RETARDATION OF ULTRAVIOLET LIGHT ACCELERATED LEAF SENESCENCE BY A CYTOKININ: N6 BENZYLADENINE

O ne clear evidence of u.v. injury is the manifestation of chlorosis after leaf irradiation, and such chlorosis can be photorepaired by blue light1]. We found that such u.v.-accelerated chlorosis could be prevented in the dark by applying N⁶ benzyladenine (BA), a synthetic cytokinin, either before or after u.v. irradiation. Cytokinins are known to retard natural senescence of detached leaves kept in the dark 2]. The present finding suggests that u.v. damage may accelerate the natural senescence process of detached leaves kept in the dark. N. glutinosa leaves were used in this experiment, because chlorosis develops quickly (within one week) when the mature leaves are detached and incubated in the dark. The plants were grown in a glasshouse without white-wash. The light intensity at noon often reached 9000 ft-c., and the temperature ranged from 19–35°C. The leaves shown in Fig. 1 were from mature plants, i.e. plants with the terminal growing point developed into a flower bud. The floral buds were cut off several days before the leaves were detached for exposure to u.v. light.