Light-induced inhibitors from intact and cultured caps of Zea roots

Growth inhibitors were assayed from extracts of intact (attached) and of excised (cultured) root caps of Zea mays L., cv. Merit, the roots of which show a positive geotropic response only after exposure to light. If caps are intact at the time of illumination, at least two inhibitory substances are produced, an acid inhibitor and a neutral inhibitor, whereas if caps are detached from roots, placed in culture and then illuminated only the neutral inhibitor is formed. Cycloheximide retards inhibitor production in both intact and cultured caps. When [(14)C]mevalonic acid is included in the culture medium and the caps are illuminated, 15-25% of the recoverable (14)C cochromatographs with the neutral inhibitor, whereas in caps cultured in the dark, this radiolabelling pattern is not observed. Cyloheximide in the light reduces the incorporation of (14)C into compounds cochromatographing at the Rf of the neutral inhibitor. It is suggested that the neutral inhibitor may be important in the light-induced bending of roots.