Nitrate nutrition enhances zinc hyperaccumulation in Noccaea caerulescens (Prayon)

Abstract

Nitrate fertilization has been shown to increase Zn hyperaccumulation by Noccaea caerulescens (Prayon) (formerly Thlaspi caerulescens). However, it is unknown whether this increased hyperaccumulation is a direct result of NO 3 − nutrition or due to changes in rhizosphere pH as a result of NO 3 − uptake. This paper investigated the mechanism of NO 3 − -enhanced Zn hyperaccumulation in N.caerulescens by assessing the response of Zn uptake to N form and solution pH. Plants were grown in nutrient solution with 300 μM Zn and supplied with either (NH 4 ) 2 SO 4 , NH 4 NO 3 or Ca(NO 3 ) 2 . The solutions were buffered at either pH 4.5 or 6.5. The Zn concentration and content were much higher in shoots of NO 3 − -fed plants than in NH 4 + -fed plants at pH 4.5 and 6.5. The Zn concentration in the shoots was mainly enhanced by NO 3 − , whereas the Zn concentration in the roots was mainly enhanced by pH 6.5. Nitrate increased Zn uptake in the roots at pH 6.5 and increased apoplastic Zn at pH 4.5. Zinc and Ca coincreased and was found co-localized in leaf cells of NO 3 − -fed plants. We conclude that NO 3 − directly enhanced Zn uptake and translocation from roots to shoots in N. caerulescens.

Nitrate facilitates cadmium uptake, transport and accumulation in the hyperaccumulator Sedum plumbizincicola

“…As a result, Cd hyperaccumulation in S. plumbizincicola was largely enhanced by NO 3 -supplementation rather than NH 4 + ( Table 2). This is consistent with previous studies showing that NO 3 -fertilisation led to both higher biomass production and higher Cd and Zn extraction than NH 4 + in N. caerulescens (Schwartz et al 2003;Monsant et al 2008Monsant et al , 2010Monsant et al , 2011Xie et al 2009), camomile (Kovacik et al 2011) and tomato . The stimulated uptake of nutrient elements such as Ca and K may be partly responsible for the stimulation of plant growth.…”

“…However, the differences in water uptake cannot fully explain the differences in local velocity of Cd transport (3.7-fold) and the differences in Cd distribution between these two N treatments. Comparatively, it is suggested that unlike NH 4 + which is mainly assimilated or stored in the roots, NO 3 -is translocated as a hydrated anion in the xylem where cationic charges are required for charge balance (Monsant et al 2010 (Arnozis and Findenegg 1986;Turan and Sevimli 2005). This is consistent with our results showing that concentrations of the cations Ca and K in the xylem sap increased but the anion P was inhibited in the NO 3 -treatment compared with the NH 4 + treatment (Table 1).…”

Accumulation and distribution of zinc in the leaves and roots of the hyperaccumulator Noccaea caerulescens

“…of the Zn is in the upper and lower epidermis whereas only 12.4% of Zn remains in the mesophyll cells (Monsant et al, 2010). In contrast to the overall plant distribution of Zn among tissue and cell types, Zn accumulation in the epidermis occurs mainly in the vacuoles, and to a lesser extent in the apoplast.…”

“…High concentrations of Zn in vacuoles and cell walls (apoplast) of epidermal cells are observed to always associate with high concentrations of Ca (Vazquez et al, 1994), and in leaf cells of N. caerulescens it is found that Zn and Ca can co-locate (Monsant et al, 2010). The Zn and Ca concentrations are 36000 and 8600 mg kg -1 , respectively, in the upper epidermis in the leaf and 20000 and 6200 mg kg -1 , respectively, in the lower epidermis.…”

“…It has been considered a suitable technique when environmental health is a priority, and lengthy treatment is acceptable or alternative remediation technologies are prohibitive or unavailable (Monsant et al, 2010). Plant species that accumulate large quantities of heavy metals in their shoot are known as heavy metalhyperaccumulator plants and are usually referred to as hyperaccumulators (Baker and Brooks, 1989).…”