Submitted to: Seed Science Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/12/1997
Publication Date: N/A
Citation: Interpretive Summary: Throughout the past ten years, considerable research has been devoted to determining the function of a series of proteins that are expressed during the latter stages of seed development and can constitute as much as 40% of the soluble protein in mature seeds. It has been suggested that these proteins (called late embryogenesis abundant or LEA) have a role in protecting cells from desiccation damage and that the mechanism of the protection involves the very hydrophilic nature of the proteins. The purpose of this paper was to document the hydration characteristics of LEA-ike proteins from wheat seeds. Our results suggest that a pure protein preparation is no more hydrophilic than common water-soluble proteins. However, we report that LEA proteins interact strongly with sugars, and are extremely hydrophilic in sugar mixtures. In combination with sugars, LEA proteins may function to buffer cells at critical hydration levels or may control the drying rate of seeds.
Technical Abstract: A heat-soluble extract from mature wheat embryos contains proteins and sugars at about a 1:1 (w/w) ratio. Many proteins in the heat-soluble fraction are late embryogenesis abundant (LEA) proteins that accumulate as the seeds mature and dry. About half of the sugars can be removed from the heat-soluble extract by exhaustive dialysis; the remaining sugars appear tightly associated with the proteins. The water sorption characteristics of dialyzed and undialyzed wheat heat-soluble fraction were compared with mixtures of other water-soluble proteins (bovine serum albumin, lysozyme or gluten) and sugars (sucrose and raffinose). At the same sugar content, the wheat heat-soluble protein preparation absorbed 2 to 3 times more water than a lysozyme/sucrose preparation. The drying rate for the wheat heat-soluble protein fractions was also unique compared to desorption rates of water-soluble protein/sugar mixes. While water-soluble proteins mixed with sugar dried either very rapidly (within 20 min) or very slowly (about 2 months) depending on the sugar content, desorption rates of the wheat heat-soluble protein preparations were intermediate (2 days to 10 days) and modulated by sugar concentration. Based on the assumption that the hydrophilic properties of wheat LEA heat-soluble proteins contribute to their function, we suggest that these proteins serve as hydration buffers. This proposed function for wheat heat-soluble proteins may be linked with the presence of sugars.