Abstract

The ARM repeat protein has emerged as a potential regulator of plant growth and development, yet its specific contributions to light dependent growth and abiotic stress responses remain poorly defined. This master’s thesis investigated the in-volvement of the ARM protein in Arabidopsis thaliana germination, seedling devel-opment, and tolerance to osmotic and hormonal stress by combining physiological, molecular, and interaction based approaches. Seed germination assays were per-formed with a range of abscisic acid (0–5 µM) and polyethylene glycol 6000 (15–20 %) concentrations, revealing that the arm 1 mutant displayed markedly lower germination percentages than the wild type Columbia ecotype under both light and dark conditions, indicative of hypersensitivity to abscisic acid (ABA) and simulated drought stress. Quantitative PCR analyses demonstrated arm 1 specific up regulation of key ABA signalling components, including a pronounced increase in ABI1 expression at 0.5 µM concentration of ABA, a significant induction of ABI8 at the same concentration, elevated ABF2 transcription at 1 µM ABA, and a transient rise in AtAHB6 at 0.5 µM ABA, highlighting altered hormonal feedback in the mutant background. Yeast two hybrid experiments confirmed physical protein interactions between ARM and spliceosome regulators STIPL1 and STIPL2, with interactions per-sisting across multiple stringency levels for STIPL2, thereby linking ARM to both RNA processing and circadian regulatory networks. Histochemical GUS and GFP re-porter analysis further showed leaf specific ARM expression under short day condi-tions, supporting a spatially regulated role in light controlled development. Collec-tively, these findings support a model in which ARM functions as a molecular integra-tor that couples RNA processing machinery with light and ABA signalling pathways to fine tune seed germination, seedling growth, and stress tolerance in Arabidopsis thaliana. …víceméně