The nucleoprotein content of fibroblasts growing in vitro. 4. Changes in the ribonucleic acid phosphorus (RNAP) and deoxyribonucleic acid phosphorus (DNAP) content.
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Journal Article↗
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[Effect of low-molecular-weight dextran (40,000) on the levels of inorganic phosphorus and lipid-bound phosphorus in the blood of patients with a transient disorder of cerebral circulation].
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Aged↗
[Determination of inorganic phosphorus in the presence of phosphorylated compounds and applications to the study of phosphorus metabolism in the rabbit vagus nerve].
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Adenine Nucleotides↗
[Adenine compounds and phosphorus esters in erythrocytes in human tuberculosis. II. Adenine nucleotides and phosphorus esters in erythrocytes].
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Adenine Nucleotides↗
The development of feedstuff retainable phosphorus values for broilers.
Presently, phosphorus requirements are based on consumption of nonphytate phosphorus (NPP), which does not account for the fact that NPP may not be completely available and that phytate phosphorus can be partially utilized to fulfill phosphorus requirements. Phosphorus retention values for feed ingredients, accounting for NPP and phytate phosphorus, and total retainable phosphorus requirements are needed to formulate diets that meet the phosphorus requirements of poultry but that do not result in excessive amounts of phosphorus in poultry excreta. A bioassay was conducted to determine retention of phosphorus from calcium phosphates. Eight levels of a reagent-grade monocalcium phosphate, monohydrate, (MCP) were added to a cornsoy, semi-synthetic basal diet containing an acid-insoluble ash marker and offered to individually caged 10-d-old male broilers. After acclimation to the diets for 3 d, excreta were collected for 48 h. Diet and excreta samples were analyzed for total phosphorus, phytate phosphorus, and acid insoluble ash. Retentions of the basal total, NPP, and phytate phosphorus were determined to be 43.2, 65.5, and 32.3%, respectively. Retention of the phosphorus from different phosphorus sources was determined to be dependent on the amount of source included in the diet. The maximum retentions of total phosphorus, NPP, and phosphorus from MCP for the basal-MCP test diets were 67.6, 80.2, and 98%, respectively. The maximum retention of dietary retainable phosphorus occurred with a 2:1 ratio of 0.48% calcium and 0.24% retainable phosphorus. The retainable phosphorus intakes for 10-to-15-d-old broilers required to provide a steady physiological state was 108 mg/d, as determined by two-line regression analysis. Retainable phosphorus requirements based on segmented line regression analysis using bone strength measurements for 0-to-3-wk-old chicks and 3-to-6-wk-old broilers were 0.39 and 0.30%, respectively.
Animal Feed↗
Fermentation of soybean meal with Aspergillus usamii reduces phosphorus excretion in chicks.
Fermentation with Aspergillus usamii almost completely degrades phytate phosphorus in soybean meal. Phosphorus excretion was investigated in chicks fed a fermented soybean meal-based diet. Thirty chicks were fed one of three experimental diets; a control soybean meal-based diet (total phosphorus, 5.2 g/kg; nonphytate phosphorus, 2.3 g/kg), a control soybean meal-based diet with added inorganic phosphorus (total phosphorus, 7.1 g/kg; nonphytate phosphorus, 4.0 g/kg), or a fermented soybean meal-based diet without supplemental inorganic phosphorus (total phosphorus, 5.8 g/kg; nonphytate phosphorus, 3.9 g/kg) for 4 wk. Body weight gain, the amount of retained phosphorus, and femoral phosphorus content were lower in the control group than in the phosphorus-supplied group and the fermented soybean meal group. The latter two groups showed similar body weight gain and femoral phosphorus content. On the other hand, phosphorus excretion was markedly more in the phosphorus-supplied group than in the other groups. As a result, phosphorus retention (percentage of intake) was lower in the phosphorus-supplied group than in the fermented soybean meal group. In conclusion, fermentation improved phosphorus bioavailability in soybean meal and supplemental inorganic phosphorus was not necessary for the fermented soybean meal-based diet, which remarkably reduced phosphorus excretion.
Animals↗
Comparison of various phosphate salts as the dietary phosphorus source on nephrocalcinosis and kidney function in rats.
