Quantitative analysis of cold hardening and dehardening in Lolium

The change in cold hardiness of three Lolium multiflorum Lam. varieties was followed in plants exposed to hardening or dehardening conditions at a range of temperatures. Hardening and dehardening were analysed as quantitative processes dependent upon temperature and time. Their time courses changed exponentially to an asymptote which was logistically related to temperature. Both components of the model were fitted simultaneously. Parameters of biological interest, such as the initial rates of hardening and dehardening for a given temperature and the percentage of the process completed in a given time, were derived and compared for varieties of contrasting hardiness. The analysis demonstrated the importance of dehardening in determining hardiness. Similar results were obtained when the model was applied to hardening and dehardening data for Lolium perenne L.

The potential of this quantitative analysis for distinguishing between possible mechanisms of cold hardiness is discussed and further experiments required to characterise the kinetics of hardening and dehardening more fully are identified.