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Water Potential and Embryonic Axis Viability in Recalcitrant Seeds of Quercus rubra

Desiccation of Quercus rubra fruits under three drying regimes of varying temperature and water potential confirmed their desiccation intolerance. However, a variable relationship between seed germination and embryonic axis moisture content was observed, indicating that the rate and temperature of drying can modify this co-plot. The modification occurred primarily between an axis moisture content of 45-20%, which is equivalent to water potentials (Vw) of —3 to — 30 MPa. The estimated critical fw for the initiation of viability loss during drying varied between —5 and — 3 MPa, depending on the desiccation environment. Drying fruits beyond an equilibrium Vw for the axis of — 30 MPa resulted in no seed germination. The extension of this time-temperature-dependent, desiccation-induced viability loss at much lower water potentials was assessed using excised axes equilibrated to V w of —100 MPa over a 7-h period. About 10% of treated axes exhibited hypocotyl/root extension, but fewer epicotyls survived. However, priming in a —07 MPa solution of polyethylene glycol for 16-20 h prior to drying raised the proportion of extending axes to that of the control (i.e. 40%). Even so, only 10% of epicotyls survived, and the addition of trehalose (100 mol m"3) to the priming solution had no ameliorating effect. Nonetheless, the response of the axes to priming suggests that the initial quality of the axis can also influence the characteristics of the desiccation-viability relationship.