Effect of abscisic acid on galactomannan degradation and endo-β-mannanase activity in seeds of Sesbania virgata (Cav.) Pers. (Leguminosae)

Abstract

Seeds of Sesbania virgata (Cav.) Pers. (Leguminosae) have an endosperm which accumulates galactomannan as a storage polysaccharide in the cell walls. After germination, it is hydrolysed by three enzymes: α-galactosidase (EC 3.2.1.22), endo-β-mannanase (EC 3.2.1.78) and β-mannosidase (EC 3.2.1.25). This work aimed at studying the effect of abscisic acid (ABA) on galactomannan degradation during and after germination. Seeds were imbibed in water or in 10−4 M ABA, and used to evaluate the effect of exogenous and endogenous ABA. Tissue printing was used to follow biochemical events by detecting and localising endo-β-mannanase in different tissues of the seed. The presence of exogenous ABA provoked a delay in the cellular disassembly of the endosperm and disappearance of endo-β-mannanase in the tissue. This led to a delay in galactomannan degradation. The testa (seed coat) of S. virgata contains endogenous ABA, which decreases ca. fourfold during storage mobilisation after germination, permitting the galactomannan degradation in the endosperm. Furthermore, endo-β-mannanase was immunolocalised in the testa, which has a living cell layer. The ABA appears to modulate storage mobilisation in the legume seed of S. virgata, and a cause–effect relationship between ABA (probably through testa) and activities of hydrolases is proposed.