The effects of various phosphate salts as the dietary phosphorus sources on the development of nephrocalcinosis and kidney function were examined in rats fed diets containing monophosphate salts (sodium dihydrogenphosphate, NaH2PO4, or potassium dihydrogenphosphate, KH2PO4) or polyphosphate salts (sodium tripolyphosphate, Na5P3O10, or potassium tripolyphosphate, K5P3O10), at levels representing normal phosphorus (normal phosphorus diet) or high phosphorus (high phosphorus diet) contents for 21 d. High phosphorus diet-feeding increased the kidney calcium and phosphorus concentrations. Kidney calcium and phosphorus concentrations were higher in rats fed the high phosphorus diet containing Na5P3O10 or K5P3O10 than in rats fed the high phosphorus diet containing NaH2PO4 or KH2PO4. Nephrocalcinosis was observed in all rats fed a high phosphorus diet, and the degree of nephrocalcinosis was more severe in rats fed Na5P3O10 or K5P3O10 than in rats fed NaH2PO4 or KH2PO4. In rats fed the high phosphorus diet, creatinine clearance was higher in rats fed Na5P3O10 or K5P3O10 than in rats fed NaH2PO4 or KH2PO4. In rats fed Na5P3O10 or K5P3O10, urinary albumin excretion and N-acetyl-beta-D-glucosaminidase (NAG) activity in the urine were increased in rats fed the high phosphorus diet. These were higher in rats fed the high phosphorus diet containing Na5P3O10 than in rats fed the high phosphorus diet containing NaH2PO4 or KH2PO4. This study observed that the development of nephrocalcinosis and kidney function in rats fed the high phosphorus diet was influenced by the difference in monophosphate or polyphosphate salts provided as the dietary phosphorus source, while the effects of sodium and potassium salts were not evident. We suggest that the development of nephrocalcinosis and kidney function in rats fed a high phosphorus diet was altered depending on the form of phosphate salts provided as the dietary source of phosphorus. Additionally, the development of nephrocalcinosis and diminished kidney function in rats fed the high phosphorus diet was more severe for polyphosphate salts as compared to monophosphate salts.
Acetylglucosaminidase↗
Sources and bioavailability of phosphorus fractions in freshwaters: a British perspective.
This paper seeks a perspective on the forms of phosphorus which promote aquatic eutrophication, with the particular quest of establishing their sources. A short background traces the development of understanding of nutrient enrichment and the suppositions about the relative contributions of agriculture, sewage and detergent residues. Most aquatic systems, and their primary producers, are naturally deficient in biologically-available phosphorus. Aquatic plants have evolved very efficient phosphorus uptake mechanisms. The biomass responses to an increase in the supply of phosphorus are stoichiometrically predictable. The most bioavailable forms of phosphorus are in solution, as orthophosphate ions, or are readily soluble or elutable from loose combinations. Ready bioavailability coincides well with what is measurable as molybdate-reactive (MRP) or soluble-reactive phosphorus (SRP). Most other forms, including phosphates of the alkaline earth metals, aluminium and iron are scarcely available at all. Orthophosphate ions sorbed to metal oxides and hydroxides are normally not biologically available either, except through weak dissociation ('desorption'). The production of alkaline phosphatase provides organisms with an additional mechanism for accelerating the sequestration of phosphate from organic compounds. Bioavailable phosphate is liberated when redox- or alkali-sensitive metal hydroxides dissolve but these processes are minor contributors to the biological responses to nutrient enrichment. Most of the familiar eutrophication is attributable to the widespread application of secondary sewage treatment methods to the wastes emanating from a burgeoning and increasingly urbanised human population. The use of polyphosphate-based detergents, now in decline, has contributed to the problem. In aquatic systems, the additional phosphorus raises the biological supportive capacity, sometimes to the capacity of the next limiting factor (carbon, light, hydraulic retention or of another nutrient). At high orthophosphate loadings, the straight stoichiometric yield relationship between biomass yield and phosphorus a vailability is lost. Movements of phosphorus and its recycling within aquatic systems do not prevent the slow gravitation of phosphorus to the bottom substrata. The phosphorus retentivity of sediments depends upon their chemical composition. While oxide-hydroxide binding