Effects of polyamine biosynthetic inhibitors on somatic embryogenesis and cellular polyamines in Hevea brasiliensis

Abstract

Summary Hevea brasiliensis , like other ligneous plants, has been considered for a long time to be a recalcitrant embryogenic species. Nevertheless, exogenous polyamines (PA) added individually or together to the culture medium constitute one among other factors, favorizing the calli embryogenic capacity. Inhibitors of enzymes involved in polyamine biosynthesis like DL-difluoromethylarginine (DFMA), DL-difluoromethylornithine (DFMO) and methylglyoxal bis(guanylhydrazone) (MGBG) are usually used to demonstrate that PA are required for normal growth and development. In Hevea , application of these inhibitors, at concentrations that did not affect callogenesis, lowered somatic embryo formation. In a few cases, the inhibition was partially reversed by addition of spermidine (Spd) (50 µM). The effect of inhibitors on PA levels was opposite to actual knowledge of the pathway for PA synthesis. MGBG, an inhibitor of S-adenosylmethionine decarboxylase (SAMDC), largely decreases the putrescine (Put) level; however, synthesis of this diamine should have been increased by this treatment. DFMO, an inhibitor specific for ornithine decarboxylase (ODC), paradoxically increases Put. The accumulation of Spd and spermine (Spm) by DFMA also appears paradoxical because DFMA, known as a specific inhibitor of arginine decarboxylase (ADC), should have produced a decrease in both PA. The specificity of the classical polyamine biosynthesis inhibitors is discussed.