involved in defense response. In addition, changes in carbohydrate concentrations were previously
associated with signal transduction pathways responsible for enhanced immune response
to pathogen infection [14].
Carbohydrate pools likely provide the carbon source for the production of aromatic amino
acids and oxidative compounds via increased flux through the pentose phosphate pathway
(PPP) (Fig 10). Glucose-6-phosphate, which increased in induced plants in this study, is the
primary precursor for the PPP. The oxidative portion of the PPP is a significant source of
NADPH that provides reducing power for the generation of reactive oxygen species through
NADPH oxidases. The non-oxidative portion of the PPP generates erythrose 4-phosphate
which is the primary precursor to the shikimate pathway for aromatic amino acids. The increased
pools of tryptophan and phenylalanine are precursors for defense related antimicrobial
and plant signaling compounds such as lignins, alkaloids, chalcones, salicylic acid, and auxins.