Calcium signaling confers nickel tolerance in Cucurbita pepo L.

Abstract

Excessive nickel (Ni) accumulation in edible parts of the plants has become a serious challenge for food security over the past few decades. Therefore, in this study, the role of calcium (Ca²⁺) signaling in imparting Ni tolerance was investigated in zucchini (Cucurbita pepo L. cv Courgette d’Italie). Exposure of zucchini seedlings to Hogland solution containing 0.28 mmol L⁻¹ Ni(NO₃)₂ reduced plant growth, the content of chlorophyll and carotenoids and the relative water content (RWC) in leaves, increased Ni accumulation that was accompanied to depletion of the essential bivalent cations and induced oxidative stress and proline accumulation in both shoots and roots. Pretreatment with the nutrient solution containing 15 mmol L⁻¹ calcium chloride (CaCl₂), significantly improved zucchini growth and photosynthetic pigment contents and maintained RWC in leaves under both control and Ni stress conditions. Pretreatment with CaCl₂ reduced Ni accumulation, modified cation homeostasis, increased the activities of peroxidase and catalase enzymes and lowered Ni-induced accumulation of hydrogen peroxide, malondialdehyde and proline in leaves and roots. Pre-exposure of root with Ca²⁺ chelator (ethylene glycol tetraacetic acid) and plasma membrane Ca²⁺ channel blocker (lanthanum chloride) impaired impact of Ca²⁺ on the aforementioned attributes. Outcomes of this study not only highlight the signaling role of Ca²⁺ in regulating defensive responses but also suggest an eco- friendly approach for reducing the Ni contamination in plants that ensure food safety.

Keywords:

• Antioxidant enzymes
• Ca²⁺ signaling
• Cucurbita pepo L.
• heavy metal
• mineral homeostasis
• nickel
• photosynthetic pigments

Disclosure statement

No potential conflict of interest was reported by the author(s).

Novelty statement

In most studies, co-application of calcium and heavy metals has been evaluated and competition between them in the medium has been discussed as a reason for reducing heavy metal uptake, while in this study pre-treatment with calcium and pre-exposure with EGTA as a Ca²⁺ chelator and LaCl₃ as a calcium channel blocker were assessed for clarifying the role of Ca²⁺ signaling in Ni tolerance of zucchini seedlings.