium triggering ecmB expression, vacuolar expansion, and cellulose deposition characteristic of stalk maturation. Calcium ionophores strongly promote prestalk fate, while chelation blocks it. High ammonia or glucose instead favor prespore differentiation and sustain slug migration, preventing premature culmination. Experimental manipulation shows calcium acts through calmodulin-dependent kinases and STAT pathways synergistic with DIF-1. In vivo anterior tip exhibits higher calcium levels, predisposing cells to stalk fate, whereas posterior region maintains lower calcium supporting prespore identity and suppressing stalk formation.