Exudation of UV-light absorbing natural products by seedlings ofNuphar lutea

Abstract

Seedlings ofNuphar lutea (L.) Sm. were raised from seeds and cultivated in a synthetic sterile nutrient solution under physiologically controlled and undisturbed conditions. The extracellular release of carbon compounds from the plants into the surrounding medium was examined by direct carbon estimation, by various specific chemical assays and by HPLC analysis. Direct carbon estimation was not sensitive enough to obtain reliable values; five of six specific chemical assays also failed. Only the Folin-Denis assay indicated there was a production of phenolic compounds, which followed a linear course that took up to six days of incubation. The phenolic compounds ranged between 0.2 and 1.3 µg/h g dry weight. Rp-HPLC with UV detection yielded a major fraction containing at least five highly polar compounds (not retainable on reversed phase), and a minor fraction of at least eight less polar (rp-retainable) compounds. Exudation followed a linear course for some days up to a distinct level of saturation in the surrounding medium. Cultures incubated in light or absolute darkness exhibit the same production rates; however, lower temperatures caused significant reduction in the production rate and on the pattern of exuded compounds as well. After withdrawing the exuded compounds by rinsing the cultures, a new production can be repeatedly induced many times until the potential of the system is seemingly exhausted. “Nuphar seedlings” procedures are introduced as a new macrophyte system suitable for studying the mechanism of extracellular secretion among aquatic macrophytes.