Graft-transformation, the mechanism for graft-induced genetic changes in higher plants

Summary

In our previous report of a series of experiments involving ordinary grafting, virus-inoculated grafting and DNA treatment in Capsicum annuum L., we described the variants as well as gene analyses of individual variants, together with the characteristics of the graft-induced genetic changes obtained.

Microhistological analysis of the stock stems revealed that chromatin masses, stained to greenish blue and in various sizes and shapes, were moving through cell wall and intercellular space from the lignifying and dying cells, stained to lighter purplish brown, towards the vascular bundles (Fig. 1). I discussed the mechanisms of chromatin transfer from the stock dying cells through the vascular system across the graft-union to the growing point(s) of the scion (Fig. 3), and how that process causes transformation in the fast dividing scion flower primordia (Fig. 4).

The significance of chromatin translocation can be understood in the following way: Genetic information is never transmitted from the stock to the scion, unless a DNA molecule larger than a functional unit such as a gene translocates from the stock, and unless the DNA molecules per se are integrated into new cell nuclei of the scion. In other words, no transmission of genetic information will take place, if DNA molecules of the stock disintegrated to nucleotides, as when a protein molecule is digested into amino acids, and are utilized by the scion simply as raw material in the formation of new cell nuclei with its own DNA strand as template.

Also discussed were the significance of ‘mentor methods’, and the importance of distinguishing between horticultural graft and genetical graft (Fig. 2).