Ionomics analysis provides new insights into the co-enrichment of cadmium and zinc in wheat grains.

Cadmium (Cd) is present in many soils and, when enter a food chain, represents a major health threat to humans. The existent large variation in grain Cd content amongst wheat genotypes opens prospects for genetic improvement for reduced Cd uptake in this species. However, selecting low-Cd-accumulating varieties comes with a possible caveat of affecting uptake other essential nutrients. In this work, we screened 134 wheat varieties in 3 various field studies and selected 15 high- and 15 low-Cd accumulating varieties in grains for ionomics analysis. Our results showed that high-Cd accumulating varieties also possessed an ability to accumulate mineral elements of calcium, magnesium, manganese, iron and zinc, while varieties with low Cd content were deficient in many essential nutrients and, especially, zinc (Zn). The above data was confirmed in an independent trail involving another 97 wheat varieties. Thus, selecting plants for high Zn accumulation (as a part of biofortification programs) resulted in an inadvertent increase in accumulation of the toxic Cd in wheat. Vice versa, selecting low Cd-accumulating varieties comes with a danger of reducing their Zn content, with major consequences to food quality and human health. We suggest that the above conundrum can be resolved by understanding the structure-function relations of various transporters isoforms involved in Zn and Cd transport and issue-specific mode of their operation, via cell-based phenotyping followed by molecular breeding.

Nitric oxide acts downstream of abscisic acid in molybdenum-induced oxidative tolerance in wheat.

KEY MESSAGE: Our study first reveals that Mo mediates oxidative tolerance through ABA signaling. Moreover, NO acts downstream of ABA signaling in Mo-induced oxidative tolerance in wheat under drought stress. Nitric oxide (NO) is related to the improvement of molybdenum (Mo)-induced oxidative tolerance. While the function of Mo in abscisic acid (ABA) synthesis and in mediating oxidative tolerance by the interaction of ABA and NO remain to be studied. The -Mo and +Mo treatment-cultivated wheat was separated and subsequently was pretreated with AO inhibitor, ABA synthesis inhibitor, exogenous ABA, NO scavenger, NO donor or their combinations under polyethylene glycol 6000 (PEG)-stimulated drought stress (PSD). The AO activity and ABA content were increased by Mo in wheat under PSD, however, AO inhibitor decreased AO activity, correspondingly reduced ABA accumulation, suggesting that AO involves in the regulation of Mo-induced ABA synthesis. Mo enhanced activities and expressions of antioxidant enzyme, while these effects of Mo were reversed by AO inhibitor and ABA synthesis inhibitor due to the decrease of ABA content, but regained by exogenous ABA, indicating that Mo induces oxidative tolerance through ABA. Moreover, NO scavenger inhibited activities of antioxidant enzyme caused by Mo and exogenous ABA, but the inhibitions were eliminated by NO donor, indicating that NO is involved in ABA pathway in the regulation of Mo-induced oxidative tolerance in wheat under PSD. Finally, we proposed a scheme for the mechanism of Mo-induced oxidative tolerance.