[Changes in the nucleoprotein influenced by auxin and ascorbic acid in the course of root formation in pea epicotyls]

Abstract

The melting point (T m) of nucleoproteins in root forming pea epicotyls is lowered during the first 48 h after culture initiation. When histone is externally applied to the epicotyls during this period, the decrease of T m is greatly diminished. The T m declines with increasing IAA-concentrations. The lowering of the T m can be brought about also by binding of small amounts of IAA to reconstituted or native nucleoproteins at pH> 8,0 in vitro. Furthermore, IAA can diminish the T m of denatured and native DNA. Histone which is bound to small amounts of IAA is no longer able to inhibit root formation significantly after being applied to regenerating pea epicotyls. Therefore it appears that IAA can partly loosen the bindings of histone to DNA and the bindings of DNA to DNA in the double helix by direct binding to both components of the nucleoprotein. The association of IAA and nucleoproteids seems to be effected by ionic bonds.Like IAA, ascrobic acid also diminishes the binding capacity of histone to DNA in vitro, but in this process the structure of the DNA double helix does not become unstable. Upon being applied to regenerating pea epicotyls, ascorbic acid does not induce root formation itself, but it intensifies IAA-induced root formation when applied during the time of DNA-activity.The results are interpreted to mean that IAA acts as a true initiator of RNA-synthesis, whereas ascorbic acid probably intensifies otherwise induced DNA-activities by binding of excessive amounts of histone.