Cold- or Heat-Tolerance of Leaves and Roots in Perennial Ryegrass Determined by 1H-NMR

Abstract

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 (T1) of leaves in Arrhenius plots linearly decreased but increased as temperature decreased below 0°C. However, spin-spin relaxation times (T2) of the leaves increased as temperature decreased from 20 to –20°C. The T2 value of the long fraction (associated with vacuole) in leaves decreased to about 600 µs at –25°C, but that of the short fraction was about 10 µs, and the relative value of signal intensity of the long fraction decreased to about 0.2 at –25°C. The T2 values of the two fractions in roots decreased to about 1ms at –10°C. Judging from T2 and electrolyte leakage, both vacuolar and cytoplasmic compartments of leaves and roots froze at these temperatures. T1 of the leaves decreased slightly as temperatureincreased from 20 to 40°C but greatly decreased as temperature increased further. On the other hand, T1 of the roots decreased linearly as temperature increased from 20 to 50°C. 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 T1 and T2 is a sensitive and non-invasive method to evaluate primary responses of perennial ryegrass organs to the temperature stresses.

Keywords

• Arrhenius plots
• Cold stress
• Dynamic states of water
• Heat stress
• NMR relaxation times (T1, T2)
• Organ
• Perennial ryegrass
• Water compartment