Nitrogen accumulation induced by phosphorus deficiency in citrus plants

Achituv, Miriam; Bar‐Akiva, A.

doi:10.1016/0304-4238(73)90037-x

Cited by 14 publications

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“…Furthermore, the fact that a-ketoglutarate which entered the amino acid metabolism was converted rapidly to arginine precursors, arginine and proline, is also consistent with our previous findings, that arginine is synthesized at the expense of other proteinous amino acids and does not result from protein degradation (1). The carbon skeleton of arginine is derived from aketoglutarate via many intermediary steps, with glutamic acid as the first one (8,15).…”

Section: Discussionsupporting

confidence: 75%

“…In P-deficient lemon seedlings we found an inverse relationship between their growth and arginine accumulation: as the rate of growth declined the concentration of arginine rose, while the other amino acids and protein remained low in comparison with seedlings grown in full nutrient solution (1). This deviation from the normal pattern of amino acid synthesis may be attributed to a decrease in activity of transaminases, enzymes which require pyridoxal phosphate as a coenzyme (2).…”

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confidence: 71%

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Metabolic Pathway of α-Ketoglutarate in Citrus Leaves as Affected by Phosphorus Nutrition

Achituv¹,

Bar‐Akiva²

1978

Plant Physiol.

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The uptake ad metabolism of a-15-14Clketoglutarate by phospborusdeficient and full nutrient (control) iemo (Citus lmn) leaves were studied over various thme intervals. After 45 minutes In P-deficient leaves, the bulk of Incorporated 14C appeared In organk acids and much less In amino acids, while In the control leaves, the 14C contests of organic and amino acids were equal. In P-efcient leaves, after loger Incubation times the 14C content of organic acids and anino acids Increased, whRe that of CO and residue fractions remaied iow. In full nutrient leaves the "C content of amino acids and organic acids decreased after ionger iocubaton time and Increased in the insolube residue and CO2. In full utient leaves the organic and amino acid metaboUsm were ciosely related and accompanied by protein synthesis and CO2 release, whie in P-deficient leaves an accelerating accumulation of arginine and citric acid was iHnked together With hibitio of protein syntheis and CO liberation.Accumulation of arginine is a well recognized metabolic disturbance induced by phosphorus deficiency in various plants (6,10,11,21). In P-deficient lemon seedlings we found an inverse relationship between their growth and arginine accumulation: as the rate of growth declined the concentration of arginine rose, while the other amino acids and protein remained low in comparison with seedlings grown in full nutrient solution (1). This deviation from the normal pattern of amino acid synthesis may be attributed to a decrease in activity of transaminases, enzymes which require pyridoxal phosphate as a coenzyme (2). In a study of the correlation among phosphate ratio, GOT2 activity, and PLP content, we found that the reduced activity of enzyme could be restored by infiltration of pyridoxal phosphate or mineral phosphate into the P-deficient leaves (2). On the other hand, determinations oforganic acids disclosed extensive accumulation ofcitrate in P-deficient lemon leaves (unpublished data).In the present study we followed the incorporation of a-ketoglutarate into various cell metabolities in P-deficient and normal citrus leaves. In each jar, a small vial containing 1.5 ml of methanol-ethanolamine (4:1, v/v), was placed to trap the "CO2.At the end of the incubation period the radioactivity of CO2 was counted in 10 ml of toluene fluor. During the incubation period, the jars were shaken gently in a water bath at 35 C. The incubation periods were 45, 90, and 180 min. Each combination of treatments (mineral nutrition and incubation period) was tested in three replicates.At the end of the incubation period the buffer solution was filtered through Miracloth. The discs were rinsed with deionized H20, blotted on filter paper, and boiled in 15 ml of 100%o ethanol for 10 min.Extraction. The discs were homogenized for 2 min in a VirTis blender set at speed 60, and centrifuged at 10,000g. The pellet was reextracted four times by shaking for 10 min with 10-ml portions of 80% (v/v) ethanol and then centrifuged (22).The insoluble residue was dried over silica ge...

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Section: Discussionsupporting

confidence: 75%

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confidence: 71%

Metabolic Pathway of α-Ketoglutarate in Citrus Leaves as Affected by Phosphorus Nutrition

Achituv¹,

Bar‐Akiva²

1978

Plant Physiol.

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“…However, total nitrogen levels increased in leaves of rough lemon plants after 6 additional weeks of low P fertilization. This result is consistent with previous reports of arginine accumulation and increased levels of total nitrogen during an extended period of P deficiency (1,23). Nitrate levels increased sooner and to a greater extent than ammonia.…”

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confidence: 83%

“…The increased activity of this pathway during P deficiency, along with reports of increased nitrogen levels in citrus cultivars grown under low P fertilization (1,23), suggested to us the possibility that P deficiency results in increased concentration of ammonia in Pdeficient leaves.…”

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Increased Arginine Biosynthesis during Phosphorus Deficiency

Rabe

Lovatt²

1986

Plant Physiol.

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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 ...

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Nitrogen Metabolism and Utilization in Citrus

Kato

1986

Horticultural Reviews

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Nitrogen accumulation induced by phosphorus deficiency in citrus plants

Cited by 14 publications

References 15 publications

Metabolic Pathway of α-Ketoglutarate in Citrus Leaves as Affected by Phosphorus Nutrition

Metabolic Pathway of α-Ketoglutarate in Citrus Leaves as Affected by Phosphorus Nutrition

Increased Arginine Biosynthesis during Phosphorus Deficiency

Nitrogen Metabolism and Utilization in Citrus

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