Histological aspects of in vitro root and shoot differentiation from cotyledon explants of Brassica juncea (L.) czern

Abstract

Under fairly simple culture conditions, excised cotyledons of Brassica juncea undergo high frequencies of either root formation on growth regulator-free Murashige and Skoog (MS) medium or shoot formation on MS + 5.0 μM N 6-benzyladenine (BA). Temporal histological events of organ differentiation processes revealed that while root formation was endogenous in origin and did not involve callusing, shoot bud differentiation occurred after the formation of meristematic nodules at the cut end. While root primordia differentiated from the petiolar cut end after 4 days in culture, the formation of a meristematic nodule at the same end occurred by 4–6 days which further lead to the differentiation of shoot meristem by 8–10 days. Although the initial accumulation of starch in organogenic cotyledons was the same during both root and shoot formation, its depletion was faster in shoot forming cultures suggesting that this process is more energy requiring than rhizogenesis.