Radicle expansion

Radicle Expansion—Cell Elongation or Cell Division ... 

The activity of a soluble DNA polymerase in wheat embryos starts to increase during the first six hours after imbibition commences and continues to do so for at least the 1st day [91]. DNA replication occurs after radicle expansion, some 15 h after the initial hydration of the embryo [90]. The polymerase appears to be synthesized de novo during germination, for if protein synthesis is inhibited during the first nine hours then subsequent DNA synthesis is inhibited. Inhibition of protein synthesis at times after nine hours is progressively less effective in preventing DNA synthesis, presumably indicating that critical levels of the polymerase are synthesized prior to the ninth hour. 

A developing embryo produces ABA, which incepts and maintains mature seed dormancy. Germination begins with the uptake of water by imbibition of the dry seed and is followed by embryo expansion. Usually, it is considered complete when the radicle is through all the covering layers. There is still controversy whether... 

Light microscopy of radish radicles from a control seed after 16 h imbibition (a, c) and from a seed treated with 1 14-diluted reverse osmosis fraction, 46 h after imbibition. The root from the treated seed (b) is much shorter and coarser than the control (a). Cell expansion is strongly inhibited in the treated root (d) relative to the control (c). 

Fig. 6.27. Changes in protein (o), lipid (x), total chlorophyll a and b ( ), a-cellulose (hatched bar) and hemicellulose/starch (unhatched bar) content per cotyledon during germination and seedling development in Lupinus albus. R time of radicle elongation H time of hypocotyl expansion L time of expansion of first leaves and plumule. Germination is epigeal. Based on Parker, 1975 [115]...

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