Dissecting the promotional effect of zinc on cadmium translocation from roots to shoots in rice.

It is often expected that Zn decreases Cd accumulation in plants due to competition for the same transporters. Here, we found that increasing Zn supply markedly increased the root-to-shoot translocation of Cd in rice. RNA sequencing showed that high Zn up-regulated expression of genes involved in glutathione biosynthesis and metabolism and the Zn/Cd transporter gene OsHMA2, but down-regulated expression of genes related to Zn uptake. Knockout of the iron or Zn transporter genes OsIRT1, OsIRT2, or OsZIP9 did not affect the Zn promotional effect on Cd translocation. Knockout of the manganese/Cd transporter gene OsNRAMP5 greatly reduced Cd uptake but did not affect the Zn promotional effect. Variation in the tonoplast transporter gene OsHMA3 affected Cd translocation but did not change the Zn promotional effect. Knockout of the Zn/Cd transporter gene OsHMA2 not only decreased Cd and Zn translocation, but also abolished the Zn promotional effect. Increased expression of OsHMA2 under high Zn conditions supports the hypothesis that this transporter participates in the promotional effect of Zn on Cd translocation. The results also show that OsIRT1, OsIRT2, and OsZIP9 made only small contributions to Cd uptake under low Zn conditions but not under high Zn conditions, whereas the dominant role of OsNRAMP5 in Cd uptake diminished under low Zn conditions.

[Effects of P on the Uptake and Transport of Cd and As in Wheat Seedlings].

The aim of this study was to explore the effect of P on the physiological mechanism of Cd and As uptake and transport of wheat seedlings. Taking Bainong 207 as the test material, we investigated the effects of exogenous P supply and P deficiency treatment on the growth, root morphology, photosynthetic parameters, antioxidant system, ion content, and rhizome transfer coefficient of wheat seedlings under Cd and As stress using hydroponic experiments. The results showed that compared with that in the P deficiency treatment, the supply of exogenous P significantly increased the chlorophyll content of wheat seedlings under As stress, promoted the growth and development of roots, and increased biomass, whereas there were no significant effects on the growth of wheat seedlings under Cd stress. The contents of P and Cd in the root system under the condition of Cd stress were significantly increased by the supply of exogenous P, and the contents of P and Cd in the aboveground part were reduced. At the same time, the P and As content in the shoot and the transfer coefficient of As from the root to the shoot under As stress were significantly improved. Therefore, the effects of P on the poisoning of wheat Cd and As in this study showed obvious differences. Under As stress, exogenous P supply mainly promoted the growth of wheat seedlings by improving the transport of As from the root to the shoot and the CAT activity in the root system, reducing the poisoning of As in wheat. Under Cd stress, P and Cd showed a certain synergistic effect, and the toxic effect of Cd on wheat was aggravated to a certain extent after the supply of P.