capacity in the surface sediments persists, they act as a sink for phosphorus and a control on further cycling. Iron-rich and clay-rich sediments perform best in these conditions; calcareous sediments least so. Eutrophication may lead to the exhaustion of sediment P-binding capacity. Non-sorbed phosphate is readily recyclable if primary producers have access to it. Recycling is most rapid in shallow waters (where sediment disturbance, by flow, by wind action and through bioturbation, is frequent and least in deep ventilated sediments. The contributions of phosphorus from catchments are assessed. The slow rate of weathering of (mostly apatitic) minerals, the role of chemical binding in soils and the incorporation and retentivity bv forested terrestrial ecosystems each contribute to the minimisation of phosphorus leakage to drainage waters. Palaeolimnological and experimental evidence confirms that clearance of land and ploughing its surface weakens the phosphorus retentivity of catchments. The phosphorus transferred from arable land to drainage remains dominated by sorbed fractions which are scarcely bioavailable. Some forms of intensive market gardening or concentrated stock rearing may mobilise phosphates to drainage but it is deduced that drainage from agricultural land is not commonly a major source of readily bioavailable phosphorus in water. Careful budgeting of the phosphates in run-off from over-fertilised soils may nevertheless show that a proportionately small loss of bioavailable phosphorus can still be highly significant in promoting aquatic plant production. The bioavailable-phosphorus (BAP) load achieving the OECD threshold of lake eutrophy (35 mg P m(-3)) is calculated to be equivalent to a terrestrial loss rate of approximately 17.5 kg BAP km(-2) year(-1)), or only 1-2% of a typical fertiliser application. The output is shown to be comparable with the P yield from secondary treatment of the sewage produced by a resident population of 30-44 persons km(-2). With tertiary treatment, the equivalence is with approximately 200 persons km(-2).
Biological Availability↗
Phosphorus cycles of forest and upland grassland ecosystems and some effects of land management practices.
The distribution of phosphorus capital and net annual transfers of phosphorus between the major components of two unfertilized phosphorus-deficient UK ecosystems, an oak--ash woodland in the Lake District and an Agrostis-Festuca grassland in Snowdonia (both on acid brown-earth soils), have been estimted in terms of kg P ha--1. In both ecosystems less than 3% of the phosphorus, totalling 1890 kg P ha--1 and 3040 kg P ha--1 for the woodland and grassland, respectively, is contained in the living biomass and half that is below ground level. Nearly all the phosphorus is in the soil matrix. Although the biomass phosphorus is mostly in the vegetation, the soil fauna and vegetation is slower (25%) than in the grassland vegetatation (208%). More than 85% of the net annual vegetation uptake of phosphorus from the soil is returned to the soil, mainly in organic debris, which in the grassland ecosystem is more than twice as rich in phosphorus (0.125% P) as in the woodland ecosystem (0.053% P). These concentrations are related to the rates of turnover (input/P content) of phosphorus in the litter layer on the soil surface; it is faster in the grassland (460%) than in the woodland (144%). In both cycles plant uptake of phosphorus largely depends on the release of phosphorus through decomposition of the organic matter returned to soil. In both the woodland and the grassland, the amount of cycling phosphorus is potentially reduced by its immobilization in tree and sheep production and in undecomposed organic matter accumulating in soil. It is assumed that the reductions are counterbalanced by the replenishment of cycling phosphorus by (i) some mineralization of organically bound phosphorus in the mineral soil, (ii) the income in rainfall and aerosols not being effectively lost in soil drainage waters and (iii) rock weathering. The effects of the growth of conifers and sheep grazing on the balance between decomposition and accumulation of organic matter returned to soil are considered in relation to the rate of phosphorus cycling and the pedogenetic changes in soil phosphorus condition leading to reduced fertility. Although controlled sheep grazing speeds up phosphorus cycling and may reverse the pedogenetic trend in favour of soil improvement, conifers may slow down phosphorus cycling and promote the pedogenetic trend towards infertility.
Agriculture↗
Phosphorus reduction through precision feeding of dairy cattle.
