Modification of Barley Seed Radiosensitivity by Post-treatment with Caffeine

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Abstract
Barley seeds (3·6 per cent moisture content) were irradiated in vacuo with 45 krads of gamma-rays and were then subjected to treatments such as wet heat shock (at 60°C for 90 sec) or oxygenated or oxygen-free hydration (at 0 to 2°C for 13 hours) in the presence or absence of caffeine. A combination of heat shock and oxygen-free hydration was found to be most protective against the post-irradiation oxygen-dependent damage (scored as seedling-injury and chromosomal aberrations). The presence of caffeine in oxygenated water prevents part of the oxygen-enhanced damage; however, the magnitude of such protection decreases after a wet heat shock to the seeds. On the other hand, caffeine counteracts the protective action of oxygen-free hydration; the role of heat shock, in this case, is to accentuate further the caffeine-induced radio-sensitization. These observations imply that the reactivity of caffeine towards the gamma-induced intermediate and end-products under oxic and anoxic conditions could be very different. The manner of influence of heat shock on the caffeine effect in the irradiated seeds remains to be elucidated.