FIGURE 2.

Proposed model of systemic long-distance signal transport in distant tissues of grafted vegetables. Grafting material: cucumber/pumpkin cotyledon-insertion grafts. Directionality: mineral elements and water acquired by the rootstock can be transported to the scion through the xylem; and plant hormones, some microRNAs, and proteins can be transported through the phloem rootstock–scion communication pathway in grafted vegetables. In addition, some binding proteins can transport RNAs. Selectivity: rootstocks of grafted vegetables will selectively absorb or reject mineral elements in the rhizosphere so as to achieve tolerance of grafted vegetables to high/low mineral element levels.