Abstract
Senescence is an important developmental process in the life span of a plant. It is affected by several endogenous and exogenous factors such as hormones, darkness, and drought. Hormones are major endogenous factors that affect senescence intensively. In this study, our aim was to investigate the effects of different plant growth regulators; benzyl adenin (BA), spermine (Spm) and spermidine (Spd) on both natural and dark-induced senescence and on γ-aminobutyric acid (GABA) content in wheat leaf segments. Following the incubation, fresh and dry weight, chlorophyll and carotenoid contents; peroxidase activity, soluble protein, GABA and malondialdehyde (MDA) contents and cell death amount were determined. Our results demonstrate that Spm and Spd accelerated senescence under light and delayed it under dark conditions. BA has delayed leaf senescence under both conditions. Cell death and MDA content showed a correlation with the senescence process. GABA content was enhanced considerably by BA, Spm and Spd applications under light conditions. According to our results we can conclude that Spm and Spd could promote senescence on wheat segments under light conditions, whereas inhibit senescence under dark conditions. In addition, BA could retard the deleterious effects on senescence under both light and dark conditions.
 
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 In press - Online First. Article has been peer reviewed, accepted for publication and published online without pagination. It will receive pagination when the issue will be ready for publishing as a complete number (Volume 47, Issue 4, 2019). The article is searchable and citable by Digital Object Identifier (DOI). DOI link will become active after the article will be included in the complete issue.
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Highlights
Leaf senescence is an important developmental process witnessed during the last stages of leaf development and characterized by catabolism (Woo et al, 2010)
In our study we found that Spm and Spd applications increased MDA content significantly under light conditions when compared to the control group
This study has demonstrated that the effect of Benzyl Adenine (BA), Spm and Spd on the senescence of wheat leaf segments under light and dark conditions
Summary
Leaf senescence is an important developmental process witnessed during the last stages of leaf development and characterized by catabolism (Woo et al, 2010). Abscisic acid (ABA), jasmonic acid (JA), and salicylic acid (SA) act as inducers of senescence, whereas cytokinins and gibberellins play important role in its suppression (Castillo and Leon, 2008). The application of exogenous cytokinins reduces the lipoxygenase activity and delays leaf senescence in the leaves of Uranium sativum L. The application of exogenous cytokinins reduces the lipoxygenase activity and delays leaf senescence in the leaves of Uranium sativum L. (Liu and Huang, 2002). Pan et al (2013) indicated that 6-Benzylaminopurine application alleviated the effects of senescence by improving antioxidant activity and they suggested spraying of BA to Oryza sativa L. to increase the grain yield
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