Differential Effects of Actinomycin D and Cordycepin in Lettuce Seed Germination and RNA Synthesis

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Abstract
Intact lettuce seed germination was inhibited by cordycepin but not by actinomycin D; however, when seeds were clipped at the cotyledonary end, actinomycin D partially inhibited germination. Uptake studies with intact seeds using 3H-actinomycin D showed that it was unable to reach the embryo prior to radical protrusion. 3H-Cordycepin uptake studies using intact seeds showed that cordycepin was able to reach the embryo during the first 3 h of incubation and at subsequent times. The pericarp and endosperm offered resistance to penetration of cordycepin into the embryo. In contrast to actinomycin D, cordycepin markedly inhibited 3H-uridine incorporation into RNA of intact seeds during the first 10 and 12 h of incubation. About 60% of 3H-adenosine incorporation into poly A-RNA was inhibited by cordycepin during 12 h of incubation, whereas actinomycin D had little effect. RNA synthesis appears to be essential for seed germination.