Cytological and physiological changes in recalcitrant Chinese fan palm (Livistona chinensis) embryos during cryopreservation

摘要

Cytological and physiological changes during cryopreservation were investigated in Livistona chinensis embryos excised 42 weeks after flowering. Both dehydration and freezing caused numerous cellular ultrastructural alterations. Dehydration seriously impaired plasma membrane integrity, while freezing caused a further increase in electrolyte leakage. Damage to cellular ultrastructure and plasmalemma integrity had an inverse relationship with water content in unfrozen embryos and a positive relationship in frozen embryos. Changes in activity of antioxidant enzymes differed during cryopreservation. Dehydration and freezing had little effect on superoxide dismutase activity, although these treatments greatly reduced embryo viability. Activity of dehydroascorbate reductase (DHAR) and glutathione reductase (GR) changed only slightly during dehydration, but dehydration markedly decreased activity of ascorbate peroxidase (APX) and catalase (CAT). Freezing further decreased APX and GR activity but increased CAT activity in dehydrated samples. A novel DHAR isozyme was induced during the freeze-thaw cycle. Membrane lipid peroxidation was detected in the control embryos, and was promoted by both dehydration and freezing. The malondialdehyde (MDA) content in post-thaw embryos increased by a maximum of 30%. Thus, changes in viability of embryos were closely related to damage to cellular ultrastructure and plasmalemma integrity, but were not directly related to antioxidant activity nor MDA accumulation.