Proteomic Analysis of Desiccation Tolerance and Its Re-Establishment in Different Embryo Axis Tissues of Germinated Pea Seeds

The model of loss and re-establishment of desiccation tolerance (DT) in germinated seeds has been well developed to explore the mechanisms associated with DT, but little attention has been paid to the tissue variation in this model. Herein, we investigated DT in different embryo axis tissues of germinated pea seeds and its re-establishment by poly(ethylene glycol) (PEG) treatment and then employed an iTRAQ-based proteomic method to explore the underlying mechanisms. DT varied among the four embryo axis parts of germinated seeds: epicotyl > hypocotyl-E (hypocotyl part attached to the epicotyl) > hypocotyl-R (hypocotyl part attached to the radicle) > radicle. Meanwhile, PEG treatment of germinated seeds resulted in a differential extent of DT re-establishment in these tissues. Proteins involved in detoxification and stress response were enriched in desiccation-tolerant hypocotyls-E and epicotyls of germinated seeds, respectively. Upon rehydration, proteome change during dehydration was recovered in the hypocotyls-E but not in the radicles. PEG treatment of germinated seeds led to numerous changes in proteins, in abundance in desiccation-sensitive radicles and hypocotyls-R, of which many accumulated in the hypocotyls-E and epicotyls before the treatment. We hypothesized that accumulation of groups 1 and 5 LEA proteins and proteins related to detoxification, ABA, ethylene, and calcium signaling contributed mainly to the variation of DT in different tissues and its re-establishment.