I've used these gestures for a few years now, even before I learned about WBT. I can still ask my former students what they are and they remember!

Parts of a plant:
Roots - hold fingers of left hand down like you're grabbing something from a bag
Stem - place right elbow on left wrist, arm straight up and hold a fist with the right hand
Leaves - open right hand and wave from side to side

Things a plant needs to live:
Sunlight - hold hands in a circle above head making a big "O"
Water - use fingers to make a rain motion downward like the Itsy Bitsy Spider song
Air - take in an exaggerated breath
Good Soil - using hands make a digging motion

Rainforest levels:
Canopy - hold hands above head like you're making an umbrella
Understory - move hands down to about chest height as if they are on a countertop
Forest Floor - move hands down near the floor
Emergents - hold one arm up above head stretching

Thanks. I will use these when teaching photosynthesis.