Unraveling Cadmium Toxicity in Trifolium repens L. Seedling: Insight into Regulatory Mechanisms Using Comparative Transcriptomics Combined with Physiological Analyses

Abstract

Trifolium repens (T. repens) can accumulate significant amounts of heavy metal ions, and has strong adaptability to wide environmental conditions, and relatively large biomass, which is considered a potential plant for phytoremediation. However, the molecular mechanisms of T. repens involved in Cd tolerance have not yet been studied in detail. This study was conducted to examine the integrative responses of T. repens exposed to a high-level CdCl2 by investigating the physiological and transcriptomic analyses. The results suggested that T. repens seedlings had a high degree of tolerance to Cd treatment. The roots accumulated higher Cd concentration than leaves and were mainly distributed in the cell wall. The content of MDA, soluble protein, the relative electrolyte leakage, and three antioxidant enzymes (POD, SOD, and APX) was increased with the Cd treatment time increasing, but the CAT enzymes contents were decreased in roots. Furthermore, the transcriptome analysis demonstrated that the differentially expressed genes (DEGs) mainly enriched in the glutathione (GSH) metabolism pathway and the phenylpropanoid biosynthesis in the roots. Overexpressed genes in the lignin biosynthesis in the roots might improve Cd accumulation in cell walls. Moreover, the DEGs were also enriched in photosynthesis in the leaves, transferase activity, oxidoreductase activity, and ABA signal transduction, which might also play roles in reducing Cd toxicity in the plants. All the above, clearly suggest that T. repens employ several different mechanisms to protect itself against Cd stress, while the cell wall biosynthesis and GSH metabolism could be considered the most important specific mechanisms for Cd retention in the roots of T. repens.

Modulation of Steroid and Triterpenoid Metabolism in Calendula officinalis Plants and Hairy Root Cultures Exposed to Cadmium Stress

“…Cadmium toxicity is represented by the replacement of biogenic metals in the active centers of enzymes and the high affinity to the thiol groups of proteins, which inhibits enzyme activity [ 4 , 5 ]. Cadmium toxicity in plants is manifested by stunted growth and chlorosis; at higher concentrations, it can lead to growth inhibition and necrosis [ 6 , 7 ] as well as reduced photosynthetic activity by decreasing the chlorophyll content [ 8 ]. As soil is the main sink for heavy metals, plant roots are the most important organs in metal ion uptake and relocation.…”

“…As soil is the main sink for heavy metals, plant roots are the most important organs in metal ion uptake and relocation. Roots are also the first organs directly affected by cadmium damage, disturbing the normal physiological metabolism of the entire plant [ 7 , 9 ].…”

A Review of Research on the Use of Selected Grass Species in Removal of Heavy Metals

“…Genetic engineering is a promising technique to increase the effectiveness of phytoremediation. Compared to the traditional selection, this method is much faster, and it is also possible to use it to add hyperaccumulation genes to plants in terms of other parameters [72]. However, there are also disadvantages, as plant detoxification mechanisms are very complex and involve many genes, so it is necessary to genetically manipulate several genes to obtain the desired result, which takes a long time and rarely gives a favorable result.…”

Effects of acid and aluminum stress on seed germination and physiological characteristics of seedling growth in Sophora davidii

“…ROS accumulation under stress can lead to lipid peroxidation, damaging plant cell membranes. 39 S. davidii seedlings respond by enhancing antioxidant enzyme activity, such as SOD, POD, CAT, and APX, to mitigate oxidative stress. 40 With the decrease in pH, the activities of SOD, POD, CAT, and APX in the antioxidant enzyme system were inhibited and decreased, indicating that the acid-induced oxidative damage was greater than the scavenging effect of antioxidant enzymes, resulting in the peroxidation of membrane lipids in seedlings.…”