Abstract
Heavy metal stress adversely affects plant growth and productivity worldwide. Alleviating the stress effect through the exogenous use of various chemical substances has become an interesting area of study in the field of plant stress tolerance. As a thiol compound, the cysteine derivative N-acetylcysteine (N-acetyl- L-cysteine, NAC) is the precursor of glutathione synthesis and a potent ROS scavenger with powerful antioxidant and free radical scavenging capabilities. This study investigated the effects of heavy metals (Cd, Hg and Pb, 100 ?M) on accumulation of soluble sugars and polyamine content in roots and shoots of wheat seedlings, the water potential and proline content in shoots and the role of NAC in protection against heavy metal toxicity. The addition of 1 mM NAC significantly increased root content of glucose, fructose and sucrose in varying degrees (avg. 1.34-, 1.20- and 1.51-fold, respectively) in comparison with heavy metals alone. The treatments led to a significant reduction of sugar content in shoots. Water potential values were highly correlated with proline and sugar content in wheat seedling shoots. Heavy metal stress significantly reduced polyamine content in both plant parts. The addition of NAC increased polyamine content in seedlings in comparison with heavy metals alone in both roots and shoots. These results suggest that NAC may protect plants from oxidative stress damage in heavy metal stress, and this enhancement of stress tolerance seems to involve soluble sugar and polyamine biosynthesis.
Highlights
Soil naturally contains heavy metals (HMs), increases in the levels of these HMs rising to harmful levels due to anthropogenic activities such as mining, disposal of sewage sludge, smelting and creation of HM pollution have become a major environmental problem for all organisms (Wuana & Okieimen 2011)
These results are in agreement with those reported by Yusuf et al (2011) indicating reduced Ψw values in Triticum aestivum L. leaves and by Schat et al (1997) indicating increased proline content in Silene vulgaris (Moench) Garcke in response to HM stress
The leaf water potential is known to be an important indicator of a plants water status (Rucińska-Sobkowiak 2016), and plants that successfully deal with lower water potentials can cope with limited water availability either by maintaining high internal water concentrations or by shrinking water-requiring root structures and accumulating compatible solutes that keep osmotic potentials low (Lee et al 2008; Rucińska-Sobkowiak 2016)
Summary
Soil naturally contains heavy metals (HMs), increases in the levels of these HMs rising to harmful levels due to anthropogenic activities such as mining, disposal of sewage sludge, smelting and creation of HM pollution have become a major environmental problem for all organisms (Wuana & Okieimen 2011). The consequences of HM toxicity include the inhibition or reduction of photosynthesis, mitochondrial respiration and carbohydrate metabolism; reduced biomass generation; and decrease in the content of grain nutrients. This toxicity threatens plants, and human health (Gill 2014). Ular-weight osmolites and signal compounds (Dhir et al 2012) These compounds contribute to reducing the adverse effects of HMs by maintaining cell turgor and membrane integrity, detoxifying reactive oxygen species (ROS) and playing a precursor role in synthesis of lignin and phenolic compounds (Rosa et al 2009; Dhir et al 2012)
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