Hydration of Cuphea seeds containing crystallized triacylglycerols

Authors: Volk, Gayle; Crane, Jennifer; Caspersen, Ann; Kovach, David; Gardner, Candice; Walters, Christina

Submitted to: Functional Plant Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2007
Publication Date: 4/1/2007
Citation: Volk, G.M., Crane, J., Caspersen, A.M., Kovach, D.A., Gardner, C.A., Walters, C.T. 2007. Hydration of Cuphea seeds containing crystallized triacylglycerols. Functional Plant Biology 34:360-367.

Interpretive Summary: The USDA-Agricultural Research Service National Plant Germplasm System maintains many species with seeds that do not appear to survive under conventional -18C storage conditions. Native North and Central American Cuphea species are of interest to plant breeders since they have unique and unusual seed lipid compositions. The lipid composition of these seeds also affects the seed storage characteristics. Some species have seed lipids that crystallize when seeds are placed at -18C. This research demonstrates that these sensitive type seeds must be warmed to temperatures to greater than 35C to ensure lipids are in the fluid state before seed imbibition and germination. Damage, such as loss of lipid body compartmentation and protein body fragmentation, is visualized when seeds are imbibed at temperatures that maintain the lipids in the crystalline state. This damage cannot be reversed, even when seeds are redried before the damage can be visually detected. Results from this work reveal that the seeds of some species with cold-sensitive physiologies can be successfully placed into conventional –18C storage facilities as long as seeds are warmed to greater than 35C prior to germination.

Technical Abstract: Seeds that exhibit intermediate storage behavior do not appear to survive under conventional -18C storage conditions. Cuphea wrightii, C. laminuligera, C. carthagenensis, and C. aequipetala are considered sensitive to low temperature storage. The seeds of these species have triacylglycerols (TAG) that are crystalline at –18C and melt when the seeds are warmed to >35C. In contrast, seeds of tolerant species, C. lanceolata and C. hookeriana, have TAG that crystallize at temperatures below -18C and are fluid at 22C. Imbibition of Cuphea seeds containing crystalline TAG fail to germinate and exhibit visual damage. Germination will proceed normally when dry seeds are warmed adequately to melt the TAG prior to imbibition. Reduced germination and cellular disruption including loss of lipid body compartmentation and fragmented protein bodies develop in seeds with crystalline TAG equilibrated to >0.1 g H2O•g dw-1. This damage cannot be reversed, even when seeds are dried before the damage can be visually detected. Results from this work reveal that the seeds of some species with intermediate type physiologies can be successfully placed into conventional –18C storage facilities.