2019 ASHS Annual Conference

To understand how the temporal and spatial distribution of auxin regulates abscission, a DR5::GUS auxin reporter was employed to examine the auxin gradient in the pedicel abscission process in tomato. During the tomato flower development, DR5::GUS assay showed that GUS activity was predominantly detected in the vascular tissues and higher on the distal side than the proximal side, suggesting the ‘distal-to-proximal’ auxin gradient in the pedicel. This gradient was altered during different developmental stages. The lowest GUS activity was detected in the pedicel abscission zone at anthesis stage compared with 2 days before anthesis and 5 days after pollination stages, suggesting that anthesis stage is susceptible to abscission. Auxin depletion by flower removal or auxin transport inhibitor N-1-napthylphthalamic acid (NPA) treatment reduced auxin gradient across the abscission zones and enhanced the abscission process at anthesis. In addition, the pedicel abscission was triggered by high temperature and retarded by low temperature, accompanied by alterations of auxin gradient. The results from analysis of the DR5::GUS activity and auxin related gene expression indicated that the reduction of auxin activity occurred before pedicel shedding, and auxin reduction on the proximal side of pedicel may be crucial for abscission initiation.