Transverse relaxation time of leaf water protons and membrane injury in wheat (Triticum aestivum L.) in response to high temperature

The relationship between high temperature stress injury and temperature dependence of the transverse relaxation time (T-2) of leaf water was examined using NMR in four cultivars of wheat differing in their sensitivity to high temperature stress. The T-2 declined with increasing temperature between 25 and 35 degrees C. A comparison of relative injury based on electrolyte leakage and T-2, between 40 and 50 degrees C, indicated that while membrane permeability increased with increasing temperature there was an increase in T-2 until 44 and 48 degrees C in susceptible and tolerant cultivars respectively, followed by a sharp decline. This pattern of change in T-2 with increasing temperature was consistent whether the same or different samples were used for each treatment temperature. Loss of temperature dependence of T-2 after heat killing indicated irreversible changes in T-2, probably due to the loss of membrane integrity. Heat tolerant varieties, which suffered less membrane injury, had a higher T-2 compared to susceptible varieties. Tolerant Varieties also maintained the T-2 of leaf water protons to higher temperatures than did sensitive varieties. This NMR-based, non-invasive, rapid technique could be used to efficiently detect heat injury in leaf tissues. (C) 1999 Annals of Botany Company.