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 dep endence 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 2 5 and 35 degrees C. A comparison of relative injury based on electrolyte le akage and T-2, between 40 and 50 degrees C, indicated that while membrane p ermeability increased with increasing temperature there was an increase in T-2 until 44 and 48 degrees C in susceptible and tolerant cultivars respect ively, followed by a sharp decline. This pattern of change in T-2 with incr easing temperature was consistent whether the same or different samples wer e 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 le ss membrane injury, had a higher T-2 compared to susceptible varieties. Tol erant Varieties also maintained the T-2 of leaf water protons to higher tem peratures 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.