Seasonal changes in the phenolic constituents of jack pine seedlings (Pinus banksiana) in relation to the purpling phenomenon
Needles of jack pine seedlings in their 1st and 2nd years of growth in the Kemptville, Ontario, forest tree nursery station were analysed during the summer and fall of 1987 for chemical changes associated with the purpling phenomenon. Anthocyanins, whose presence is responsible for the purple colour, appeared in 1st year needles only after the first frost in early September and increased in amount in both 1st and 2nd year needles throughout October and November. A proanthocyanidin reaction was always present during the summer at variable levels but increased markedly in late fall. Total phenolics showed a gradual increase over the season. Paper chromatograms of crude extracts showed that glucose was the major free sugar and remained at a more or less constant level, whereas free amino acids gradually declined. Soluble proteins increased in late autumn. Total chlorophyll content showed no significant seasonal change. Experiments on 1st year plants showed that nutrient deficiencies resulted in some purpling at normal temperatures that was markedly enhanced by exposure to cold. Depurpling occurred in warm temperature. Plants transplanted from the nursery in early September to a warm greenhouse and exposed to natural light and daylengths did not purple. It is concluded that low temperature is the major factor in purpling and that maintenance of the pigmentation depends on a balance of low temperature enhanced synthesis and warm temperature enhanced degradation.