Zinc Deficiency Up-Regulates Expression of High-Affinity Phosphate Transporter Genes in Both Phosphate-Sufficient and -Deficient Barley Roots

Abstract

Phosphate (P) is taken up by plants through high-affinity P transporter proteins embedded in the plasma membrane of certain cell types in plant roots. Expression of the genes that encode these transporters responds to the P status of the plants, and their transcription is normally tightly controlled. However, this tight control of P uptake is lost under Zn deficiency, leading to very high accumulation of P in plants. We examined the effect of plant Zn status on the expression of the genes encoding the HVPT1 and HVPT2 high-affinity P transporters in barley (Hordeum vulgare L. cv Weeah) roots. The results show that the expression of these genes is intimately linked to the Zn status of the plants. Zn deficiency induced the expression of genes encoding these P transporters in plants grown in either P-sufficient or -deficient conditions. Moreover, the role of Zn in the regulation of these genes is specific in that it cannot be replaced by manganese (a divalent cation similar to Zn). It appears that Zn plays a specific role in the signal transduction pathway responsible for the regulation of genes encoding high-affinity P transporters in plant roots. The significance of Zn involvement in the regulation of genes involved in P uptake is discussed.Although relatively large amounts of phosphate (P) are essential to plant growth, forms that can be taken up directly by plants are only found in low concentrations (0.01-3.0 m) in most soil solutions (Barber, 1995). Low availability of P in soils limits crop yields. Under normal growing conditions the uptake of P by plants is tightly controlled. Plants normally moderate their capacity to take up P to maintain the P concentration in their tissues within physiological limits (Mimura, 1999). They therefore restrict their capacity to take up P when grown under high-P conditions but enhance this capacity when grown under low-P conditions (Clarkson and Scattergood, 1982; Jungk et al., 1990). However, under Zn-deficient conditions, high levels of P accumulate in the tissues of both dicotyledon and monocotyledon plant species (Welch et al., 1982;Cakmak and Marschner, 1986;Webb and Loneragan, 1988;Welch and Norvell, 1993) and can reach levels that are toxic to the plants if high concentrations of P are supplied (Loneragan et al., 1982; Welch et al., 1982;Cakmak and Marschner, 1986;Norvell and Welch, 1993). This suggests that Zn-deficient plants somehow lose control over the P absorption mechanism (Safaya and Gupta, 1979;Marschner and Cakmak, 1986).The kinetic characterization of the P uptake system by whole plants indicates a high-affinity transporter activity operating at the micromolar range . The high-affinity transporters are a key component of P uptake by plants at the very low concentrations of P found in many soil solutions. When the P concentration is low in the root growth medium, expression of genes encoding high-affinity P transporters is up-regulated in plant roots (Muchhal et al., 1996;Smith et al., 1997Smith et al., , 1999 Leggewie et al., 1997; Liu et al., 1998;Smi...

Phosphorus Availability Influences Elemental Uptake in the Mycorrhizal Fungus Glomus intraradices , as Revealed by Particle-Induced X-Ray Emission Analysis

“…Excess P repressed the expression of the high-affinity P transporter gene in extraradical AM fungal mycelia (14). In plants, the high-affinity P transporter is regulated by Zn limitation, leading to increased P uptake (9). Our observations show that the uptakes of these compounds influence each other, although we do not yet know the mechanism behind this.…”

Efficiency of Zinc and Phosphorus Applied to Open-pollinated and Hybrid Cultivars of Maize

“…Soil deficiency of the one nutrient can regulate plant status of the other, as excessive Zn application to soil has been shown to decrease P concentration in plants (Soltangheisi et al, 2013). Under soil Zn deficiency, uptake of P by roots and its accumulation in leaves increases (Cakmak et al, 1986;Huang et al, 2000;Khan et al, 2014). On other hand, excessive application of P fertilizers to soil decreases plant available Zn (Lambert et al, 2007;Zorrig et al, 2010).…”

Zinc sulphate improved microspore embryogenesis in barley

“…Zn 2+ is another important micronutrient which plays a fundamental role in many physiological and biochemical cellular processes, such as structural and functional integrity of biomembranes, photosynthesis, auxin metabolism, response to oxidative stress, apoptosis inhibition, phosphate transport, etc. (Marschner 1995;Cakmak 2000;Huang et al 2000;Chimienti et al 2001;Hoseini and Mulligan 2002). Zinc is also an essential component of enzymes and transcription factors involved in plant morphogenesis and organogenesis (Kobayashi et al 1998;Yanagisawa 2004).…”