De Novo Arginine Biosynthesis in Leaves of Phosphorus-Deficient Citrus and Poncirus Species

Publisher Website
Google Scholar
Abstract
Young, fully expanded leaves from 7-mo.-old P-deficient citrus rootstock seedlings had levels of nonprotein arginine that were 10- to 50-fold greater than those from P-sufficient control plants. Arginine content of the protein fraction increased 2- to 4-fold in P-deficient leaves. Total arginine content, which averaged 72 .+-. 6 .mu.mol/g dry wt of P-sufficient leaf tissue (mean .+-. SE, n = the 4 rootstocks) was 207, 308, 241 and 178 .mu.mol in P-deficient leaves from C. limon cv. Rough Lemon, P. trifoliata .times. C. sinensis cv. Carrizo citrange and cv. Troyer citrange, and P. trifoliata cv. Australian trifoliate orange, respectively. For each rootstock, the accumulation of arginine paralleled and increase in the activity of the pathway for the de novo biosynthesis of arginine. The ratio of nmol NaH14CO3 incorporated into the combined pool of arginine plus urea per gram fresh wt intact leaf tissue during a 3-h labeling period for P-deficient to P-sufficient plants was 91:34 49:11, 35:11, and 52:41, respectively. When P-deficient plants were supplied with P, incorporation of NaH14CO3 into arginine plus urea was reduced to the level observed for the P-sufficient control plants of the same age and arginine ceased to accumulate. Arginase and arginine decarboxylase activity were either unaffected or slightly increased during P deficiency. Arginine accumulation during P deficiency is evidently due to increased activity of the de novo arginine biosynthetic pathway.