Radiation damage in shoots of sweet cherry ( Prunus avium L.)

Abstract

An anatomical study of radiation damage was made in growing sweet cherry buds exposed in a dormant condition to 0–8000 rads of γ-rays. Buds of Bing or Black Tartarian were fixed from dormant scions, from scions forced in water, or from growing shoots on recently budded rootstocks. The dormant buds of Bing and Black Tartarian contained an average of 7·1 foliage leaves and 2·5 leaf primordia. Secondary buds developed from the lower axillary meristems during bud burst. Irradiated buds on scions forced in water until the green tip stage showed radiation-damaged cells in the axillary buds but not in the apical meristems. In buds established on rootstocks, such cells appeared in the leaf primordia, apical and axillary meristems, the vascular tissue and the pith. Radiation-damaged cells were characterized by darkly stained thickened cell walls, and the virtual absence of division. Irradiation greatly retarded the production of new leaves by the apical but not by the axillary meristems. The stratification of both apical meristems and axillary buds became increasingly disturbed as growth proceeded. Recovery of the apical meristem was not observed anatomically but it evidently occurred, as shown by the absence of budless shoots or branching. The first seven leaves of a typical shoot from an irradiated bud showed a fine, light green or whitish mosaic; the next three leaves had a coarse mosaic; the next two-four leaves, the number increasing with dose, bore light green sectors; the remaining two-three leaves were normal. The number of leaves with different types of mosaic corresponded to the number and differentiation of leaves in the dormant bud. Radiation damage in shoot meristems of cherry was random in its distribution and recovery probably resulted from the activity of the less injured cells throughout the apical and axillary meristems. Patterns of radiation damage in apical meristems, as reported for higher plants, fall into three categories, localized, random or uniform. Random damage in buds has apparently not been previously described.