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The metal tolerance profile of Thlaspi goesingense is mimicked in Arabidopsis thaliana heterologously expressing serine acetyl-transferase.

Freeman JL, Salt DE - BMC Plant Biol. (2007)

Bottom Line: Based on the relative concentrations of each metal used a relatively low level of resistance to Cd was observed in both T. goesingense and TgSATm expressing lines and Cd resistance was least correlated to GSH accumulation.Such data supports the conclusion that elevated glutathione levels, driven by constitutively enhanced SAT activity in the hyperaccumulator T. goesingense, plays an important role in the Ni, Co and Zn tolerance of this and other Thlaspi species.The hyper-activation of S assimilation through SAT is an excellent strategy for engineering enhanced metal tolerance in transgenic plants potentially used for phytoremediation.

View Article: PubMed Central - HTML - PubMed

Affiliation: Center for Plant Environmental Stress Physiology, Purdue University, Horticulture and Landscape Architecture Department, West Lafayette, Indiana 47907, USA. John.Freeman@ColoState.edu

ABSTRACT

Background: The Ni hyperaccumulator Thlaspi goesingense is tolerant to Ni congruent with Zn, congruent with Co and slightly resistant to > Cd. We previously observed that elevated glutathione, driven by constitutive activation of serine acetyltransferase (SAT), plays a role in the Ni tolerance of T. goesingense.

Results: Here we show that the elevated shoot concentration of glutathione, previously shown to cause elevated Ni tolerance in Arabidopsis thaliana heterologously expressing T. goesingense mitochondrial serine acetyltransferase (SATm), also causes tolerance to Co and Zn while slightly enhancing resistance to Cd. The level of tolerance afforded to each metal is ranked Ni congruent with Co, > Zn > Cd. The Ni congruent with Co, > Zn tolerances are positively correlated with both the accumulation of glutathione (GSH) and the ability to resist the oxidative damage induced by these different metals. Based on the relative concentrations of each metal used a relatively low level of resistance to Cd was observed in both T. goesingense and TgSATm expressing lines and Cd resistance was least correlated to GSH accumulation.

Conclusion: Such data supports the conclusion that elevated glutathione levels, driven by constitutively enhanced SAT activity in the hyperaccumulator T. goesingense, plays an important role in the Ni, Co and Zn tolerance of this and other Thlaspi species. The hyper-activation of S assimilation through SAT is an excellent strategy for engineering enhanced metal tolerance in transgenic plants potentially used for phytoremediation.

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Bar graph showing the slopes of trend lines obtained through plotting metal tolerance to Ni, Co, Zn and Cd for each line against shoot GSH accumulation. Metal tolerance was scored as the percentage of seedlings with normal upright cotyledons (A) or the formation of a root hook (B). Data represent means of slopes (n = 3 for each metal ± SD). Lower case letters (a, b, c and d) represent significantly different means, using the Tukey-Kramer test comparing all pairs (P < 0.05). Fits of the metal tolerance verses GSH plots for Ni, Co, Zn and Cd in shoots, R2 = 0.99, 0.96, 0.98, and 0.99, respectively, and for roots R2 = 1.0, 1.0, 0.98 and 1.0.
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Figure 7: Bar graph showing the slopes of trend lines obtained through plotting metal tolerance to Ni, Co, Zn and Cd for each line against shoot GSH accumulation. Metal tolerance was scored as the percentage of seedlings with normal upright cotyledons (A) or the formation of a root hook (B). Data represent means of slopes (n = 3 for each metal ± SD). Lower case letters (a, b, c and d) represent significantly different means, using the Tukey-Kramer test comparing all pairs (P < 0.05). Fits of the metal tolerance verses GSH plots for Ni, Co, Zn and Cd in shoots, R2 = 0.99, 0.96, 0.98, and 0.99, respectively, and for roots R2 = 1.0, 1.0, 0.98 and 1.0.

Mentions: Heterologous expression of TgSATm was previously shown to increase both shoot GSH levels and Ni tolerance (Freeman et al., 2004). We observe here that in addition to increased Ni tolerance, elevated GSH also leads to increased tolerance to the growth inhibitory effects of Co, Zn and a low level of resistance to Cd. However, by comparing the magnitude of the tolerance to Ni, Co, Zn, and Cd resistance conferred by heterologous expression of TgSATm with the concentration of shoot GSH, across lines with different levels of SAT expression, we established that the effectiveness of GSH in enhancing metal tolerance varies with the metal. The percent toxicity, scored for both shoot and root, was calculated for each line and metal at the seedling ring, which had the maximum difference in tolerance when the highest SATm expressing line was compared to the control line. These tolerance values were plotted against the GSH synthesis capacity of each line, and the relationship was found to be linear, with increasing GSH conferring increasing metal tolerance to Ni, Co, Zn, and resistance to Cd (DNS). From the slope of these plots the metal tolerance vs GSH concentration value is obtained for each metal in both shoot and root (Fig. 7). The equivalent increase in shoot GSH concentrations was most effective at increasing shoot tolerance to Ni and Co, followed closely by Zn then least effective was Cd resistance. GSH also caused elevated metal tolerances in roots to Co followed by Ni and Zn, while Cd resistance in roots was least correlated to total GSH production. However, metal levels in the roots were not measured and Cd may have been much higher here, as Cd is known to accumulate in roots.


