The Basis of Spartina Seed Desiccation Tolerance Using Comparative Proteomics.

While orthodox seeds can be stored dry, recalcitrant seeds die when dried. In studies of either recalcitrant seeds or germinating orthodox seeds, desiccation intolerance has been ascribed to physical damage, oxidative stress and/or a lack of protective molecules, particularly late embryogenesis abundant (LEA) proteins and sugars. A comparative approach between recalcitrant and orthodox species within the same genus would enhance our understanding of seed desiccation tolerance. Therefore, the physiology of orthodox Spartina species and recalcitrant Spartina alterniflora is studied in my lab. Historically reported symptoms associated with recalcitrance (embryo solute leakage, increased lipid oxidation, loss of antioxidants; protein carbonylation) were observed as Spartina alterniflora seeds were dried and died; however, viable seeds from orthodox Spartina species exhibited the same responses to drying. Comparative proteomics between S. alterniflora and orthodox Spartina seeds identified 38 heat-stable proteins that correlated with desiccation tolerance. When orthodox Spartina pectinata seeds germinate and lose desiccation tolerance, these proteins disappear or are greatly reduced in abundance. The identified proteins are LEAs, chaperones, moonlighting proteins such as glyceraldehyde-3-phosphate dehydrogenase, antioxidants, nucleic acid binding proteins, proteins associated cellular recycling, and protease inhibitors. Many of these proteins or expression of their genes have been associated previously with response to water stress and desiccation in various plant and non-plant species. These data suggest that seed desiccation tolerance is associated with a suite of protective proteins, rather than just the presence of LEAs.