Plants grow on soils that not only provide support for root anchorage but also act as a reservoir of water and nutrients important for plant growth and development. However, environmental factors, such as high salinity, hinder the uptake of nutrients and water from the soil and reduce the quality and productivity of plants. Under high salinity, plants attempt to maintain cellular homeostasis through the production of numerous stress-associated endogenous metabolites that can help mitigate the stress. Both primary and secondary metabolites can significantly contribute to survival and the maintenance of growth and development of plants on saline soils. Existing studies have suggested that seed/plant-priming with exogenous metabolites is a promising approach to increase crop tolerance to salt stress without manipulation of the genome. Recent advancements have also been made in genetic engineering of various metabolic genes involved in regulation of plant responses and protection of the cells during salinity, which have therefore resulted in many more basic and applied studies in both model and crop plants. In this review, we discuss the recent findings of metabolic reprogramming, exogenous treatments with metabolites and genetic engineering of metabolic genes for the improvement of plant salt tolerance.

Verticillium wilt caused by Verticillium dahliae is a serious vascular disease in cotton (Gossypium spp.). V. dahliae induces the expression of the CAROTENOID CLEAVAGE DIOXYGENASE 7 (GauCCD7) gene involved in strigolactone (SL) biosynthesis in Gossypium australe, suggesting a role for SLs in Verticillium wilt resistance. We found that the SL analog rac-GR24 enhanced while the SL biosynthesis inhibitor TIS108 decreased cotton resistance to Verticillium wilt. Knock-down of GbCCD7 and GbCCD8b genes in island cotton (Gossypium barbadense) decreased resistance, whereas overexpression of GbCCD8b in upland cotton (Gossypium hirsutum) increased resistance to Verticillium wilt. Additionally, Arabidopsis (Arabidopsis thaliana) SL mutants defective in CCD7 and CCD8 putative orthologs were susceptible, whereas both Arabidopsis GbCCD7- and GbCCD8b-overexpressing plants were more resistant to Verticillium wilt than wild-type (WT) plants. Transcriptome analyses showed that several genes related to the jasmonic acid (JA)- and abscisic acid (ABA)-signaling pathways, such as MYELOCYTOMATOSIS 2 (GbMYC2) and ABA-INSENSITIVE 5, respectively, were upregulated in the roots of WT cotton plants in responses to rac-GR24 and V. dahliae infection but downregulated in the roots of both GbCCD7- and GbCCD8b-silenced cotton plants. Furthermore, GbMYC2 suppressed the expression of GbCCD7 and GbCCD8b by binding to their promoters, which might regulate the homeostasis of SLs in cotton through a negative feedback loop. We also found that GbCCD7- and GbCCD8b-silenced cotton plants were impaired in V. dahliae-induced reactive oxygen species (ROS) accumulation. Taken together, our results suggest that SLs positively regulate cotton resistance to Verticillium wilt through crosstalk with the JA- and ABA-signaling pathways and by inducing ROS accumulation.

The influence of pulsed electric field (PEF) (0.5–2 kV/cm) treatment of wheatgrass (Triticum aestivumL.) seeds, with different water contents, on antioxidant metabolism in the resultant seedlings was investigated. Imbibing seeds to a water content of 45% or greater prior to PEF treatment increased the glutathione level and activities of superoxide dismutase, catalase, glutathione reductase, glutathione peroxidase and ascorbate peroxidase in the resultant seedlings, compared to untreated controls. Pre-culture of human intestinal Caco-2 cells with simulated gastrointestinal digests of electrostimulated seedlings enhanced the ability of Caco-2 cells to cope with H₂O₂-induced oxidative damage, determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and lactate dehydrogenase (LDH) release assays. The Caco-2 cell MTT and LDH assays correlated better with the increases in seedling glutathione content and antioxidant enzyme activities compared to the 2, 2-diphenyl-1-picrylhydrazyl (DPPH) total antioxidant capacity assay, an assay commonly used to determine the ability of plant extracts to protect cells from oxidative damage. These results demonstrate for the first time that PEF treatment of imbibed seeds can stimulate changes in metabolism in the resultant seedlings, increasing the bioprotective potential of their shoots/sprouts and hence value as functional foods.

The early stages of intertidal mussels, including the green-lipped mussel, Perna canaliculus, face both direct and indirect environmental threats. Stressors may influence physiological status and, ultimately, survival. An understanding of the nature of stress experienced is critical to inform conservation and aquaculture efforts. Here, we investigated oxidative stress dynamics in juvenile P. canaliculus in relation to emersion duration (1–20 h) and relative humidity (RH, 29–98%) by quantifying oxidative damage (protein carbonyls, lipid hydroperoxides, 8-hydroxydeoxyguanosine) and enzymatic antioxidants (superoxide dismutase, catalase, glutathione peroxidase and reductase). Mussels held in low RH during emersion experienced severe water loss (>70%), high mortality (>80%) and increased oxidative damage (35–45% increase compared to control conditions), while mussels held at high RH were not impacted, even after 20 h of air exposure. Following re-immersion, reoxygenation stress resulted in further increases in damage markers in mussels that had experienced dryer emersion conditions; protective action of antioxidants increased steadily during the 10 h re-immersion period, apparently supporting a reduction in damage markers after 1–5 h of immersion. Clearly, conditions during emersion, as well as duration, substantially influence physiological performance and recovery of juvenile mussels. Successful recruitment to intertidal beds or survival in commercial aquaculture operations may be mediated by the nature of emersion stress experienced by these vulnerable juveniles.