Functional significance of dauciform roots: exudation of carboxylates and acid phosphatase under phosphorus deficiency in Caustis blakei (Cyperaceae)

Caustis blakei produces an intriguing morphological adaptation by inducing dauciform roots in response to phosphorus (P) deficiency. We tested the hypothesis that these hairy, swollen lateral roots play a similar role to cluster roots in the exudation of organic chelators and ectoenzymes known to aid the chemical mobilization of sparingly available soil nutrients, such as P. Dauciform-root development and exudate composition (carboxylates and acid phosphatase activity) were analysed in C. blakei plants grown in nutrient solution under P-starved conditions. The distribution of dauciform roots in the field was determined in relation to soil profile depth and matrix. The percentage of dauciform roots of the entire root mass was greatest at the lowest P concentration ([P]) in solution, and was suppressed with increasing solution [P], while in the field dauciform roots were predominately located in the upper soil horizons, and decreased with increasing soil depth. Citrate was the major carboxylate released in an exudative burst from mature dauciform roots, which also produced elevated levels of acid phosphatase activity. Malonate was the dominant internal carboxylate present, with the highest concentration in young dauciform roots. The high concentration of carboxylates and phosphatases released from dauciform roots, combined with their prolific distribution in the organic surface layer of nutrient-impoverished soils, provides an ecophysiological advantage for enhancing nutrient acquisition.

Linking physiological processes with mangrove forest structure: phosphorus deficiency limits canopy development, hydraulic conductivity and photosynthetic carbon gain in dwarf Rhizophora mangle

Spatial gradients in mangrove tree height in barrier islands of Belize are associated with nutrient deficiency and sustained flooding in the absence of a salinity gradient. While nutrient deficiency is likely to affect many parameters, here we show that addition of phosphorus (P) to dwarf mangroves stimulated increases in diameters of xylem vessels, area of conductive xylem tissue and leaf area index (LAI) of the canopy. These changes in structure were consistent with related changes in function, as addition of P also increased hydraulic conductivity (K-s), stomatal conductance and photosynthetic assimilation rates to the same levels measured in taller trees fringing the seaward margin of the mangrove. Increased xylem vessel size and corresponding enhancements in stern hydraulic conductivity in P fertilized dwarf trees came at the cost of enhanced midday loss of hydraulic conductivity and was associated with decreased assimilation rates in the afternoon. Analysis of trait plasticity identifies hydraulic properties of trees as more plastic than those of leaf structural and physiological characteristics, implying that hydraulic properties are key in controlling growth in mangroves. Alleviation of P deficiency, which released trees from hydraulic limitations, reduced the structural and functional distinctions between dwarf and taller fringing tree forms of Rhizophora mangle.

Identification of micronutrient deficiency of wheat in the Peshawar Valley, Pakistan

A field experiment was conducted to study the effect of micronutrients, zinc (Zn), copper (Cu), iron (Fe), manganese (Mn), boron (13) and a commercial fritted micronutrient product called Zarzameen, on the yield and the yield components of wheat (Triticum aestivum L.), in the Peshawar valley, Pakistan. Different combinations of Zn, Cu. Fe. Mn, B, and Zarzameen were applied at the rate of 4.0, 2.0, 5.0, 2.0, 1.0 kg ha(-1) and 1.0 kg ha(-1), respectively, along with a basal dose of 100 kg ha(-1) nitrogen(N), 75 kg ha(-1) phosphorus (P) and 50 kg ha(-1) potassium (K). The fertilizer treatments (macro- and micronutrients) increased wheat dry matter, grain yield, and straw yield significantly over an unfertilized control. Soil tests for B and Zn were increased both at boot and harvesting stage, and Fe at boot stage, with the addition of micronutrients. Plants without B had showed classical B deficiency symptoms at grain formation stage, but not at vegetative stage. Boron concentration in the dry matter of wheat plants increased with the addition of the B fertilizer in the soil. Boron deficiency was not observed in plants containing >4 mg B kg(-1) at the boot stage, or in soils containing > 1.4 mg kg(-1) hot water soluble B.

