Galaktomannanabbau in keimenden Johannisbrotsamen (Ceratonia siliqua L.)

Abstract

In the first days of germination of carob seeds (Ceratonia siliqua L., Leguminosae) (until penetration of the seed coat by the radicle) oligosaccharides of the raffinose series present in the endosperm and embryo are hydrolysed. The mobilisation of the reserve galactomannan of the endosperm begins after the emergence of the radicle. Its degradation is effected by hydrolytic enzymes (α-galactosidase [EC 3.2.1.22], β-mannanase, [EC 3.2.1.25] and β-mannosidase [EC 3.2.1.25]) and the breakdown products-galactose and mannose-are continuously metabolised by the embryo. At the same time starch synthesis is observed in the embryo.

In the germination of Ceratonia siliqua seeds the embryo does not have a direct effect on the mobilisation of the reserve polysaccharide as it does in the case of barley. The endosperm consists of living cells which, independently of the embryo, synthesise the enzymes used for galactomannan breakdown. A weak α-galactosidase activity is already present in the endosperm of mature dry seeds. This activity cannot be suppressed by inhibitors of transcription or translation, so that their presence does not prevent degradation of oligosaccharides of the raffinose series.

A high proportion of the α-galactosidase responsible for the breakdown of the galactomannan is synthesised de novo during germination. Such synthesis could be demonstrated by the incorporation of [U-¹⁴C]serine and could be inhibited by actinomycin D or cycloheximide.