Developing physical seed priming as a practical tool for stress-resilient crop production

Seed priming is a common approach to improve germination and seedling stress tolerance. Most priming treatments involve imbibition of seeds in water or in solutions of different chemicals, followed by redrying seed before the completion of germination. Physical priming treatments based on various forms of radiation or non-thermal plasma, for example, are also possible. Physical priming has some advantages over imbibition-based priming treatments, including avoiding negative impacts on the longevity of primed seed. Physical priming has potential for applications in agriculture, but questions remain about mechanisms of action and the range of outcomes generated by different types of treatment. Here, we suggest potential mechanisms by which physical treatments might impact the future performance of seeds and seedlings, including physiochemical modifications of the seed coat, generation of reactive oxygen species, and DNA-damage responses. In particular, we discuss how biological responses may be triggered by treatment of dry seeds that lack significant metabolic activity. We also briefly consider downstream molecular and biochemical responses to physical priming in germinating seeds. We conclude our review by briefly reflecting on key steps required for effective commercial exploitation.