A similar series on Amazonian species is emerging from Manaus, Brazil ( INPA, 2014). However, it would be valuable to consolidate these and other resources on one web site under a general theme of ‘Tree seeds of the world’ so that ex situ conservation actions can be supported. Sources of information should include compendia of national and regional forest seed programmes. Target 8 Akt inhibitor of the GSPC directs that approximately 75% of threatened plant species
be present in ex situ collections by 2020. This target can present particular challenges for mega-diverse countries, in terms of the scale of the task, the range of species for protection, and in the application of the most appropriate techniques and innovations, particularly for recalcitrant seeds Caspase inhibitor ( Harding et al., 2013 and Walters et al., 2013). The lifespan of fully hydrated recalcitrant seeds is limited mainly by the extent to which they can be safely cooled. For both temperate and tropical species cooling is limited by the risk of ice formation and chilling stress, respectively. Thus in practice, storage can be close to 0 °C for temperate
recalcitrant seeds and 15 °C for tropical representatives on this functional trait. Generally under such conditions, lifespan is limited to a few months to rarely more than one year. Consequently, alternative conservation solutions are needed if the seeds of these species are to be conserved longer-term ex situ. Cryopreservation (usually storage below c. −130 °C, often in the vapour phase above liquid nitrogen) is the method of choice ( Li and Pritchard, 2009). However, as whole recalcitrant seeds tend to be large, the development of innovative approaches has mainly related to shoot tip and embryo (and embryonic axis) tissue preservation, followed by recovery in vitro. By reducing tissue mass, it is possible to control better the target MC for cryopreservation, and the cooling and warming phases of the process. The main development of the last
25 years in plant cryopreservation has been the improvement in vitrification methodologies, particularly encapsulation-dehydration (Fabre and Dereuddre, 1990) and the use of complex solutions of cryoprotectants that reduce the risk of ice formation in partially hydrated tissues during Histidine ammonia-lyase cooling and rewarming. These ‘plant vitrification solutions’ (PVS) combine cryoprotectants that vary in permeability, enable removal of cellular water, increase cell viscosity and alter the properties of any remaining water (Volk and Walters, 2006). PVS2 is the most commonly used cryoprotectant, consisting of 30% glycerol, 15% dimethyl sulfoxide and 15% ethylene glycol in Murashige and Skoog medium with 0.4 M sucrose (Sakai et al., 1990). Across the various compositions of vitrification solutions and methodological variations (i.e.