Mitigating cadmium accumulation in dicotyledonous vegetables by iron fertilizer through inhibiting Fe transporter IRT1-mediated Cd uptake.

The solubility of cadmium (Cd) in soil and its transfer to plants are influenced by soil pH. While increasing soil pH reduces Cd solubility and accumulation in rice plants grown in acidic soils, its effect on Cd accumulation in vegetables remains inconclusive. Here, we investigated the impact of soil pH on Cd accumulation in dicotyledonous vegetables and elucidated the underlying molecular mechanisms. Soils collected from various locations were supplemented with varying quantities of lime to achieve soil pH values of around 5.0, 6.0, 7.0, and 8.0. Raising soil pH from around 5.0 to 8.0 markedly decreased extractable Cd. However, increasing soil pH tended to promote shoot Cd accumulation in dicotyledonous vegetable species including lettuce, pakchoi, and Chinese cabbage, and the model dicotyledonous plant Arabidopsis thaliana. Conversely, soil pH increase resulted in a monotonic decrease in rice Cd accumulation. In our hydroponic experiments, we discovered that iron (Fe) deficiency substantially increased Cd uptake and accumulation in dicotyledonous plants but not in rice. Increasing soil pH reduced soil Fe availability and induced the Fe transporter gene IRT1 expression in dicotyledonous vegetables roots, which led to an increase in IRT1-mediated Cd uptake and subsequently increased Cd accumulation as soil pH increases. A comprehensive model incorporating extractable Cd and root IRT1 expression better explained Cd accumulation in vegetable shoots. The application of 50 mg/kg of Fe fertilizer in neutral or alkaline soils resulted in a significant reduction in Cd accumulation by 34-58% in dicotyledonous vegetables. These findings reveal that increasing soil pH has two opposite effects, decreasing soil Cd availability while promoting Cd uptake through IRT1 upregulation, reconciling the inconsistency in its effect on Cd accumulation in dicotyledonous plants. Our findings provide important insights for understanding the factors affecting Cd uptake in plants and offer a practical solution to mitigate Cd contamination in vegetables.

Rapid identification of high and low cadmium (Cd) accumulating rice cultivars using machine learning models with molecular markers and soil Cd levels as input data.

Excessive accumulation of cadmium (Cd) in rice grains threatens food safety and human health. Growing low Cd accumulating rice cultivars is an effective approach to produce low-Cd rice. However, field screening of low-Cd rice cultivars is laborious, time-consuming, and subjected to the influence of environment × genotype interactions. In the present study, we investigated whether machine learning-based methods incorporating genotype and soil Cd concentration can identify high and low-Cd accumulating rice cultivars. One hundred and sixty-seven locally adapted high-yielding rice cultivars were grown in three fields with different soil Cd levels and genotyped using four molecular markers related to grain Cd accumulation. We identified sixteen cultivars as stable low-Cd accumulators with grain Cd concentrations below the 0.2 mg kg-1 food safety limit in all three paddy fields. In addition, we developed eight machine learning-based models to predict low- and high-Cd accumulating rice cultivars with genotypes and soil Cd levels as input data. The optimized model classifies low- or high-Cd cultivars (i.e., the grain Cd concentration below or above 0.2 mg kg-1) with an overall accuracy of 76%. These results indicate that machine learning-based classification models constructed with molecular markers and soil Cd levels can quickly and accurately identify the high- and low-Cd accumulating rice cultivars.

The ferroxidases LPR1 and LPR2 control iron translocation in the xylem of Arabidopsis plants.

Iron (Fe) deficiency is common in agricultural crops and affects millions of people worldwide. Translocation of Fe in the xylem is a key step for Fe distribution in plants. The mechanism controlling this process remains largely unknown. Here, we report that two Arabidopsis ferroxidases, LPR1 and LPR2, play a crucial and redundant role in controlling Fe translocation in the xylem. LPR1 and LPR2 are mainly localized in the cell walls of xylem vessels and the surrounding cells in roots, leaves, and stems. Knockout of both LPR1 and LPR2 increased the proportion of Fe(II) in the xylem sap, and caused Fe deposition along the vascular bundles especially in the petioles and main veins of leaves, which was alleviated by blocking blue light. The lpr1 lpr2 double mutant displayed constitutive expression of Fe deficiency response genes and overaccumulation of Fe in the roots and mature leaves under Fe-sufficient supply, but Fe deficiency chlorosis in the new leaves and inflorescences under low Fe supply. Moreover, the lpr1 lpr2 double mutant showed lower Fe concentrations in the xylem and phloem saps, and impaired 57Fe translocation along the xylem. In vitro assays showed that Fe(III)-citrate, the main form of Fe in xylem sap, is easily photoreduced to Fe(II)-citrate, which is unstable and prone to adsorption by cell walls. Taken together, these results indicate that LPR1 and LPR2 are required to oxidize Fe(II) and maintain Fe(III)-citrate stability and mobility during xylem translocation against photoreduction. Our study not only uncovers an essential physiological role of LPR1 and LPR2 but also reveals a new mechanism by which plants maintain Fe mobility during long-distance translocation in the xylem.