W-A radiation (360 nm) affects the photomorphogenesis and essential-oil che
mical composition of Mentha piperita. Total phenols and chlorophyll b are a
lso affected by UV-A. When UV-A is given during the day (UV-A + W), a signi
ficant increase is found in total leaf area, leaf-area index, chlorophyll a
/b ratio, total phenols, total essential-oil content, menthofuran and menth
ol. UV-A irradiation during the night period induces a typical shade-avoida
nce syndrome, with stem elongation, decreased leaf area and leaf-area index
, decreased protein and total phenol content, and decreased essential-oil a
nd menthol content. The possible interference of W-A with phytochrome is di
scussed. (C) 1999 Elsevier Science S.A. All rights reserved.