Resin vesicles in conifer seeds: morphology and allelopathic effects

The seed coat of fir (Abies), hemlock (Tsuga), and cedar (Thuja) species contain terpenoid resin vesicles. Although information is limited about the morphology and allelopathy of these vesicles, their damage during seed processing can negatively impact germination success. We examined resin vesicle morphology of western redcedar (Thuja plicata Donn ex D. Don), eastern white cedar (Thuja occidentalis L.), amabilis fir (Abies amabilis Douglas ex J. Forbes), balsam fir (Abies balsamea (L.) Mill.), grand fir (Abies grandis (Douglas ex D. Don) Lindl), and subalpine fir (Abies lasiocarpa (Hook.) Nutt.) seeds by 1H magnetic resonance imaging to characterize resin vesicle volume, shape, and number. Western redcedar genotypes with known differences in the quantity of foliar monoterpenes also had parallel differences in the resin vesicle volume of corresponding seeds. Germination assays with the cedar and fir species, eastern hemlock (Tsuga canadensis (L.) Carriere), mountain hemlock (Tsuga mertensiana (Bong.) Carriere), and western hemlock (Tsuga heterophylla (Raf.) Sarg.) confirmed that resin vesicle damage prior to stratification (moist chilling) significantly reduced germination success for most species. Extracts of these resin vesicles from the Abies and Thuja species strongly inhibited the germination of Arabidopsis Col-0 seeds but inhibited the germination of only a small percentage of Arabidopsis abscisic acid insensitive mutant abi3-6 seeds. Resin extracts from Thuja species were 10 times more effective than those from Abies species in inhibiting Arabidopsis Col-0 germination.