Seed germination - The biochemical and molecular mechanisms

The chemical energy synthesized during photosynthesis as carbohydrates, lipids and proteins accumulates in seeds and provides a food source for animals. Seeds are also important genetic delivery systems essential for sustainable agriculture and environmental control. Genetic information in elite cultivars of crop species accumulated during breeding programs is distributed in the form of seeds. Ensuring successful germination and seedling establishment is a significant first step in agricultural production. The molecular and biochemical mechanisms of seed germination are not fully understood. Our knowledge of the interactions between the embryo, endosperm and testa has been advanced through tomato seed research, a model system for seed germination research. Recent discoveries using Arabidopsis thaliana have provided additional information about the molecular and genetic mechanisms of seed dormancy and germination. Genes expressed during seed development determine the size, shape and chemical properties of mature seeds and affect seed dormancy. In imbibed seeds, genes associated with hormone biosynthesis and degradation play critical roles in radicle emergence. The physical, chemical and physiological changes in the embryo, endosperm and testa, as well as the interactions between these tissues all contribute to successful germination. Recent literature on seed science research needs to be compiled to provide a clear picture for seed germination. Hypotheses to explain global mechanisms of seed germination are examined in this review.