Regulation of seed dormancy and germination in Arabidopsis thaliana

Seed germination is one of the most important developmental steps in the life cycle of a higher plant. Because of this, seed producing plants have evolved mechanisms, such as dormancy, that time germination based on environmental cues. The present study uses Arabidopsis thaliana as a model to address questions about seed dormancy and germination. Three different lines of investigation were followed. The first involved an investigation of how light quality regulates phytohormones in order to control germination. This identified a light-dependent mechanism that differentially regulates expression of the ALLENE OXIDE SYNTHASE and OXOPHYTODIENOATE-REDUCTASE 3 genes resulting in accumulation of cis-12-oxo-phytodienoic acid (cis-OPDA) and repression of seed germination under FR conditions. The second line of investigation involved a re- examination of the role of the ABSCISIC ACID INSENSITIVE (ABI) 5 and ABI4 transcription factors in regulating seed germination and oil mobilization respectively. The study found that abscisic acid (ABA) is able to block testa rupture in nicked seeds and this involves the ABI5, but not the ABI4, transcription factor. Furthermore, it was found that ABI4 is involved in the repression of ABA and cis-OPDA biosynthesis in a light- dependent manner, but has only a minor role in regulating oil mobilization in seeds. The third line of investigation focused on the regulation of dormancy during after-ripening and found that changes in phytohormone levels over an extended period can account for changes in dormancy state.