l-Canavanine Transport and Utilization in Developing Jack Bean, Canavalia ensiformis (L.) DC. [Leguminosae]

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Abstract
L-Canavanine, the guanidinooxy structural analog of L-arginine, is an important nonprotein amino acid of many leguminous plants with N storage a major proported role. L-[Guanidinooxy-14C]canavanine, [14C] urea and [15N]urea were injected separately into the fleshy, green cotyledons of 9-day old jack bean plants, C. ensiformis (L.) DC. [Leguminosae]. There was significant transport of canavanine from the cotyledons to the aboveground portions of the plant, but not to the roots. Within 1.5 h of isotope administration, the remaining labeled canavanine was divided equally between the cotyledons and the aboveground portions of the plant. During the 48-h postinjection period, the contribution of L-[guanidinooxy-14C]canavanine to the total 14C of the cotyledons decreased rapidly while it increased in the aboveground portions of the plant. [14C]Urea is degraded very rapidly; only 4.4% of the initial dose remained after 1.5 h. Urea is catabolized so effectively within the cotyledons that not even 2% of the administered urea can be detected in tissues outside of these storage organs. [15N]Urea supplied to the developing cotyledons leads to rapid 14N incorporation into the amino N of glutamic acid and/or glutamine (28% 15N abundance after 3 h). Other amino acids are labeled but less heavily. The data are consistent with the proported role for L-canavanine of N storage within the developing cotyledons and cotyledonary canavanine is transported very effectively to the aboveground portions of the plant. How efficiently this transported canavanine supports the N metabolism of the developing plant is not yet clear.