Environmental trends in the variation of biologically active phenolic compounds in Labrador tea, Rhododendron groenlandicum, from northern Quebec, Canada.

The impact of several environmental factors on the production of phenolic compounds in a North American medicinal plant, Labrador tea ( Rhododendron groenlandicum (Oeder) Kron & Judd), was studied. Leaves were harvested in 2006 and 2010 over a latitudinal gradient in northern Quebec, and known phenolic markers were quantified by HPLC-DAD. The concentration of selected compounds varied geographically where they were higher between the 51st and 53rd parallel of northern Quebec and lower in the peripheral northern and southern region. Major variations were observed in the following marker compounds: (+)-catechin, (-)-epicatechin, quercetin-3-galactoside, and an undetermined quercetin-glycoside. The variation in phenolic compounds was best explained by short-term changes in annual temperature range and long-term estimates of insolation parameters such as solar radiation and photoperiod in the month of June. [ABSTRACT FROM AUTHOR]