COMPUTATION OF MECHANICAL STRESS IN MELON (CUCUMIS MELO L.) HYPOCOTYLS DURING TRANSPLANT PRECONDITIONING BY BRUSHING

Pretransplant brushing is a recommended horticultural technique to control stem elongation. In melon (Cucumis melo L., inodorus group), when applied at fully expanded cotyledon stage (15 days after emergence) it promotes hypocotyl shortening and significantly improves postransplant performance. Thigmomorphogenesis has been attributed to the physiological response for fast developmental changes observed in the hypocotyl after its flexure by brushing. The mechanostimulus signal transduction pathway leading to thigmomorphogenesis is not yet well defined but it has been proposed that an efficient thigmo stimulus transport to growth centers should be present. In this contribution it is hypothesized that hypocotyl bending by brushing induces a significant mechanical stress at a vascular level. That would contribute to the rapid long distance intra-plant signaling transport. For validating this hypothesis, tensions generated on the surface and in the vascular tissues during bending by brushing were dynamically simulated, located, and calculated in a 3D model of the hypocotyl using the finite element method. From the simulation a significant high bending stress at the ground level parenchyma near the xylem and phloem was observed. The proximity of stressed cells to the phloem and xylem elements supports the hypothesis that mechanical stimulus cannot only act at the stem surface but at the vascular tissue level as well.