Title: "Intermediate" seed storage physiology: populus as a natural model system Authors
Submitted to: International Society for Horticultural Science Meeting
Publication Type: Abstract Only
Publication Acceptance Date: August 13, 2013
Publication Date: August 13, 2013
Citation: Hill, L.M., Haiby, K., Volk, G.M., Walters, C.T. 2013. "Intermediate" seed storage physiology: populus as a natural model system. International Society for Horticultural Science Meeting. p.88. Technical Abstract: “Intermediate” seeds are short lived because they are sensitive to the combined stresses of low moisture and temperature during storage. We hypothesize that intermediate seeds either 1) exhibit intermediate sensitivity to desiccation compared to orthodox and recalcitrant seeds; 2) are damaged by subfreezing temperatures as a result of first order phase changes (i.e., crystallization of water or lipids; 3) are relatively unresponsive to low temperature effects. Seeds of Populus sp. age very quickly in storage, dying within 2 months when stored at room temperature and within 3-5 years if stored in the freezer (seeds of most species usually survive at least 1 and up to 75 years under room temperature and freezer conditions). Hence, physiology of Populus seeds is consistent with attributes of intermediate seed storage behavior. The objective of the study is to determine which factors contribute to Populus’ “intermediate” physiology, determine optimum water content for storage, measure the temperature coefficient of aging reactions, and evaluate whether cryogenic storage slows or stops aging once it has started. P. tremuloides and P.deltoides seeds were harvested yearly in May between 2009 and 2012 from locations in Oregon, Montana and Minnesota, USA. Seeds were equilibrated to different relative humidities (1-75% RH) and placed at temperatures ranging from 25oC to -196oC to test for desiccation tolerance and determine temperature response. Seed germination at 25oC was assessed 7 and 14 days after sowing on damp blotter paper. Longevity is expressed as the time for germination to decrease to 50% of initial germination (P50) which was calculated by fitting deterioration time courses to the Avrami relationship. Longevity of Populus seed is greatest when seeds are stored between 13 and 30% RH, conditions comparable to orthodox seeds. Populus seeds also do not exhibit unusual water or lipid crystallization properties according to differential scanning calorimetry measurements. Longevity of Populus seeds appeared rather insensitive to storage temperature, and this was most apparent when cryopreservation treatments were delayed. These results lead us to conclude that the preserved state of the cytoplasm in Populus seeds is intrinsically unstable either as a result of high viscosity of cellular glasses or high susceptibility of cellular constituents to autocatalytic reactions. Future experiments are planned to test the feasibility of increasing longevity by pre and post-harvest treatments and to investigate gene expression during embryogenesis. These studies will further our understanding of the mechanisms that contribute to “intermediate” seed storage physiology.