MAGNETIC-RESONANCE-IMAGING OF TISSUE-SPECIFIC THERMAL RESPONSES OF GERANIUM STEM IN-VIVO

1. Tissue-specific variations in the responses of geranium stems to hy perthermia were investigated in vivo by acquiring tissue water proton spin-spin (T-2) relaxation images at different sample temperatures and calculating the apparent activation energy (E-a) and entropy (Delta S ++) for each image voxel [(39 mu m x 39 mu m) x 500 mu m]. 2. After pa rtitioning the images by tissue type, Eyring analyses of the temperatu re dependence of water proton T-2 relaxation demonstrated increases in E-a or Delta H++ when the sample temperature exceeded 26.5, 45.7, 32. 4 and 31.1 degrees C for the pith parenchyma, fibrous sheath/vascular tissues, cortical parenchyma/epidermal tissues and whole stem, respect ively. 3. The results suggest that the changes in T-2 thermodynamics a re caused primarily by direct temperature-dependent variations in the physical state of tissue water, while a standard viability assay measu res thermally-induced protein denaturation. 4. This is apparently the first in vivo demonstration of tissue-specific variations in a plant r esponse to hyperthermia. (C) 1997 Published by Elsevier Science Ltd.