Gibberellic-acid-induced synthesis and release of cell-wall-degrading endoxylanase by isolated aleurone layers of barley.

When aleurone layers of barley (Hordeum vulgare L.) are incubated with gibberellic acid (GA3) xylose and arabinose-both as free sugars and bound to larger molecules-are released into the medium. Release begins 10-12h after the start of incubation and continues for at least 60h. At the same time there is a GA3-induced breakdown of the cell wall resulting in a loss of 2/3 of the cell-wall pentose during 60h of incubation. GA3 causes the appearance in the medium of an enzyme (or enzymes) which hydrolyze larchwood xylan and aleurone-layer arabinoxylan. Release of the enzyme(s) into the medium begins 28-32h after the start of incubation. Enzyme activity does not accumulate to any large extent in the tissue prior to release into the medium, and is present in very low levels only in the absence of GA3. Xylanase activity is associated with a protein (or proteins) with a molecular weight of 29,000. The hydrolysis of the xylans is largely caused by endoxylanase activity, indicating the importance of endoglycosidases in the GA3-induced breakdown of the aleurone cell wall.