Ultrastructural changes during cryopreservation of plumules and embryos of coconut (Cocos nucifera L.)

This article aims to show the changes occurring during cryopreservation of embryos and plumules of coconut which are responsible of their death or survival. Embryos have been cryopreserved by preculture-dehydration for 24h, 28h, 30h, 34h, 38h and 48h on agar medium containing 600g/L of glucose combined with silica gel. The plumules were cryopreserved by encapsulation dehydration on solid medium containing 0.5 M, 0.75 M and 1M followed by dehydration with 40g of silica gel for different durations before rapid freezing. This study indicates that the damages undergone by seed samples can be divided into three types. The first stage of changes concerned the plasmolysis of cells with small vacuoles, condensation of chromatin, changing in the conformation of the DNA and the nucleus and stopping of mitosis. These types of changes are described in general in the context of a desiccation tolerance. The second degree of the changes was the retraction of the cytoplasm inside the cell, the increase in the periplasmic volume. The third degree of modification concerned the deformation of the walls, the invagination or the lysis of the plasma membrane resulting in the observation of distorted cells and and the bursting of the nucleus. These two types of modifications are irreversible and correspond to an absence of regrowth of the samples. Understanding the damage or changes that occur in cryopreserved cells is an important part of understanding how dehydration and frozen affect the viability of recalcitrant plants cells. These changes are made by dehydration and accentuated by freezing