Influences of phosphorus starvation on OsACR2.1 expression

Influences of phosphorus starvation on OsACR2.1 expression ...

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REGULAR ARTICLE Influences of phosphorus starvation on OsACR2.1 expression and arsenic metabolism in rice seedlings Li-Hong Wang & Gui-Lan Duan & Paul N. Williams & Yong-Guan Zhu Received: 3 March 2008 /Accepted: 9 June 2008 / Published online: 11 July 2008 # Springer Science + Business Media B.V. 2008 Abstract The effects of phosphorus (P) status on arsenate reductase gene ( OsACR2.1 )e x p r e s s i o n , arsenate reductase activity, hydrogen peroxide (H 2 O 2 ) content, and arsenic (As) species in rice seedlings which were exposed to arsenate after - P or +P pretreatments were investigated in a series of hydroponic experiments. OsACR2.1 expression in- creased significantly with decreasing internal P con- centrations; more than 2-fold and 10-fold increases were found after P starvation for 30 h and 14 days, respectively. OsACR2.1 expression exhibited a signif- icant positive correlation with internal root H 2 O 2 accumulation, which increased upon P starvation or exposure to H 2 O 2 without P starvation. Characteriza- tion of internal and effluxed As species showed the predominant form of As was arsenate in P-starved rice root, which contrasted with the +P pretreated plants. Additionally, more As was effluxed from P- starved rice roots than from non-starved roots. In summary, an interesting relationship was observed between P-starvation induced H 2 O 2 and OsACR2.1 gene expression. However, the up-regulation of OsACR2.1 did not increase arsenate reduction in P- starved rice seedlings when exposed to arsenate. Keywords Arsenate reductase . Arsenic species . Hydrogen peroxide . Phosphatase . Phosphate . Rice ( Oryza sativa L) Introduction Arsenic (As), a group A carcinogen (Smith et al. 1992 ), is commonly found in rice ( Oryza sativa L.) at higher grain concentrations than in other cereals, such as wheat ( Triticum aesticum L.) and barley ( Hordeum vulgare L.) (Williams et al. 2007 ). Being a phyto- toxin, As can also impair crop yields and degrade arable lands (Heikens 2006 ). Although rice is often grown in sub-oxic conditions where arsenite prevails, a significant amount of arsenate (the oxidized form of inorganic As) can exist in paddy rhizospheres, due principally to oxygen release from rice roots (Chen et al. 2008 ). Rice agro-ecosystems can be contaminated by As mainly by irrigation with As-tainted ground- water, mineral exploration, processing industries, and as a result of As pesticide use (Zhu et al. 2008a ). When rice is grown in paddy soils which did not exceed global background As levels, internal plant As concentrations in rice straw and grain can still be high in comparison with other cereal crops (Williams et al. 2007 ). Plant Soil (2008) 313:129 139 DOI 10.1007/s11104-008-9685-2 Responsible Editor: Fangjie J. Zhao. L.-H. Wang : G.-L. Duan : P. N. Williams : Y.-G. Zhu ( * ) Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China e-mail: [email protected]
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In contrast, phosphorus (P), the chemical analogue of As, is one of 17 essential elements required for plant growth (Bieleski 1973 ; Raghothama 1999 ), and often the overriding nutritional limitation in modern cereal farming (Runge-Metzger 1995 ; von Uexküll and Mutert 1995 ). It is estimated that crop yields on
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Influences of phosphorus starvation on OsACR2.1 expression ...

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