Exogenous Abscisic Acid Alleviates Cadmium Toxicity by Restricting Cd2+ Influx in Populus euphratica Cells
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Abscisic acid (ABA), a widely known phytohormone involved in the plant response to abiotic stress, plays a vital role in mitigating Cd2+ toxicity in herbaceous species. However, the role of ABA in ameliorating Cd2+ toxicity in woody species is largely unknown. In the present study, we investigated ABA restriction on Cd2+ uptake and the relevance to Cd2+ stress alleviation in Cd2+-hypersensitive Populus euphratica. ABA (5 μM) markedly improved cell viability and growth but reduced membrane permeability in CdCl2 (100 μM)-stressed P. euphratica cells. Moreover, ABA significantly increased the activity of the antioxidant enzymes catalase (CAT), superoxide dismutase (SOD), and ascorbate peroxidase (APX), contributing to the scavenging of Cd2+-elicited H2O2 within P. euphratica cells during the period of CdCl2 exposure (100 μM, 24–72 h). ABA alleviation of Cd2+ toxicity was mainly the result of ABA restriction of Cd2+ uptake under Cd2+ stress. Steady-state and transient flux recordings showed that ABA inhibited Cd2+ entry into Cd2+-shocked (100 μM, 30 min) and short-term-stressed P. euphratica cells (100 μM, 24–72 h). Non-invasive micro-test technique data showed that H2O2 (3 mM) stimulated the Cd2+-elicited Cd2+ influx but that the plasma membrane (PM) Ca2+ channel inhibitor LaCl3 blocked it, suggesting that the Cd2+ influx was through PM Ca2+-permeable channels. These results suggested that ABA up-regulated antioxidant enzyme activity in Cd2+-stressed P. euphratica and that these enzymes scavenged the Cd2+-elicited H2O2 within cells. The entry of Cd2+ through the H2O2-mediated Ca2+-permeable channels was subsequently restricted; thus, Cd2+ buildup and toxicity were reduced in the Cd2+-hypersensitive species, P. euphratica.
KeywordsABA Antioxidant enzyme H2O2 NMT Cd2+ influx Populus euphratica
The research was supported jointly by the Beijing Forestry University Young Scientist Fund (Grant No. BLX005), the National Natural Science Foundation of China (Grant Nos. 31270654, 31200207, 31200470, 31570587, 31500504), the Research Project of the Chinese Ministry of Education (Grant No. 113013A), the key project for Oversea Scholars by the Ministry of Human Resources and Social Security of PR China (Grant No. 2012001), the Program for Changjiang Scholars and Innovative Research Teams in University (Grant No. IRT13047), the Program of Introducing Talents of Discipline to Universities (111 Project, Grant No. B13007), the Fundamental Research Funds for the Central Universities (Grant No. TD2012-04), the Research Support Project of Shanxi University (Grant No. 113533801004), and the Plan Project for Scientific Research and Entrepreneurship Action of College Students in Beijing (Grant No. S201510022037).
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