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 Communicated by U. Lüttge ABA (probably through testa) and activities of hydrolases is proposed.

Seeds of Sesbania virgata (Cav.) Pers. (Leguminosae) contain galactomannan as a cell wall storage polysaccharide in the endosperm. 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 role of the testa (seed coat) on galactomannan degradation during and after germination. Seeds were imbibed in water, with and without the testa, and used to evaluate the effect of this tissue on storage mobilisation, as well as its possible role in the galactomannan hydrolases activities. Immunocytochemistry and immunodotblots were used to follow biochemical events by detecting and localising endo-β-mannanase in different tissues of the seed. Endo-β-mannanase and α-galactosidase activities were found in the testa and latter in the endosperm during galactomannan degradation. The former enzyme was immunologically detected in the testa, mainly during germination. The absence of the testa during imbibition led to the anticipation of protein mobilisation and increased of the α-galactosidase activity and galactomannan degradation. Thus, the testa appears to play a role during storage mobilisation in the legume seed of S. virgata probably by participating in the control of the production, modification and/or storage of the hydrolases.

Abbreviations: ABA, abscisic acid; BSA, bovine serum albumin; CAP, micropylar area around the radicle emergence point or endosperm cap; DAB, diaminobenzidine; DEAE, diethylaminoethyl; IgG, immunoglobulin G; LAT, lateral coat plus endosperm; LBG, locust bean gum; η sp , specific viscosity; PBS, phosphate buffer saline; pI, isoelectric point; RAD, radicle tip; SDS-PAGE, sodium dodecyl sulfate polyacrylamide gel electrophoresis; Visc. U., viscometric units.Galactomannans are storage cell wall polysaccharides present in seeds of some legumes. Their degradation is carried out by three hydrolases (α-galactosidase (EC 3.2.1.22), endo-β-mannanase (EC 3.2.1.78) and ß-mannosidase (EC 3.2.1.25)). In the present study we purified and characterised an endo-β-mannanase from seeds of Sesbania virgata and addressed its role in germination and seedling development. The polypeptide purified by Ion Exchange Chromatography and Affinity Chromatography on Sepharose-Concanavalin A, showed a pH optimum between 3.5 and 5 at 45 o C and high stability at pH 7.8. The low stability at pH 5 appears to be associated with isoelectric precipitation, in view of the pI of the enzyme being 4.5. The purified enzyme is a glycoprotein with a molecular mass of 26 KDa by SDS-PAGE and 36 KDa by gel chromatography. The purified polypeptide attacked galactomannan from different sources, being more effective on polymers with a lower degree of galactosylation (from carob gum), in comparison with medium or highly galactosylated galactomannans (from guar, S. virgata and fenugreek), respectively. A peak of endo-β-mannanase activity was detected during radicle protrusion in the endosperm tissue surrounding the radicle and later on in the lateral endosperm. This second peak was associated with the period of reserve mobilisation. Using an antibody raised against coffee endo-β-mannanase, the enzyme could be detected in immunodot-blots performed with extracts of S. virgata endosperms. The results are consistent with the hypothesis that the peak of endo-mannanase during germination facilitates radicle protrusion through the surrounding endosperm by weakening it in the region close to the radicle tip. Key words: Sesbania virgata, endo-β-mannanase, galactomannan, germination, Leguminosae.Endo-β-mananase do endosperma de sementes de Sesbania virgata (Cav.) Pers. (Leguminosae): purificação, caracterização e seu duplo papel na germinação e crescimento inicial da plântula: Galactomananos são polissacarídeos de reserva de parede celular presentes em sementes de leguminosas. Sua degradação é efetuada por três hidrolases (α-galactosidase (EC 3.2.1.22), endo-β-mananase (EC 3.2.1.78) e β manosidase (EC 3.2.1.25)). No presente estudo, nós purificamos e caracterizamos uma endo-β-mananase de sementes de Sesbania virgata e focamos no seu papel na germinação e no desenvolvimento da plântula. A enzima foi purificada por cromatografia de troca iônica e cromatografia de afinidade em sepharose-concanavalina A, mostrando um pH ótimo entre 3,5 e 5 a 45 o C e alta estabilidade em pH 7,8. ...