Studies on the Formation of Adventitious Root Initial in Mung Bean Seeding Hypocotyl

The formation of adventitious roots was studied by using 7-day-old mung bean hypocotyl cuttings. The cuttings presoaked for 24 hrs in NAA at a concentration of 1x10^(-4) M produced more adventitious roots than at any other concentration of NAA used and more than in any other auxin tested. The basal part of the cuttings formed the roots in four rows; these originated from the phloem parenchyma cells. Cell division of these parenchyma cells was evident after 36 hrs of incubation in distilled water. The formation of adventitious roots was inhibited by cycloheximide (5 μg/ml), and 5-fluorouracil (1x10^(-3) M) but not by α- amanitin ( 1 μg/ml). Presence of 5-FU in the beginning of the incubation period in distilled water following 24 hrs presoaking inhibited the cell division and consequently inhibited the formation of root inhitials. 5-FU also inhibited the formation of adventitious roots even after cell divisions had occurred. Using 3H-uridine as a tracer, RNA synthesis was measured before any cell division had occurred in the root initials. NAA stimulated the RNA synthesis nearly 2 fold and this was inhibited by 5-FU. It is concluded that rRNA synthesis is essential before cell division can occur in the formation of root initials. The ultimate formation of adventitious roots from root initials also requires continuous cell division and also continuous synthesis of rRNA.