Search

Abstract Drought and salt stress are two important environmental factors that significantly restrict plant growth and reproduction. Malate dehydrogenase is essential to life as it is engaged in numerous physiological processes in cells, particularly those related to abiotic stress reactions. However, a complete understanding of MDH family members in kenaf is not clear yet. In this study, subcellular localization analysis and a yeast transcriptional activation assay revealed that HcMDH1 was localized in chloroplasts but had no transcriptional activation activity. When exposed to salt or drought stress, yeast cells expressing the HcMDH1 gene exhibit an increased survival rate. Overexpression of HcMDH1 in Arabidopsis increased seed germination rate and root growth when transgenic lines were exposed to varying concentrations of mannitol and NaCl. Subsequent physiological studies revealed that transgenic lines had higher concentrations of soluble carbohydrates, proline, and chlorophyll and lower concentrations of malondialdehyde (MDA) and reactive oxygen species (ROS). Furthermore, inhibiting HcMDH1 in kenaf using virus-induced gene silencing (VIGS) decreased salt and drought tolerance due to elevated ROS and MDA levels. In these silenced lines, the expression of six essential genes engaged in stress-resistance and photosynthesis, namely HcGAPDH, HcGLYK, HcFBA, HcFBPase, HcPGA, and HcLSD, is significantly altered under salt and drought stress. In summary, HcMDH1 is a complex and positive regulatory gene that plays a key role in regulating chlorophyll content, antioxidant enzyme activity and osmotic regulation under salt and drought stress, which may have implications for kenaf transgenic breeding. Graphical Abstract

IntroductionCadmium (Cd) is a highly toxic trace element that occurs in large quantities in agricultural soils. The cultivation of industrial crops with high phytoremediation potential, such as kenaf, could effectively reduce soil Cd contamination, but the mechanisms of toxicity, tolerance, and detoxification remain unclear.MethodsIn this study, the effects of different Cd concentrations (0, 100, 250, and 400 µM) on growth, biomass, Cd uptake, physiological parameters, metabolites and gene expression response of kenaf were investigated in a hydroponic experiment.Results and discussionThe results showed that Cd stress significantly altered the ability of kenaf to accumulate and transport Cd; increased the activity of hydrogen peroxide (H2O2), superoxide anion (O2−), and malondialdehyde (MDA); reduced the activities of superoxide dismutase (SOD) and catalase (CAT); and decreased the content of photosynthetic pigments, resulting in significant changes in growth and biomass production. Exposure to Cd was found to have a detrimental effect on the ascorbate–glutathione (AsA–GSH) cycle in the roots, whereas it resulted in an elevation in AsA levels and a reduction in GSH levels in the leaves. The increased content of cell wall polysaccharides under Cd stress could contribute to Cd retention in roots and limited Cd transport to above-ground plant tissues. Metabolomic analyses revealed that alanine, aspartate, and glutamate metabolism, oxidative phosphorylation, ABC transporter, and carbon metabolism were the major metabolic pathways associated with Cd stress tolerance. Cd stress increased gene expression of IRT1 and MTP1 in roots, which resulted in kenaf roots accumulating high Cd concentrations. This study extends our knowledge of the factors regulating the response of kenaf to Cd stress. This work provided a physiological and metabolomic perspective on the mechanism controlling the response of kenaf to Cd stress.