Effects of gamma-irradiation on elongation and indole-3-acetic acid level of maize (Zea mays) coleoptiles

The effects of gamma-irradiation on elongation and the level of indole-3-ac etic acid (IAA) of maize (Zea mays) coleoptiles were investigated. When 3-d ay-old seedlings of maize were exposed to gamma-radiation lower than 1 kGy, a temporal retardation of coleoptile elongation was induced. This retardat ion was at least partly ascribed to a temporal decrease in the amount of fr ee IAA in coleoptile tips on the basis of the following facts: (1) the reac tivity to IAA of the elongating coleoptile cells was not altered by irradia tion; (2) endogenous IAA level in the tip of irradiated coleoptiles was at first unchanged, but then declined before returning to nearly the same leve l as that of the non-irradiated control; and (3) the amount of IAA that dif fused from coleoptile tip sections showed a similar pattern to that of endo genous IAA. The rate of conversion between free and conjugated IAA was not significantly affected by irradiation. These results suggest that a tempora l inhibition of maize coleoptile elongation induced by gamma-irradiation ca n be ascribed to the reduction of endogenous IAA level in the coleoptile ti p, and this may originate from the modulation in the rate of IAA biosynthes is or catabolism. (C) 1999 Elsevier Science B.V. All rights reserved.