Phosphorus, sulfur, potassium and calcium were measured by particle-induced X-ray emission (PIXE) in horizontally oriented, light-irradiated or non-irradiated primary roots of Zea mays L., cv. Golden Cross Bantam 70 which exhibit gravitropic response only after exposure to light. The content of the four elements increased in the lower half of horizontally oriented roots which had been briefly exposed to white or red light, while there were no marked differences in distribution between the upper and lower halves of non-irradiated roots. The increase of each element in the lower half was observed 15–30 min after irradiation in root caps and 30–60 min after irradiation in the elongation zones. The effect of red light was not reversed by far-red light given immediately after the red irradiation. Ethylene glycol-bis(β-aminoethyl ether)-N, N, N′,N′-tetraacetic acid (EGTA) treatment of root tips inhibited the gravitropic curvature of roots, and the addition of Ca reduced this inhibition. The meaning of Ca redistribution in root caps and elongation zones during light-induced gravitropic curvature of maize roots is discussed.
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Miyazaki et al. (1986) studied this question.