Wild watermelon from the Botswana desert had an ability to survive under severe drought conditions by maintaining its water status (water content and water potential). In the analysis by two-dimensional electrophoresis of leaf proteins, seven spots were newly induced after watering stopped. One with the molecular mass of 40 kilodaltons of the spots was accumulated abundantly. The cDNA encoding for the protein was cloned based on its amino-terminal sequence and the amino acid sequence deduced from the determined nucleotide sequences of the cDNA exhibited homology to the enzymes belong to the ArgE/DapE/Acy1/Cpg2/YscS protein family (including acetylornithine deacetylase, carboxypeptidase and aminoacylase-1). This suggests that the protein is involved in the release of free amino acid by hydrolyzing a peptidic bond. As the drought stress progressed, citrulline became one of the major components in the total free amino acids. Eight days after withholding watering, although the lower leaves wilted significantly, the upper leaves still maintained their water status and the content of citrulline reached about 50% in the total free amino acids. The accumulation of citrulline during the drought stress in wild watermelon is an unique phenomenon in C3-plants. These results suggest that the drought tolerance of wild watermelon is related to (1) the maintenance of the water status and (2) a metabolic change to accumulate citrulline.

The binding energies of the ground states and several excited states related to single-particle and -hole states in nuclei around 16 O are calculated taking charge dependence into account. Effective interactions on the particle basis are constructed from modern charge-dependent nucleon-nucleon interactions and the Coulomb force within the framework of the unitary-model-operator approach. Single-particle (-hole) energies are obtained from the energy differences of the binding energies between a particle (hole) state in 17 O or 17 F ( 15 N or 15 O) and the ground state of 16 O. The resultant spin-orbit splittings are small for the hole state and large for the particle state in comparison with the experimental values though the differences between the experimental and calculated values are not very large. The charge dependence of the calculated single-particle energies for the ground states are in good agreement with the experimental values. Furthermore, the Thomas-Ehrman shift due to the Coulomb force for the 1s 1/2 states in 17 O and 17 F can be observed.