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Front. Plant Sci. | doi: 10.3389/fpls.2018.01892

Mechanism enhancing Arabidopsis resistance to cadmium: The role of NRT1.5 and proton pump

Tao Wang1, Yingpeng Hua1, Moxian Chen2, Jianhua Zhang2, Chunyun Guan1 and  Zhenhua ZHANG1*
  • 1Hunan Agricultural University, China
  • 2Hong Kong Baptist University, Hong Kong

Aims Heavy metal pollution is serious in China, and abscisic acid (ABA) is an important stress hormone.How it regulates plant tolerance to cadmium remains unclear, so we aimed to explore the molecular mechanism responsible for enhanced cadmium resistance in Arabidopsis wild-type and mutant plants and Brassica napus seedlings.
Methods Arabidopsis/B. napus were cultured hydroponically for 28/15 days and then treated with 20/10 µM Cd/Cd+ABA (5 M) for 3/4 days. Chlorophyll degradation rate, SPAD values, proline, MDA, ABA, NO3-, and Cd concentrations were measured in root vacuoles and protoplasts; root to shoot NO3- and Cd concentration ratios were determined and NRT1.5-, NRT1.8-, BnNRT1.5- and BnNRT1.8-related gene expression was studied.
Results Cytoplasmic ABA levels in root cells of bglu10 and bglu18 Arabidopsis mutants were significantly lower than those in the wild-type, apparently making the latter more resistant to Cd. NO3- long-distance transporter NRT1.5 responded to ABA signaling by downregulating its own expression, while NRT1.8 did not respond. Concomitantly, proton pump activity in wild-type plants was higher than in the bglu10 and bglu18 mutants; thus, more NO3- and Cd accumulated in the vacuoles of wild-type root cells. ABA application inhibited Cd absorption by B. napus. BnNRT1.5 responded to exogenous ABA signal by downregulating its own expression, while the lack of response by BnNRT1.8 resulted in increased amount of NO3- accumulating in the roots to participate in the anti-cadmium reaction.
Conclusions NRT1.5 responds to the ABA signal to inhibit its own expression, whereas unresponsiveness of NRT1.8 causes accumulation of NO3- in the roots; thus, enhancing Cd resistance. In Arabidopsis, because of proton pump action, more NO3- and Cd accumulate in the vacuoles of Arabidopsis root cells, thereby reducing damage by Cd toxicity. However, in B. napus, the addition of exogenous ABA inhibited Cd absorption. Our data provide a sound basis to the theoretical molecular mechanism involved in hormone signaling during response of plants to heavy metal stress.

Keywords: ABA signaling, NRT1.5, NRT1.8, NO3-, Cd, vacuole

Received: 29 Aug 2018; Accepted: 06 Dec 2018.

Edited by:

Sergey Shabala, University of Tasmania, Australia

Reviewed by:

Honghong Wu, University of California, Riverside, United States
Qi Wu, Foshan University, China  

Copyright: © 2018 Wang, Hua, Chen, Zhang, Guan and ZHANG. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Zhenhua ZHANG, Hunan Agricultural University, Changsha, China,