Influence of Seed Moisture Content and Post-irradiation Hydration Temperature on the Kinetics of Reactivity Towards Oxygen or Decay of Oxygen-sensitive Sites

Summary

The rate of development of post-irradiation oxygen-dependent damage when oxygen is available, and its rate of elimination when seeds are first post-hydrated in oxygen-free water prior to their transfer to oxygenated water, was studied in barley seeds of ∼3 per cent, ∼8 per cent and ∼9 per cent moisture contents at 3°C, 25°C and 37°C. The magnitude of oxic damage at a given dose (35 krad) decreases as the initial seed moisture content increases from ∼3 per cent to ∼9 per cent. Significant (P=0·01) oxic damage is observed in seeds of all the three moisture contents at 3°C and 25°C; however, at 37°C significant (P=0·01) oxic damage is observed only in seeds of ∼3 per cent and ∼8 per cent moisture contents. The magnitude of oxic damage in seeds of a given moisture content remains unaltered following oxygenated post-hydration of seeds at 3°C and 25°C, but it registers a significant (P=0·01) decrease if post-hydration in oxygenated water is carried out at 37°C. The radiation-induced oxygen-sensitive (A_n) sites react with oxygen ∼6 to 8 times faster as compared to their rate of decay in the absence of oxygen at both 3°C and 25°C; however, at 37°C they react only ∼3 to 4 times faster, in seeds of all the three moisture contents. Moreover, the initiation of the decay of A_n sites becomes evident much earlier in very dry (∼3 per cent moist) seeds than in relatively moist (∼8 per cent and ∼9 per cent) seeds. It is also observed that this fraction of A_n sites which is capable of a very rapid rate of decay in the absence of oxygen is capable also of an even more rapid rate of reactivity towards oxygen.