Endo-beta-mananase de endosperma de Sesbania virgata (Cv.) Pers : purificação, caracterização e importancia na germinação e desenvolvimento da plantula

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

Many plant seeds have an endosperm, a tissue specialised either as storage or mechanical constraint to embryo growth. In many legume species, endosperms contain galactomannan. This polyssacharide is composed of a main chain of 1,4-β-mannan branched with variable amounts of 1,6-ά-linked galactosyl residues. Three enzymes produced by an aleurone layer are involved in galactomannan hydrolysis: endo-β-mannanase, ά-galactosidase and β-mannosidase. The former with mannanase attacks the polymer producing galactosylated oligossacharides which are further hydrolysed by the two last exo-enzymes to free mannose and galactose. In the present work, an endo-β-mannanase was purified from the endosperm of Sesbanía vírgata, a Brazilian native legume. The time-course shows that the activity of mannanase appears initially in the endosperm cap of seeds prior to radicle emergence and subsequently increases in the remaining lateral endosperm following seedling growth. Measuring the activity at pH 5 and 45°C, endo-mannanase peaked at 120h and then decreased. We used these conditions to perform purification procedures in DEAE-cellulose followed by affinity chromatography with Sepharose Concanavaline-A. The enzyme is a glycoprotein with an apparent molecular weight of 30Kda, optimum pH at 4.5 and temperature at 45°C, pI at 4.5. The mode of action of the enzyme on different galactomannans indicates the modulation of mannanase activity by the branching pattems of the polymers with galactose. From these observations it was concluded that mannanase activity facilitates radicle protrusion through the surrounding endosperm by weakening it in the area close to the radicle tip. On the basis that the pure enzyme can not degrade the fenugreek galactomannan (a fully substituted polysaccharide), we suggest that there is an inverse relationship between galactose branching and the degree of hydrolysis.

ASSUNTO(S)

parede celular vegetal germinação

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