Effect of osmotic stress on the growth of epicotyls of Cicer arietinum in relation to changes in the autolytic process and glycanhydrolytic cell wall enzymes

Abstract

Simulation of drought by polyethylene glycol (PEG) inhibited elongation of epicotyls of Cicer arietinum L. cv. Castellana but had no effect on growth capacity sin ce growth was restored once the inhibitory condition had been removed. The amount of proteins in the cell wall was correlated with the elongation of the epicotyls and decreased when elongation was inhibited. PEG-induced inhibition of elongation had different effects on the various glycanhydrolytic cell wall enzymes. Only alpha-galactosi­dase (EC 3.2.1.22) seemed related to the lack of elongation, increasing its activity when elongation was inhibited. The beta-galactosidase (EC 3.2.1.23) and beta-glucosidase (EC 3.2.1.21) studied did not show changes in their specific activities during the inhibition of elongation. beta-Galactosidase is responsible for the autolytic process in Cicer arietinum. This enzyme hydrolyzes specified linkages in the cell wall, releasing sugar constituents. Our present results show that beta-galactosidase is not directly related with elongation because no changes could be observed during inhibition of elongation. The autolytic process is related with chemical processes taking place in the cell wall and preceding elongation of the epicotyls, i.e. the loosening process. Cell wall loosening is necessary for elongation to take place but elongation does not necessarily follow loosening if the osmotic conditions are unfavorable.