SUMMARY

Cleavage and budding polyembryony occurs predominantly in conifers adapted to severe environments as found near the Arctic. Cleavage and budding polyembryony are processes that reconstitute multiple proembryos originating by the division or cloning of a single proembryo into a group of identical proembryos. This process provides little selective genetic advantage since all embryos have the same genotype, but it significantly increases the ability for that genotype to survive and to adapt to climatic vagaries by producing multiple viable embryos. With several Norway spruce and pine genotypes from northern latitudes and/or high elevations, the processes of cleavage and budding can be repeated and controlled in bioreactors that serve as an artificial ovule. In the mother tree, nutrients and water are provided to polyembryogenic masses in ovules through the xylem and phloem connections between the ovuliferous scale and the tree. In bioreactors, process controls now consider the effects of climate on the composition of seeds at the seed source. For each seed source, the composition of nutrients derived from the mother tree is reformulated in the culture medium to precondition the polyembryonic process and to contribute to the recovery of viable embryos. Before a zygotic model reference can be developed for the reconstitution process, factors associated with the seed habit and rest period, based on climatic stress, need to be sorted out and identified. Studies with dry seeds oiPinus banksiana Lamb, have revealed that covalently labeled tritium, derived from tritiated water, can be recovered from metabolites in the soluble and insoluble phases of tissues during imbibition. […]