Seasonal variation in Daucus carota leaf-surface and leaf-tissue chemical profiles

The purpose of this work was to document seasonal changes in leaf-surface and whole-leaf chemistry of Daucus carota cohorts that differed in life-cycle phenology (winter annual, annual, or biennial), with particular focus on compounds that serve as contact oviposition stimulants for Papilio polyxenes, the black swallowtail butterfly. Cohorts of carrot plants exhibiting different life-cycle phenologies were established, and plants from each cohort were sampled periodically over two growing seasons. Extracts of leaf surfaces and leaf tissues were analyzed using HPLC and were compared quantitatively for the content of chlorogenic acid (CA), luteolin-7-O-(6"-O-malonyl)-beta-D-glucopyranoside (L7MG), and luteolin-7-glucoside (L7G). The pattern of seasonal variation in L7G and L7MG concentrations in leaf tissues of each cohort followed the predictions of the tissue value hypothesis: flavonoid concentrations are highest in the tissues of new alternate leaves of the reproductive shoot or in new spring foliage. Chlorogenic acid concentrations in leaf tissues increased throughout the growing season. Patterns of leaf-surface seasonal variation did not correlate with patterns in leaf-tissue chemistry for any carrot cohort. Rather, leaf-surface amounts of CA, L7G, and L7MG were highest at the point in the lifecycle when plants were differentiating or bolting. (C) 2004 Elsevier Ltd. All rights reserved.