Michael J. Line

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

Abstract 1. 1. Tissue-specific variations in the responses of geranium stems to hyperthermia 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 (ΔS ‡ ) for each image voxel [(39 μm × 39 μm) × 500 μm]. 2. 2. After partitioning the images by tissue type, Eyring analyses of the temperature dependence of water proton T 2 relaxation demonstrated increases in E a or ΔH ‡ when the sample temperature exceeded 26.5, 45.7, 32.4 and 31.1°C for the pith parenchyma, fibrous sheath/vascular tissues, cortical parenchyma/epidermal tissues and whole stem, respectively. 3. 3. The results suggest that the changes in T 2 thermodynamics are caused primarily by direct temperature-dependent variations in the physical state of tissue water, while a standard viability assay measures thermally-induced protein denaturation. 4. 4. This is apparently the first in vivo demonstration of tissue-specific variations in a plant response to hyperthermia.