[Possibilities of the regulation of differential DNA activities in higher plants by histone]

[Studies of nucleic acids and protein metabolism during initiation of adventitious roots]

Changes in the metabolism of nucleic acids and proteins were followed during the initiation of adventitious roots of Cicer arietinum. During the first 24 h, several phases of activation of the metabolism were found. The use of inhibitors of RNA synthesis showed that an early phase of incorporation of precursors into RNA is essential for the initiation phenomena. This phase is more sensitive to inhibitors and activators (hormones) than all other phases. The rapid turn-over of RNA synthesized during the first 6 h and the inefficience of inhibitors after this time suggested that a stable (non-RNA) factor maintains the activation. This factor must be synthesized soon after the stimulus of cutting.

[Isolation of auxins from the chromatin of regenerating pea seedlings]

Etiolated pea epicotyls were treated with IAA, NAA or 2,4-D for 48 hours. From the chromatin (purified by gel-chromatography) of the treated seedlings growth substances could be isolated which significantly promote growth of Avena coleoptiles. The isolated growth substances showed the same RF as the applied auxins. When the seedlings were treated for 48 hours either with auxin or with water only the extract from the auxin treated plants promoted Avena growth significantly. The ether extract from the auxin treated seedlings still had growth promoting effect when the seedlings were treated 24 hours with auxin and then 24 hours with water to remove most of the free auxin in the cells and in the cell walls.

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

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.

[Inhibition of root formation by acidic and neutral proteins from chromatin]

An acidic (Fs) and a nearly neutral (Fn) protein fraction were extracted from the chromatin of calf thymus and pea seedlings. Both fractions are able to combine with protein-free DNA to form a complex, which, however, has a lower thermal stability than a DNA-histone complex. Fs and Fn inhibit root initiation in a similar manner as histone, actinomycin-D, streptomycin and 5-bromouracil do when these substances are applied to regenerating pea epicotyls during different times after culture initiation.Oxidized and thermally denaturated Fs and Fn inhibit root initiation less than untreated proteins do. Furthermore the treated proteins act in a more specific way on special steps of development such as root differentiation or root growth. In a very similar manner inhibition of root regeneration is also restricted to special developmental steps by treatment of Fs or Fn with small amounts (1 μg/ml) of IAA, GS or KI at pH≧8. With increasing acidity of the chromatin proteins treatment with IAA diminishes the inhibition of root growth, whereas root differentiation is preserved.The results support the suggestion that acidic and neutral proteins of the chromatin may act as regulators of DNA-activity as histone does. During IAA-induced root formation Fs acts as an antagonist to histone, because these two protein fractions are specialized in their action by IAA treatment in a contrary manner.