Abstract
Triacontanol (TRIA) role in improving growth, physiological activities and tolerance against abiotic stresses has been reported. Yet, the mechanism by which TRIA executes its effects remains elusive. This work therefore studied the possible role of TRIA exogenous application in counteracting the adverse effects of nickel (Ni) treated maize seedlings. Maize seedlings (15-day-old) were grown in washed sand irrigated with nutrient solution provided with 100 μM NiCl2. Two concentrations of TRIA (25 and 50 µM) were applied twice as a foliar spray for Ni-stressed seedlings. Shoot and root growth attributes, Ni content, and antioxidant defence systems of maize seedlings were determined. Ni treatment reduced the shoot and root length and biomass, causing necrosis of the old leaves,greater reduction was shown in the roots. The shoot and root length was negatively correlated with their Ni content, which was consistent with their content of H2O2, but not with their malondialdehyde (MDA) content. As the roots had the greatest Ni content, maximum peroxidase (PX) and glutathione reductase (GR) activity as well as the highest ascorbic acid (ASA) and reduced glutathione (GSH) content were observed in the roots. The Ni-induced deleterious effects were alleviated by foliar application of TRIA concentrations. Also, TRIA treatment minimized root Ni content, whereas it maintained the shoots unharmed by Ni. Such mitigative effects of TRIA are explained by its key role in enhancing antioxidant capacity (expressed as IC50), increased PX and ascorbate oxidase (AO) activity, GSH, and total phenolic contents.
Author Contributions
Copyright© 2019
Abdelrazk Younis Abeer, et al.
License
This work is licensed under a Creative Commons Attribution 4.0 International License.
This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Competing interests The authors have declared that no competing interests exist.
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Introduction
Heavy metal pollution is a global concern as it adversely affecting crop production. Heavy metals (HMs) are naturally occurring metals with atomic numbers greater than 20 and an elemental density greater than 5 g cm−3 Ni toxicity induces high levels of reactive oxygen species (ROS) which triggers lipid peroxidation, oxidation of proteins, degradation of chlorophyll pigments and DNA damage TRIA is one of relatively new plant growth regulators (PGRs) which has been established to play a critical role in plant growth and development when exogenously applied to various plant species
Materials And Methods
Maize ( The maximum quantum efficiency of PSII( Dried samples (roots and shoots from each treatment were extracted by dry ashing as described by Chapman and Pratt Lipid peroxidation was evaluated by measuring the production of malondialdehyde (MDA) by thiobarbituric acid reaction (TBAR)-based colorimetric method as described by Heath and Packer The measurement of diphenylpicrylhydrazyl (DPPH) radical scavenging activity was carried out according to the method of Hatano et al. Antioxidant enzymes were extracted from maize shoots and roots by using a known volume of phosphate buffer (PH 7) (1:4 W/V). The crude extracts were used for enzyme assays. Superoxide dismutase (SOD, EC 1.15.1.1) activity was assayed according to method for Kong et al. The results were subjected to one-way analysis of variance (ANOVA) using the software package SPSS v20.0 (SPSS Inc., Chicago, USA). The comparison of the means of different treatments was carried out using Duncan s multiple range test at a significance level of 5% (P ≤ 0.05).
Results
Maize seedlings exposed to Ni treatment exhibited a major decrease in shoot height, circumference and fresh weight, as well as root length ( Application of TRIA (50 μM) markedly decreased root Ni content, however, both TRIA treatments (25 and 50 μM) did not show any prominent effect on shoot Ni content ( The values of the maximum quantum efficiency of PSII( The lowest IC50 values indicating the highest antioxidant capacity was recorded in 25 μM TRIA-treated stressed shoots, whereas, the highest IC50 value was obtained in Ni-stressed roots of maize seedlings ( Interestingly maize roots revealed similar behavior in both ASA and GSH contents (
Discussion
Decreased growth of maize seedlings exposed to 100 µM Ni could be attributed to inhibition of cell division Increased Ni accumulation in the roots but not in the shoots of maize seedlings could possibly be due to the contention that roots are directly contacted with soil solution including Ni, and root water absorption likely increased Ni accumulation with low translocation of Ni to the shoots Our results showed nonsignificant effect on Accumulation of H2O2 and Niin the roots of maize seedlings agrees with previous studies on roots of TRIA enhanced enzymatic (mainly peroxidases) and non-enzymatic (phenolic compounds) antioxidants under Ni stress, which is previously reported in response to heavy metal-stressed plants In conclusion, our results showed that TRIA foliar spray did not only alleviate the toxicity and oxidative stress imposed by Ni stress, but also provoked the growth to be comparable with that of the untreated plants. We propose three mechanisms by which TRIA express its effect: extrusion of Ni from roots, enhancing enzymatic and non-enzymatic antioxidants, and stimulating growth-related enzymes.