To study the stability of a transition section of a tunnel from soft to hard surrounding rock under seepage conditions, FLAC3D software was used to numerically simulate the transition section of the Laomushan Tunnel from the Shiqian to Yuping (Dalong) Expressways in Guizhou Province, China, and to explore different working conditions. The characterization of the tunnel seepage field, stress field, and displacement field and the analysis of the force of the primary lining support structure describe the influence of the seepage field on the stress field distribution and displacement field changes. The reliability of the calculation results is verified by comparison with displacement measurements collected during field monitoring. The design values of the primary support structure parameters of the transition section from soft to hard surrounding rock of the Laomushan Tunnel basically met the strength requirements. The research results provide references for the design and construction of similar projects.
Melatonin, a multifunctional signaling molecule, has been shown to play a significant role in response to abiotic stress. Several species have been reported to unveil melatonin’s effect on osmotic stress; however, the signal transduction mechanism of phytohormone-mediated melatonin biosynthesis in plant species remains unclear. In this study, although plants can biosynthesize melatonin, the exogenous application of melatonin to watermelon cells can improve cell growth in response to osmotic stress by regulating the antioxidant machinery of cells. Regarding the melatonin synthesis pathway, ClOMT (ClASMT and ClCOMT) is a multi-gene family, and ClSNAT has two members. Both ClOMTs and ClSNATs harbor the cis-elements in their promoter regions responding to various hormones. Among abscisic acid (ABA), methyl jasmonate (MeJA), and salicylic acid (SA), ABA treatment observably upregulated the expression of ClOMTs and ClSNATs, and the accumulation of melatonin with ABA treatment reached a level comparable to that with osmotic stress by mannitol treatment. Furthermore, when hormone biosynthesis inhibitors were added to cells before osmotic stress, the expression of ClOMTs and ClSNATs, as well as melatonin accumulation, were significantly suppressed with the ABA biosynthesis inhibitor. This study demonstrated the crucial role of melatonin biosynthesis in response to osmotic stress via plant hormone signal transduction. It showed that ABA signaling plays a dominant role in melatonin synthesis under osmotic stress.
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