A Nuclear Magnetic Resonance Study of Water in Cold-acclimating Cereals

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Abstract
Continuous wave NMR studies indicated that the line width of the water absorption peak (.DELTA..nu. 1/2) from crowns of winter and spring wheat (Triticum aestivum L.) increased during cold acclimation. There was a negative correlation between .DELTA..nu.1/2 and crown water content, and both of these parameters were correlated with the lowest survival temperature at which 50% or more of the crowns were not killed by freezing (LT50). Regression analyses indicated that .DELTA..nu.1/2 and water content account for similar variability in LT50. Slow dehydration or unacclimated winter wheat crowns by artificial means resulted in similarly correlated changes in water content and .DELTA..nu.1/2. Rapid dehydration of unacclimated crowns reduced water content but did not influence .DELTA..nu.1/2. The incubation of unacclimated winter wheat crowns in a sucrose medium reduced water content and increased .delta..nu.1/2 appears to be dependent in part on a reduction in water content and an increase in solutes. Longitudinal (T1) and transverse (T2) relaxation times of water protons in cereals at different stages of cold acclimation were measured using pulse NMR methods. The T1 and T2 signals each demonstrated the existence of 2 populations of water, 1 with a short and 1 with a long relaxation time. During the first 3 wk of acclimation, the long T2 decreased significantly in winter-hardy cereals, and did not change in a spring wheat until the 5th wk of hardening. There was no change in the long T1 until the 3rd wk of hardening for the winter cereals and until the 7th wk of hardening for the spring wheat. No simple relationship could be established between T1 or T2 and cold hardiness. Neither continuous wave or pulsed NMR spectroscopy can be used as a diagnostic tool in predicting the cold hardiness of winter wheats. An increase in .DELTA..nu.1/2 or a reduction in relaxation times does not provide evidence for ordering of the bulk of the cell water.