A study was conducted on 4 dairy farms in the Cannonsville Reservoir Basin (Delaware County, NY) to identify feeding strategies in commercial dairy herds that will reduce manure phosphorus and mass farm phosphorus balance. Lactating cow diets on all 4 farms were evaluated monthly for 28 mo using the Cornell Net Carbohydrate and Protein System. Milk production and herd reproductive performance were measured monthly. Manure phosphorus content was measured every 6 mo. Reduced phosphorus diets (precision feeding) were implemented in 2 of the herds. Mean herd phosphorus intakes in the 4 herds ranged from 107 to 165% of requirement. Dietary phosphorus intakes in the 2 herds where diets were modified were reduced from 153% of requirement to 111%, an average reduction of 25%. Predicted phosphorus intakes and manure excretions were reduced 11.8 kg/yr per cow. After dietary adjustments in the 2 herds, fecal phosphorus concentrations decreased 33%. Milk production was not adversely affected by reduced phosphorus diets. Whole farm mass phosphorus balances (amount of phosphorus remaining on the farm) on the 2 farms were reduced 49%, with the percentage of imported phosphorus remaining on the farm reduced to less than 45%. Achieving feed phosphorus reductions similar to those of this study on all of the estimated 7000 to 8000 mature dairy cattle in the Cannonsville Basin could reduce feed phosphorus imports and manure phosphorus excretions more than 64,000 kg/yr. This would slow the rate of phosphorus accumulation in agricultural soils in the Cannonsville Basin, which over time could reduce the 50,000 kg/yr average total phosphorus loading of the Cannonsville Reservoir.
Animal Feed↗
Relationship between serum phosphorus levels and various outcome measures in adult hemodialysis patients.
OBJECTIVE: To compare three different mean serum phosphorus ranges on outcomes related to the control and treatment of hyperparathyroidism (HPTH), to nutritional status, and to quality of life (QOL) in adult hemodialysis (HD) patients. DESIGN: Patients were grouped based on the mean of five monthly phosphorus levels achieved during the study period. Group 1 included patients whose mean phosphorus levels over the period was <6.0 mg/dL (n = 24); group 2 averaged between 6.0 and 6.9 mg/dL (n = 14); and group 3 averaged >7.0 mg/dL (n = 16). Descriptive comparisons were made between phosphorus groups. PATIENTS: Fifty-four stable, adult HD patients participated voluntarily. MAIN OUTCOME MEASURES: Intact-parathyroid hormone (iPTH), calcium x phosphorus product (Ca x P), and change in iPTH, albumin (alb), total protein (tpro), weight (wt) and body mass index (BMI), and scores on a QOL survey. Baseline physical and lab characteristics. RESULTS: No difference was found between phosphorus levels of <6.0 mg/dL and levels of 6.0 to 6.9 mg/dL in iPTH, Ca x P levels allowing safe calcitriol therapy, nor response to calcitriol treatment. Patients with phosphorus levels >7.0 mg/dL had midstudy iPTH greater than phosphorus levels <6.0 mg/dL. Otherwise the three groups did not differ significantly in iPTH levels. Phosphorus levels 6.0 to 6.9 mg/dL was associated with lowest wt and BMI, but alb and tpro did not differ between the phosphorus groups. Phosphorus levels of >7.0 was associated with highest creatinine levels and youngest age. Subjects in the phosphorus levels of <6.0 mg/dL gp were more likely than the 6.0 to 6.9 mg/dL gp to describe their diet as sufficient and, at baseline, were more likely to relate diet to QOL. CONCLUSION: Comparison of three levels of serum phosphorus on indicators of outcome in the control and treatment of secondary hyperparathyroidism showed no significant difference in outcome between phosphorus levels of <6.0 mg/dL and phosphorus levels 6.0 to 6.9 mg/dL. However, the data suggests that phosphorus levels of >7.0 mg/dL may relate to significantly higher iPTH and unacceptable Ca x P levels. There were no differences between the groups, suggesting less favorable outcome at any of the three phosphorus levels regarding nutritional status or QOL in this small group of stable, adult HD patients.
Adult↗
Hypophosphatemia and phosphorus depletion in respiratory and peripheral muscles of patients with respiratory failure due to COPD.
