Cell wall structure regulates the autolytic process throughout growth of Cicer arietinum epicotyls

Abstract

The autolytic process in epicotyl cell walls of Cicer arietinum L. cv. Castellana, and also the hydrolysis of heat-inactivated cell walls as mediated by a cell wall {beta-­galactosidase (EC 3.2.1.23) (named betaIII and previously characterized as responsible for the autolysis), are maximal on the fourth day of germination and coincide with the maximal growth capacity. They decrease during the following days, in which the growth rate diminishes. In both cases, no differences were observed in the percent­ages of the different sugars released, galactose being the principal one. The betaIII fraction from aged epicotyl cell walls hydrolyzed young walls in proportion to its specific activity, and more efficient than when cell walls from aged material were used as the substrate. ThebetaIII fraction from 4 day-old epicotyls (the time for maximal autolysis) was incapable of hydrolyzing aged epicotyl cell walls to the same extent as young ones. These results, together with the levels and activity of the enzyme throughout growth, allow the assumption that the variations in the autolysis and hydrolysis caused by betaIII during growth processes are due to structural modifications in the cells walls, modifications that would limit access of the enzyme to its substrate, thus impeding the release of galactose, even though the enzyme is present.