Priming memory invokes seed stress-tolerance

Seed priming is a pre-sowing treatment that partially hydrates seeds without allowing radicle emergence. Consequently, primed seeds are equipped with advanced germination and exhibit improved germination rate and uniformity. Moreover, seed priming is often implicated in improving the stress-tolerance of germinating seeds, cellular mechanism of which is not well understood. Here we propose a hypothetical model illustrating the cellular physiology of priming-induced stress-tolerance, likely achieved via two strategies. First, seed priming sets in motion germination-related activities (e.g. respiration, endosperm weakening, and gene transcription and translation, etc.) that facilitate the transition of quiescent dry seeds into germinating state and lead to improved germination potential. Secondly, priming imposes abiotic stress on seeds that represses radicle protrusion but stimulates stress responses (e.g. accumulation of LEAs), potentially inducing cross-tolerance. Together, these two strategies constitute a ‘priming memory’ in seeds, which can be recruited upon a subsequent stress-exposure and mediates greater stress-tolerance of germinating primed seeds.

► Seed-priming might improve seed stress-tolerance through ‘priming memory’, which is established during priming and can be recruited later when seeds are exposed to stresses during germination.
► ‘Priming memory’ may not be abolished by post-priming drying and is constituted by two strategies: advanced germination potential and cross-tolerance.
► Priming provides a ‘head-start’ of seed transition from quiescent to germinating state, thus increasing the germination potential.
► Priming imposes abiotic stress on seeds that represses radicle protrusion but stimulates stress-responsive elements conferring cross-tolerance.