Recherches recentes sur l'irradiation d'un Riz Francais de camargue

Abstract

This paper summarizes experiments carried out in the south of France to define some radiobiological characteristics of a certain variety of rice seeds in the Camargue: Oryza sativa L. c. v. Cigalon Marie, and to test treatments which provide radioprotection or promote recovery. Radio-induced damage is measured by means of the sum of seedling heights, this criterion being sometimes specified by the examination of its two components: the average height of the seedlings and the number of survivors.

The results show that if high exposures to ⁶⁰Co γ-rays are used then seeds must be used with a water content of not less than 13% and sowing must take place as soon as possible after exposure to minimize storage effect.

A natural result of protection appears after soaking seeds at a low temperature (5°C) then dehydrating them at 32°C to bring back their initial moisture content, before irradiation. This effect is maximum when the time sequence of the treatment allows a complete hydration of the seeds. It is not due to the elimination of a radiosensitizer through soaking but might be ascribed to modifications in enzymatic protein structure during soaking at a low temperature. On the contrary, soaking at a high temperature (32°C) results in an increased radio-sensitivity.

It is possible to induce recovery after irradiation if irradiated seeds are grown on a medium containing commercial yeast extract. The earlier and longer the application, the better the recovery. Extracts prepared from yeast cell culture, as well as RNA extracted from them, promote a recovery effect. All these extracts which stimulate growth of rice seedlings during their exponential stage in the laboratory and increase the number of surviving plants in the field, might contain a recovery-promoting constituent whose chemical composition is still to be found.