Cryo-SEM observation of high lipid content seeds stored at low temperature

ALINE SCHNEIDER TEIXEIRA; LORENA DELADINO; ANTONIO D. MOLINA-GARCÍA

Congreso; 57th Meeting of the Society of Low Temperature Biology (SLTB); 2021

There is an increasing interest in extending the germplasm storage capabilities to a wider and more diverse cohort of plants, both wild and cultivated, with agricultural, biotechnological or diversity preservation aims. Among the candidates for preservation are some seeds characterized by both having a significant oil content and suffering unexpected storage aging. When seeds are stored at water contents and temperature conditions under the glass transition temperature of their aqueous solutions, the lack of mobility of water molecules is guaranteeing an absolute halt to any diffusion-driven chemical reaction, while at the same time, ice crystals (if under the freezing point) are not developed. These factors usually ensure indefinite preservation. Some fat-rich seeds, however, show unexplained aging and viability and germination decreases when stored in those conditions (Walters, 2004; Ballesteros & Walters, 2011). To gain some information on the causes of this storage-aging, oil-rich seeds (peanut: Arachis hypogeae and papaya: Carica papaya) were stored at a range of sub-cero temperatures, after equilibration at different relative humidities (RH). Their temporal evolution was studied by cryo-SEM, a technique that is able to differentiate between cells able to form ice crystals and vitrified ones (Teixeira et al., 2012, 2013). Seeds were transferred from storage conditions to the microscope stage quenched in liquid nitrogen, where they were fractured in situ and observed, after etching and metal-coating. The micrographs show volume and tissue structural changes (lipid phase reorganization, alterations of cell wall unions) that can be possible related to lipid changes during storage. This lipid evolution could be related to the aging behaviour observed, either through mechanical effects derived from crystallinity changes or via the release of fat bound water that could be an unexpected ice crystals source.