Differences in plant function in phosphorus- and nitrogen-limited mangrove ecosystems

Mangrove ecosystems can be either nitrogen (N) or phosphorus (P) limited and are therefore vulnerable to nutrient pollution. Nutrient enrichment with either N or P may have differing effects on ecosystems because of underlying differences in plant physiological responses to these nutrients in either N- or P-limited settings. Using a common mangrove species, Avicennia germinans, in sites where growth was either N or P limited, we investigated differing physiological responses to N and P limitation and fertilization. We tested the hypothesis that water uptake and transport, and hydraulic architecture, were the main processes limiting productivity at the P-limited site, but that this was not the case at the N-limited site. We found that plants at the P-deficient site had lower leaf water potential, stomatal conductance and photosynthetic carbon-assimilation rates, and less conductive xylem, than those at the N-limited site. These differences were greatly reduced with P fertilization at the P-limited site. By contrast, fertilization with N at the N-limited site had little effect on either photosynthetic or hydraulic traits. We conclude that growth in N- and P-limited sites differentially affect the hydraulic pathways of mangroves. Plants experiencing P limitation appear to be water deficient and undergo more pronounced changes in structure and function with relief of nutrient deficiency than those in N-limited ecosystems.

Phosphorus nutrition of Caustis blakei grown with two phosphorus sources of different solubility in two soils of differing phosphorus adsorption capacity

A barrier to the domestication of the phosphorus (P) sensitive Australian species Caustis blakei (Cyperaceae) is the standard production systems used commercially which invariably result in problems associated either with P deficiency or P toxicity. This paper reports on the growth responses of Caustis blakei cv. M63 to applications of fertiliser P as either monocalcium phosphate (MCP) or granulated Guano Gold (R) rock phosphate (RP) in two soils with different capacities to adsorb P. The Caustis M63 plants grown in the two soils did not show P toxicity symptoms when fertilised with RP, but shoot dry weight was 30-60% lower than the control in both soils at the highest rate of MCP-P application (156 kg ha(-1), 184 g m(-3)) and this was associated with visible symptoms of drying of the tips of the ultimate branchlets, in the Mt Cotton soil only. The greatest shoot and root dry weights were achieved by plants grown in the higher P adsorbing Palmwoods soil fertilised with RP at P rates of 30-184 g m(-3). Caustis plants grown in the Palmwoods soil had 2.3 times greater root dry weights than plants grown in the Mt Cotton soil irrespective of the P fertiliser type used. Caustis plants growing in Mt Cotton soil which did not receive P showed significantly lower shoot and root dry weight when compared to plants in the Palmwoods soil, probably due to the low initial bicarbonate-extractable P and the high buffering capacity of the Mt Cotton soil. The P concentration in shoots of Caustis fertilised with MCP at 184 g m(-3) was higher when grown in Mt Cotton soil (0.22%) than in the Palmwoods soil (0.15%). The P concentration was lower in the terminal ultimate branchlets (TUB); 0.15% for the Mt Cotton soil and 0.10% for the Palmwoods soil, suggesting that shoots would provide a more useful indicator of P toxicity than the TUB. It is interesting to speculate as to why plants in the Palmwoods soil showed greater root growth and fewer symptoms of P toxicity. This could be because the Palmwoods soil had the greater P adsorption capacity. These results indicate in ground production of Caustis cut foliage will require careful management of P nutrition and understanding of the complex soil/plant interactions associated with the acquisition of P. (c) 2006 Elsevier B.V. All rights reserved.

