Abstract
Kenaf (Hibiscus cannabinus L.) with high tolerance to chromium (Cr) can be used in the phytoremediation of chromium-contaminated soil. However, the mechanisms of chromium accumulation and tolerance in kenaf are still unclear. A hydroponic experiment was taken to screen two kenaf cultivars with Cr tolerance among nine kenaf cultivars via a tolerance index. This is first time the ascorbate-glutathione (AsA-GSH) cycle and chloroplast structural changes involved in Cr tolerance of two kenaf cultivars are explored. This study indicated that enhancement of chromium concentrations reduced nine kenaf growth rates and plant biomass. In addition, in all the nine cultivars, the roots had higher Cr accumulation than the shoots. Cr-tolerant cultivar Zhe70-3 with the maximum tolerant index had the significantly higher enzymatic activities of ascorbate peroxidase (APX), glutathione reductase (GR), dehydroascorbate reductase (DHAR) and mono- dehydroascorbate reductase (MDHAR) in non-enzymatic antioxidant system compared to Cr-sensitive cultivar Zhe77-1. In addition, higher GSH and AsA contents and lower damages of chloroplast ultrastructure were observed in Zhe70-3 under Cr treatment. In conclusion, Cr stress can cause less oxidative stress and destruction of chloroplast ultrastructure in Cr-tolerant cultivar Zhe70-3, and the AsA-GSH cycle may play a crucial role in kenaf Cr tolerance.
Highlights
Chromium (Cr), an inorganic environmental contaminant in agricultural soil, is non-essential and toxic beyond a certain threshold level [1]
The toxic effects of chromium on the morphology and productivity are shown in the Supplementary
The root dry mass of all genotypes were insignificantly decreased under Cr stress compared with their controls, respectively, and the reduction rates of Zhe77-1 was 2.5 times that of Zhe70-3 (Table S2)
Summary
Chromium (Cr), an inorganic environmental contaminant in agricultural soil, is non-essential and toxic beyond a certain threshold level [1]. Chromium and its compounds were used in many industries, such as leather tanning, pigment manufacturing, metal finishing, drilling muds and electroplating cleaning agents, all of which can cause environmental Cr contamination [2,3,4]. Hexavalent chromium [Cr (VI)] and trivalent chromium [Cr (III)] are the most stable forms of Cr occurring in soil [5]. Cr (VI) is reduced to Cr (III) in soil [1,5]. Due to the seriousness of Cr pollution, it is necessary to identify practicable methods for the remediation of Cr-contaminated soil
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