Molecular mobility in the cytoplasm: an approach to describe and predict lifespan of dry germplasm

Molecular mobility is increasingly considered a key factor influencing storage stability of biomolecular substances, because it is thought to control the rate of detrimental reactions responsible for reducing the shelf life of, for instance, pharmaceuticals, food, and germplasm. We investigated the relationship between aging rates of germplasm and the rotational motion of a polar spin probe in the cytoplasm under different storage conditions using saturation transfer electron paramagnetic resonance spectroscopy. Rotational motion of the spin probe in the cytoplasm of seed and pollen of various plant species changed as a function of moisture content and temperature in a manner similar to aging rates or longevity. A linear relationship was established between the logarithms of rotational motion and aging rates or longevity. This linearity suggests that detrimental aging rates are associated with molecular mobility in the cytoplasm. By measuring the rotational correlation times at low temperatures at which experimental determination of longevity is practically impossible, this linearity enabled us to predict vigor loss or longevity. At subzero temperatures, moisture contents for maximum life span were predicted to be higher than those hitherto used in genebanks, urging for a reexamination of seed storage protocols.