Factors Modifying the Radio-Sensitivity of Seeds 



and the Theoretical Significance of the Acute 



Irradiation of Successive Generations 1 



RICHARD S. CALDECOTT and D. T. NORTH 2 



University of Minnesota, St. Paul, Minn. 



The purpose of this report is twofold, namely, to present data 

 which demonstrate the nse of dormant seeds in biophysical 

 stndies and to discuss the possible genetic and applied significance of 

 the irradiation of successive seed generations of the small-grained 

 cereals. 



Part I. Modification of the Radiosensitivity of Seeds 



For years it has been obvious to investigators working with seeds 

 that these biological structures apparently represent an unique system 

 in that they can be subjected to extremes of environment without 

 impairment of function when restored to the conditions required for 

 normal growth and development. Using seeds, it has been possible 

 to study the biological consequences of treatments that were other- 

 wise only possible in vitro. This was perhaps best shown in studies 

 where, by decreasing the water content well below levels at which 



7 J o 



physiological activity was possible, seeds tolerated temperature 

 extremes ranging from those of liquid nitrogen to 112° C. 



It also was shown that under conditions where physiological 

 activity was not detectable, the expression of damage to X-rayed seeds 

 could progressively increase for weeks after initial photon absorption 

 (1, 2, 5, 12). 3 Furthermore, the rate and degree of this injury enhance- 



This work was conducted under Contract No. AT (1 1—1)— 332 between the University 

 of Minnesota and the U. S. Atomic Energy Commission. The report is a compilation of 

 two reports previously presented at symposia sponsored by the IAEA and FAO in 

 Karlsruhe, Germany, August, 1960, and the AAAS in Chicago, 111., in December, 1959. 

 Contribution from the U. S. Department of Agriculture, Field Corps Research Branch, 

 ARS. 



2 The writers are pleased to acknowledge the help of Dr. Alessandro Bozzini on the 

 studies relating to seedling height and genetic injury, Miss Victoria L. Bergbush on all 

 phases of the temperature investigations, and Miss Louise Heine and Mr. Fa-ten Kao 

 for assistance with the cytological investigations. 



3 See References, page 398. 



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