A general description of barley coleoptile growth behaviour under low LET radiations

The effect on coleoptile growth of irradiating dry barley caryopses with 60Co gamma radiation and 1.0 MeV electrons, under similar experimental conditions, was studied. The results on growth inhibition led to the development of a dose-response description for low LET radiations. For the general description to be valid it was necessary to prove that the number of cells, the cell length and the cell width of the coleoptile behave similarly under the two types of radiations. This was verified. The effects of the radiations on germination were also found to be similar. The dose-response description consisted of various regions. There was an initial exponential decline of the curve to 100 kr, which was followed by a trough between 125 and 175 kr. Next, an inversion of the curve occurred in a recovery zone where an increase in coleoptile length accompanied increasing doses. The final portion showed a decline in growth at high doses. The initial slope was related to a decrease in cell number, which in turn reflected the inhibition of cell division. However, the cell number remained constant from 100 kr on to higher doses for both radiations. The recovery zone of the dose-response of coleoptile growth reflected an increase in cell length which, at 500 kr, reached a maximum of 1.63 times the control value. At doses higher than 800 kr the length decreased. These results supported the conclusion that cell division was more sensitive than cellular elongation to low LET radiations. (author)