Long-term effects of externally applied ABA on plant development

Pirko Jalakas, Hanna Hõrak
Institute of Technology, University of Tartu, Nooruse 1, Tartu, 50411, Estonia

Abscisic acid (ABA) is a well-known phytohormone involved in plant development from seed dormancy to reproduction phase, as well as in response to both biotic and abiotic stress. ABA’s role in stomatal closure is well-established, however, ABA also functions in stomatal development. Mutant analysis in Arabidopsis has shown that ABA deficiency and insensitivity lead to increased stomatal density. Here we explore the role of externally applied ABA in regulating stomatal development in emerging leaves of wild-type and ABA-deficient nced3nced5 double mutant. We sprayed ABA solution in different concentrations (0, 1, 5, 10, 25, and 50 µM ABA) on two-week-old plants for 10 consecutive days. After ABA treatment, plants treated with the higher concentrations of ABA, 25 and 50 µM, showed visibly reduced plant growth and damage both in wild-type and mutant. Lower concentrations of ABA resulted in rounder leaves in the nced3nced5 double mutant compared to mock-treated mutant plants. At the start of the bolting stage leaves 8 and 10 from each plant were sampled for stomatal impressions from both the adaxial and abaxial sides to determine the long-term effect of ABA treatment on stomatal developmental traits such as stomatal density, index, and ratio.