Function of Light in the Light-induced Geotropic Response in Zea Roots

The light doses just above the threshold energy value for inducing the geotropic responsiveness in the roots of Zea mays L., cv. Golden Cross Bantam 70, caused a drastic rise in the NADPH level and a drop in the NADP level in 2-millimeter root tips. Some reducing agents lowered the threshold energy value up to about one-third of the control. From these results, we deduce that light may exert two functions in the geotropic response of Zea primary roots, one being the photochemical transformation of a photoreceptor and the other being the induction of a reduction state in the tissue.