Cytological and physiological changes related to cryotolerance in orthodox maize embryos during seed development

Cytological and physiological changes were studied in orthodox maize (Zea mays L.) embryos following the acquisition of cryotolerance to liquid nitrogen during seed development. It was found that the embryonic cells at radicle portion were hydrated at all stages investigated, but those at early stages contained fully functional organelles, which disappeared at last developmental stages, and reserve materials accumulated intensively during seed development. Total soluble sugar content in the embryos had a steady rise on fresh weight and moisture weight basis; meanwhile, soluble and heat-stable proteins increased progressively in their number and contents as embryos matured. These cytological and biochemical changes had good correspondence with acquisition of cryotolerance in maize embryos.