Uncovering the basis of viability loss in desiccation sensitive Trichilia dregeana seeds using differential quantitative protein expression profiling by iTRAQ

Abstract

Recalcitrant seeds, unlike orthodox types, are desiccation sensitive and hence, cannot be stored using conventional seed storage methods In this study, relative changes of protein expression in T. dregeana seeds during desiccation and hydrated storage (a short- to medium-term storage method) were analysed to understand the basis of their desiccation- and storage-induced viability loss. Isobaric Tags for Relative and Absolute Quantitation (iTRAQ) were used to compare (selected) protein expression levels across fresh, partially dehydrated and stored seeds. A total of 114 proteins were significantly differentially expressed in embryonic axes of fresh seeds and those seeds exposed to dehydration and hydrated storage (which exposed seeds to a mild dehydration stress). Proteins involved in protein synthesis were up-regulated in stored and dehydrated seeds, possibly in response to dehydration-induced repair processes and/or germinative development. A range of proteins related to antioxidant protection were variably up- and down-regulated in stored and dehydrated seeds, respectively. Additionally, a class I heat shock protein was down-regulated in dehydrated and stored seeds; no late embryogenesis abundant proteins were identified in both stored and dehydrated seeds; and storage and dehydration up-regulated proteins involved in the provision of energy for cell survival. The results suggest that dehydration- and storage-induced viability loss in recalcitrant seeds may be based on proteomic changes that lead to cellular redox imbalance and increased cell energy demands. This, together with the absence/down-regulation of proteins associated with desiccation tolerance in plant tissues may form part of the proteomic footprint for desiccation sensitivity in seeds.