GLYCEOLLIN ELICITORS INDUCE MAJOR BUT DISTINCTLY DIFFERENT SHIFTS IN ISOFLAVONOID METABOLISM IN PROXIMAL AND DISTAL SOYBEAN CELL-POPULATIONS

Biotic and abiotic glyceollin elicitors were examined for their effects on isoflavonoid metabolism in discrete soybean cotyledon cell populations proximal and distal to the point of elicitor application. Phytophthora megasperma f. sp. glycinea wall glucan elicited glyceollin to levels as high as 1,800 nmoles/g of tissue, but only in the uppermost cell layers of treated cotyledons. In these same cell layers, P. m. f. sp. glycinea wall glucan elicited even larger accumulations (> 4,000 nmoles/g of tissue) of conjugates of the glyceollin precursor daidzein and the related isoflavone genistein. In underlying cell populations, 5-20 cells away from the point of elicitor application, P. m. f. sp. glycinea wall glucan induced accumulations of daidzein and genistein conjugates as high as 9,000 nmoles/g of tissue, but no glyceollin. Accumulation of the isoflavone conjugates, but not of glyceollin, was highly light-dependent in all sections. Glyceollin accumulation induced in the upper cells by abiotic elicitors was accompanied by large decreases in existing daidzein and genistein conjugates, suggesting that abiotic elicitors may act, in part, by releasing the precursor daidzein from preexisting pools. Although abiotic elicitors also caused a buildup of isoflavone conjugates in underlying cell layers, the response was far less dramatic when compared with the biotic elicitors.