Polyamine and ethylene changes during floral initiation in response to paclobutrazol in mango (Mangifera indica L.)

Use of paclobutrazol is common strategy for inducing uniform and profuse flowering in mango. The possible mechanism by which paclobutrazol exert such responses are less understood. The present investigation was carried out to investigate possible role of polyamines and ethylene biosynthesis in the paclobutrazol induced floral induction in mango. Following paclobutrazol soil drenching application (1.25 g a.i. m -1 ) to mango cv. Totapuri, the free polyamine contents, ethylene production, 1-amino cyclopropane carboxylic acid (ACC) content and ACC oxidase activity were determined in the apical buds and leaves of growing shoots at 4 distinct bud developmental stages numerically characterized as 510 (initiation of bud swelling), 511 (swollen buds), 513 (bud burst) and 515 (panicle emergence) according to standard BBCH scale. The total free polyamines, spermidine and spermine contents increased and ethylene production, ACC content and ACC oxidase activity decreased in the buds and leaves of paclobutrazol treated as compared to untreated trees. In general under paclobutrazol treatment, buds accumulated more polyamines than the leaves. With respect to the bud growth stages, total free polyamines, spermidine and spermine were high at 510/511 stage both in the paclobutrazol treated and untreated trees which declined progressively as shoots approached panicle emergence stage (515). The ethylene production, ACC and ACC oxidase activity exhibited trends opposite to that of polyamines. The study showed that polyamine – ethylene balance may control paclobutrazol induced floral bud induction in mango and accumulation of polyamines-spermidine and spermine in buds appeared as an important factor in facilitating floral induction response. Keywords— Ethylene biosynthesis, mango flowering, paclobutrazol, polyamines.