Treatment conditions and biochemical processes influencing seed priming effectiveness

A review of the scientific literature indicates osmotic priming (osmopriming) as the principal method of seed priming and polyethylene glycol (PEG) as the principal osmotic agent. An analysis of the available data across experiments carried out with different species under varying conditions showed an average 11% increase in percent germination and 36% shorter mean germination time (MGT) in primed vs. unprimed seeds. Moreover, in primed seeds MGT was less dependent on temperature, which is consistent with the effects expected from the treatment. Priming effects are mainly influenced by osmotic potential, temperature and time; major biochemical processes (repair of damaged DNA and RNA, preparation for cell division and increased antioxidant activity) are involved in treatment effects to an extent which is not fully ascertained in literature. A reduction of seed storage life is the major disadvantage of priming and the principal constraint to its diffusion, since dehydration to the initial moisture (drying-back) is needed to allow seed storage. Seed behaviour during drying-back, the role of the raffinose family oligosaccharides in cell membrane integrity and the expression of antioxidant enzymes in germinating seeds need to be further elucidated in a sufficient number of species, to promote a more reliable use of this technique.