Novel Phytase from Pteris vittata Resistant to Arsenate, High Temperature, and Soil Deactivation

Abstract

Arsenate interferes with enzymatic processes and inhibits inorganic phosphorus (Pi) uptake in many plants. This study examined the role of phytase and phosphatase in arsenate tolerance and phosphorus (P) acquisition in the arsenic hyperaccumulator Pteris vittata . Enzyme-mediated hydrolysis of phytate in P. vittata extracts was not inhibited by arsenate at 5 mM or by heating at 100 °C for 10 min. Root exudates of P. vittata exhibited the highest phytase activity (18 nmol Pi mg(-1) protein min(-1)) when available P was low, allowing its growth on media amended with phytate as the sole source of P. Phosphorus concentration in P. vittata gametophyte tissue grown on phytate was equivalent to plants grown with inorganic phosphate at 2208 mg kg(-1), and arsenic was increased from 1777 to 2630 mg kg(-1). After 2 h of mixing with three soils, P. vittata phytase retained more activity, decreasing from ∼ 26 to ∼ 25 nmol Pi mg(-1) protein min(-1), whereas those from Pteris ensiformis and wheat decreased from ∼ 18 to ∼ 1 nmol Pi mg(-1) protein min(-1). These results suggest P. vittata has a uniquely stable phytase enabling its P acquisition in P-limiting soil environments. Furthermore, the P. vittata phytase has potential use as a soil amendment, a transgenic tool, or as a feed additive supplement, reducing the need for nonrenewable, polluting P fertilizers.

Phytate induced arsenic uptake and plant growth in arsenic-hyperaccumulator Pteris vittata

“…However, this was not the case for phytate-P. It is reported that PV roots secrete phytase, which is the only enzyme that hydrolyzes phytate to inorganic P (Lessl et al, 2013). Moreover, enzyme-mediated hydrolysis of phytate in PV root extracts is not inhibited by 0.5e5 mM AsV (Lessl et al, 2013).…”

“…Their spores were first sterilized with 75% alcohol for 2 min and rinsed three times with sterile deionized (DI) water, then surface sterilized in a 10% sodium hypochlorite for 12 min and rinsed thoroughly with sterile DI water before being sown in Petri dishes with solid medium Lessl et al, 2013 (Mathews et al, 2010). Spores were suspended in 2 mL sterile DI water and uniformly dispersed on agar in sterile Petri dishes (100 mm  13 mm; 500 mL per plate).…”

“…However, the direct evidence and mechanistic basis for the beneficial role of As on PV growth is unknown. Besides, Lessl et al (2013) found that PV can effectively utilize phytate as a sole source of P for growth. They attributed PV's ability to grow directly with phytate to an adaptive trait of phytase exudation (Lessl et al, 2013).…”

“…It is reported that PV roots secrete phytase, which is the only enzyme that hydrolyzes phytate to inorganic P (Lessl et al, 2013). Moreover, enzyme-mediated hydrolysis of phytate in PV root extracts is not inhibited by 0.5e5 mM AsV (Lessl et al, 2013). As such, it might be expected that some P would have been released into the media due to phytate application and phytase exudation.…”

“…Organic P consists of a large pool of unavailable P in soils, accounting for 30e80% of total soil P, predominantly as phytate (inositol hexakisphosphate) (Richardson et al, 2005;Turner et al, 2006). Within the soil fraction, phytate generally makes up 50% organic P and~25% total P (Lessl et al, 2013;Richardson et al, 2005). However, phytate is a stable compound resistant to biochemical degradation, rendering it unavailable for plant uptake (Turner et al, 2002).…”