Effect of X-rays on the Number and Growth-rate of Lateral Roots inVicia Faba

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Abstract
Partial exposure of primary roots of Vicia faba to 300 kv X-rays caused a decrease in the number and growth-rate of secondary (lateral) roots arising in the irradiated region. There were no abscopal effects: irradiation of the primary meristem, or cutting off the tip of the primary roots, did not influence the number of laterals produced. When the number of laterals emerging was expressed as a percentage of those appearing in unirradiated roots, and the log percentage survival plotted against X-ray dose, the greatest sensitivity was shown by the distal portion of the primary root from 1 to 5 cm from the tip (D0 = 30 rad, N 8). Above 6 cm the tissue became progressively less sensitive to inhibition of lateral root production. It is suggested that the lateral root initials are suppressed by cell-killing whose effects are magnified by tissue disorientation.