SEASONAL-VARIATION AND DISTRIBUTION OF 2 PHENOLIC-COMPOUNDS, ROSMARINIC ACID AND CAFFEIC ACID, IN LEAVES AND ROOTS-RHIZOMES OF EELGRASS (ZOSTERA-MARINA L)

The seasonal variation and distribution of rosmarinic acid and caffeic acid in leaves and roots-rhizomes of eelgrass (Zostera marina L.) wer e examined by using an isocratic high-performance liquid chromatograph y (HPLC) method developed for separation and quantification of the two phenolic compounds in crude plant extracts. The variation in phenolic content was compared to variations in tissue concentrations of nitrog en and phosphorus, in order to test a proposed relationship between nu trient status of the plant and biosynthesis of the secondary metabolit es. The concentration of rosmarinic acid (not previously found in a mo nocotyledon) plus caffeic acid ranged from 0.4 to 19.2 mg(g dw)-1 with rosmarinic acid being the quantitatively most important component. Th e figures represent low estimates due to loss of phenolics during samp le preparation. High phenolic concentrations occurred in spring and lo w concentrations during summer and fall, and the highest concentration s were most often found in the young and actively growing leaves and r oots-rhizomes. Concentrations of phenolic acids were positively correl ated with tissue concentrations of nitrogen and phosphorus. The observ ed variation in the two phenolic compounds did not support hypotheses relating the role of plant nutrient status or herbivore grazing to reg ulation of phenolic biosynthesis and was inconsistent with a proposed function of phenolics as inhibitors of epiphytic colonization.