& Key message Adequate storability of black poplar (Populus nigra L.) seeds at temperatures below 0°C was associated with preservation of proteins of energy and carbohydrate metabolism, protein turnover, and proteins maintaining longterm stability of dehydrated tissue. & Context Understanding seed storability is a key factor for effective seed preservation and conservation. Black poplar is an endangered tree species and its seed loses rapidly viability during storage. & Aims The aim of this study was to determine, and functionally characterise, the proteins associated with storability of black poplar seeds. & Methods Dried seeds (7.1% MC) were stored at 3°C, − 3°C, − 20°C, and − 196°C, for a period of 12 and 24 months. Proteins were extracted and separated according to their isoelectric point (pI) and mass using 2-dimensional electrophoresis. Proteins that varied in abundance for temperature and time of storage were identified by mass spectrometry. & Results A germination test showed that seeds remained viable at − 3, − 20, and − 196°C. Storage at 3°C caused loss of seed viability. This loss in seed vigour was related to the largest changes in protein abundance. As storage temperature decreased, a smaller number of proteins displayed changed abundance. & Conclusion Good storability of black poplar seeds under freezing conditions may be associated with the following: an inhibition of synthesis of energy and carbohydrate metabolism and protein turnover proteins, LEA proteins that maintain long-term stability of dehydrated tissue, GDSL esterases/lipases that inhibit hydrolysing activity, and by chaperonins that protect protein functionality. Storage conditions influence the preservation of protein function that governs seed viability.