Abstract
Low-temperature stress is a type of abiotic stress that limits plant growth and production in both subtropical and tropical climate conditions. In the current study, the effects of 24-epi-brassinolide (EBR) as analogs of brassinosteroids (BRs) were investigated, in terms of hormone content, antioxidant enzyme activity, and transcription of several cold-responsive genes, under low-temperature stress (9 °C) in two different tomato species (cold-sensitive and cold-tolerant species). Results indicated that the treatment with exogenous EBR increases the content of gibberellic acid (GA3) and indole-3-acetic acid (IAA), whose accumulation is reduced by low temperatures in cold-sensitive species. Furthermore, the combination or contribution of BR and abscisic acid (ABA) as a synergetic interaction was recognized between BR and ABA in response to low temperatures. The content of malondialdehyde (MDA) and proline was significantly increased in both species, in response to low-temperature stress; however, EBR treatment did not affect the MDA and proline content. Moreover, in the present study, the effect of EBR application was different in the tomato species under low-temperature stress, which increased the catalase (CAT) activity in the cold-tolerant species and increased the glutathione peroxidase (GPX) activity in the cold-sensitive species. Furthermore, expression levels of cold-responsive genes were influenced by low-temperature stress and EBR treatment. Overall, our findings revealed that a low temperature causes oxidative stress while EBR treatment may decrease the reactive oxygen species (ROS) damage into increasing antioxidant enzymes, and improve the growth rate of the tomato by affecting auxin and gibberellin content. This study provides insight into the mechanism by which BRs regulate stress-dependent processes in tomatoes, and provides a theoretical basis for promoting cold resistance of the tomato.
Highlights
The opposite was true for cold-tolerant species that received EBR treatment compared with the control under the low-temperature stress
The opposite was true for cold-tolerant species: in all cases (IAA, abscisic acid (ABA), GA3), treatment with EBR led species: in all cases (IAA, ABA, GA3), treatment with EBR led to a higher accumulation of to a higher accumulation of hormones in unstressed plants with respect to untreated ones, hormones in unstressed plants with respect to untreated ones, whereas it did not affect the whereas it did not affect the hormone concentration in stressed plants
The EBR application increased the content of endogenous ABA, and a synergetic interaction was observed between BR and ABA in response to low-temperature stress
Summary
Low-temperature stress in plants, categorized as freezing stress or chilling stress, is one of the main environmental stresses that adversely affects plant production across the world, especially in subtropical and tropical climate conditions. This environmental extreme is escalating due to global climate change and is, threatening sustainable crop production [1,2]. A low temperature negatively impacted plants, especially in regards to macromolecules activity, altering the fluidity of the membrane, and reducing osmotic
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