An ultrastructural study of embryo and endosperm development during in vitro culture of maize ovaries (Zea mays)

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Abstract
A culture method is described which allows the continuous supply of fresh liquid medium and which prevents the accumulation of toxic metabolites. Development of maize embryos and endosperm after various periods of in vitro ovary culture was studied by light and electron microscopy. Using this method the ultrastructural features of embryo development in vitro were similar to those of in vivo embryos. In contrast, the formation of endosperm was irregular with the absence of cellularization of the inner endosperm being frequent. In some cases, only the endosperm developed without any indication of embryo formation. In a calcium-depleted medium, embryo development was normal but again, endosperm formation was aberrant. No cells were formed in the central part of the endosperm and near the placental region degeneration took place, resulting in vacuoles with dark inclusions, clumps of rough endoplasmic reticulum membranes, and cellular breakdown. The events occurring after in vitro culture strongly resemble those taking place after intergeneric crosses or crosses between diploid and tetraploid strains. It is concluded that defective endosperm development is probably the main factor for the failure of embryo development.