Regulation on copper-tolerance in Citrus sinensis seedlings by boron addition: Insights from root exudates, related metabolism, and gene expression

• Published in: Journal of hazardous materials 2023-10, Vol.459, p.132277-132277, Article 132277
• Main Authors: Chen, Huan-Huan, Zheng, Zhi-Chao, Chen, Wen-Shu, Rao, Rong-Yu, Chen, Xu-Feng, Ye, Xin, Guo, Jiuxin, Yang, Lin-Tong, Chen, Li-Song
• Format: Article
• Language: English
• Subjects: Boron mitigation; Citrus sinensis; Copper toxicity; Internal detoxification; Root exudates
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2023.132277

Boron (B) can alleviate Citrus copper (Cu)-toxicity. However, the underlying mechanism by which B mitigates Cu-toxicity is unclear. ‘Xuegan’ (Citrus sinensis) seedlings were exposed to 0.5 (control) or 350 (Cu-toxicity) µM Cu and 2.5 or 25 µM B for 24 weeks. Thereafter, we investigated the secretion of low molecular weight compounds [LMWCs; citrate, malate, total soluble sugars (TSS), total phenolics (TP), and total free amino acids (TFAA)] by excised roots and their concentrations in roots and leaves, as well as related enzyme gene expression and activities in roots and leaves. Cu-stress stimulated root release of malate and TFAA, which might contribute to citrus Cu-tolerance. However, B-mediated-mitigation of Cu-stress could not be explained in this way, since B addition failed to further stimulate malate and TFAA secretion. Indeed, B addition decreased Cu-stimulated-secretion of malate. Further analysis suggested that Cu-induced-exudation of malate and TFAA was not regulated by their levels in roots. By contrast, B addition increased malate, citrate, and TFAA concentrations in Cu-toxic roots. Cu-toxicity increased TP concentration in 25 μM B-treated leaves, but not in 2.5 μM B-treated leaves. Our findings suggested that the internal detoxification of Cu by LMWCs played a role in B-mediated-alleviation of Cu-toxicity. [Display omitted] •Root secretion of malate and amino acids plays a vital role in Citrus Cu-tolerance.•Secretion of malate and amino acids was not regulated by their levels in roots.•Internal detoxification of Cu plays a role in B-mediated-mitigation of Cu-toxicity.•LWMC metabolism responses to Cu and B treatments differed between leaves and roots.