Tolerance mechanism: Membrane transport Rhizosphere microbial communities Root architecture Chelation/ Conjugation Comments
Reference: Lu et al., 2019 Overexpression of rice HMA3 promotes Cd sequestration in root vacuoles and hence reduces grain Cd. Given the strong 35S promoter that was used, it is remarkable that HMA3 overexpression did not affect grain yield and/or essential micronutrients such as Zn, Fe, Cu and Mn, which can all be substrates for HMA3.
Tang et al., 2017 Gene editing approach to knock out rice NRAMP5. Reduced Cd in roots, shoots and grain. The mutation also affects the micronutrient Mn but not other metals such as Fe, Zn or Cu. Nor did the loss of function lead to yield penalties.
Chang et al., 2020 Overexpression of NRAMP5 in rice, as expected, increases Cd uptake but, counterintuitively, greatly reduced grain Cd content. The latter may be caused by the use of strong promoters that disrupt the normal expression patterns.
Ma et al., 2008 Loss of function in Lsi1 and Lsi2 reduces rice arsenic uptake and translocation. These mutations also negatively impact on Si uptake and hence are detrimental to rice growth and yield.
Nong et al., 2020 Soil amended with a mixture of bacteria showed decreased levels of bioavailable Cd and Pb in soil and reduced Cd, Pb and As in grain of brown rice but had no positive impact on plant growth.
Hui et al., 2015 Colonisation of tobacco roots by the endophytic fungus Piriformospora indica increases root storage of Cd and improves tolerance. The mechanism appears to be based on an enhanced antioxidant response.
Gao et al., 2010 Three year field trial showing that inoculation of wheat by micorrhizal fungi did not alter growth or grain Cd content. Grain Cd was generally low and negatively correlated to Zn.
Wu et al., 2011 Rice plants with high porosity (i.e. high proportion of aerenchyma) accumulate less As in grains. No data given about plant tolerance and/or growth.