The metal tolerance profile of Thlaspi goesingense is mimicked in Arabidopsis thaliana heterologously expressing serine acetyl-transferase.

Freeman JL, Salt DE - BMC Plant Biol. (2007)

Bar graph showing the slopes of trend lines obtained through plotting metal tolerance to Ni, Co, Zn and Cd for each line against shoot GSH accumulation. Metal tolerance was scored as the percentage of seedlings with normal upright cotyledons (A) or the formation of a root hook (B). Data represent means of slopes (n = 3 for each metal ± SD). Lower case letters (a, b, c and d) represent significantly different means, using the Tukey-Kramer test comparing all pairs (P < 0.05). Fits of the metal tolerance verses GSH plots for Ni, Co, Zn and Cd in shoots, R2 = 0.99, 0.96, 0.98, and 0.99, respectively, and for roots R2 = 1.0, 1.0, 0.98 and 1.0.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2233625&req=5

Figure 7: Bar graph showing the slopes of trend lines obtained through plotting metal tolerance to Ni, Co, Zn and Cd for each line against shoot GSH accumulation. Metal tolerance was scored as the percentage of seedlings with normal upright cotyledons (A) or the formation of a root hook (B). Data represent means of slopes (n = 3 for each metal ± SD). Lower case letters (a, b, c and d) represent significantly different means, using the Tukey-Kramer test comparing all pairs (P < 0.05). Fits of the metal tolerance verses GSH plots for Ni, Co, Zn and Cd in shoots, R2 = 0.99, 0.96, 0.98, and 0.99, respectively, and for roots R2 = 1.0, 1.0, 0.98 and 1.0.
Mentions: Heterologous expression of TgSATm was previously shown to increase both shoot GSH levels and Ni tolerance (Freeman et al., 2004). We observe here that in addition to increased Ni tolerance, elevated GSH also leads to increased tolerance to the growth inhibitory effects of Co, Zn and a low level of resistance to Cd. However, by comparing the magnitude of the tolerance to Ni, Co, Zn, and Cd resistance conferred by heterologous expression of TgSATm with the concentration of shoot GSH, across lines with different levels of SAT expression, we established that the effectiveness of GSH in enhancing metal tolerance varies with the metal. The percent toxicity, scored for both shoot and root, was calculated for each line and metal at the seedling ring, which had the maximum difference in tolerance when the highest SATm expressing line was compared to the control line. These tolerance values were plotted against the GSH synthesis capacity of each line, and the relationship was found to be linear, with increasing GSH conferring increasing metal tolerance to Ni, Co, Zn, and resistance to Cd (DNS). From the slope of these plots the metal tolerance vs GSH concentration value is obtained for each metal in both shoot and root (Fig. 7). The equivalent increase in shoot GSH concentrations was most effective at increasing shoot tolerance to Ni and Co, followed closely by Zn then least effective was Cd resistance. GSH also caused elevated metal tolerances in roots to Co followed by Ni and Zn, while Cd resistance in roots was least correlated to total GSH production. However, metal levels in the roots were not measured and Cd may have been much higher here, as Cd is known to accumulate in roots.

Bottom Line: Based on the relative concentrations of each metal used a relatively low level of resistance to Cd was observed in both T. goesingense and TgSATm expressing lines and Cd resistance was least correlated to GSH accumulation.Such data supports the conclusion that elevated glutathione levels, driven by constitutively enhanced SAT activity in the hyperaccumulator T. goesingense, plays an important role in the Ni, Co and Zn tolerance of this and other Thlaspi species.The hyper-activation of S assimilation through SAT is an excellent strategy for engineering enhanced metal tolerance in transgenic plants potentially used for phytoremediation.

View Article: PubMed Central - HTML - PubMed

Affiliation: Center for Plant Environmental Stress Physiology, Purdue University, Horticulture and Landscape Architecture Department, West Lafayette, Indiana 47907, USA. John.Freeman@ColoState.edu

ABSTRACT

Background: The Ni hyperaccumulator Thlaspi goesingense is tolerant to Ni congruent with Zn, congruent with Co and slightly resistant to > Cd. We previously observed that elevated glutathione, driven by constitutive activation of serine acetyltransferase (SAT), plays a role in the Ni tolerance of T. goesingense.

Results: Here we show that the elevated shoot concentration of glutathione, previously shown to cause elevated Ni tolerance in Arabidopsis thaliana heterologously expressing T. goesingense mitochondrial serine acetyltransferase (SATm), also causes tolerance to Co and Zn while slightly enhancing resistance to Cd. The level of tolerance afforded to each metal is ranked Ni congruent with Co, > Zn > Cd. The Ni congruent with Co, > Zn tolerances are positively correlated with both the accumulation of glutathione (GSH) and the ability to resist the oxidative damage induced by these different metals. Based on the relative concentrations of each metal used a relatively low level of resistance to Cd was observed in both T. goesingense and TgSATm expressing lines and Cd resistance was least correlated to GSH accumulation.

Conclusion: Such data supports the conclusion that elevated glutathione levels, driven by constitutively enhanced SAT activity in the hyperaccumulator T. goesingense, plays an important role in the Ni, Co and Zn tolerance of this and other Thlaspi species. The hyper-activation of S assimilation through SAT is an excellent strategy for engineering enhanced metal tolerance in transgenic plants potentially used for phytoremediation.

Show MeSH
Related in: MedlinePlus