Jahan Mohammad Shah, Shu Sheng, Wang Yu, Hasan Md Mahadi, El-Yazied Ahmed Abou, Alabdallah Nadiyah M, Hajjar Dina, Altaf Muhammad Ahsan, Sun Jin, Guo Shirong
Key Laboratory of Southern Vegetable Crop Genetic Improvement in Ministry of Agriculture, College of Horticulture, Nanjing Agricultural University, Nanjing, China.
Department of Horticulture, Faculty of Agriculture, Sher-e-Bangla Agricultural University, Dhaka, Bangladesh.
Front Plant Sci. 2021 Mar 25;12:650955. doi: 10.3389/fpls.2021.650955. eCollection 2021.
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 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 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.
热胁迫和脱落酸（ABA）会诱导叶片衰老，而褪黑素（MT）和赤霉素（GA）在抑制叶片衰老中起关键作用。最近的研究结果证实，植物对多种胁迫的耐受性与叶片寿命密切相关。然而，关于热诱导叶片衰老，MT与GA和ABA信号相互作用的分子机制在很大程度上仍未确定。在此，我们研究了褪黑素在抑制番茄热诱导叶片衰老中的假定功能，以及在MT存在下ABA和GA如何相互协调。番茄幼苗用100μM MT或水处理进行预处理，并在高温（38/28°C）下处理5天（d）。热胁迫显著加速衰老、对光系统的损伤以及活性氧（ROS）的上调，从而产生基因表达。褪黑素处理显著减轻了热诱导的叶片衰老，表现为叶片黄化减少、Fv/Fm比值增加和ROS产生减少。添加MT可显著抑制 基因、叶绿素分解代谢基因和衰老相关基因的表达水平。在高温处理的植物中，外源施用MT提高了内源MT和GA含量，但降低了ABA含量。然而，多效唑（PCB，一种GA生物合成抑制剂）和钨酸钠（ST，一种ABA生物合成抑制剂）处理抑制了GA和ABA含量。在两种抑制剂处理的植物中，MT诱导的耐热性均受到损害。ABA生物合成和信号基因的转录丰度受到抑制；然而，在MT处理的植物中，生物合成基因MT和GA被上调。此外，MT处理抑制了GA信号抑制因子和分解代谢基因的表达，同时上调了ABA分解代谢基因的表达。综上所述，MT介导的对热诱导叶片衰老的抑制与番茄中MT和GA生物合成的激活以及ABA生物合成途径的抑制协同作用。