In 22 patients (19 men, 3 women; mean [+/- SD] age, 63 +/- 6 years) with chronic obstructive pulmonary disease (COPD), phosphorus content was measured by spectrophotometric methods on muscle fragments of both peripheral (quadriceps femoris needle biopsy in 22 patients) and respiratory muscles (external intercostal muscle surgical biopsy in 14 patients). Thirty age- and sex-matched subjects were used as controls (19 for quadriceps femoris muscle biopsy and 11 for intercostal muscle biopsy). Serum phosphorus levels, as well as the main determinants of overall phosphorus metabolism (dietary intake of phosphorus and renal phosphate handling), were also obtained in all patients and control subjects. Muscle phosphorus content of both respiratory and peripheral muscles was significantly reduced in the COPD patient group, no matter what reference index was used (fat-free dry muscle weight or muscle fragment DNA content); muscle phosphorus depletion was present in about 50 percent of patients with COPD. In the same patient group, a significant relationship between muscle and serum phosphorus levels was demonstrable in the case of peripheral muscles only. No relationship was found between phosphorus content of both types of skeletal muscles and dietary phosphorus intake levels or with nutritional status, even though patients with COPD had significantly reduced anthropometric, biochemical, and immunologic indices as compared with controls. Renal phosphorus handling indices of the COPD patient group were compatible with a condition of inadequacy of the renal compensatory mechanism to hypophosphatemia and phosphorus depletion (low percent tubular reabsorption of phosphorus, low renal threshold concentration values). Our study suggests that phosphorus depletion occurs frequently in COPD, but in this clinical condition serum phosphorus levels are not representative of cellular phosphorus levels. Phosphorus depletion, which is equally severe in respiratory and peripheral muscles, could depend, at least in part, on malnutrition and a condition of renal phosphorus wasting possibly linked to some drugs commonly used in patients with COPD (xanthine derivatives, diuretics, etc).
Aged↗
Effect of dietary phosphorus on circulating concentrations of 1,25-dihydroxyvitamin D and immunoreactive parathyroid hormone in children with moderate renal insufficiency.
The hyperparathyroidism characteristic of patients with moderate renal insufficiency could be caused by decreases in the plasma concentration of ionized calcium (Ca++) evoked by: (a) recurring increases in the plasma concentration of inorganic phosphorus that may be detectable only in the post-prandial period; (b) a reversible, phosphorus-mediated suppression of renal 25-hydroxyvitamin D-1 alpha-hydroxylase that decreases the plasma concentration of 1,25-dihydroxyvitamin D (1,25-(OH)2D) enough to decrease both gut absorption and bone resorption of Ca++; (c) both of these. In a group of eight children with moderate renal insufficiency, mean glomerular filtration rate (GFR) 45 +/- 4 (SE) ml/min per 1.73 M2, ages 6-17 yr, we tested these hypotheses by determining the effect of short term (5 d) restriction and supplementation of dietary intake of phosphorus on the plasma concentration of 1,25-(OH)2D, the serum concentrations of immunoreactive parathyroid hormone (iPTH) and phosphorus, and the fractional renal excretion of phosphorus ( FEPi ). When dietary phosphorus was normal, 1.2 g/d, the serum concentrations of phosphorus throughout the day were not greater than those of normal control children, and the serum concentrations of carboxyl-terminal iPTH (C-iPTH) were greater, 59 +/- 9 vs. 17 +/- 3 mu leq/ml, and unchanging; the serum concentration of intact-iPTH was also greater, 198 +/- 14 vs. 119 +/- 8 pg/ml. The plasma concentration of 1,25-(OH)2D was lower than that of age-matched controls, 27 +/- 3 vs. 36 +/- 2 pg/ml (P less than 0.01). When dietary phosphorus was restricted to 0.35 g/d, the plasma concentration of 1,25-(OH)2D increased by 60% to a mean value not different from that of normal controls, while serum concentrations of C-iPTH and intact-iPTH decreased by 25%, the latter concentration to a mean value not different from that of controls. FEPi decreased from 31 to 9%. When dietary phosphorus was supplemented to 2.4 g/d, the plasma concentration of 1,25-(OH)2D decreased 32%, while those of C-iPTH and intact-iPTH increased by 131 and 45%, respectively; FEPi increased from 27 to 53%. Plasma concentrations of 25-hydroxyvitamin D remained normal and unchanged, and GFR did not change when dietary phosphorus was manipulated. The data demonstrate that in children with moderate renal insufficiency: (a) A normal dietary intake of phosphorus in attended by a decreased circulating concentration of 1,25-(OH)2D and an increased concentration of iPTH, but not by recurring increases in the serum concentration of phosphorus at any time of the day; (b) Dietary phosphorus is, however, a major determinant of the circulating concentrations of both 1,25-(OH)2D and iPTH, which vary inversely and directly, respectively, with dietary intake of phosphorus, and increase and decrease, respectively, to normal values when phosphorus is restricted for 5 d; (c) Restriction and supplementation of dietary phosphorus induces changes in the serum concentration of iPTH that correlate strongly but inversely with those induced in the plasma concentration of 1,25-(OH)2D (r = -0.88, P < 0.001); and (d) The physiologic responsiveness of the renal tubule to changes in dietary phosphorus is to a substantial extent intact. The data provide support for the second hypothesis stated.
