Seasonal variation and distribution of two phenolic compounds, rosmarinic acid and caffeic acid, in leaves and roots-rhizomes of eelgrass (Zostera Marina L.)

Abstract

The seasonal variation and distribution of rosmarinic acid and caffeic acid in leaves and roots-rhizomes of eelgrass (Zostera marina L.) were examined by using an isocratic high-performance liquid chromatography (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 nitrogen and phosphorus, in order to test a proposed relationship between nutrient status of the plant and biosynthesis of the secondary metabolites.

The concentration of rosmarinic acid (not previously found in a monocotyledon) plus caffeic acid ranged from 0.4 to 19.2 mg (g dw)^-1 with rosmarinic acid being the quantitatively most important component. The figures represent low estimates due to loss of phenolics during sample preparation. High phenolic concentrations occurred in spring and low concentrations during summer and fall, and the highest concentrations were most often found in the young and actively growing leaves and roots-rhizomes. Concentrations of phenolic acids were positively correlated with tissue concentrations of nitrogen and phosphorus. The observed variation in the two phenolic compounds did not support hypotheses relating the role of plant nutrient status or herbivore grazing to regulation of phenolic biosynthesis and was inconsistent with a proposed function of phenolics as inhibitors of epiphytic colonization.

Key Words:

• Eelgrass
• rosmarinic acid
• caffeic acid
• nutrients
• epiphytes