The Change in Arginine Levels and the Metabolism of Urea and Ornithine in Cucurbita moschata Seedlings

During germination a decrease in both soluble and protein argmine occurs in pumpkin cotyledons ( Cucurbita moschata Poir.) and this decrease parallels the decrease in total nitrogen. Arginine is readily metabolized to urea and ornithine and the metabolism of the latter compounds were studied by allowing cotyledons of intact plants to absorb urea −14 C and by incubating cotyledon discs with ornithine‐2 −14 C. Of the urea absorbed, 90 % of the label was metabolized to 14 CO 2 with little free urea remaining in the plant. Urease activity in the cotyledons reached a maximum at 4 to 6 days of germination. Ornithine was extensively metabolized with 37 % of the label being incorporated into protein by 3 h. Soluble and protein arginine accounted for 23 % of the label suggesting that Krebs‐Henseliet cycle enzymes were present.