Abstract
Hulless barley, grown in the Qinghai Tibet Plateau, has a wide range of environmental stress tolerance. Alternative pathway (AP) and hydrogen peroxide (H2O2) are involved in enhancing plant tolerance to environmental stresses. However, the relationship between H2O2 and AP in hulless barley tolerance to cadmium (Cd) stress remains unclear. In the study, the role and relationship of AP and H2O2 under Cd stress were investigated in hulless barley (Kunlun14) and common barley (Ganpi6). Results showed that the expression level of alternative oxidase (AOX) genes (mainly AOX1a), AP capacity (Valt), and AOX protein were clearly induced more in Kunlun14 than in Ganpi 6 under Cd stress; moreover, these parameters were further enhanced by applying H2O2. Malondialdehyde (MDA) content, electrolyte leakage (EL) and NAD(P)H to NAD(P) ratio also increased in Cd-treated roots, especially in Kunlun 14, which can be markedly alleviated by exogenous H2O2. However, this mitigating effect was aggravated by salicylhydroxamic acid (SHAM, an AOX inhibitor), suggesting AP contributes to the H2O2-enhanced Cd tolerance. Further study demonstrated that the effect of SHAM on the antioxidant enzymes and antioxidants was minimal. Taken together, hulless barley has higher tolerance to Cd than common barley; and in the process, AP exerts an indispensable function in the H2O2-enhanced Cd tolerance. AP is mainly responsible for the decrease of ROS levels by dissipating excess reducing equivalents.
Highlights
To explore whether H2 O2 is involved in enhancing hulless barley tolerance to Cd stress, the H2 O2 content was analyzed under Cd Stress by 3,3-diaminobenzidine (DAB)
These results indicated that Cd stress can significantly induce H2 O2 accumulation, which was significantly lower in Kunlun14 than that in Ganpi6, suggesting that Ganpi6 suffered more oxidative stress in comparison with Kunlun 14 under Cd stress
This study aimed to explore the physiological role of H2 O2 and alternative pathway (AP) in hulless barley response to Cd stress and the relationship between H2 O2 and AP in this process
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Cadmium (Cd), the third major contaminant to the environments, is seriously harmful to organisms, even human health [1,2]. Cd can affect plant growth and development, such as yellowing of leaves, necrosis of roots, inhibition of photosynthesis, changes of transpiration and respiration rate [3,4]. Cd can damage DNA and change protein structure [5]. The over-accumulated Cd can disrupt the redox homoeostasis and further result in oxidative stresses [6]. In order to reduce the toxicity of Cd, plants have developed a variety of defense mechanism [7]
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