Cold- or heat-tolerance of leaves and roots in perennial ryegrass determined by 1H-NMR

Dynamic states of water in the leaves and roots of perennial ryegrass (Lolium perenne L.) exposed to cold and heat stresses were studied by using H-1-NMR. NMR spin-lattice relaxation times (T-2) of leaves in Arrhenius plots linearly decreased but increased as temperature decreased below 0degreesC. However, spin-spin relaxation times (72) of the leaves increased as temperature decreased from 20 to -20degreesC. The T-2 value of the long fraction (associated with vacuole) in leaves decreased to about 600mus at -25degreesC, but that of the short fraction was about 10mus, and the relative value of signal intensity of the long fraction decreased to about 0.2 at -25degreesC. The T, values of the two fractions in roots decreased to about 1ms at -10degreesC. judging from T-2 and electrolyte leakage, both vacuolar and cytoplasmic compartments of leaves and roots froze at these temperatures. T-1 of the leaves decreased slightly as temperature increased from 20 to 40degreesC but greatly decreased as temperature increased further. On the other hand, T-1 of the roots decreased linearly as temperature increased from 20 to 50degreesC. The levels of electrolyte leakage from leaves exposed to the above beat stress was low suggesting that membrane was not severely injured. In conclusion, analysis of Arrhenius plots of T-1 and T-2 is a sensitive and non-invasive method to evaluate primary responses of perennial ryegrass organs to the temperature stresses.