Copper, cadmium and nickel pollution inhibit growth and promote ascorbate catabolism in cell cultures of Arabidopsis thaliana and Zea mays

Abstract

We established model systems for exploring the roles of symplastic and apoplastic ascorbate in heavy-metal-polluted dicot and monocot cells. Cell-suspension cultures of Arabidopsis and maize were treated with copper, cadmium or nickel; growth and ascorbate metabolism were measured. Growth was halved by ∼80 µM Cu²⁺, 90 µM Cd²⁺ or 1200 µM Ni²⁺ in Arabidopsis, and ∼90 µM Cu²⁺, 650 µM Cd²⁺ or 650 µM Ni²⁺ in maize. Cu²⁺ (128 µM) and Cd²⁺ (512 µM) caused partial loss of symplastic ascorbate, especially in Arabidopsis; Ni²⁺ (512 and 2048 µM) had moderate effects. Added apoplastic l-ascorbate (1 mM) was consumed by the cultures (half-life ∼23 and 44 min in Arabidopsis and maize, respectively), consumption rate being 3–6-fold increased by Cu²⁺, Cd²⁺ and Ni²⁺ in Arabidopsis, and by Cu²⁺ in maize; Cd²⁺ and Ni²⁺ had relatively little effect on apoplastic ascorbate consumption in maize. Radioactivity from exogenous 1 mM l-[1-¹⁴C]ascorbate remained extracellular; catabolites formed were dehydroascorbic acid, diketogulonate and oxalyl-threonates. In conclusion, suspension-cultured cells respond to heavy-metal stresses by maintaining symplastic ascorbate concentrations, which may beneficially scavenge symplastic reactive oxygen species (ROS). Apoplastic ascorbate is catabolised in metal-polluted cultures via several oxidative and non-oxidative reactions, the former potentially scavenging stress-related apoplastic ROS.

Keywords:

• Heavy metal stress
• reactive oxygen species
• ascorbate turnover
• cell cultures
• defence response
• metal detoxification

Acknowledgement

The authors thank Dr. R. A. Dewhirst for helpful advice on the electrophoresis of ascorbate metabolites.

Authors’ contribution

SCF designed the research. FF performed most of the experiments. FF and SCF wrote the manuscript.

Disclosure statement

There are no competing interests to declare.

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

FF thanks the Higher Education Commission, Islamabad, Pakistan for financial assistance under the International Research Support Initiative Programme (IRSIP). SCF thanks the UK Biotechnology and Biological Sciences Research Council (BBSRC) for supporting this work (grant BB/I015531/1).