Effect of X-ray Irradiation on Regeneration and Geotropic Function of Barley Root Caps

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Abstract
Root-cap regeneration and geotropic function after removal of the differentiated part of the cap were studied in barley roots. Geotropic response was regained when about 35 per cent of the root-cap length was regenerated. The geotropic response progressively increased with increasing length of the differentiated part of the root cap. Irradiation of the root-cap meristem inhibited the regeneration of the root cap. After irradiation in air, the geotropic response of the regenerated root cap decreased with increasing doses. Hypoxic (about 12 p.p.m. of O2 in a gas phase) conditions during irradiation with doses as high as 2400 rads completely protected the function of the partially regenerated root cap. Iodine tests on starch statoliths, and electron micrographs of root-cap cells regenerated from cap initials irradiated in the presence of oxygen, revealed a reduction in the number and size and changes in the chemical composition of starch statoliths in the amyloplasts; but there were no such effects in the absence of oxygen. It is suggested that the inhibition of the geotropic response of the root caps regenerated from cap initials irradiated in air is due to damage suffered by the genetic apparatus controlling the synthesis of the starch statoliths.