Effect of high temperature on condensed tannin accumulation in leaf tissues of big trefoil (Lotus uliginosus Schkuhr)

Plants from three clones of big trefoil (Lotus uliginosus Schkuhr) having low, medium and high concentrations of tannin in their leaves were subjected to growing conditions with normal (20 degrees C) and high (30 degrees C) temperature regimes. Plants were tested every 3 weeks for foliar condensed tannin content using the vanillin-HCl and the butanol-HCl assays. Plants from clones growing under high temperatures matured more quickly and by 14 days had condensed tannin levels substantially greater than plants from the same clones grown under normal temperatures. Clones remained consistent with respect to their parental tannin levels throughout two trials. Leaves from high-temperature clones suffering additional nutrient stress symptoms had very low levels of foliar condensed tannins and cross-sections of chlorotic leaves revealed an absence of large tannin vacuoles. It is concluded that high-temperature stress can induce the formation of additional condensed tannin in the leaves of this species.