| In recent years, with the development of industrial and agricultural production, the heavy metal pollution of soils is becoming a serious environmental problem. Cadmium (Cd) is one of the most concerned heavy metals, as it has a long life cycle, high toxicity and persistence in soil. Excess Cd in soils will reduce yield of crops, and Cd will also transfer into food chain via the crops. As a result, the Cd would inevita-bly enter into human bodies, and then pose a serious threat to human health. Therefore, developing efficient remediation technologies for Cd-contamintated soil is extremely urgent. Nitrogen (N) management is a promising agronomic strategy to minimize cadmium (Cd) contamination in crops. However, it is still unclear how N affects Cd uptake by plants.Wild-type and iron uptake-inefficient tomato (Solanum lycopersicum) mutant (T3238fer) plants were grown in pH-buffered hydroponic culture to investigate the direct effect of N-form on Cd uptake. The research results showed:wild-type plants fed NO3-accumulated more Cd than plants fed NH4+. Iron uptake and LeIRTI expres-sion in roots were also greater in plants fed NO3-. However, in mutant T3238fer which loses FER function, LeIRT1expression in roots was almost completely terminated, and the difference between NO3-and NH4+treatments vanished. As a result, the N-form had no effect on Cd uptake in this mutant. Furthermore, suppression of LeIRTI expression by NO synthesis inhibitors tungstate or L-NAME, also substantially inhi-bited Cd uptake in roots, and the difference between N-form treatments was dimi-nished. Considering all of these findings, it was concluded that the up-regulation of the Fe uptake system was responsible for NO3--facilitated Cd accumulation in plants.Nitrate (NO3-) significantly induces the expression of non-symbiotic hemoglobin gene Hbl in plants, and Hb1protein plays an important role in clearing NO in plants. So in this article, we also select Arabidopsis ecotype Columbia-0(wt), transgenic Arabidopsis of overexpressing AHb1(H7) and transgenic Arabidopsis plants express-ing AHb1in antisense orientation (L3) as experimental plants. When these3plants were grown with NO3-as the sole N source, we found that the effect of Cd on the growth of plants is closely correlated with AHb1expression, with the trend of Cd-induced suppression rate of their biomass at:L3<wt<H7. However, in the NH4+-N growth medium, the effect of Cd on the growth has no relation with the expression of AHb1in plants. Consequently, we investigated the mechanism of AHbl affecting Cd tolerance in plants in the NO3-growth condition. We determined the Cd content in plants, and we observed that there was no difference in both root and shoot Cd con-centrations among the3plants. H7plants had a more decrease of biomass production, greater H2O2burst and severer oxidative stress under Cd treatment than the other two plants. Cd treatment also caused a significant increase of NO level in all of3plants, but the increase seems less in H7plants. Interestingly, exogenous application of NO donor SNP could clearly reverse the Cd-induced growth inhibition, H2O2burst and oxidative stress in H7plants. Considering all above findings, we suggest that NO3-induced Hb1clears the Cd-induced NO production in plants, and as a result, increases the ROS burst and oxidative stress in plants, which aggravates Cd toxicity in plants. |
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