Studies on plant growth‐regulating substances.: The effects of light and hormone inhibitors on plant root growth

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Abstract
SUMMARY: Light inhibition of primary root elongation in Zea mays seedlings was found to be an almost instantaneous response and the inhibitory effect was shown to persist for at least six hours following a short exposure to white light. Removal of the root cap completely removed the inhibitory effect of light. The apical region of the root appeared to be mainly responsible for perceiving light and initiating the production of factors involved in the inhibition of elongation.Extraction of the roots of light‐exposed Zea seedlings revealed the presence of the carotenoid pigments, violaxanthin, neoxanthin and lutein, together with an unidentified non‐acidic growth‐inhibitory compound. Xanthoxin, however, was not detected.