Yoji Arata

Visualization of Freezing Behaviors in Leaf and Flower Buds of Full-Moon Maple by Nuclear Magnetic Resonance Microscopy

1H-Nuclear magnetic resonance (NMR) microscopy was used to study the freezing behavior of wintering buds of full-moon maple (Acer japonicum Thunb.). The images obtained predominantly reflected the density of mobile (i.e. non-ice) protons from unfrozen water. A comparison of NMR images taken at different subfreezing temperatures revealed which tissues produced high- and low-temperature exotherms in differential thermal analyses. In leaf and lower buds of A. japonicum, the scales and stem bark tissues were already frozen by -7[deg]C, but the primordial inflorescence and terminal primordial shoots remained supercooled at -14[deg]C, and the lateral primordial shoots were unfrozen even at -21[deg]C. The freezing of these supercooled tissues was associated with their loss of viability. The size of the supercooled primordial shoots and inflorescences was gradually reduced with decreasing temperature, indicating extraorgan freezing in these tissues. During this process the formation of dark regions beneath the primordia and subsequent gradual darkening in the basal part of supercooled primordia were visible. As the lateral shoot primordia were cooled, the unfrozen area was considerably reduced. Since the lateral primordia remained viable down to -40[deg]C, with no detectable low-temperature exotherms, they probably underwent type I extraorgan freezing. Deep supercooling in the xylem was clearly imaged. NMR microscopy is a powerful tool for noninvasively visualizing harmonized freezing behaviors in complex plant organs.

A pulsed field gradient NMR study of the aggregation and hydration of parvalbumin

Pulsed field gradient NMR is a convenient alternative to traditional methods for measuring diffusion of biological macromolecules. In the present study, pulsed field gradient NMR was used to study the effects of calcium binding and hydration on carp parvalbumin. Carp parvalbumin is known to undergo large changes in tertiary structure with calcium loading. The diffusion coefficient is a sensitive guide to changes in molecular shape and in the present study the large changes in tertiary structure were clearly reflected in the measured diffusion coefficient upon calcium loading. The (monomeric) calcium-loaded form had a diffusion coefficient of 1.4 x 10(-10) m(2) s(-1) at 298 K, which conforms with the structure being a nearly spherical prolate ellipsoid from X-ray studies. The calcium-free form had a significantly lower diffusion coefficient of 1.1 x 10(-10) m(2) s(-1). The simplest explanation consistent with the change in diffusion coefficient is that the parvalbumin molecules form dimers upon the removal of Ca(2+) at the protein concentration studied (1 mM).