Phytotropin-induced root phototropism in maize

Phytotropins, even those not absorbing in the visible region of the spectrum, can induce a phototropic response in maize ( Zea mays L. cv. PX-75) roots when illuminated unilaterally with white light. The most active phytotropin, 2-(1-pyrenoyl) benzoic acid (PBA) can elicit a full response at 10 μ M , while the other active molecules, 2-carboxyphenyl-3-phenylpropane-1,3-dione (CPD), 2-carboxyphenyl-3-phenyl-1,2-pyrazole (CPP), 1-N-naphthylphthalamic acid (NPA) and erythrosin elicit a full response at 100 μ M . The less active phytotropins BBA and fluorescein give a reduced response. It is suggested that the observed effect cannot be explained solely on the basis of auxin transport inhibition. There is a photoreceptor in the extension zone of the root, which may be associated in some way with the receptor for NPA. The results are consistent with the proposal that the phototropic process may form part of the root gravitropic response mechanism.