Saline-alkaline stress is a common problem in Akebia trifoliata cultivation. In this study, the enhancing effects of 5-azacytidine (5-AzaC) on the resistance of A. trifoliata to saline-alkaline stress and the underlying mechanisms were investigated. Plant height, stem diameter, biomass, root length, fresh weight of root, and root/shoot ratio of 6-month-old A. trifoliata seedlings were measured after saline-alkaline stress with or without 5-AzaC treatment. Moreover, the contents of photosynthetic pigments, malondialdehyde (MDA), H2O2, sodium, soluble sugar, and proline; activities of superoxide dismutase, peroxidase (POD), and catalase (CAT); and anatomical structures of root, stem, and leaf were assessed. Furthermore, comparative transcriptome sequencing was performed. The results demonstrated that growth and development of A. trifoliata were severely inhibited under saline-alkaline stress, suggesting that the seedlings were exposed to severe oxidative and osmotic stresses. Treatment with exogenous 5-AzaC could significantly relieve the symptoms of saline-alkaline stress in A. trifoliata. Under saline-alkaline stress, 5-AzaC could increase the stem diameter, biomass, root length, fresh weight of root, and root/shoot ratio and minimize damages to the anatomical structure. Moreover, absorption of Na+ was reduced; ionic balance was maintained; POD and CAT activities were significantly improved; proline and soluble sugar contents increased, and H2O2 and MDA contents decreased. Transcriptome analysis revealed that 5-AzaC functioned via regulating KEGG pathways such as plant hormone signal transduction, phenylpropanoid biosynthesis, photosynthesis, amino sugar and nucleotide sugar metabolism, and glutathione metabolism under saline-alkaline stress. Particularly, enhanced expression of genes from the auxin pathway in plant hormone signal transduction; the lignin synthetic pathway in phenylpropanoid biosynthesis; and photosystem II, photosystem I, photosynthetic electron transport, and F-type ATP pathway in photosynthesis may be related to 5-AzaC-induced saline-alkaline resistance. The results provided theoretical references for A. trifoliata cultivation in saline-alkaline soil and application of 5-AzaC to improve saline-alkaline tolerance in plants.

Woody plants have received considerable attention for the phytoremediation of heavy metal-contaminated soil. This study aimed to investigate the changes in antioxidant enzyme activity, macroelement uptake and microstructure of the woody plant Robinia pseudoacacia (black locust) for the phytoremediation of cadmium (Cd) and lead (Pb) co-contaminated soil based on dynamic sampling. The results show that black locust demonstrates strong tolerance in Cd and Pb co-contaminated soil. After 30-120 days of cultivation, the activities of superoxide dismutase, peroxidase and the macroelement (potassium [K] and calcium [Ca]) content in plant leaves significantly declined in response to Cd and Pb. However, after 160 d of cultivation, the antioxidant enzyme activities, chlorophyll, sulfhydryl and soluble protein contents, as well as Ca and magnesium content in plant leaves were returned to normal levels under the 40 mg kg(-1) Cd and 1000 mg kg(-1) Pb contaminated soil (CdPb3). Meanwhile, K content in plant leaves under the CdPb3 treatment was significantly (P < 0.05) increased by 68.9% compared with the control. Cadmium and Pb were primarily accumulated in black locust roots. Scanning electron microscope analysis indicated that the sieve tubes in the roots and stems of plant might block the transport of Cd and Pb. Transmission electron microscope analysis indicated that the number and volume of osmiophilic particles in plant leaves were increased and the cell walls were thickened in response to Cd and Pb stress. Path analysis further indicated that the growth of plant was related to macroelements uptake and physiological change (photosynthesis, antioxidant enzyme activity and chelation). Thus, black locust could effectively regulate the antioxidant defense system, macroelement absorption and microstructure to enhance plant tolerance to Cd and Pb stress. Moreover, black locust could maintain the normal urease, acid phosphatase and sucrase activities in the Cd and Pb co-contaminated soil. These findings suggest that black locust could be considered as a useful woody plant for the phytostabilization in Cd- and Pb-contaminated soil.

BackgroundGlobally, salinity poses a threat to crop productivity by hindering plant growth and development via osmotic stress and ionic cytotoxicity. Plant extracts have lately been employed as exogenous adjuvants to improve endogenous plant defense mechanisms when grown under various environmental stresses, such as salinity. This study investigated the potential of melatonin (Mt; 0, 50, and 100 mM) as an antioxidant and licorice root extract (LRE; 0.0 and 3%) as an organic biostimulant applied sequentially as a foliar spray on faba bean (Vicia faba L.) grown in cadmium (Cd)-contaminated saline soil conditions [Cd = 4.71 (mg kg- 1 soil) and ECe = 7.84 (dS m- 1)]. Plants not receive any treatment and sprayed with H2O were considered controls. The experimental treatments were laid out in strip plot in a randomized complete block design replicated thrice, where the LRE and Mt were considered as vertical and horizontal strips, respectively. Growth characteristics, photosynthetic pigments, nutrient uptake, physiology and metabolic responses, anatomical features, and yield were assessed.ResultsCadmium (Cd) and salinity-induced stress significantly altered leaf integrity, photosynthetic efficiency, total soluble sugars (TSS), free proline (FPro), total phenolic, DPPH, and total soluble proteins (TSP), non-enzymatic and enzymatic antioxidants, growth characteristics and yield-related traits. However, the application of LRE + Mt considerably improved these negative effects, with higher improvements were observed due to application of LRE + Mt100. Application of LRE + Mt significantly reduced hydrogen peroxide (H2O2) accumulation, lipid peroxidation and Cd content in leaves and seeds, all of which had increased due to Cd stress. Application of LRE + Mt significantly mitigated the Cd-induced oxidative damage by increasing the activity of reactive oxygen species (ROS) scavenging enzymes such as superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase, in parallel with enhanced ascorbate and reducing glutathione content. Exogenous application of LRE + Mt significantly increased osmolyte content, including FPro, TSS, and total phenols and mitigated Cd-induced reduction to considerable levels.ConclusionsOur findings showed that LRE + Mt increased V. faba plants' morphological, physiological, and biochemical properties, reducing Cd stress toxicity, and promoting sustainable agricultural practices.Clinical trial numberNot applicable.