You probably would not be able to grow corn upside down because
gravitropism would cause the stem to bend back upward. Gravitropism is
usually stronger than phototropism. If you had a mutant plant that did
not respond to gravity, then you could do it. There are mutant pea
plants (ageotropum) whose roots do not respond to gravity but its
shoots do respond to gravity in the light.

There are many weeping plant cultivars (e.g. Sargent's weeping hemlock,
weeping cherry, weeping willows, weeping beech, weeping mulberry,
weeping crabapple, Cedrus atlantica 'Glauca Pendula', etc.) with branch
tips that normally grow toward the force of gravity. Rooting cuttings
from weeping branches might be an easy way of growing upside down
plants.

A clinostat is a device that slowly rotates a plant, about 1 revolution
per minute, and can prevent phototropism and gravitropism. The motion
would be like sitting a potted plant on a record turntable and spinning
it at a slower speed. If the potted plant is firmly attached to the
clinostat and then the whole apparatus is placed so the potted plant is
horizontal, then the plant should continue to grow straight. Both
gravitropism and phototropism would be negated because the plant has no
time to orient itself because it is constantly changing position
relative to gravity and any directional light source.

Reference

Jaffe, M.J., Takahashi, H. and Biro, R.L. 1985. A pea mutant for the
study of hydrotropism in roots. Science 230: 445-447.


David R. Hershey