Graduate student Auburn University Auburn, Alabama
Body of Abstract: Cytokinin (CK) is a well-known plant hormone involved in many aspects of plant growth and development. Importantly CK maintains leaf integrity during the senescence/aging stage by protecting chloroplast machinery from degrading and enhancing photosystem efficiency. CK is present in planta in a wide range of chemical isoforms, with differing levels of hormone activity, where base-forms are considered to be active while the N7- and N9- glucose-conjugated forms (NCKs) have been assumed to be inactive. Recent studies revealed that certain NCKs do have hormone activity to delay leaf senescence similar to their corresponding base forms; however, it is yet to be discovered how the NCKs do so on a molecular level. In this study, we explore the physiological and transcriptional distinctions between CK-bases and NCKs by conducting dark-induced senescence experiments on Arabidopsis leaves across a range of time intervals to investigate differences in developmental trajectories of senescence. Despite similarities in physiological patterns measured by examining PSII efficiency (or Fv/Fm), transcriptomic patterns were distinct between base form CKs and NCKs at different stages of senescence. Base forms predominantly regulate the expression of CK-responsive, senescence-related, photosynthesis-related, and Chl degradation genes during the earliest time points. While NCKs tend to regulate the expression of similar classes of these genes at later stages of senescence resulting in unique transcriptional patterns compared to base forms. Findings in this research provide an insightful understanding of the time-dependent dynamics of CK isoforms during senescence, highlighting their distinct roles in modulating key genes contributing to leaf senescence.