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

Abstract

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) .

Graft Incompatibility

“…These graft-induced genetic changes occur only during "mentor" grafts, when the scion is maintained without leaves while the stock, having vigorous branches and leaves, serves as the DNA donor. Graft transformation ofthe scion occurs when chromatin masses migrate from the lignified cells of the stock's stem, through the vascular system, and are incorporated into new cell nuclei at the active primordia of the scion (Ohta 1991).…”

Studies of Grafts in vegetables, an alternative for agricultural production under stress conditions: Physiological responses

“…Recently it was observed that grafted plants of beans had similar characteristics to non-grafted ones, however, factors such as plant height, number of leaves and lowers increased in plants grafted 28 days after the graft (DDI) Bernal-Alzate et al [27],these modi ications can be mediated by the production of growth regulators from the root transported via xylem to the aerial part of the plant [28,29]. On the other hand Kudo and Harada [30], observed how the morphology of the leaves of potato plants were modi ied due to the transport of RNA from the tomato rootstock towards the aerial part, determining that the amount of genetic material transported was enough to modify size, shape and quantity of trichomes in the leaves of grafted plants, these and other types of morphological changes have been documented by other researchers [31][32][33].…”

Effects of Cutting after Grafted on Nutrient Uptake of Nasturtium officinale under Selenium Stress

“…Some studies indicate that grafting can limit the uptake of heavy metals in shoots of plants, and increase the absorption of nutrients [5]. Grafting causes the exchanges between the scion and rootstock of two different plants species [6][7], which also leads to the transfer and integration of the genetic material of the rootstock and scion [8][9][10]. These studies provide a theoretical basis for cutting after grafted to affect plant nutrient uptake under stress conditions.…”