Changes in Lipid Status and Glass Properties in Cotyledons of Developing Sunflower Seeds

Biochemical events involved in the acquisition of germinability and storability during orthodox seed development are well documented; however, the roles played by the physical organization of lipids and water are poorly characterized. The aim of this work was to determine, using a thermodynamic approach, whether changes in thermal properties of lipid reserves, and intracellular glasses might play a role in sunflower (Helianthus annuus L.) seed development. Triacyglycerols (TAGs) accumulated in cotyledons until the end of seed filling, which occurred 42 days after anthesis (DAA). Further seed development, leading to mature seed at 58 DAA, was mainly associated with an enlargement of lipid bodies without significant changes either in the lipid content or in their composition. When cooled to -100 degrees C, lipid reserves from cotyledons of mature seeds displayed alpha and beta' polymorphic crystalline structures; however, the ability to form alpha crystals, which was an indicator of lipid purity, progressively appeared during seed development. Characteristics of lipid melting confirmed that seed maturation drying was associated with changes in TAG physical organization. Cotyledon development was associated with an increase in the temperature of glass to rubber transition (Tg), thus suggesting a decrease in molecular mobility during maturation drying. This phenomenon was concomitant with an increase in raffinose content. Our results demonstrate that physical characteristics of lipid reserves and glasses of sunflower cotyledons are developmentally regulated and might play a role in acquisition of seed germinability and storability.