Cytoplasmic physical state governs the influence of oxygen on Pinus densiflora seed ageing

Abstract

During desiccation, the cytoplasm of orthodox seeds solidifies in a glass with highly restricted diffusion and molecular mobility, which extend longevity. Temperature and moisture determine seed cellular physical state, and oxygen can promote deteriorative reactions of seed ageing. However, whether seed physical state affects O2-mediated biochemical reactions during ageing remains unknown. Here, we answered this question using oil-rich Pinus densiflora seeds aged by controlled deterioration (CD) at 45 {degrees}C and distinct relative humidities (RHs), resulting in a glassy (9 and 33% RH) or fluid (64 and 85% RH) cytoplasm. Regardless of CD regimes, the cellular lipid domain remained always fluid. Hypoxia (0.4% O2) prevented seed deterioration only in the glassy state, limiting non-enzymatic lipid peroxidation, consumption of antioxidants (glutathione, tocopherols) and unsaturated fatty acids, accompanied by decreased lipid melt enthalpy and lower concentrations of aldehydes and reactive electrophile species (RES). In contrast, a fluid cytoplasm promoted faster seed deterioration and enabled the resumption of enzymatic activities implicated in glutathione metabolism and RES detoxification, regardless of O2 availability. Furthermore, seeds stored under dry/cold seed bank conditions showed biochemical profiles similar to those of CD-aged seeds with glassy cytoplasm under normoxia. These findings are discussed in the context of germplasm management. Highlightlipid peroxidation occurred during seed ageing in the glassy state and, like viability loss, could be prevented by hypoxia. Seeds with fluid cytoplasm aged faster and irrespective of oxygen availability.