Salicylic Acid and Sodium Salicylate Alleviate Cadmium Toxicity to Different Extents in Maize (Zea mays L.).

Orsolya Kinga Gondor,Éva Darkó,Tibor Janda,Gabriella Szalai,Magda Pál,Maya Dimova Lambreva

doi:10.1371/journal.pone.0160157

Orsolya Kinga Gondor, Éva Darkó + Show 4 more

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https://doi.org/10.1371/journal.pone.0160157

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Abstract

The role of salicylic acid in Cd tolerance has attracted more attention recently but no information is available on the efficiency of different forms of salicylic acid. The aim was thus to investigate whether both the acid and salt forms of salicylic acid provide protection against Cd stress and to compare their mode of action. Young maize plants were grown under controlled environmental conditions. One group of 10-day-old seedlings were treated with 0.5 mM SA or NaSA for 1 day then half of the pants were treated with 0.5 mM Cd for 1 day. Another group of seedlings was treated with 0.5 mM CdSO4 for 1 day without pre-treatment with SA or NaSA, while a third group was treated simultaneously with Cd and either SA or NaSA. Both salicylic acid forms reduced the Cd accumulation in the roots. Treatment with the acidic form meliorated the Cd accumulation in the leaves, while Na-salicylate increased the phytochelatin level in the roots and the amount of salicylic acid in the leaves. Furthermore, increased antioxidant enzyme activity was mainly induced by the acid form, while glutathione-related redox changes were influenced mostly by the salt form. The acidic and salt forms of salicylic acid affected the two antioxidant systems in different ways, and the influence of these two forms on the distribution and detoxification of Cd also differed. The present results also draw attention to the fact that generalisations about the stress protective mechanisms induced by salicylic acid are misleading since different forms of SA may exert different effects on the plants via separate mechanisms.

Highlights

In plants, cadmium is an absorbed and rapidly translocated heavy metal, and causes strong toxicity even at relatively low concentrations
A schematic presentation of the various treatments can be seen in S1 Fig. One group of seedlings was treated with 0.5 mM Salicylic acid (SA) (SigmaUltra; S5922, Sigma Aldrich) or Na salt (NaSA) (Fluka; 71945, Sigma Aldrich) for 1 day, after which half of the plants were moved on the original growth solution and the second half were treated with 0.5 mM CdSO4 for 1 day (SA pre Cd, NaSA pre Cd)
In plants treated with SA or NaSA the roots contained less Cd than in plants treated with Cd alone; the lowest level of Cd was detected in the roots when SA and Cd were added together (SA+Cd)

Summary

Introduction

Cadmium is an absorbed and rapidly translocated heavy metal, and causes strong toxicity even at relatively low concentrations. Maize (Zea mays L.) is a relatively Cd-tolerant plant, many toxic symptoms may result if the Cd concentration exceeds a critical level, 7–70 mg/kg or more depending on the soil conditions [1,2,3]. The antioxidant system plays an important role in protection against various. The most important non-enzymatic antioxidants are glutathione (reduced form GSH, oxidised form GSSG), ascorbic acid (AsA) and phenolic metabolites. GSH is the substrate for the synthesis of phytochelatins (PCs), which play a special role in the detoxification of toxic heavy metals [5,6]

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