Phosphate deprivation decreases cadmium (Cd) uptake but enhances sensitivity to Cd by increasing iron (Fe) uptake and inhibiting phytochelatins synthesis in rice (Oryza sativa)

Cadmium (Cd) pollution and phosphate (Pi) deficiency are two important problems in some Asian countries, but the researches on effects and mechanisms of Pi deficiency on Cd uptake in rice are limited. Herein, 3-week-old rice seedlings were treated with 3 Pi levels (-Pi, +Pi, and +2Pi) under Cd stress for 3 weeks. The results showed that in the hydroponics experiments, Pi deprivation (-Pi) treatment significantly decreased Cd accumulation in rice seedlings but aggravated Cd phytotoxicity symptoms with decreased tillers, root length, shoot height, and dry weight. In contrast, Pi addition (+2Pi) treatment increased Cd accumulation but alleviated Cd phytotoxicity symptoms in rice seedlings. These results indicate that Pi physiologically regulates Cd accumulation and sensitivity in rice. Furthermore, -Pi treatment not only significantly decreased carbon (C) assimilation by reducing net photosynthesis rate and transpiration rate but also decreased glutathione (GSH) and phytochelatins (PCs) contents in rice seedlings. In addition, -Pi treatment significantly increased iron (Fe, a well-known competitive metal of Cd) accumulation in rice plantlets. Based on these results, we suggest that Pi deprivation decreases rice Cd uptake by competitively increasing Fe uptake and accumulation, Pi deprivation also enhances the sensitivity to Cd in rice plants by inhibiting biomass accumulation and reducing PCs synthesis.