STUDIES ON THE STRUCTURE OF RICE EMBRYO AND INITIAL STAGES OF RICE SEED GERMINATION

Abstract

When the pericarp and the seed coat covering the rice embryo have been removed, the ventral structures (viz. two ventral scales, the epiblast and the coleorhiza) ensheathing the embryo become exposed. At the point where the tip of the coleoptile, the two ventral scales and the epiblast are situated, there is an inverted "Y" shaped gap (or "coleoptile protrusion lacuna"). The initial stages of rice seed germination, under aerated conditions, involve the following sequence of events: The ventral scales, the epiblast and the coleorhiza first swell. The swelling of the ventral scales, the epiblast and the coleorhiza then slit open the pericarp and the lemma, thus allowing the ventral scales and the coleorhiza to protrude out of the pericarp and lemma slits. After the lemma has opened up, the coleoptile then begins to grow out of the inverted "Y" shaped gap and the lemma slit. This is then followed by the radicle, which unlike the coleoptile has to break through the coleorhiza first before protruding out of the lemma slit. Once the radicle has penetrated through the coleorhiza, it then elongates faster than the coleoptile.During rice seed germination epidermal hairs will develop on the ventral scales, the epiblast and coleorhiza; but if the seeds germinated were submerged in wator, then no epidermal hairs would develop. For comparison, we have also looked at the ventral faces of the embryos of wheat and barley after the pericarp and the seed coat have been removed. In those two crop plants no ventral scales or inverted "Y" shaped gap are present.