Salinity alleviates zinc toxicity in the saltmarsh zinc-accumulator Juncus acutus

Abstract

The potential importance of Juncus acutus for remediation of Zn-contaminated lands has been recognized, because of its Zn tolerance and capacity to accumulate Zn. Since it is also a halophyte, the extent to which salinity influences its Zn tolerance requires investigation. A factorial greenhouse experiment was designed to assess the effect of NaCl supply (0 and 85 mM NaCl) on the growth, photosynthetic physiology and tissue ions concentrations of plants exposed to 0, 30 and 100 mM Zn. Our results indicated that NaCl supplementation alleviated the effects of Zn toxicity on growth, as Zn at 100 mM reduced relative growth rate (RGR) by 60% in the absence of NaCl but by only 34% in plants treated also with NaCl. This effect was linked to a reduction in Zn tissue concentrations, as well as to overall protective effects on various stages in the photosynthetic pathway. Thus, at 85 mM NaCl plants were able to maintain higher net photosynthesis (A) than in the absence of added NaCl, although there were no differences in stomatal conductance (g). This contributed to preserving the trade-off between CO acquisition and water loss, as indicated by higher intrinsic water use efficiency (WUE). Hence, A differences were ascribed to limitation in the RuBisCO carboxylation, manifested as higher intercellular CO concentration (C), together with dysfunction of PSII photochemistry (in term of light harvest and energy excess dissipation), as indicated by higher chronic photoinhibition percentages and variations in the photosynthetic pigment profiles in presence of Zn under non-saline conditions.

24-Epibrassinolide Improves Root Anatomy and Antioxidant Enzymes in Soybean Plants Subjected to Zinc Stress

“…These benefits induced by EBR enhanced pigment biosynthesis and promoted a positive impact on the photosynthetic apparatus. Mateos-Naranjo et al (2018) found reductions in Chl a, Chl b and Car levels in Juncus acutus plants exposed to Zn toxicity (100 mM Zn). However, Ramakrishna and Rao (2015) demonstrated that foliar application of EBL and HBL at concentrations of 0.5, 1.0 and 2.0 μM effectively alleviated the deleterious effects of Zn toxicity on Raphanus sativus, protecting mainly the chloroplast membranes and increasing Chl a, Chl b and Car.…”

Importance of Physiological Traits Vulnerability in Determine Halophytes Tolerance to Salinity Excess: A Comparative Assessment in Atriplex halimus

“…Among specific tolerance mechanisms, it is well recognized that halophytes use osmoprotective and ion-detoxification strategies [3][4][5] to regulate their tissues' Na concentration patterns or K/Na ratio variations [2]. Many studies have been carried out to evaluate the effect of salt excess carboxylation capacity and energy use efficiency in halophytes [6][7][8][9][10][11][12], showing how these plants are able to maintain metabolic processes despite being exposed to high salt concentration. However, studies focused on the effect of salt on xylem anatomy and functioning, plant-water relations, and photosynthetic capacity are scarce [13], despite the relevance of these traits to determine plant tolerance to environmental stress [14][15][16].…”

Ecophysiology and Uses of Halophytes in Diverse Habitats

“…This species has been widely studied for its capacity of Zn tolerance and accumulation in land contaminated with this metal. Mateos-Naranjo et al (2018) studied the effect on this hydrohalophyte of NaCl at concentrations representative of estuarine environments. Salt considerably reduced the harmful effects of high Zn concentrations on the growth and development of this halophyte.…”