The influence of seed water content on the oxygen effect in irradiated barley seeds

Chemical modification of postirradiation damage under varying oxygen concentrations in barley seeds

The influence of ascorbic acid, potassium permanganate and caffeine on the postirradiation seedling injury of dry barley seeds was studied, irradiated (350 Gy 60Co gamma-rays) in vacuo and post-hydrated with varying oxygen concentrations in the soaking medium. The oxygen concentration in the post-hydration medium (OCHG) was adjusted at 0%, 10%, 30%, 50%, 80% and 100%. A linear response between the seedling injury and O2 concentration in the range of 0-80% was observed. These chemicals potentiated, protected or exerted no effect, depending upon the OCHG. Thus, ascorbic acid did not exert any effect on seeds post-hydrated at OCHG of less than or equal to 30%, but afforded radio-protection at OCHG of greater than or equal to 50%. Caffeine, on the other hand, potentiated the postirradiation injury at OCHG of less than or equal to 30%, exerted no influence at OCHG of approximately 50% and afforded radioprotection at OCHG of greater than or equal to 80%. Potassium permanganate enhanced the injury at OCHG of less than or equal to 10%, exerted no effect at OCHG of approximately 30% and afforded radioprotection at OCHG of greater than or equal to 50%. The possible radiation-chemical events in the dry irradiated seeds following their post-hydration containing different OCHG and the three test chemicals which are known free radical scavengers are discussed.

Influence of seed moisture content and post-irradiation hydration temperature on the kinetics of reactivity towards oxygen or decay of oxygen-sensitive sites

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 approximately 3 per cent, approximately 8 per cent and approximately 9 per cent moisture contents at 3 degrees C, 25 degrees C and 37 degrees C. The magnitude of oxic damage at a given dose (35 krad) decreases as the initial seed moisture content increases from approximately 3 per cent to approximately 9 per cent. Significant (P = 0.01) oxic damage is observed in seeds of all the three moisture contents at 3 degrees C and 25 degrees C; however, at 37 degrees C significant (P = 0.01) oxic damage is observed only in seeds of approximately 3 per cent and approximately 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 degrees C and 25 degrees C, but it registers a significant (P = 0.01) decrease if post-hydration in oxygenated water is carried out at 37 degrees C. The radiation-induced oxygen-sensitive (An) sites react with oxygen approximately 6 to 8 times faster as compared to their rate of decay in the absence of oxygen at both 3 degrees C and 25 degrees C; however, at 37 degrees C they react only approximately 3 to 4 times faster, in seeds of all the three moisture contents. Moreover, the initiation of the decay of An sites becomes evident much earlier in very dry (approximately 3 per cent moist) seeds than in relatively moist (approximately 8 per cent and approximately 9 per cent) seeds. It is also observed that this fraction of An 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.

Modification of the radiosensitivity of barley seed by post-treatment with caffein. IV. Effect of the moisture content of seed and storage temperature after irradiation

The oxygen-dependent damage which develops in barley seeds with approximately 7-8 per cent moisture content disappears after post-irradiation storage in vacuo for 48 hours at 40 degrees C and for 24 hours at 50 degrees C. When the diration of storage at 40 degrees C is extended to 384 hours, oxygen-independent damage becomes potentiated. There is oxygen-dependent damage in seeds of approximately 13.3 per cent moisture content and after the seeds have been stored in vacuo at 50 degrees C, the oxygen-dependent damage begins to increase by 168 hours, and it is very significantly potentiated by 192 hours. Under these circumstances, caffeine acts as a radioprotector only as long as the precursors of oxic damage are present in the seeds. Once these sites are lost, caffeine acts only as a radiosensitizer. The oxygen-independent damage which increases with storage at high temperature is further potentiated by caffeine.

Maximum r.b.e. of fission neutrons for induction of somatic mutations in maize

This investigation was conducted to determine the maximum r.b.e. of fission neutrons for the induction of yellow-green sectors in maize. Seeds heterozygous for the yg2 locus were adjusted to 13 per cent water content, irradiated with varying doses for eitherfission neutrons or 60Co gamma-radiation, and soaked for 2 hours in nitrogen-bubbled water at ambient temperature before planting. Frequency of yg2 sectors, as scored in leaves 4 and 5, increase linearly for both radiations. The r.b.e. values were greater than1100 at 0.40 sectors per leaf 4 and greater than 600 at 0.20 sectors per leaf 5; however, at these low frequencies, the standard errors were 3 times greater than the r.b.e. At 6.0 sectors per leaf 4, the r.b.e. values were 111 plus or minus 9; and at 3.0sectors per leaf 5, 118 plus or minus 21. As measured by sectors per krad, mutagenic efficiency increased with increased dose of gamma-radiation; the opposite was true for fission neutrons. This trend was more evident for leaf 4 than for leaf 5.

Radiobiological damage: a new class identified in barley seeds stored after irradiation

A new class of radiobiological damage has been identified in irradiated barley seeds. Consisting of both physiological and genetic damage, it appears to be independent of oxygen and long-lived free radicals, and develops very slowly during storage after irradiation. Increasing the storage temperature accelerates its development.