Research on modeling germination response to salinity of barley seeds

Abstract

Aims Salinization is a worldwide problem, and some researchers focus on the effect of salt on seed germination. The results are variable, and quantifying germination response to salt is significant. Furthermore, seed germina- tion is affected by salinity, as a result of both osmotic and ion effects. How the two effects act together is unclear. Thus our objectives are to propose a model to accurately describe the effect of salt on seed germination and to clarify the role of the osmotic and the ion effect act under different salinities. Methods Two varieties of barley (Hordeum vulgare) seeds ('Cask' and 'County') were cultured in five binate iso-osmotic polyethylene glycol (PEG) and NaCl solutions (-0.45, -0.88, -1.32, -1.76 and -2.20 MPa, distilled water as the control) at four constant temperatures of 5, 12, 20 and 27 °C. Germination time courses were re- corded and germination rates (the reciprocal of germination time) were calculated. The hydrotime model and the new salinity model were used to calculate the parameters and test which was the better fit. Important findings Results indicated that not only were seeds in saline conditions able to germinate at lower osmotic potentials than seeds germinating in an isotonic PEG-6000 solution, but that they were also able to do so faster. The hydrotime parameters of the NaCl treatments had great differences with the isotonic PEG treatments, which indicated the hydrotime model cannot describe salt effects on seed germination well. Barley seed germina- tion rates in salt solutions were negatively linear with salinity. We proposed a salinity model to quantify germina- tion response to salt. The germination time calculated from the salinity model approached the real data, compared to that calculated from the hydrotime model. Differences of germination rates in NaCl and the isotonic PEG treatments increased and then decreased with decreasing water potential. We suggest three situations of function mode by the osmotic and ion effects of salt. First, at low salinities the osmotic effect acts as the main negative role. Second, at medium salinities the two effects act together, with the positive ion effect stronger than the nega- tive osmotic effect. Third, at high salinities the ion effect begins to harm the germination process.