Thermodynamic analysis of the physical state of water during freezing in plant tissue, based on the temperature dependence of proton spin‐spin relaxation
作者:
M. M. MILLARD,
O. B. VEISZ,
D. T. KRIZEK,
M. LINE,
期刊:
Plant, Cell&Environment
(WILEY Available online 1996)
卷期:
Volume 19,
issue 1
页码: 33-42
ISSN:0140-7791
年代: 1996
DOI:10.1111/j.1365-3040.1996.tb00224.x
出版商: Blackwell Publishing Ltd
关键词: activation energy;cold acclimation;freezing injury;NMR imaging;non‐freezable water;Poaceac;spin‐spin relaxation;temperature dependence;Triticum aestivumL.;water dynamics
数据来源: WILEY
摘要:
ABSTRACTMulti‐proton spin‐echo images were collected from cold‐acclimated winter wheat crowns (Triticum aestivumL.) cv. Cappelle Desprez at 400 MHz between 4 and −4 °C. Water proton relaxation by the spin‐spin (T2) mechanism from individual voxels in image slices was found to be mono‐exponential. The temperature dependence of these relaxation rates was found to obey Arrhenius or absolute rate theory expressions relating temperature, activation energies and relaxation rates, Images whose contrast is proportional to the Arrhenius activation energy (Ea), Gibb's free energy of activation (ΔG‡), and the entropy of activation (ΔS‡) for water relaxation on a voxel basis were constructed by post‐image processing. These new images exhibit contrast based on activation energies rather than rules of proton relaxation. The temperature dependence of water protonT2relaxation rates permits prediction of changes in the physical state of water in this tissue over modest temperature ranges. A simple model is proposed to predict the freezing temperature kof various tissue in wheat crowns. The averageEaand ΔH‡for water protonT2relaxation over the above temperature range in winter wheat tissue were −6.4 ± 14.8 and −8.6 ± 14.8kj mol−1, respectively. This barrier is considerably lower than theEafor proton translation in ice at 0°C, which is reported to
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