Hormonal and Environmental Regulation of Seed Germination Rates

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Seed germination is a critical phase of the plant life cycle, both ecologically and agriculturally, and is sensitive to both endogenous hormones and environmental factors. A quantitative mathematical model has been developed to characterize the responses of seed germination to abscisic acid (ABA), gibberellins (GA), and water potential (psi). Single-gene mutations in tomato (Lycopersicon esculentum Mill.) resulting in deficiencies of ABA or GA have contrasting effects on dormancy, germination rates, and sensitivity to reduced psi. This project will utilize these mutant genotypes within the framework provided by the mathematical model to identify the biochemical processes controlling germination. Germination occurs when endosperm cell layers opposite the radicle tip weaken and separate to allow embryo expansion. Cell wall hydrolysis in this endosperm tissue and its relationship to germination rates will be investigated. The composition of tomato endosperm cell walls will be characterized, the substrates, products, and enzymes involved in cell wall hydrolysis will be identified, and the relationship of cell wall hydrolysis to tissue weakening will be critically analyzed in mutant and wild-type seeds. Extending the mathematical description of seed germination to the physiological and biochemical levels provides a powerful new method for studying the integration of regulatory controls in plant development.