Age-related regulation of induced isoflavonoid responses in soybean lines differing in inherent elicitation competency

Abstract

The accumulation of the pterocarpan phytoalexin glyceollin in soybean tissues, in response to the general resistance wall glucan elicitor from Phytophthora sojae, requires both the synthesis (or release from pre-formed conjugates) of the glyceollin precursor daidzein and the pre-activation of a state of glyceollin elicitation competence in responding cells by factors associated with wounded or hypersensitively dying cells. While many soybean cultivars (e.g. Williams) do not produce glyceollin in response to elicitor in the absence of competence activation, the cultivar Harosoy is partially inherently elicitation competent, although its capacity for elicitation competence can be further induced. To gain some insight into the fundamental differences in these lines, developmental and age-related effects were compared on various isoflavonoid responses in the two lines. The activation of glyceollin elicitation competency in Williams (and its enhancement in Harosoy) are both dramatically affected by the developmental age of tissues, being maximal in cotyledons of intermediate age. In both cultivars these effects are similar and appear to relate to the capacity of the tissues to generate the endogenous competency factors. Parallel developmental age effects were also observed in hypocotyl and root tissues. However, very clear differences in the light and glucan induction of the isoflavones genistein and daidzein, respectively, were observed in the two cultivars depending on tissue age. Thus, the differences in glyceollin elicitation competency in Williams and Harosoy may relate more to inherent differences in the net accumulations of isoflavone precursor pools than to the generation of the elicitation competent state per se.