Cold- or Heat-Tolerance of Leaves and Roots in Perennial Ryegrass Determined by ^1H-NMR(Crop Physiology and Ecology)

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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 ^1H-NMR. NMR spin-lattice relaxation times (T_1) of leaves in Arrhenius plots linearly decreased but increased as temperature decreased below 0℃. However, spin-spin relaxation times (T_2) of the leaves increased as temperature decreased from 20 to -20℃. The T_2 value of the long fraction (associated with vacuole) in leaves decreased to about 600μs at -25℃, but that of the short fraction was about 10μs, and the relative value of signal intensity of the long fraction decreased to about 0.2 at -25℃. The T_2 values of the two fractions in roots decreased to about 1ms at -10℃. 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 40℃ but greatly decreased as temperature increased further. On the other hand, T_1 of the roots decreased linearly as temperature increased from 20 to 50℃. The levels of electrolyte leakage from leaves exposed to the above heat 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 Drimarv responses of perennial rveerrass organs to the temperature stresses.
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