Abstract
Cadmium (Cd) and lead (Pb) are two toxic heavy metals (HMs) whose presence in soil is generally low. However, industrial and agricultural activities in recent years have significantly raised their levels, causing progressive accumulations in plant edible tissues, and stimulating research in this field. Studies on toxic metals are commonly focused on a single metal, but toxic metals occur simultaneously. The understanding of the mechanisms of interaction between HMs during uptake is important to design agronomic or genetic strategies to limit contamination of crops. To study the single and combined effect of Cd and Pb on durum wheat, a hydroponic experiment was established to examine the accumulation of the two HMs. Moreover, the molecular mechanisms activated in the roots were investigated paying attention to transcription factors (bHLH family), heavy metal transporters and genes involved in the biosynthesis of metal chelators (nicotianamine and mugineic acid). Cd and Pb are accumulated following different molecular strategies by durum wheat plants, even if the two metals interact with each other influencing their respective uptake and translocation. Finally, we demonstrated that some genes (bHLH 29, YSL2, ZIF1, ZIFL1, ZIFL2, NAS2 and NAAT) were induced in the durum wheat roots only in response to Cd.
Highlights
The distribution of heavy metals (HMs) in soils is variable from one place to another
The molecular mechanisms activated in the roots were investigated paying attention to transcription factors, heavy metal transporters and genes involved in the biosynthesis of metal chelators
L-Cd near-isogenic lines (NILs), the near isogenic line characterized by the ability to accumulate a low level of Cd in leaves, collected, as expected, a low level of Cd in leaves compared to H-Cd NIL and to Svevo (Figure 1), whereas it showed the presence of a high level of Pb in leaves in comparison with all other genotypes (Figure 2), suggesting the presence of different molecular mechanism for the transport of
Summary
The distribution of heavy metals (HMs) in soils is variable from one place to another. A concern with HMs is that they can enter the food chain through consumption of vegetables and plant parts. The toxicity is due mainly to chronic exposure by eating HM-contaminated foods. Since low levels of HMs in soil generally do not affect plant growth and development (no visible symptoms), HMs could endanger human health [2] if adequate counteractions are not implemented. Soil metal contamination usually occurs with a combination of different metals. Cadmium (Cd) and lead (Pb) are considered environmental hazards, as they are toxic for humans and other living organisms [3,4] and the Codex Alimentarius (CDX 193-1995, Amended 2019) has set a maximum level of 0.2 mg kg−1 for both Cd and Pb in wheat [5]
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