Effects of growth substances on rice seedlings grown from seeds irradiated with gamma rays

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Studies were made on the modifications of biological effects caused by ionizing radiations by post-treatment with growth substances, i.e., gibberellic acid (GA 3), indole acetic acid (IAA) and indole butyric acid (IBA). Dormant rice seeds (moisture content 13%) variety IR8 were exposed to gamma ray doses of 10, 20, 30 and 40 kR. The irradiated and non-irradiated seeds were soaked for 24 hr in 10 ppm of either GA 3, IAA, IBA or distilled water at 29°C Gamma rays induced a remarkable decrease in plant height. However, reversal of the radiation effect was obtained by applying GA 3, IAA or IBA. The magnitude of the reversal effect decreased with increasing doses of gamma rays. The lengths of the coleoptile and the first leaf were markedly decreased by the radiation treatment. The application of IAA and IBA produced no significant reversal effect in either case but GA 3 showed a slight reversal for both parameters. Seminal root length was inhibited by radiation. Furthermore, IAA or IBA alone showed some inhibiting effect on seminal root length, while GA 3 did not produce any effect. The total number of crown roots was not affected by 10 kR, but was decreased at higher doses. On the other hand, all doses increased the number of “stunted roots”. GA 3 failed to show any effect on the number of total crown as well as on “stunted roots”. IAA and IBA increased the total number of crown roots up to 20 kR but not at higher doses. The number of “stunted roots” showed a further increase when treated with IAA and IBA.