Cold‐induced purpling of Pinus contorta seedlings depends on previous daylength treatment

The characteristic cold‐induced foliar accumulation of anthocyanin (‘purpling’) seen in many species of pine seedlings in the autumn can be contingent upon photoperiod received months previously. In nursery‐grown seedlings of Pinus contorta Dougl. var. latifolia Engelm., a 4‐week exposure during August of 10‐h days followed by return to ambient photoperiod diminished the frequency of purpling following the November onset of cold weather (21% compared to 71% of the untreated controls). Anthocyanin accumulation (primarily cyanidin 3‐glucoside) was controlled differently than general phenolic metabolism, and involved the integration of two temporally separated environmental signals.