Genetic basis of inosine triphosphate pyrophosphohydrolase (ITPA) deficiency

Inosine triphosphate pyrophosphohydrolase (ITPase) deficiency is a common inherited condition characterized by the abnormal accumulation of inosine triphosphate (ITP) in erythrocytes. The genetic basis and pathological consequences of ITPase deficiency are unknown. We have characterized the genomic structure of the ITPA gene, showing that it has eight exons. Five single nucleotide polymorphisms were identified, three silent (138GMA, 561GMA, 708GMA) and two associated with ITPase deficiency (94CMA, IVS2+21AMC). Homozygotes for the 94CMA missense mutation (Pro32 to Thr) had zero erythrocyte ITPase activity, whereas 94CMA heterozygotes averaged 22.5% of the control mean, a level of activity consistent with impaired subunit association of a dimeric enzyme. ITPase activity of IVS2+21AMC homozygotes averaged 60% of the control mean. In order to explore further the relationship between mutations and enzyme activity, we examined the association between genotype and ITPase activity in 100 healthy controls. Ten subjects were heterozygous for 94CMA (allele frequency: 0.06), 24 were heterozygotes for IVS2+21AMC (allele frequency: 0.13) and two were compound heterozygous for these mutations. The activities of IVS2+21AMC heterozygotes and 94CMA/IVS2+21AMC compound heterozygotes were 60% and 10%, respectively, of the normal control mean, suggesting that the intron mutation affects enzyme activity. In all cases when ITPase activity was below the normal range, one or both mutations were found. The ITPA genotype did not correspond to any identifiable red cell phenotype. A possible relationship between ITPase deficiency and increased drug toxicity of purine analogue drugs is proposed.

Effect of Mn deficiency and legume inoculation on rhizosphere pH in highly alkaline soils

Although plant growth is often limited at high pH, little is known about root-induced changes in the rhizospheres of plants growing in alkaline soils. The effect of Mn deficiency in Rhodes grass (Chloris gayana cv. Pioneer) and of legume inoculation in lucerne (Medicago sativa L. cv. Hunter River), on the rhizosphere pH of plants grown in highly alkaline bauxite residue was investigated. Rhizosphere pH was measured quantitatively, with a micro pH electrode, and qualitatively, with an agar/pH indicator solution. Manganese deficiency in Rhodes grass increased root-induced acidification of the rhizosphere in a soil profile in which N was supplied entirely as NO3-. Rhizosphere pH in the Mn deficient plants was up to 1.22 pH units lower than that of the bulk soil, while only 0.90 to 0.62 pH units lower in plants supplied with adequate Mn. When soil N was supplied entirely as NO3-, rhizosphere acidification was more efficient in inoculated lucerne (1.75 pH unit decrease) than in non-inoculated lucerne (1.16 pH unit decrease). This difference in capacity to lower rhizosphere pH is attributable to the ability of the inoculated lucerne to fix atmospheric N2 rather than relying on the soil N (NO3 ) reserves as the non-inoculated plants. Rhizosphere acidification in both Rhodes grass and lucerne was greatest in the meristematic root zone and least in the maturation root zone.

Effect of pH on Na induced Ca deficiency

Although it is well known that high Na concentrations induce Ca deficiency in acidic conditions, the effect of high pH on this competitive mechanism is not so well understood. The effect of Ca activity ratio (CAR) and pH on the Ca uptake of mungbeans (Vigna radiata (L.) Wilczek cv. Emerald) and Rhodes grass (Chloris gayana cv. Pioneer) in Na dominated solution cultures and in soil was investigated. Changes in pH in the alkaline range were shown not to affect the critical CAR of 0.024 (corresponding to 90 % relative root length) for mungbeans grown in solution culture. Results from soil grown mungbeans confirmed those from solution culture, with a critical CAR of 0.025. A critical CAR of 0.034 was also established for soil grown Rhodes grass. The similarity of critical values established for mungbeans and Rhodes grass in solution culture and soil justifies the use of both solution culture and soil solution measurement as techniques for studying plant growth and limitations across plant species.

Mg induced Ca deficiency under alkaline conditions

Little is known about Mg induced Ca deficiency in alkaline conditions, and the relationship between Mg induced Ca deficiency and Na induced Ca deficiency. Dilute nutrient solutions (dominated by Mg) were used to investigate the effect of Ca activity ratio (CAR) on the growth of mungbeans (Vigna radiata (L.) Wilczek cv. Emerald). At pH 9.0, root growth was reduced below a critical CAR of 0.050 (corresponding to 90 % relative root length). Root growth was found to be limited more in Mg solutions than had been previously observed for Na solutions. Using a CAR equation modified with plasma membrane binding constants (to incorporate the differing antagonistic effects of Mg and Na), new critical CAR values were calculated for both Na (0.56) and Mg (0.44) dominated solutions. This modified CAR equation permits the calculation of CAR irrespective of the dominant salt present.

