Abstract
Induction and secretion of acid phosphatase (APase) is a universal adaptive response of higher plants to low-phosphate stress ( Tran et al., 2010 ). The intracellular APases are likely involved in the remobilization and recycling of phosphate (Pi) from intracellular Pi reserves, whereas the extracellular or secreted APases are believed to release Pi from organophosphate compounds in the rhizosphere. The phosphate starvation-induced secreted APases can be released into the rhizosphere or retained on root surfaces (root-associated APases). In this article, we describe the protocols for analyzing root-secreted APase activity in the model plant Arabidopsis thaliana (Arabidopsis). In Arabidopsis, the activity of both root-associated APases and APases that are released into the rhizosphere can be quantified based on their ability to cleave a synthesized substrate, para-nitrophenyl-phosphate (pNPP), which releases a yellow product, para-nitrophenol (pNP) ( Wang et al., 2011 and 2104). The root-associated APase activity can also be directly visualized by applying a chromogenic substrate, 5-bromo-4-chloro-3-indolyl-phosphate (BCIP), to the root surface ( Lloyd et al., 2001 ; Tomscha et al., 2004 ; Wang et al., 2011 and 2014) whereas the isozymes of APases that are released into rhizosphere can be profiled using an in-gel assay (Trull and Deikman, 1998; Tomscha et al., 2004 ; Wang et al., 2011 and 2014). The protocol for analysis of intracellular APase activity in Arabidopsis has been previously described (Vicki and William, 2013).