Citrate, Malate, and Succinate Concentration in Exudates from P-Sufficient and P-Stressed Medicago sativa L. Seedlings

Abstract

Under P deficiency amino acids in the root exudates increased from 104.5 to 248.5 umol/plant, which contrasted sharply with the almost 4-fold decrease under N deficiency (104.5-25.1 zmol/ plant; 1). Graham et al. (5) observed P deficiency to result in a 3-fold increase in amino acid exudation with only a concentration increase of 60% within the root.The effective study of the rhizosphere has been limited in the past due to the difficulty of isolating root effects from general soil and microbiological effects and quantifying those effects. The objective of this research was to identify and measure the effect of P deficiency upon the exudation of organic acids by the growing aseptic roots of alfalfa (Medicago sativa L.) seedlings.

Secretion of acid phosphatase by the roots of several crop species under phosphorus-deficient conditions

“…TADANO and H. SAKAI Large amounts of citric acid have been shown to be secreted by lupin roots under phosphorus-deficient conditions, and it has been indicated that citric acid was able to release inorganic phosphate from phosphated ferric hydroxide (Gardner et al 1983). It has also been reported that the secretion of citric acid and succinic acid by alfalfa roots increased when the plant was deficient in phosphorus (Lipton et al 1987).…”

“…It has also been reported that the secretion of citric acid and succinic acid by alfalfa roots increased when the plant was deficient in phosphorus (Lipton et al 1987).…”

“…TADANO and H. SAKAI Large amounts of citric acid have been shown to be secreted by lupin roots under phosphorus-deficient conditions, and it has been indicated that citric acid was able to release inorganic phosphate from phosphated ferric hydroxide (Gardner et al 1983). It has also been reported that the secretion of citric acid and succinic acid by alfalfa roots increased when the plant was deficient in phosphorus (Lipton et al 1987).The secretion of carbohydrates and amino acids by maize roots (Matsumoto et al 1979), that of soluble amino acids and reducing sugar by the roots of sudangrass and sour orange (Ratnayake et al 1978), and that of amides and amino acids by pine roots (Bowen 1969) also increased under phosphorus-deficient conditions, and it was postulated that these compounds enhanced the activity of microorganisms in the rhizosphere.It has been frequently reported that the activity of acid phosphatase in plant tissues increased under phosphorus-deficient conditions (Silberbush et al 198 I;Dracup et al 1984;Szabo-Nagy et al 1987;Flasinski and Rogozinska 1988). However, evidence for the root secretion of acid phosphatase is comparatively limited.…”

The spatial expression patterns of a phosphate transporter (MtPT1) from Medicago truncatula indicate a role in phosphate transport at the root/soil interface

“…The stability and insolubility of these complexes, coupled with rapid adsorption of phosphate ions to clay and organic matter, results in phosphate concentrations of less than 10 mM in the soil solution (Bieleski and Ferguson, 1975;Holford, 1997). Consequently, plants have evolved strategies to enhance phosphate mobilization and acquisition by increased secretion of phosphatases, organic acids and protons (Duff et al, 1991;Dunlop and Gardiner, 1983;Lefebvre et al, 1990;Lipton et al, 1987), and by enhanced root growth and modi®cation of root architecture (Lynch, 1995;Mengel and Kirkby, 1987). In addition, the vast majority of land plants are able to form symbioses with arbuscular mycorrhizal fungi and bene®t from phosphate acquisition mediated by these fungi (Harrison, 1999;Smith and Read, 1997).…”

Comparison of aluminum tolerance and phosphate absorption between rape (Brassica napusL.) and Tomato (Lycopersicum esculentumMill.) in relation to organic acid exudation

“…High levels of citric acid in the solution around white lupin roots were detected (Gardner et al 1983). Lipton et al (1987) reported a 2-fold increase in the amount of citric acid released from the roots of P-deficient alfalfa seedlings compared with P sufficient seedlings. It was suggested that the exudation of organic acids was increased the phosphate availability through the release of phosphate ions from sparingly soluble inorganic phosphate compounds (Grierson 1992).…”