Abstract
How auxin transport regulates organ abscission is a long-standing and intriguing question. Polar auxin transport across the abscission zone (AZ) plays a more important role in the regulation of abscission than a local concentration of this hormone. We recently reported the existence of a spatiotemporal sequential pattern of the indole-3-acetic acid (IAA) localization in the area of the yellow lupine AZ, which is a place of flower detachment. In this study, we performed analyses of AZ following treatment with an inhibitor of polar auxin transport (2,3,5-triiodobenzoic acid (TIBA)). Once we applied TIBA directly onto the AZ, we observed a strong response as demonstrated by enhanced flower abscission. To elucidate the molecular events caused by the inhibition of auxin movement, we divided the AZ into the distal and proximal part. TIBA triggered the formation of the IAA gradient between these two parts. The AZ-marker genes, which encode the downstream molecular components of the inflorescence deficient in abscission (IDA)-signaling system executing the abscission, were expressed in the distal part. The accumulation of IAA in the proximal area accelerated the biosynthesis of abscisic acid and ethylene (stimulators of flower separation), which was also reflected at the transcriptional level. Accumulated IAA up-regulated reactive oxygen species (ROS) detoxification mechanisms. Collectively, we provide new information regarding auxin-regulated processes operating in specific areas of the AZ.
Highlights
Abscission is a developmentally programmed phenomenon that facilitates the shedding of damaged, senescent, or unnecessary organs, such as leaves, petals, or in some cases, infected parts of a plant
Fruit abscission in olive and melon is accompanied by down-regulation of genes encoding auxin receptors and transporters (transport inhibitor response 1 (TIR) and auxin efflux carriers (AEC)) [46,47]
The basipetal auxin movement prevents organ detachment, whereas its decay increases the sensitivity of the abscission zone (AZ) to ET [1,48]
Summary
Abscission is a developmentally programmed phenomenon that facilitates the shedding of damaged, senescent, or unnecessary organs, such as leaves, petals, or in some cases, infected parts of a plant. Regardless of the factor that induces abscission, this process always takes place in a specialized group of cells that form what is called an abscission zone (AZ) [3]. The most recent studies about organ abscission are mainly focused on the events that accompanied the activation of separation processes directly taking place in the AZ cells. Most of the abscission-induced genes are expressed directly in the AZ following the activation of the separation. The precisely regulated timing of organ detachment is determined by the metabolic activity of the AZ cells, which highly depends on the presence of phytohormones, including abscisic acid (ABA), ethylene (ET), and auxin [4,5]
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