This is an expression that comes from the world of baseball. The `plate’ refers to `home plate’; the base a batter stands next to, as he gets ready to receive his first pitch. When a batter steps up to the plate, he is ready to deal with whatever the pitcher may decide to throw at him. In other words, he is ready for the challenges in store.
*I don’t think there is anyone among you who would willingly step up to the plate. *When it came to crunch time, Sujatha really stepped up to the plate.