Desiccation, cryopreservation and water relations parameters of white spruce (Picea glauca) and interior spruce (Picea glauca x engelmannii complex) somatic embryos

Effects of drying and cryopreservation on survival of spruce (Picea glauca (Moench) Voss and Picea glauca x engelmannii complex) somatic embryos (SEs) were investigated with the aim of developing simple and robust protocols for embryo storage. Somatic embryos dried over salt solutions of known water potential (Psi) survived removal of virtually all free water, to a relative water content (RWC) of approximately 0.13, a value similar to that for spruce zygotic embryos from dry seed. Desiccated SEs also survived subsequent freezing in liquid nitrogen, without the addition of cryoprotectant or preculture steps. Highest survival (> 80%) after freezing in liquid nitrogen was in embryos pre-dried to Psi of -15 to -20 MPa, which yielded RWC close to predicted bound (apoplastic) water values. Low (< 35%) or no survival after freezing was observed in embryos pretreated at higher Psi (above -5 MPa) or at very low Psi (-540 MPa, using silica gel), respectively.