[The effects of the cytostatic drug "proresid" on growth and chloroplast differentiation induced by blue light in excised and normal seedling roots of Pisum sativum].

"Proresid" (podophyllic acid ethylhydrazide; SP-1, Sandoz), a cytostatic drug with rapid but reversible effects on mitosis, inhibits growth, fresh weight increase and chlorophyll synthesis in excised roots of pea seedlings (var. Alaska) cultured in blue light (350-550 nm). Upon transferal of the treated fragments to normal culture medium the activity of these processes is fully restored within a few days. The reactions of intact seedlings on exposure of only the root tip to Proresid indicate that the drug exerts its action indirectly by blocking certain activities of the apical meristem. The important role of the latter in supporting or inhibiting various processes in the root is demonstrated by the observation that removal of the root tip from excised roots reduced the chloroplast differentiation in blue light to a very low yield, but induced cell divisions and lateral root formation. Moreover, there is good evidence that the drug is not actively transported in the root when supplied to the root tip only. Exposure of the whole root of a seedling to Proresid for longer periods does not only prevent its growth and differentiation but also gives rise to the formation of adventitious roots in the epicotyl region of the shoot.