The Effect of Mineral Nutrients Calcium and Magnesium on Production and Bioactivity of Condensed Tannins in Illinois Bundleflower.

Macronutrients are used by plants in relatively large concentrations and impact primary metabolism, growth and development processes. Little is known about the impact of macronutrients on secondary metabolite production. We determined how altering Ca and Mg in a nutrient solution impacts production of total phenolics (TP) and condensed tannins (CT) by a warm-season perennial forage legume. Desmanthus illinoensis (Illinois bundleflower) was reared in a greenhouse and subjected to one of 7 treatments: watered with a complete nutrient solution containing 2.0 mM Ca and 0.5 mM Mg (1X control) or a nutrient solution containing 1/2X, 2X or 3X Mg or Ca. Leaves were harvested at flowering-stage and analyzed for TP, CT and protein binding ability (PB). The greatest TP (P<0.05) were produced by plants grown in 1/2X Ca and 1/2X Mg (322.61 and 361.63 g/kg DM, respectively). Plants grown in 1/2X Ca and 1/2X Mg also produced the greatest CT (P<0.05; 205.8 and 201.8 g/kg DM, respectively). Total phenolic and CT concentrations were not different (P>0.05) among 1X control, 2X Ca, 2X Mg and 3X Ca. However, CT produced by plants grown in 3X Ca demonstrated the greatest PB (P<0.05; 0.86 g protein/g PPP), whereas 2X Mg and 1/2X Ca demonstrated the least (P<0.05; 0.45 and 0.42 g protein/g PPP, respectively). The 1/2X Mg ranked second only to 3X Ca for greatest PB and resulted in the greatest combination of TP, CT and PB by Illinois bundleflower. Plants grown in 1/2X Ca produced the greatest concentrations of CT with the least bioactivity suggesting a tradeoff exists between quality and quantity of polyphenolic compounds produced under Ca stress. Results suggest that availability of Ca and Mg impacts the concentration and bioactivity of CT and that Illinois bundleflower responded to nutrient stress by increasing TP and CT production.