l-Canavanine Transport and Utilization in Developing Jack Bean, Canavalia ensiformis (L.) DC. [Leguminosae].
l-Canavanine, the guanidinooxy structural analog of l-arginine, is an important nonprotein amino acid of many leguminous plants with nitrogen storage a major proported role. l-[Guanidinooxy-(14)C]canavanine, [(14)C] urea, and [(15)N]urea were injected separately into the fleshy, green cotyledons of 9-day old jack bean plants, Canavalia 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 hours of isotope administration, the remaining labeled canavanine was divided equally between the cotyledons and the aboveground portions of the plant. During the 48-hour postinjection period, the contribution of l-[guanidinooxy-(14)C]canavanine to the total (14)carbon of the cotyledons decreased rapidly while it increased in the aboveground portions of the plant.[(14)C]Urea is degraded very rapidly; only 4.4% of the initial dose remained after 1.5 hours. 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. [(15)N]Urea supplied to the developing coytledons leads to rapid (15)N incorporation into the amino nitrogen of glutamic acid and/or glutamine (28% (15)N abundance after 3 hours). Other amino acids are labeled but less heavily. The data are consistent with the proported role for l-canavanine of nitrogen storage within the developing cotyledons and cotyledonary canavanine is transported very effectively to the aboveground portions of the plant. It is not yet clear how efficiently this transported canavanine supports the nitrogen metabolism of the developing plant.
Rosenthal
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GA
T. H. Morgan School of Biological Sciences, University of Kentucky, Lexington, Kentucky 40506.
Rhodes
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