Abstract
Melle-pasture type perennial ryegrass seeds ( Lolium perenne: a crossfertilizer) were subjected, after equilibration to 4 different moisture levels, to acute X-rays (90 kVp–4 mA: 2000 rad/min) and semi-chronic Co 60 γ-rays (25 rad/min) with the same total energy dissipation in the tissues. For each moisture level a survival dose curve was constructed. The percentage survival of the seedlings after 4-weeks growth in a Knop's nutrient solution was used as a criterion of radiation damage. A definitely higher potency of the semi-chronic γ-ray treatment of dry seeds (watercontents respectively: 4·60 and 6·65%) could be observed by germinating them immediately after irradiation as well as with a 3-week storage period prior to germination. However with moist seeds (water-contents respectively: 14·24 and 16·93%) the same total amount of damage for both radiation sources could be observed, by germinating them immediately as well as with a 3-week storage period. Thus the differential effect immediate as well as after storage with dry seeds really represents a difference in the potency of the two sources. As with dry seeds the indirect action of both radiations is at work, the cause of this differential action should be sought in a possible quenching effect of excited molecules either because of the higher dose rate of acute X-rays, or simply because of the higher LET-value of 90 kVp X-rays (100 ionpairs/μ) over Co 60 γ-gays (8 ionpairs/μ). The differential LET-value seems to play no role in the direct action with moist seeds.
Published Version
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