Effects of Growth Regulators on Polyamine Content and Peroxidase Activity in Hevea brasiliensis Callus

3, 4-dichlorophenoxyacetic acid (3,4-D) and benzylaminopurine (BAP) at 9 μM (control medium) was compared with 4.5, 2.25, and 0.45 μM for ability to induce callogenesis and embryogenesis from seed explants of Hevea brasiliensis. Supplying these growth regulators at 4.5 μM for 20 d improved embryogenic potential compared with the control medium (El Hadrami, Carron and d'Auzac, 1991, Annals of Botany 67, 511–515), sustained putrescine, spermidine and spermine at a higher level throughout of much of the culture period (40–70 d), and maintained low levels of peroxidase activity. In the control medium, poor callus embryogenesis is considered a consequence of rapid ageing of tissues characterized by (i) acceleration of an early but transient production of polyamines, which promoted embryogenic capacity, and (ii) an early peak in peroxidase activity that was positively correlated with callus browning, one of the factors limiting embryogenesis.