Structure and properties of sperm cells isolated from the pollen of Zea mays

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Abstract
Sperm cells can be isolated from maize pollen grains by gentle osmotic treatment. After the initial osmotic burst, the slurry is sieved through nylon mesh and then subjected to sucrose density gradient centrifugation to remove as much starch as possible. The isolated cells are spherical and approximately 7.2 μm in diameter, exclude Evans blue stain up to several hours at room temperature, and can be frozen and stored with reasonable retention of viability. Little alteration of the appearance of the living cells is seen after preparation for transmission electron microscopy. There is ultrastructural confirmation that maize sperm cells are protoplasts. Furthermore, there is no evidence of vegetative cell inner membrane on the outside of the sperms. Internally, there is a normal organelle complement including mitochondria, dictyosomes, protein bodies, and endoplasmic reticulum. The latter component is extensive and has associated ribosomes. Some coated vesicles occur in maize sperm protoplasts. Nuclear morphology is quite variable, including spherical, lobed, and irregular shapes.