Adolescent↗
The efficiency of Arabidopsis thaliana (Brassicaceae) root hairs in phosphorus acquisition.
Arabidopsis thaliana root hairs grow longer and denser in response to low-phosphorus availability. In addition, plants with the root hair response acquire more phosphorus than mutants that have root hairs that do not respond to phosphorus limiting conditions. The purpose of this experiment was to determine the efficiency of root hairs in phosphorus acquisition at high- and low-phosphorus availability. Root hair growth, root growth, root respiration, plant phosphorus uptake, and plant phosphorus content of 3-wk-old wild-type Arabidopsis (WS) were compared to two root hair mutants (rhd6 and rhd2) under high (54 mmol/m) and low (0.4 mmol/m) phosphorus availability. A cost-benefit analysis was constructed from the measurements to determine root hair efficiency. Under high-phosphorus availability, root hairs did not have an effect on any of the parameters measured. Under low-phosphorus availability, wild-type Arabidopsis had greater total root surface area, shoot biomass, phosphorus per root length, and specific phosphorus uptake. The cost-benefit analysis shows that under low phosphorus, wild-type roots acquire more phosphorus for every unit of carbon respired or unit of phosphorus invested into the roots than the mutants. We conclude that the response of root hairs to low-phosphorus availability is an efficient strategy for phosphorus acquisition.
Journal Article↗
Dietary phosphorus regulates serum fibroblast growth factor-23 concentrations in healthy men.
CONTEXT: Fibroblast growth factor 23 (FGF-23) is important in the regulation of phosphorus and vitamin D metabolism. States of excess circulating FGF-23 are associated with renal phosphate wasting and inappropriately low serum 1,25-dihydroxyvitamin D [1,25(OH)(2)D] concentrations. Conversely, states of absent or biologically inactive circulating FGF-23 are associated with increased serum phosphorus and 1,25(OH)(2)D concentrations. Restriction of the dietary intake of phosphorus increases renal phosphate reabsorption and 1,25(OH)(2)D production, whereas the opposite occurs when dietary phosphorus is supplemented. OBJECTIVE: We sought to determine whether serum FGF-23 concentration is regulated by dietary phosphorus and thereby mediates the physiological response of serum 1,25(OH)(2)D to changes in dietary phosphorus. DESIGN, SETTING, AND PARTICIPANTS: We studied 13 healthy men as inpatients during a 4-wk dietary phosphorus intervention study. INTERVENTION: Subjects consumed a constant diet that provided 500 mg of phosphorus per day, which was supplemented to achieve three phosphorus intakes, each of 9 d: 1) control = 1500 mg/d; 2) supplemented = 2300 mg/d; 3) restricted = 625 mg/d. Intakes of calcium, sodium, potassium, magnesium, and energy were constant. MAIN OUTCOME MEASURE: Serum FGF-23, 1,25(OH)(2)D, phosphorus, and calcium concentrations were measured. RESULTS: Serum FGF-23 concentrations decreased significantly from 30.7 +/- 8.7 pg/ml during phosphorus supplementation to 19.6 +/- 7.0 pg/ml during phosphorus restriction. Serum 1,25(OH)(2)D concentrations increased significantly from 29 +/- 10 pg/ml (75 +/- 26 pmol/liter) during phosphorus supplementation to 40 +/- 16 pg/ml (104 +/- 42 pmol/liter) during phosphorus restriction (P < 0.001). Serum 1,25(OH)(2)D concentrations varied inversely with those of serum FGF-23 (r = -0.67, P < 0.001). CONCLUSIONS: We conclude that in healthy men, changes in dietary phosphorus within the physiological range of intakes regulate serum FGF-23 concentrations and suggest that dietary phosphorus regulation of 1,25(OH)(2)D production is mediated, at least in part, by changes in circulating FGF-23.
Adult↗
Detection of quantitative trait loci for seminal root traits in maize (Zea mays L.) seedlings grown under differential phosphorus levels.
