Introduction: Phytohormones, molecular biology, and the “real world” of early seedling ecology

The seedling stage is arguably the busiest phase in a plant's lifetime. A miniscule individual, possessing only a rudimentary cotyledon and radicle, must quickly make its way in the world before a host of environmental challenges and larger competitors bully it out of existence. The maternal reserves from the seed must be mobilized to provide the fuel for producing the first pair of photosynthetically competent leaves and proliferating roots that will assimilate nutrients and firmly secure the seedling to its new home in the soil. These critical activities are initiated within minutes of germination, requiring a flurry of rapid signal transduction, protein synthesis, and tissue differentiation. To grasp how the seedling accomplishes all this demands an examination of physiological mechanisms that govern life after germination.

Studies at the molecular level are making great headway in understanding the complex and fascinating physiological events that mark the early infancy of plants. Phytohormones (a broad term that encompasses a range of organic and polypeptide compounds) are increasingly recognized as the primary integrators of environmental signals that enable the nascent seedling to evaluate and adjust to existing conditions. Biologists working across the spectrum of organizational levels – from cells to trees, from genes to populations – are now in an exciting position to elucidate how phytohormones modulate phenotype, and seedlings from a variety of taxa are natural model systems for study and synthesis (Table 7.1).