Quality and quantity of piperidine alkaloids in needles and bark of Scots pine (Pinus sylvestris) seedlings

Abstract

The Northern boreal forest zone is dominated by two coniferous species that synthesize piperidine alkaloids: Scots pine (Pinus sylvestris) and Norway spruce (Picea abies). These compounds are known to have antifeedant properties. We have earlier shown that Norway spruce has a diverse alkaloid chemistry, but reports from P. sylvestris are few, and no quantitative analysis has been conducted so far. Here we have studied 2-year-old seedlings of P. sylvestris to reveal possible differences in alkaloid chemistry compared to P. abies. Alkaloids were extracted from bark and mature needles by solid-phase partitioning and analysed by GC–MS. We detected only four individual compounds from P. sylvestris samples, confirming earlier assumptions that the species lacks large parts of the biosynthesis pathway of coniferous alkaloids. Euphococcinine, also present in mature P. abies needles, is the sole end-product of alkaloid biosynthesis in P. sylvestris, although a compound tentatively identified as an isomer of euphococcinine was also detected. The two other alkaloid compounds detected are also encountered in P. abies, but only in juvenile plant parts, such as developing needles and stems. Concentrations of all alkaloids were extremely low, with totals amounting to about 25% of the amount found in P. abies. It is also notable that concentrations in three out of ten seedlings were under the detection limit, in bark or in both plant parts, whereas in P. abies individuals lacking alkaloids are virtually non-existent. The compound composition, concentrations and absence of alkaloids in some individuals emphasize the difference between these two major boreal zone species, and this calls for further studies on the ecological significance of these compounds.