Phosphite, an Analog of Phosphate, Suppresses the Coordinated Expression of Genes under Phosphate Starvation

Abstract

Phosphate (Pi) and its analog phosphite (Phi) are acquired by plants via Pi transporters. Although the uptake and mobility of Phi and Pi are similar, there is no evidence suggesting that plants can utilize Phi as a sole source of phosphorus. Phi is also known to interfere with many of the Pi starvation responses in plants and yeast (Saccharomyces cerevisiae). In this study, effects of Phi on plant growth and coordinated expression of genes induced by Pi starvation were analyzed. Phi suppressed many of the Pi starvation responses that are commonly observed in plants. Enhanced root growth and root to shoot ratio, a hallmark of Pi stress response, was strongly inhibited by Phi. The negative effects of Phi were not obvious in plants supplemented with Pi. The expression of Pi starvation-induced genes such as LePT1, LePT2, AtPT1, and AtPT2 (high-affinity Pi transporters); LePS2 (a novel acid phosphatase); LePS3 and TPSI1 (novel genes); and PAP1 (purple acid phosphatase) was suppressed by Phi in plants and cell cultures. Expression of luciferase reporter gene driven by the Pi starvation-induced AtPT2 promoter was also suppressed by Phi. These analyses showed that suppression of Pi starvation-induced genes is an early response to addition of Phi. These data also provide evidence that Phi interferes with gene expression at the level of transcription. Synchronized suppression of multiple Pi starvation-induced genes by Phi points to its action on the early molecular events, probably signal transduction, in Pi starvation response.Phosphate (Pi) is one of the major plant nutrients that influences virtually all the biochemical processes and developmental phases of plants. In the absence of Pi, plants exhibit characteristic deficiency symptoms including anthocyanin accumulation, enhanced root growth, and increased root to shoot ratio. The ability of plants to acquire Pi also increases during this period. Molecular dissection of responses to Pi starvation has provided evidence for coordinated expression of genes, including Pi transporters (Raghothama, , 2000. Pi transporters are involved in acquiring Pi against the concentration gradient by an energy-mediated proton cotransport mechanism (Ullrich-Eberius et al., 1981). They are also known to transport ions such as arsenate, vanadate, and phosphite (Phi; Guest and Grant, 1991;Marschner, 1995).Phi (HPO 3 2Ϫ ), also referred to as phosphorous acid or phosphonate, is an isostere of the Pi anion in which one of the oxygens bound to the P atom is replaced by hydrogen. The term Phi is used here to describe the alkali metal salts of phosphorous acid as suggested by Carswell et al. (1996). Phi is used extensively as a fungicide and also sold as a superior source of Pi (Guest and Grant, 1991;Rickard, 2000; McDonald et al., 2001a). Phi is rapidly absorbed and translocated within the plant (Guest and Grant, 1991). The uptake is pH dependent and subject to competition by Pi (Ouimette and Coffey, 1990). Furthermore, mobility of Phi in both xylem and phloem is similar to that of Pi (Ouimette...

Interação fosfito e fosfato no crescimento e na nutrição fosfatada do feijoeiro em solução nutritiva

“…Os resultados do primeiro experimento demonstraram claramente que o fosfito não substituiu o fosfato na nutrição fosfatada do feijoeiro, fato observado em outros trabalhos com outras culturas, tanto em solo (Lucas et al, 1979;Schröetter et al, 2006) quanto em solução nutritiva (Carswell et al, 1996;Föster et al, 1998;Ticconi et al, 2001;Varadarajan et al, 2002;Singh et al, 2003;Ávila et al, 2011). Destacou-se a alta sensibilidade do feijoeiro ao fosfito na ausência de fosfato, tendo em vista a rápida manifestação de toxicidade e a paralisação de seu crescimento, sob a concentração maior que 0,5 mg L -1 de P-Phi.…”

“…Destacou-se a alta sensibilidade do feijoeiro ao fosfito na ausência de fosfato, tendo em vista a rápida manifestação de toxicidade e a paralisação de seu crescimento, sob a concentração maior que 0,5 mg L -1 de P-Phi. Em outras espécies vegetais, esse efeito foi observado apenas em concentrações entre 2,0 e 30 mg L -1 de P-Phi (Föster et al, 1998;Ticconi et al, 2001;Varadarajan et al, 2002;Singh et al, 2003). Os mecanismos fisiológicos e, ou, bioquímicos da toxicidade por fosfitos são pouco compreendidos em vegetais.…”

“…Pouco se sabe como os fosfitos podem atuar negativamente ou positivamente no crescimento e, ou, na produção das culturas, bem como não há evidências que os fosfitos possam substituir o fosfato no metabolismo vegetal (Ticconi et al, 2001;Varadarajan et al, 2002). Ao contrário, em alguns trabalhos, observaram-se inibição da atividade de fosfatases ácidas (Ticconi et al, 2001;Lee & Tsai, 2005), que atuam na quebra do P orgânico sob deficiência de P, e diminuição dos teores de P inorgânico solúvel por efeito de inibição competitiva desse ânion com o fosfato (Lee & Tsai, 2005;Thao et al, 2008).…”

Phosphite as phosphorus source to grain yield of common bean plants grown in soils under low or adequate phosphate availability

“…. The literature shows that some previous studies also found harmful effects of phosphite anion on plants grown under low phosphate availability, but no harmful effects have been reported when this anion was applied in plants grown under adequate phosphate availability (TICCONO et al, 2001;VARADARAJAN et al, 2002;LEE et al, 2005;SCHROETTER et al, 2006;DEVAIAH et al, 2007;THAO et al, 2008;MOOR et al, 2009;ÁVILA et al, 2011). However, most of these studies were based in Arabidopsis, vegetables, seedlings, citrus, and some cereals, but there is still little information on the effects of phosphite on leguminous plants, especially on grain yield of leguminous.…”

“…The causes of this effect are not well understood. There is the hypothesis that plants did not metabolize phosphite anion, and this anion may suppress some plant responses to phosphate deficiency, such as synthesis of phosphatases and P transporters (TICCONI et al, 2001;VARADARAJAN et al, 2002;ÁVILA et al, 2011).…”