Increased Arginine Biosynthesis during Phosphorus Deficiency

Abstract

ABSTRACIT he accumulation of arginine in leaves of four citrus rootstock cultivars during P deficiency has been demonstrated to be due to increased de novo synthesis rather than decreased catabolism or increased protein degradation (E Rabe, CJ Lovatt, 1984, Plant Physiol 76: 747-752). In this report, we provide evidence (a) that the increased activity of the arginine biosynthetic pathway observed for citrus rootstocks grown under Pdeficient conditions for 7 months is due to an increase in the concentration of ammonia in leaves of P-deficient plants and (b) that ammonia accumulation and removal through arginine systhesis are early responses to phosphorus deficiency for both a woody perenniaL rough lemon (Citrus limon), and an herbaceous annuaL summer squash (Cucurbita pepo). Transferring 5-day-old squash plants to a phosphorus-deficient nutrient solution for only 10 days resulted in a 2-fold increase in the concentration of nitrate in the youngest fully expanded leaves (YFE). Concomitantly, the specific activity of nitrate reductase doubled and the ammonia content of P-deficient YFE leaves increased to a concentration significantly greater that of leaves from healthy control plants (P < 0.05). Consistent with increased availability of ammonia, the incorporation of NaH'4CO3 into arginine plus urea doubled during phosphorus deficiency and arginine accunlulated. Despite the accumulation of nitrate and ammonia in YFE leaves during phosphorus deficiency, the total nitrogen content of these leaves was less than that of the healthy control plants. Similar results were obtained for rough lemon. Nitrate content of the YFE leaves increased 1.5-and 3.0-fold in plants deprived of phosphorus for 6 and 12 weeks, respectively. Ammonia content of the leaves increased as P deficiency progressed to 1.4 ± 0.08 mg (± sE, n = 4) per gram dry weight, a level 1.8-fold greater than that of the P-sufficient control plants. During P deficiency de novo arginine biosynthesis in rough lemon increased 10-fold. Immersing the petiole of YFE leaves from P-sufficient squash and rough lemon plants in 50 millimolar NH4' for 3 hours resulted in the accumulation of ammonia in the leaves, and a 4-fold increase in the incorporation of NaH"CO3 into arginine plus urea. Taken together, these results provide strong evidence that the accumulation of nitrate and ammonia in leaves is an early response of both woody and herbaceous plants to P deprivation. The data are consistent with the hypothesis that increased de novo arginine biosynthesis in leaves during P deficiency is in response to ammonia content of the leaves.We have recently demonstrated that the accumulation of arginine in the leaves of four citrus rootstock cultivars 'Supported by a grant from the Chancellor's Patent Funds awarded to ER, by a grant from the Academic Senate of the University of California to CJL, and by the Agricultural Experiment Station of the University of California, Riverside, CA 92521. 2The work presented here is also submitted in partial fulfillment of requirements for ...

Metabolomic profiling from leaves and roots of tomato ( Solanum lycopersicum L.) plants grown under nitrogen, phosphorus or potassium-deficient condition

“…Tyrosine functions as a receiver of phosphate groups that are transferred by protein kinases to activate target proteins, and thus the accumulation of Tyr and aromatic amino acids, Phe and Trp might be from degradation of proteins [45]. Additionally, the large accumulation of Arg during P deficiency is consistent with previous reports [21,51] that ammonia accumulates during P deficiency and that the Arg biosynthetic pathway is an early response to detoxify ammonia from P-deficient tissue. However, the reason for the differences in the levels of amino acids is not clear, and it is merely presumed that enzymes using these amino acids as substrates might be activated under P deficiency.…”

Foliar ammonium accumulation as an index of stress in plants

“…PuritchandBarker (1967) reported that the ultrastructure of tomato chloroplasts degenerates with ammonium toxicity, which is manifested by ammonium accumulation, diminished photosynthesis, and foliar chlorosis and necrosis. Rabe and Lovatt (1986) noted the similarity between symptoms of P deficiency and ammonium feeding of squash (Cucurbitapepo L.); both processes led to ammonium accumulation. Table 2.…”

“…Endogenously generated ammonium accumulation also occurs in physiologically stressed plants. Ammonium accumulation has been detected in tissues stressed by diseases (Bashan etal., 1980), nutrient deficiency (Feng and Barker, 1992a;Rabe and Lovatt, 1986), salinity (Adler and Wilcox, 1988;Feng and Barker, 1992c), water-deficit (Feng and Barker, 1992c;Frota and Tucker, 1978), and ammonium toxicity (Barker and Corey, 1991). Ammonium accumulation has been associated with degradation of plant ultrastructure and visual symptoms of injury (Barker et al, 1966;Bashan et al, 1980;Puritch and Barker, 1967).…”

Plant Analyses and Interpretation

“…These methods are based on the activity of certain enzymes being lower or higher in deficient than normal plant tissue (Osaki et al, 1993;Osuji et al, 1998;Rabe and Lovatt, 1986;Romer et al, 1995;Stewart et al, 2001). June July August September Fig.…”