Phosphorus Deficiency in Lupinus albus (Altered Lateral Root Development and Enhanced Expression of Phosphoenolpyruvate Carboxylase)

Abstract

The development of clustered tertiary lateral roots (proteoid roots) and the expression of phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) in roots were studied in white lupin (Lupinus albus L.) grown with either 1 mM P (+P-treated) or without P (-P-treated). The +P-treated plants initiated fewer clustered tertiary meristems and the emergence of these meristems was delayed compared with -P-treated plants. Proteoid root zones could be identified 9 d after emergence in both P treatments. Amounts of PEPC mRNA, PEPC specific activity, and enzyme protein were greater in proteoid roots than in normal roots beginning at 1 O, 12, and 14 d after emergence, respectively. The increases in PEPC mRNA, PEPC enzyme, and PEPC specific activity suggest that this enzyme is in part under transcriptional regulation. Recovery of organic acids from root exudates coincided with the increases in PEPC specific activity. The -P-treated plants exuded 40-, 20-, and 5-fold more citrate, malate, and succinate, respectively, than did +P-treated plants. Data presented support the hypothesis that white lupin has concerted regulation of proteoid root development, transcriptional regulation of PEPC, and biosynthesis of organic acids for exudation in response to P deficiency.Proteoid root formation is enhanced by P deficiency in white lupin (Lupinus albus L.) (Gardner et al., 1981; Marschner et al., 1986; Dinkelaker et al., 1989; Johnson et al., 1994; Braum, 1995). The amount of citrate exuded by proteoid roots ranges from 6 to 23% of total plant dry weight (Dinkelaker et al., 1989; Braum, 1995). These amounts are phenomenal when compared with amounts in alfalfa (Medicago sativa L.), which exudes the equivalent of 0.3% of the total dry weight as citrate when P deficient (Lipton et al., 1987). Citrate exudation into the rhizosphere increases the P available to the plant by mobilizing the sparingly soluble mineral P and, possibly, organic P sources (Gardner et al

Reciprocal Control of Anaplerotic Phosphoenolpyruvate Carboxylase by in Vivo Monoubiquitination and Phosphorylation in Developing Proteoid Roots of Phosphate-Deficient Harsh Hakea

“…S7). This is not surprising, since levels of PEPC protein and phosphorylation status and/or activity are known to be markedly up-regulated in response to Pi deprivation in a wide range of plant species (Duff et al, 1989;Johnson et al, 1996;Uhde-Stone et al, 2003;Vance et al, 2003;Gregory et al, 2009;O'Leary et al, 2011a;Plaxton and Tran, 2011). Immunoblots of extracts prepared from meristematic root tips of +Pi and -Pi plants had equivalent ratios of immunoreactive p110: p107 subunits.…”

“…This suggests that PEPC might have been activated by some type of PTM. In the wellstudied model crop white lupin (Lupinus albus), optimal PEPC activity also increases as its proteoid roots attain maturity (Johnson et al, 1996;Massonneau et al, 2001;Uhde-Stone et al, 2003).…”

Developmental Physiology of Cluster-Root Carboxylate Synthesis and Exudation in Harsh Hakea. Expression of Phosphoenolpyruvate Carboxylase and the Alternative Oxidase

“…These short-lived structures have been termed proteoid roots because they were first described for Proteaceae (Purnell, 1960) but have since been found in a wide range of other species and families and are now often referred to as cluster roots . Most of our advances in cluster-root biology have been derived from studies of the crop species Lupinus albus (Fabaceae family) (Gardner et al, 1983;Johnson et al, 1994Johnson et al, , 1996aJohnson et al, , 1996bKeerthisinghe et al, 1998;Neumann et al, 1999;Evans, 1999a, 1999b). The importance of developing short-lived cluster roots, in terms of nutrient acquisition from the rhizosphere, is illustrated by the tremendous increase in fine-root surface area following cluster-root initiation (Lamont, 1972;Dell and Kuo, 1980).…”

“…The evidence to support metabolic specialization comes predominately from studies with L. albus (Johnson et al, 1994(Johnson et al, , 1996a(Johnson et al, , 1996bKeerthisinghe et al, 1998;Neumann and Rö mheld, 1999;Neumann et al, 1999;Evans, 1999a, 1999b), and is based on three sets of observations: (1) genes involved in citrate synthesis are up-regulated when citrate exudation occurs from cluster roots (e.g. phosphoenolpyruvate carboxylase [PEPC]; Neumann et al, 1999;Kania et al, 2003;Uhde-Stone et al, 2003); (2) genes involved in citrate catabolism are down-regulated when citrate exudation occurs from cluster roots (e.g.…”

“…citrate, malate; Johnson et al, 1996aJohnson et al, , 1996bWatt and Evans, 1999a;Ryan et al, 2001). The role of PEPC is to replenish TCA intermediates by catalyzing the carboxylation of phosphoenolpyruvate to form oxaloacetate (Johnson et al, 1994).…”