Unfortunately, Muscle SpikerBox or any other box won't work with plants. It isn't software or code, but the physical amplifiers and hardware which allow us to record from the plants. So in order to record from the plant you will need Plant SpikerBox.
The different kits we develop have different circuits to best record the variety of signals we're interested in studying. The Muscle, Heart and Brain, Invertebrate and Plant kits cannot be modified to perform recordings outside of their scope.