Breaking down the walls - a role for endo-beta-mannanase in release from seed dormancy?

Dormancy is imposed in some seeds by the tissues that surround the embryo, which act as a mechanical barrier to the emergence of the radicle. Thus it has been proposed that germination is completed following the production of hydrolases within the surrounding tissues: these are secreted into the cell walls, causing weakening and so allowing the radicle to break out. Mannose is a prominent component of the endosperm cell walls of dormant seeds of several species and, in these, production of endo-beta-mannanase has been suggested to be essential for germination. It is possible that this is the case in Datura ferox seeds, but evidence for a causal link between the enzyme and germination in seeds of tomato and lettuce is more equivocal.