Kinetics of ethylene biosynthesis and its effects during maturation of white spruce somatic embryos

Abstract

The objective of the current investigation was to study the role of ethylene in the maturation of white spruce (Picea glauca [Moench.] Voss) somatic embryos. This was carried out by examining the effects of (1) 1-aminocyclopropane-1-carboxylic acid (ACC), a direct precursor of ethylene in plant tissue, (2) silver nitrate (AgNO 3 ), an inhibitor of ethylene action, (3) α-aminooxyamino acid (AOA), a potent inhibitor of ethylene biosynthesis, and (4) enrichment with ethylene. Ethylene biosynthesis was biphasic and gradually increased during embryo development, whereas endogenous ACC and N-malonylaminocyclopropane-1-carboxylic acid (mACC) decreased. Addition of ACC or AOA to the culture medium increased or decreased, respectively, ethylene biosynthesis by altering endogenous ACC levels during the culture period. In contrast to AOA and AgNO 3 , ACC and ethylene enrichment significantly decreased the production of mature somatic embryos and increased the browning of the cultures. However, the structure of the shoot apex in mature cotyledonary stage embryos formed under ethylene enrichment was similar to that in control systems. This shows that a reduction in ethylene is beneficial to maturation of white spruce somatic embryos. This is further substantiated by the finding that the inhibitory effects of AOA were partially reversed by the addition of ethylene. The possible effects of the interaction between ethylene and polyamines on somatic embryo development are also discussed.