Acid phosphatase activity in phosphorus‐deficient white lupin roots

Abstract

White lupin (Lupinus albus L.) develops proteoid roots when grown in phosphorus (P)-deficient conditions. These short, lateral, densely clustered roots are adapted to increase P availability. Previous studies from our laboratory have shown proteoid roots have higher rates of non-photosynthetic carbon fixation than normal roots and altered metabolism to support organic acid exudation, which serves to solubilize P in the rhizosphere. The present work indicates that proteoid roots possess additional adaptations for increasing P availability and possibly for conserving P in the plant. Roots from P-deficient (-P) plants had significantly greater acid phosphatase activity in both root extracts and root exudates than comparable samples from P-sufficient (+P) plants beginning 10 d after emergence. The increase in activity in -P plants was most pronounced in the proteoid regions. In contrast, no induction of phytase activity was found in -P plants compared to +P plants. The number of proteoid roots present was not affected by the source of phosphorus supplied, whether organic or inorganic forms. Adding molybdate to the roots increased the number of proteoid roots in plants supplied with organic P, but not inorganic P. Increased acid phosphatase activity was detected in root exudates in the presence of organic P sources. Nativepolyacrylamide gel electrophoresis demonstrated that under P-deficient conditions, a unique isoform of acid phosphatase was induced between 10 and 12 d after emergence. This isoform was found not only within the root, but it comprised the major form exuded from proteoid roots of -P plants. The fact that exudation of proteoid-root-specific acid phosphatase coincides with proteoid root development and increased exudation of organic acids indicates that white lupin has several coordinated adaptive strategies to P-deficient conditions. Key-words: Lupinus albus; acid phosphatase; exudates; phosphorus deficiency; phytase; proteoid roots; white lupin INTRODUCTIONWhite lupin is a nitrogen-fixing legume that can acquire soil P that is unavailable to other plants, despite its lack of mycorrhizal symbioses (Avio, Sbrana & Giovannetti 1990;Gardner, Parberry & Barber 1982b;Trinick 1977). Instead, its adaptation to P deficiency is the development of proteoid or cluster root morphology, which is characteristic of members of the Proteaceae (for review, Dinkelaker, Hengelar & Marschner 1995). Proteoid roots are short, lateral, densely clustered tertiary roots that are initiated under P-deficient conditions. In white lupin, these proteoid regions display altered carbon metabolism, in which nonphotosynthetic CO 2 fixation supplies up to 30% of the carbon necessary for the production of the large quantities of organic acids exuded (Johnson, Allan & Vance 1994;Johnson et al. 1996a). Organic acids such as citrate, excreted by the proteoid roots of white lupin, are thought to increase P availability by mobilizing sparingly soluble Fe, Al, and Ca phosphates (Dinkelaker, Romheld & Marschner 1989;Gardner, Parberry &...

Legume nodules from nutrient-poor soils exhibit high plasticity of cellular phosphorus recycling and conservation during variable phosphorus supply

“…Although the extracellular APase activities in nodules are known to be higher during P deficiency a,b, Tang et al 2013, the relative contribution is much less compared to intracellular APase under P stress. Furthermore, the increased intracellular and extracellular phosphohydrolase (APase and phytase) activity, would serve as an additional route of Pacquisition from organically-bound sources of P, during conditions of limiting soil P. The importance of increased APase activity for P metabolism has been extensively reported (Gilbert et al 1998, Miller et al 2001. Intracellular APases break down P nucleotides, sugar-P and P-monoesters and recycle P through the supply of P for amino acid biosynthesis and nodule metabolism during P-deprivation (Penheiter et al 1997).…”

The future of grain legumes in cropping systems

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Impacts of alien invasive plants on soil nutrients are correlated with initial site conditions in NW Europe

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