Search

The change in the positron annihilation lifetime (PAL) of vacancies containing hydrogen atoms was investigated by taking PAL measurements in tungsten. The vacancies were introduced by electron irradiation, and hydrogen atoms were charged under a high-pressure hydrogen atmosphere (5.8 MPa). The PAL of single vacancies was measured to be approximately 175 ps, which decreased to approximately 155 ps after hydrogen charging. The PAL of single vacancies containing hydrogen atoms was calculated using the electron density obtained by a first principles calculation. The change in the PAL of vacancies containing hydrogen atoms was measured in experiments and calculated in simulations, and then, the two values were compared. It was found that one vacancy captured one or two hydrogen atoms (an average of 1.6 atoms). The binding energy of hydrogen to vacancies of 1.19 eV was obtained under the assumption of a thermal equilibrium state, which was slightly higher than the value determined by a previous study (1.06 eV). It is believed that the effect of impurities causes this discrepancy. The elucidation of the effect of impurities on the change in the PAL and the binding energy leads to greater accuracy in the quantitative evaluation of the hydrogen atoms trapped at single vacancies.

A wide range of metabolites accumulates under water stress depending on certain metabolic alterations. For example, free amino acids, especially free proline, accumulate in response to water stress ((l)). Proline accumulation is closely connected with carbohydrate metabolism. Thus, a carbohydrate requirement for proline accumulation in water-stressed leaves has been reported (2, 3).

Greenhouse-grown soybean (Glycine max L.) plants were subjected to water stress and diurnal changes in the contents of free amino acids were determined. In non-stressed plants with full water supply, the major parts of the free amino acids showed a similar diurnal variation, and the maximum contents were obtained between 11 a.m. and 2 p.m. except for aspartate. The maximum content of aspartate was obtained during the night. Glycine, serine and alanine, in particular, showed a light-sensitive response. In water-stressed plants, the water potential of the leaves fell from -12.8 bars at 7 a.m. to -22.2 bars at 7 p.m. and returned to -19.0 bars after sunset. When the leaf water potential fell, the total protein decreased with increase in the total free amino acids. Water stress induced a remarkable accumulation of free amino acids: histidine, valine, isoleucine, leucine, tyrosine, phenylalanine, and especially proline and asparagine. The maximum contents of proline and asparagine were 31 and 24% of t...