To elucidate the mechanism underlying the enhancement of salinity tolerance by tea polyphenols (TPs), we employed seedlings of the wheat cultivar Longchun 30 to explore the individual and combined effects of 150 mM sodium chloride (NaCl) and 25 mg L-1 (25) or 100 mg L-1 (100) TPs on growth parameters, element absorption and transport, as well as polyphenols including anthocyanin metabolism. Compared to the control, treatment with NaCl significantly reduced plant biomass, relative growth rate (by 62%), leaf area (by 61%), AS(K)(+), Na+ levels (by 38%), and AS(Ca2)(+), Na+ levels (by 54%) in wheat seedlings. Conversely, it led to an increase in TSK+, Na+ (by 88%) and TSCa2+, Na+ levels (by 257%). Moreover, the NaCl treatment diminished the antioxidant activity in the in vitro leaf extract, resulting in enhanced reactive oxygen species levels and oxidative damage in wheat leaves. Furthermore, the levels of total polyphenols (by 27%), flavonoids (by 31%), and anthocyanins (by 27%) in wheat leaves were markedly reduced under salt stress. This was accompanied by the down-regulation of the activities of 4-coumaroyl: CoA ligase (4CL), chalcone synthase, chalcone isomerase (CHI), flavanone-3-dioxygenase (F3H), dihydroflavonol reductase (DFR), and anthocyanidin synthase, along with the down-regulation of their gene expression. In contrast, individual TPs exposure resulted in weak, ineffective, or even opposite effects on most of these parameters. More importantly, the addition of TPs partly counteracted salinity-induced changes in these parameters, particularly by increasing total polyphenols, flavonoids, and anthocyanins levels, upregulating the activities of the aforementioned six enzymes, and enhancing the expression of Ta4CL, TaCHI, TaF3H, and TaDFR in wheat leaves under salinity stress. Additionally, the growth-promoting effect of 100 mg L-1 TPs on salinity-stressed seedlings was stronger than that of 25 mg L-1 TPs. Overall, TPs application significantly enhanced the growth of salinity-stressed wheat seedlings by improving K+ and Ca2+ absorption and elevating polyphenols, including flavonoids and anthocyanins levels. Moreover, the accumulation of anthocyanins in salinity-stressed wheat leaves induced by TPs was attributed to the up-regulation of the activities and gene expression of synthesis-related enzymes.

Silicon (Si) plays an important role in enhancing the tolerance of plants to biotic and abiotic stress in soil ecosystems. Root-lesion nematodes (Pratylenchus scribneri; RLNs) cause root damage and diseases that result in quality deterioration and economic loss. This study investigated the effects of Si application on maize plants and its interaction with RLN infection. We set up different treatments to evaluate the role of silicon application in maize root growth and RLN resistance. This study conducted analysis by combining measurements of the metabolism and root activity of maize under different conditions. The results suggested that Si application (0.5 g/kg) significantly promoted fresh shoot weight, plant height, SPAD value (chlorophyll content), and root activity of maize, regardless of RLN inoculation. The highest SPAD value was observed in the Si treatment, which was significantly higher than in the control (CK) and RLN (N) treatments. Analysis of enzyme activity revealed that nematode inoculation reduced catalase (CAT) activity and increased malondialdehyde (MDA) concentration, while Si application increased CAT activity and decreased MDA concentration. In the SiN treatment, there was increased CAT activity at 0, 12, 48, 72 and 96 h compared with the N treatment. In parallel, nematode inoculation increased phenylalanine ammonia-lyase (PAL), and polyphenol oxidase (PPO) activities, while SiN treatment further enhanced their activities. These findings indicate that Si application enhances maize resistance to nematode infection and improves plant growth and antioxidant defence mechanisms.