Abstract
Drought-tolerant wild watermelon plants accumulate citrulline massively in the leaves under drought. To explore the mechanism of its accumulation, we analyzed glutamate acetyltransferase (GAT) that simultaneously catalyzes the first and fifth steps in citrulline biosynthesis.
The GAT purified from the leaves of watermelon was composed of two subunits. N-terminal amino acid sequences of these subunits were significantly homologous to the 37th to 49th and the 249th to 283rd residues of putative Arabidopsis GAT. The analysis of the corresponding watermelon cDNA suggested the presence of chloroplast transit peptide at its N-terminus. The watermelon GAT was not inhibited by the L-citrulline and L-arginine. Moreover, the enzyme showed optimum temperature of 70 οC, suggesting that this enzyme is suitable for the thermogenic condition of the leaf tissue under drought. These results suggest that the watermelon GAT contributes effectively to the massive accumulation of citrulline.
