Embryology of Barley III: Synergids and Pollen Tube Before and After Fertilization

Abstract

This study is a part of an investigation of details in the embryology of Hordeum vulgare cv. Bomi. Earlier investigations (Engell 1988a, 1988b) have been made on the fertilization and the embryo formation from the time of pollination and the next 3–4 days followed in details every minutes or hours, based on light microscopy (LM) studies of serial sections. This is a preliminary report of an investigation of the synergids before and after fertilization observed with LM as well as transmisssion electron microscopy (TEM). 48 hours before the stigma is receptive for pollen grains the synergids are cells of equal size, pyriformed and with a characteristically hooked shape. The persistent synergid preserves this shape more than 26–28 hours after pollination but the other synergid begins to degenerate between 20–0 hours before the pollination takes place. The nucleus disappears, the membranes of the organelles are more sensible for staining and the organelles are difficult to recognize. Thus in Hordeum vulgare cv. Bomi one of the synergids is degenerated before pollination, probably a necessity because of the short time interval (45 minutes) between pollination and fertilization. The cytoplasm of the degenerated synergid is pressed towards the periphery when the pollen tube contents is disharged in this cell. Because of rod-shaped starch grains only in the pollen tube it is easy to distinquish between pollen tube- and degenerated synergid contents. The egg cell as well as the central cell has many sphaerical starch grains in their plastids, whereas the persistent synergid has lots of plastids without starch grains. Remnants of the persistent synergid can still be seen as late as 50 hours after pollination.