Effects of exogenous polyamines and inhibitors of polyamine biosynthesis on endogenous free polyamine contents and the maturation of white spruce somatic embryos

Abstract

The maturation of somatic embryos is a pivotal stage of somatic embryogenesis process. Thus, this study is aimed at investigating the role of polyamines on the maturation of somatic embryos of white spruce (Picea glauca). Two inhibitors of the biosynthesis of polyamines methylglyoxal bis-(guanylhydrazone) (MGBG) and dicyclohexylamine (DCHA) or three exogenous polyamines (putrescine, spermidine and spermine) were added into a modified HLM-1 maturation medium inoculated with embryogenic tissues. Medium responses were assessed with respect to the production of mature somatic embryos, the cellular concentration of free polyamines and the concentration of 1- aminocyclopropane-1-carboxylic acid (ACC) and N-malonylaminocyclopropane-1-carboxylic acid (mACC), the precursor of ethylene biosynthesis and its conjugate, respectively. Results show that DCHA brought about a significant decrease in the concentration of free cellular putrescine during the first two weeks of maturation, whereas MGBG induced a significant decrease of both spermidine and spermine. Moreover, both inhibitors (1 mM DCHA or 1 mM MGBG) reduced the total number (63 and 52%, respectively) and the number of normal (62 and 54%, respectively) somatic embryos. Addition of 5 mM spermidine or 1 mM spermine increased the total number (94 and 113%, respectively) and the number of normal (134 and 143%, respectively) somatic embryos. Finally, the intracellular concentrations of ACC and mACC significantly increased in the presence of exogenous spermidine while decreasing in the presence of MGBG, suggesting that spermidine interacts with ethylene metabolism. These results clearly demonstrate that polyamines play an important quantitative and qualitative role during the maturation of white spruce somatic embryos.