Citric acid inhibits Cd uptake by improving the preferential transport of Mn and triggering the defense response of amino acids in grains

• Published in: Ecotoxicology and environmental safety 2021-03, Vol.211, p.111921, Article 111921
• Main Authors: Xue, Weijie, Wang, Peipei, Tang, Li, Zhang, Changbo, Wang, Changrong, Huang, Yongchun, Zhang, Xin, Li, Yaokui, Zhao, Bingran, Liu, Zhongqi
• Format: Article
• Language: English
• Subjects: Amino acids; Amino Acids - metabolism; Biological Transport; Cadmium; Cadmium - metabolism; Citric acid; Citric Acid - pharmacology; Edible Grain - physiology; Environmental Pollution; Manganese; Manganese - metabolism; Metals, Heavy - analysis; NRAMP family genes; Oryza - metabolism; Plant Leaves - metabolism; Plant Roots - metabolism; Protective Agents - pharmacology; Rice; Soil - chemistry; Soil Pollutants - analysis
• ISSN: 0147-6513; 1090-2414
• DOI: 10.1016/j.ecoenv.2021.111921

Citric acid (CA) can regulate the balance of anions and cations in plants, and improve their resistance to heavy metals. It is not clear if foliar application with CA has any effect on migration of Cd and Mn in rice plant. In this work, a low-Cd-accumulating indica rice line (P7) and a high-Cd-accumulating line (HZ) were used to investigate the influence of CA on the transport of Cd and Mn as well as amino acid metabolism in grains. Content of Cd in grains and other organs increased with the increase of Cd content (0.1–2.4 mg kg−1) in soil, while decreased with the foliar application with CA. With the increase of Cd content in rice grains, the content of most amino acids in HZ, P7, HZ+CA and P7 + CA showed an obvious decline trend. Foliar application with CA efficiently raised the Mn:Cd ratio in grains and nodes of both HZ and P7. Meanwhile, the expression levels of OsNramp2, 3 and 5 in panicles were efficiently enhanced by CA application when plants grew in soil with Cd content of 0.6–2.4 mg kg−1. The increasing effect of CA on the content of 4 amino acids (i.e., Glu, Phe, Thr and Ala) in grains was related to varieties and Cd pollution. These results indicate that foliar application with CA can regulate the transport of Cd and Mn in the opposite directions in tissues and inhibit Cd accumulation in grains by enhancing expression of OsNRAMP 2, 3 or 5 and triggering the defense response of some amino acids in Cd-contaminated environment. [Display omitted] •Citric acid regulates migration of Cd and Mn in rice in the opposite directions and increase Mn:Cd ratio in grains and nodes.•The expression of Nramp family genes in panicles is inhibited by Cd stress and enhanced by exogenous citric acid.•Citric acid promotes the synthesis of Glu, Phe, His, Ser and Thr in rice for alleviating Cd toxicity.