Abstract
Odontarrhena lesbiaca is an endemic species to the serpentine soils of Lesbos Island (Greece). As a nickel (Ni) hyperaccumulator, it possesses an exceptional Ni tolerance; and it can accumulate up to 0.2–2.4% Ni of its leaves’ dry weight. In our study, O. lesbiaca seeds from two geographically separated study sites (Ampeliko and Loutra) were germinated and grown on control and Ni-containing (3000 mg/kg) soil in a rhizotron system. Ni excess induced significant Ni uptake and translocation in both O. lesbiaca ecotypes and affected their root architecture differently: plants from the Ampeliko site proved to be more tolerant; since their root growth was less inhibited compared to plants originated from the Loutra site. In the roots of the Ampeliko ecotype nitric oxide (NO) was being accumulated, while the degree of protein tyrosine nitration decreased; suggesting that NO in this case acts as a signaling molecule. Moreover, the detected decrease in protein tyrosine nitration may serve as an indicator of this ecotype’s better relative tolerance compared to the more sensitive plants originated from Loutra. Results suggest that Ni hypertolerance and the ability of hyperaccumulation might be connected to the plants’ capability of maintaining their nitrosative balance; yet, relatively little is known about the relationship between excess Ni, tolerance mechanisms and the balance of reactive nitrogen species in plants so far.
Highlights
Nickel (Ni) is the fifth most abundant element on Earth [1], frequently used in the steel, galvanic and electric industry
During the 14 days-long growth period, O. lesbiaca seedlings from both Ampeliko and Loutra sites removed a significant amount of Ni, resulting in 2443 and 2480 ppm residual soil Ni content, respectively (Figure 1B)
We found from the Loutra site showed no such response (remained around that zinc (Zn) in a growth-promoting amount resulted in a more horizontal orientation, while thatinzinc (Zn) in inhibiting a growth-promoting amount aresulted in a more horizontal orientation, while
Summary
Nickel (Ni) is the fifth most abundant element on Earth [1], frequently used in the steel, galvanic and electric industry. The average Ni content of the soil is usually not higher than 100 mg/kg [2], but it can be increased by industrial and municipal wastewaters, mining, cement industry or by burning diesel oil [3,4]. In addition to anthropogenic causes, high Ni content occurs naturally as well: serpentine soils might contain several thousand mg/kg Ni. Serpentine soils are far from ideal for most plants: besides their granular-rocky texture, they possess low water-holding capacity [5]. According to the criteria of the “serpentine syndrome” the availability of calcium is relatively low to magnesium, such soils usually deficient in essential nutrients as phosphorous, nitrogen and potassium, while they contain excessive amount of toxic heavy metals such as, manganese, cobalt, chromium or nickel [6].
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