Amelioration of copper and nickel toxicity by iron plaque on roots of rice (Oryza sativa)

Abstract

Deposition of an iron oxide plaque or coating on roots of rice (Oryza sativa L. cv. M-201 84 Biggs) ameliorated the toxic effects of copper (Cu), nickel (Ni), and Cu + Ni on plant growth and affected patterns of metal uptake and accumulation. Plaque was formed on plants during 24 h in an anaerobic solution containing 20 mg ∙ L−1 iron at pH 5.5. Subsequently two additional coatings were deposited after new growth of roots. Plants were grown hydroponically in one-quarter strength Hoagland's solution and exposed to Cu (0.5 mg ∙ L−1), Ni (2.0 mg ∙ L−1), or Cu + Ni; exposure to metals lasted 21 – 45 days. At the end of the experimental period growth was estimated as total biomass, dry weight of root, dry weight of shoot, length of leaf, and length of root. After harvesting, Fe, Cu, and Ni concentrations in plaque were measured using a dithionite–citrate–bicarbonate extraction, and internal Fe, Cu, and Ni concentrations were measured in roots and leaves using atomic absorption spectrophotometry. Formation of the palque did not affect growth of plants in control solutions. When exposed to Cu, plants with plaque had significantly larger biomass, dry weight of roots, dry weight of leaves, and growth increments of root and leaf than plants without plaque. When exposed to Ni, plants with plaque had signifiantly higher increment in leaf growth than plants without plaque. When exposed to Ni + Cu, plants with plaque had significantly higher biomass than plants without plaque. Toxic symptoms were not observed on plants with plaque grown with excess copper, while all other plants exposed to metals showed chlorosis, necrosis, or both. Metals were detected on the surface of roots, whether plants were allowed to develop a plaque or not. Cu, Ni, and Fe were concentrated in plaque and in roots. Lower concentrations of Cu and Ni were found in leaves of plants with a plaque than in plants without plaque. Comparisons of concentrations of Fe, Cu, and Ni with those of other species grown under field conditions are made. Key words: rice, iron plaque, toxicity of Cu and Ni.

Copper and nickel uptake, accumulation and tolerance in Typha latifolia with and without iron plaque on the root surface

“…These results show some differences from those of Greipsson & Crowder (1992) and Greipsson (1994). Greipsson & Crowder (1992) grew rice {Oryza sativa) with and without plaque on roots in control, Cu, Ni, and Cu-I-Ni solutions for 34-70 d. Their results indicated that formation of plaque improved growth and ameliorated Cu and Ni toxicity under mildly toxic conditions of Cu and (or) Ni exposure. Greipsson (1994) also reported that plaque improved growth when rice seedlings were exposed to 0"5 fig ml^^ Cu solution.…”

“…Before the second and third exposure to Fe^"^, roots were placed in water for 4 h and then exposed to \S fig ml"^ Fe^"f or 48 h. Control plants were treated similarly but without Fe. The plants were subsequently placed directly into the solutions containing metals (Greipsson & Crowder, 1992). Growth was measured every 6 d (as the length of the longest leaf in each plant).…”

“…It has not been accepted that iron plaque acts entirely as an external barrier to toxic metals; it might influence tolerance in other ways, such as leading to a higher concentration of 'active iron' within leaves (Greipsson, 1995), as well as absorbing and immobilizing metals. Although the relationship between iron plaque on roots and metal absorption and accumulation by plants has been studied in recent years , 1990Greipsson & Crowder, 1992;Otte et al, 1989Otte et al, , 1991St-Cyr, Fortin & Campbell, 1993;Greipsson, 1994), this relationship is still unclear. Typha latifolia L. is a common and productive wetland plant of world-wide geographical distribution.…”

Influence of external zinc and phosphorus supply on Cd uptake by rice (Oryza sativa L.) seedlings with root surface iron plaque

“…However, no visible Fe toxicity symptoms were observed even though root dry weight decreased at Fe50 (Table 1), indicating that roots were more sensitive to the external Fe supply. In the literature, decreases (Ye et al 2001;Liu et al 2007) or increases (Greipsson and Crowder 1992;Greipsson 1994Greipsson , 1995 or no changes in root dry weight have been reported in response to pre-treatment to induce the formation of iron plaque on root surfaces. The distributions of P and Zn in different plant parts were in contrast with that of Cd (Fig.…”

“…Iron plaque therefore has chemical properties similar to those of iron oxides in the soil and can thus sequester both cations and anions and alter the uptake and accumulation of elements by plants. Iron plaque on rice root surfaces has been shown to sequester As (Liu et al 2004a,b andLiu et al 2005), Al (Chen et al 2006) and Se (Zhou et al 2007), alleviate toxicities of Cu, Ni and Zn to plants (Greipsson 1994(Greipsson , 1995Greipsson and Crowder 1992) and enhance Zn uptake when the amount of iron plaque was up to 12.1 g kg −1 root dry weight (Zhang et al 1998) and P uptake up to 24.5 g kg −1 root dry weight when Fe(OH) 3 was supplied to induce the formation of iron plaque (Zhang et al 1999). However, studies have also suggested that iron plaque is not the main barrier to Cd uptake by rice (Liu et al 2007).…”