Supercooling ability in apple seeds as affected by temperature‐induced modifications in water relations in the seed parts

Abstract

Prolonged storage of apple fruits (Pyrus malus L. cv. Golden Delicious) at different temperatures (0, 12 and 35°C) decreased the water content in seed coats and endosperms, higher temperatures being much more effective than the lower (0°C) one. No effect of the temperature on the embryo hydration was found. However, a pronounced decrease in water potential in the embryos was observed during the first 9 weeks. The decrease was much faster and the water potential reached lower levels in embryos isolated from seeds pretreated with higher temperatures (12 or 35°C) than from cold‐pretreated (0°C) material. Higher temperatures of fruit storage also resulted in a decreased permeability of the embryo membranes to electrolytes and sugars. At the same time, membrane permeability to water was not modified. It is proposed that the previously observed occurrence of the discontinuous type of freezing in apple seeds (Nguyen and Kacperska, Physiologia Plantarum (X): 000‐000, 1989) is associated with the temperature‐induced dehydration of seed coat and endosperm, whereas a higher super cooling ability of the high‐temperature‐pretreated embryos is due to a decrease in the free energy of water in the system, and to the effective protection of embryo cells against heterogenous ice nucleation. The changes in water potential showed a high negative correlation with the embryo phospholipid content determined in the other work (Nguyen et al. Plant Physiol. Bio chem. 25: 697–703, 1987). Therefore, it is proposed that changes in matrix potential play an important role in the regulation of the water potential in the embryo cells.