Suboptimal phosphorus availability is a primary constraint for terrestrial plant growth. Seminal roots play an important role in acquisition of nutrients by plant seedlings. The length and number of seminal roots may be particularly important in acquisition of immobile nutrients such as phosphorus by increasing soil exploration. The objective of this study was to identify quantitative trait loci (QTL) controlling seminal root growth in response to phosphorus stress in maize, and to characterize epistatic interactions among QTL. Seminal root length and number were evaluated in 162 recombinant inbred lines derived from a cross between B73 and Mo17 in seedlings grown in a controlled environment. B73 and Mo17 significantly differed for seminal root length under low phosphorus, but not under adequate phosphorus conditions. Seminal root length of the population grown under low phosphorus ranged from 0 to 79.2 cm with a mean of 32.3 cm; while seminal root length of plants grown under high phosphorus ranged from 0.67 to 59.0 cm with a mean of 23.4 cm. Under low phosphorus, one main-effect QTL was associated with seminal root length and three QTL with seminal root number; under high phosphorus, two QTL with seminal root length and three QTL for seminal root number. These accounted for 11, 25.4, 22.8, and 24.1% of the phenotypic variations for seminal root length and number at low phosphorus, and seminal root length and number at high phosphorus, respectively. Di-genic epistatic loci were detected for seminal root length at low phosphorus (two pairs) seminal root number at low phosphorus (eight pairs), seminal root length at high phosphorus (four pairs), and seminal root number at high phosphorus (two pairs), which accounted for 23.2, 50.6, 32.2, and 20.3% of the total variations, respectively. Seminal root traits observed here were positively yet weakly correlated with shoot biomass in the field under low phosphorus, although no coincident QTL were detected. These results suggest that epistatic interactions are important in controlling genotypic variation associated with seedling seminal root traits.
Chromosome Mapping↗
III. Quantitative aspects of phosphorus excretion in ruminants.
Ruminant phosphorus excretion and metabolism were studied through a database. Faecal endogenous phosphorus is the main pathway of phosphorus excretion and averages 0.85 of total faecal phosphorus. The remaining 0.15 is unabsorbed dietary phosphorus. Faecal endogenous phosphorus is mainly unabsorbed phosphorus, with saliva being the major source, and is correlated to factors influencing saliva secretion (DM intake, physical dietary characteristics and dietary phosphorus content). Another source of faecal endogenous phosphorus is rumen microbial phosphorus that escaped solubilisation during post-rumen digestion. All factors stimulating microbial growth would increase phosphorus uptake by the rumen microbes and consequently the faecal endogenous phosphorus. Understanding the determinants of faecal endogenous phosphorus flow will help to precise the determination of net phosphorus requirements for maintenance. The role of plasma phosphorus in urinary phosphorus loss is discussed.
Animals↗
Relationship between phosphorus and creatinine clearance in peritoneal dialysis: clinical implications.
Elevated serum phosphorus levels are associated with increased morbidity and mortality in dialysis patients. To study the determinants of serum phosphorus levels and phosphorus clearance, we measured phosphorus concentrations in 24-hour collections of dialysate and residual urine output during routine urea kinetics in 56 peritoneal dialysis patients. Dietary records were used to estimate oral phosphorus intake, and the net gastrointestinal absorption of phosphorus was determined measuring the amount of phosphorus excreted in 24 hours. Dialysate to plasma ratios of phosphorus and creatinine were very similar, and the peritoneal clearances of phosphorus and creatinine correlated well and were of the same magnitude. High transporters in the peritoneal equilibration test had greater phosphorus and creatinine clearances than low transporters. In patients with residual urine output, the renal clearances of phosphorus and creatinine also correlated well. Comparing two groups of patients with a similar Kt/V of 2 and greater but different levels of creatinine clearance, either greater or less than 60 L/wk, the patients with the greater creatinine clearance also had a greater phosphorus clearance (7.0 +/- 2.2 versus 4.3 +/- 0.7 mL/min/1.73 m(2)) and significantly lower serum phosphorus levels (4.8 +/- 0.9 versus 5.9 +/- 1.4 mg/dL) despite a greater daily amount of phosphorus absorption (490 +/- 190 versus 336 +/- 100 mg/d). In summary, creatinine clearance measurements provide a good estimate of phosphorus clearance and how much dietary phosphorus and therefore protein can be tolerated.
Creatinine↗