Signalling in seed stress response: eustress versus distress

Abstract

Seed treatment with cold plasma (CP) or electromagnetic field (EMF) is a modern eco-agricultural technology for stimulation of plant agricultural performance. Numerous studies demonstrated that such treatments can be effective for enhancing agronomic seed ąuality, however the results are controversive and the molecular basis of plant response to seed treatments remains elusive. The majority of performed studies in this area are focused on assessment of CP and EMF effects on physiological (germination), structural (changes in seed coat suface) and morphometric (early seedling growth) estimates It is commonly expected that positive effects on germination correlate with further enhancement of plant growth, biomass production, shortened harvesting time and higher yields. By long time observations on perennials we demonstrated that this dogma is invalid: negative effects on germination and early growth (distress) can be later follovved by the improved plant performance (eustress) in comparison to the control plants. Our fmdings indicated that germination and early plant growth are important only as a part of early response to stress experienced by seed, but the received stress signal develops further and can result in different patterns of response on the later stages of seedling development. Although effects on germination are commonly used for the assessment of seed stress response, there was no attempt until now to estimate CP and EMF effects on the content of seed phytohormones that control of germination. We report that the extent of the observed effects on germination is dependent on seed dormancy status characterized by seed hormonai balance (the most important is ratio between absisic acid, ABA and gibberrelins, GA). Dormant R. sativus seed treatments induce rapid decrease in ABA/GA ratio indicating that CP and EMF are extremely powerful dormancy breaking agents. Shift in seed ABA/GA ratio was induced both by the capacitatively coupled plasma (at 200 Pa)