Production, Translocation and Accumulation of Alkaloids in Tobacco Scions Grafted to Tomato Rootstocks.

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Abstract
Alkaloid yields and distribution patterns were investi-gated in the system tobacco scion-tomato rootstock. Consistent with earlier findings, yields were greatly lowered as a result of grafting with tomato rootstocks. Removal of the apical bud (topping) of the to-bacco scion led to a virtual restoration of alkaloid yields normal for the variety. Substituting a tomato bud for the apical bud of the tobacco scion gave intermediate yields. Defoliation of the tobacco scion did not reduce alkaloid yields. Most of the alkaloid of the tobacco scion was located in the graft union and in the stem immediately above the graft union. Such localization was not found in tomato scions grafted upon tobacco scions. Alkaloid was found in tomato stems and leaves below an approach-graft union with a topped tobacco scion grown on a tomato rootstock. Labelled (with tritium) nicotinic acid was not converted to nicotine in excised tomato scions that had grown atop tobacco scions. It is concluded that the principal site of alkaloid synthesis in the system tobacco scion-tomato rootstock is the graft union and the tobacco stem immediately above it. Some of this alkaloid is translocated upward to be deposited in leaf and stem higher on the plant Evidence from approach-grafting experiments is interpreted to mean that alkaloid can be translocated downward but that the graft union presents a barrier to such translocation. The possible nature of this barrier is discussed. It is indicated that the high alkaloid yielding capacity of the graft union and of the adjacent stem tissues is probably atypical. Thus, the direct contribution of the shoot to its own alkaloid content in intact tobacco plants is probably over-estimated when calculations are based upon the alkaloid yields of grafted plants.