Melatonin Pretreatment Confers Heat Tolerance and Repression of Heat-Induced Senescence in Tomato Through the Modulation of ABA- and GA-Mediated Pathways

Abstract

Heat stress and abscisic acid (ABA) induce leaf senescence, whereas melatonin (MT) and gibberellins (GA) play critical roles in inhibiting leaf senescence. Recent research findings confirm that plant tolerance to diverse stresses is closely associated with foliage lifespan. However, the molecular mechanism underlying the signaling interaction of MT with GA and ABA regarding heat-induced leaf senescence largely remains undetermined. Herein, we investigated putative functions of melatonin in suppressing heat-induced leaf senescence in tomato and how ABA and GA coordinate with each other in the presence of MT. Tomato seedlings were pretreated with 100 μM MT or water and exposed to high temperature (38/28°C) for 5 days (d). Heat stress significantly accelerated senescence, damage to the photosystem and upregulation of reactive oxygen species (ROS), generating RBOH gene expression. Melatonin treatment markedly attenuated heat-induced leaf senescence, as reflected by reduced leaf yellowing, an increased Fv/Fm ratio, and reduced ROS production. The Rbohs gene, chlorophyll catabolic genes, and senescence-associated gene expression levels were significantly suppressed by MT addition. Exogenous application of MT elevated the endogenous MT and GA contents but reduced the ABA content in high-temperature-exposed plants. However, the GA and ABA contents were inhibited by paclobutrazol (PCB, a GA biosynthesis inhibitor) and sodium tungstate (ST, an ABA biosynthesis inhibitor) treatment. MT-induced heat tolerance was compromised in both inhibitor-treated plants. The transcript abundance of ABA biosynthesis and signaling genes was repressed; however, the biosynthesis genes MT and GA were upregulated in MT-treated plants. Moreover, GA signaling suppressor and catabolic gene expression was inhibited, while ABA catabolic gene expression was upregulated by MT application. Taken together, MT-mediated suppression of heat-induced leaf senescence has collaborated with the activation of MT and GA biosynthesis and inhibition of ABA biosynthesis pathways in tomato.

Melatonin Ameliorates Thermotolerance in Soybean Seedling through Balancing Redox Homeostasis and Modulating Antioxidant Defense, Phytohormones and Polyamines Biosynthesis

“…Similar results were reported in kiwifruit seedlings [ 44 ] and basil plants [ 45 ] under salinity stress. In our experiments, pretreatment with 100 µmol MT also increased the endogenous MT level during heat stress ( Figure 5 ), consistent with Xu et al [ 25 ] and Jahan et al [ 46 ] in cucumber and tomato plants, respectively, during heat stress, and this could have contributed to augmenting the antioxidant defense mechanisms. The present study revealed a significant decrease in the PAs (Put, Spd, and Spm) due to heat stress.…”

Characterization of SlBAG Genes from Solanum lycopersicum and Its Function in Response to Dark-Induced Leaf Senescence

“…Finally, we can confirm that sufficient overexpression of SlBAG2 and SlBAG5b is beneficial for dark-induced stress tolerance. Although many efforts have been made to investigate senescence [ 39 , 55 ], the exact mechanisms underlying this event are not well understood [ 1 ]. Our evidence provides a clue for the function of these genes in the regulation of dark-induced, and probably natural, senescence [ 12 , 25 ].…”

“…Leaf senescence is a fine regulatory mechanism caused by multiple internal factors, such as cell death, plant hormones, nutrient deficiency, senescence related genes, and environmental factors, such as drought, high temperature, salinity, weak light and darkness, and so on [ 1 ]. The change of leaf color is the most obvious trait of leaf senescence, and the internal structure of leaves changes obviously during senescence, which is manifested in decreased chlorophyll content and abnormal chloroplast structure [ 1 ]. Therefore, the most significant feature of leaf senescence is the process of chlorophyll degradation.…”

The Crosstalk of Melatonin and Hydrogen Sulfide Determines Photosynthetic Performance by Regulation of Carbohydrate Metabolism in Wheat under Heat Stress

“…We still do not know how H2S affects carbohydrate metabolism under heat stress and its relationship with melatonin. Melatonin is known as a biopromoter as it regulates numerous physiological methods and improves heat stress resistance in plants [74,75]. It is a small molecular weight indoleamine hormone explicitly being measured as a candidate phytohormone due to its various responses under biotic and abiotic stresses.…”