ELICITATION OF H-2O2 PRODUCTION IN CUCUMBER HYPOCOTYL SEGMENTS BY OLIGO-1,4-ALPHA-D-GALACTURONIDES AND AN OLIGO-BETA-GLUCAN PREPARATION FROM CELL-WALLS OF PHYTHOPHTHORA-MEGASPERMA F SP GLYCINEA

The production of H2O2 by cucumber hypocotyl segments (Cucumis sativus L. cv. Wisconsin SMR 58) in response to alpha-1,4-linked oligomers of galacturonic acid and oligo-beta-glucans from the cell walls of Phylo phthora megasperma f.sp. glycinea was studied. Oligogalacturonides wit h degrees of polymerization of 9 to 13 elicited H2O2 production, the m ost effective being the deca-, undeca- and dodecamers. A similar relat ionship between size and effect was previously obtained when oligogala cturonides were tested for their ability to elicit lignification in cu cumber hypocotyls. The oligogalacturonide-induced increase in H2O2 con centration was detected after 4 h, reaching a maximum after 10 h of in cubation. The glucan elicitor induced lignification at a 100-fold lowe r concentration than the oligogalacturonides, but yielded only 10% of the maximum H2O2 accumulation seen with oligogalacturonides. The gluca n elicitor-induced H2O2 production was detectable after 2 h, and reach ed a maximum after 4 to 6 h. Catalase abolished the elicitation of bot h phenol red oxidation and lignification in cucumber hypocotyls. At le ast part of the oligogalacturonide-induced H2O2 production appeared to be dependent upon de novo protein synthesis.