Development, prevention and treatment of iron deficiency in women

Iron deficiency is the most common nutritional deficiency in the world. Women of childbearing age are at particular risk of developing iron deficiency due to the iron losses associated with menstruation and childbirth. Women in less developed countries are often unable to obtain adequate dietary iron for their needs due to poor food supplies and inadequate bioavailable iron. In this situation, fortification and supplementation of the diet with extra iron is a reasonable approach to the prevention and treatment of iron deficiency. In Western countries however, food supply is unlikely to be an issue in the development of iron deficiency, yet studies have shown that many women in these countries receive inadequate dietary iron. Research has shown that the form of iron and the role of enhancers and inhibitors of iron absorption may be more important than total iron intake in determining iron status. Despite this, very little research attention has been paid to the role of diet in the prevention and treatment of iron deficiency. Dietary modification would appear to be a viable option for the prevention and treatment of iron deficiency in Western women, especially if the effects of enhancers/inhibitors of absorption are considered. While dietary modification has the potential to address at least part of the cause of iron deficiency in women of childbearing age, its efficacy is yet to be proven. (C) 1998 Elsevier Science Inc.

A simplified, sequential, phosphorus fractionation method

Hedley er al. (1982) developed what has become the most widely used land modified), phosphorus (P) fractionation technique. It consists of sequential extraction of increasingly less phytoavailable P pools. Extracts are centrifuged at up to 25000 g (RCF) and filtered to 0.45 mu m to ensure that soil is not lost between extractions. In attempting to transfer this method to laboratories with limited facilities, it was considered that access to high-speed centrifuges, and the cost of frequent filtration may prevent adoption of this P fractionation technique. The modified method presented here was developed to simplify methodology, reduce cost, and therefore increase accessibility of P fractionation technology. It provides quantitative recovery of soil between extractions, using low speed centrifugation without filtration. This is achieved by increasing the ionic strength of dilute extracts, through the addition of NaCl, to flocculate clay particles. Addition of NaCl does not change the amount of P extracted. Flocculation with low speed centrifugation produced extracts comparable with those having undergone filtration (0.025 mu m). A malachite green colorimetric method was adopted for inorganic P determination, as this simple manual method provides high sensitivity with negligible interference from other anions. This approach can also be used for total P following digestion, alternatively non-discriminatory methods, such as inductively coupled plasma atomic emission spectroscopy, may be employed.

Iron deficiency, general health and fatigue: Results from the Australian Longitudinal Study on Women's Health

Associations between self-reported 'low iron', general health and well-being, vitality and tiredness in women, were examined using physical (PCS) and mental (MCS) component summary and vitality (VT) scores from the MOS short-form survey (SF-36). 14,762 young (18-23 years) and 14,072 mid-age (45-50 years) women, randomly selected from the national health insurance commission (Medicare) database, completed a baseline mailed self-report questionnaire and 12,328 mid-age women completed a follow-up questionnaire 2 years later. Young and mid-age women who reported (ever) having had 'low iron' reported significantly lower mean PCS, MCS and VT scores, and greater prevalence of 'constant tiredness' at baseline than women with no history of iron deficiency [Differences: young PCS = -2.2, MCS = -4.8, VT = -8.7; constant tiredness: 67% vs. 45%; mid-age PCS = -1.4, MCS = -3.1, VT = -5.9; constant tiredness: 63% vs. 48%]. After adjusting for number of children, chronic conditions, symptoms and socio-demographic variables, mean PCS, MCS and VT scores for mid-age women at follow-up were significantly lower for women who reported recent iron deficiency (in the last 2 years) than for women who reported past iron deficiency or no history of iron deficiency [Means: PCS - recent = 46.6, past = 47.8, never = 47.7; MCS - recent = 45.4, past = 46.9, never = 47.4; VT - recent = 54.8, past = 57.6, never = 58.6]. The adjusted mean change in PCS, MCS and VT scores between baseline and follow-up were also significantly lower among mid-age women who reported iron deficiency only in the last 2 years (i.e. recent iron deficiency) [Mean change: PCS = -3.2; MCS = -2.1; VT = -4.2]. The results suggest that iron deficiency is associated with decreased general health and well-being and increased fatigue.