The physiology of seed germination
In temperate climates, most mature seeds, consisting of an embryo surrounded by endosperm and a seed coat (testa), are dispersed from the mother plant in a state of low moisture content (5-15%) and with metabolic activity at a standstill. Some physiologists have hypothesized that with regard to their structure, genetic information and macromolecular content, dry seeds are in a state of readiness to resume metabolism [6]. For germination to occur, quiescent seeds need only be hydrated under conditions that encourage metabolism, such as a suitable temperature and the presence of oxygen (Figure (Figure1).1). The uptake of water by the seed, which is considered to be a trigger for germination, and the metabolic processes that take place as a result, are described in Figure Figure1.1. Seed germination can be delayed by dormancy, a process that involves interactions between two plant growth factors, gibberellins (GAs) and abscisic acid (ABA) [7]. This overall picture results from fragmentary physiological and biochemical studies in numerous species and remains to be refined with information from model species.