Melatonin-mediated photosynthetic performance of tomato seedlings under high-temperature stress

• Published in: Plant physiology and biochemistry Vol. 167; pp. 309 - 320
• Main Authors: Jahan, Mohammad Shah, Guo, Shirong, Sun, Jin, Shu, Sheng, Wang, Yu, El-Yazied, Ahmed Abou, Alabdallah, Nadiyah M, Hikal, Mohamed, Mohamed, Mostafa H.M., Ibrahim, Mohamed F.M., Hasan, Md. Mahadi
• Format: Journal Article
• Language: English
• Published: Elsevier Masson SAS 01-10-2021
• Subjects: CO2 assimilation; High temperature; Melatonin; Photosynthesis; Photosystem I and II; Tomato; CO2 assimilation; Melatonin; High temperature; Photosynthesis; Tomato; Photosystem I and II
• ISSN: 0981-9428; 1873-2690
• DOI: 10.1016/j.plaphy.2021.08.002

Photosynthesis is a fundamental biosynthetic process in plants that can enhance carbon absorption and increase crop productivity. Heat stress severely inhibits photosynthetic efficiency. Melatonin is a bio-stimulator capable of regulating diverse abiotic stress tolerances. However, the underlying mechanisms of melatonin-mediated photosynthesis in plants exposed to heat stress largely remain elucidated. Our results revealed that melatonin treatment (100 μM) in tomato seedlings increased the endogenous melatonin levels and photosynthetic pigment content along with upregulated of their biosynthesis gene expression under high-temperature stress (42 °C for 24 h), whereas heat stress significantly decreased the values of gas exchange parameters. Under heat stress, melatonin boosted CO2 assimilation, i.e., Vc,max (maximum rate of ribulose-1,5-bisphosphate carboxylase, Rubisco), and Jmax (electron transport of Rubisco generation) and also enhanced the Rubisco and FBPase activities, which resulted in upregulated photosynthetic related gene expression. In addition, heat stress greatly reduced the photochemical chemistry of photosystem II (PSII) and photosystem I (PSI), particularly the maximum quantum efficiency of PSII (Fv/Fm) and PSI (Pm). Conversely, melatonin supplementation increased the chlorophyll a fluorescence parameters led to amplifying the electron transport efficiency. Moreover, heat stress decreased the actual PSII efficiency (ΦPSII), electron transport rate (ETR) and photochemical quenching coefficient (qP), while increasing nonphotochemical quenching (NPQ); however, melatonin reversed these values, which helps to fostering the dissipation of excess excitation energy. Taken together, our results provide a concrete insight into the efficacy of melatonin-mediated photosynthesis performance in a high-temperature regime.
•Melatonin increased photosynthetic pigment contents and CO2 assimilation of tomato seedlings exposed to heat stress.•Melatonin protected the photosystem II and photosystem I reaction center and reduced photoinhibition under thermal stress.•Melatonin enhanced photosynthesis efficiency by elevating the Rubisco and FBPase enzyme activities.•Melatonin treatment efficiently enhanced the heat-induced reduction of chlorophyll a fluorescence photochemistry.