Localization of acid phosphatase activities in the roots of white lupin plants grown under phosphorus-deficient conditions

Abstract

Acid phosphatase (APase) produced by the cluster roots of white lupin (Lupinus albus L.) plays an important role in inorganic phosphate (Pi) acquisition. Although the importance of cluster roots in Pi acquisition is well known, information on the distribution of APase within tissues of normal and cluster roots is lacking. Isoelectric focusing of APase isoforms as well as histochemical localization and visualization of APase were used to clarify the importance of secretory APase for P nutrition of white lupin grown under P deficiency. Isoelectric focusing revealed that both the secretory type and other major APase isoforms probably involved in P translocation were inducible. The major activity in the rhizosphere soil of cluster roots and roots grown under hydroponic conditions corresponded to LASAP2, a previously purified APase secreted from white lupin roots. Histochemical localization using enzyme-labeled fluorescence (ELF)-97 phosphate as a substrate was applied to rhizosphere samples. This substrate provides fluorescent precipitates after hydrolysis by phosphatase. Strong APase activity in the epidermal tissues of normal roots and cluster rootlets and in root hairs of cluster rootlets under P deficiency was detected. These results support the hypothesis that APase activities in the rhizosphere liberate Pi and supply it to white lupin plants grown under P-deficient conditions.

Acid phosphatases and growth of barley (Hordeum vulgare L.) cultivars under diverse phosphorus nutrition

“…Our other studies showed the strong activity of APases detected in the root epidermis (and outer cortex cells) of different oat varieties, which indicated that at least a part of these enzymes might be secreted from the roots to the ground (data not published). Histochemical visualization of APases activity in roots of white lupine also showed a strong enzyme activity in the epidermis and root hairs under Pi deficiency (Wasaki et al 2008); white lupine can produce both cell wall-bound APase and enzymes than can be released into the rhizosphere, LASAP2, a form of secreted APase from white lupin roots (Wasaki et al 2008). Similarly, in Arabidopsis under Pi starvation a strong expression of the promoter region of secreted APases was detected in young lateral roots and in the vascular tissues (Haran et al 2000).…”

“…APases expression is mediated by different environmental and developmental factors, including Pi deficit (Duff et al 1994;Olczak et al 2003). Under low Pi conditions the activities of extracellular and/or internal APases are often increasing; additionally, some plants might secrete nonspecific APase from roots to the rhizosphere (Duff et al 1994;Gilbert et al 1999;Yun and Kaeppler 2001;Wasaki et al 2008). Specific acid phosphatases that exhibit phytasic activities (phosphohydrolases with the capability of initiating dephosphorylation of myoinositol-hexakisphosphate) are active not only mainly in germinating seeds but also in cells of primary roots (Asmar 1997;Richardson et al 2000;Gregory 2006).…”

Nodules from Fynbos legume Virgilia divaricata have high functional plasticity under variable P supply levels

“…White lupin secretes copious amounts of APases from its roots and proteoid roots when subjected to Pi starvation (Miller et al, 2001, Wasaki et al, 2008.…”

Differential responses of oat cultivars to phosphate deprivation: plant growth and acid phosphatase activities

“…Histochemical visualization of APases activity for cluster roots of white lupine, developed under Pi deficiency, indicated high enzyme activity in the epidermis and root hairs (Wasaki et al 2008). LASAP2 is believed to be a major form of secreted APase, released from white lupine roots into the rhizosphere (Wasaki et al 2009).…”

“…Various developmental and environmental conditions may influence gene expression, protein synthesis, and activity of APases in plant tissue or in soil (Duff et al 1994;_ Zebrowska and Ciereszko 2009). Activities of both extracellular and internal APases might increase in response to phosphorus depletion and several plants can secrete APase from roots to the rhizosphere (Duff et al 1994;Gilbert et al 1999;Wasaki et al 2008;Tran et al 2010). Extracellular APases are involved in Pi release from organic phosphate monoesters in soils, whereas intracellular APases are thought to be pivotal in the remobilization of Pi from phosphorus-rich components in cells (Duff et al 1994;Tomscha et al 2004;Tran et al 2010).…”