Biomechanical study of the effect of a controlled bending on tomato stem elongation: local strain sensing and spatial integration of the signal.

In a previous paper it has been demonstrated that tomato stems, submitted to a controlled basal bending, had a reduced terminal primary elongation, indicating mechanosensing and intra plant signalling. The 'intensity' of the growth response, as measured by the time to recover an elongation rate similar to the control, varied hugely between plants. However, no relation was found between the intensity of this response and the mechanical variables characterizing the global mechanical state of the stem. In this paper, a local analysis of mechanical state of each bent stem is performed in the context of beam theory. The spatial distributions of local variables all along the stem (curvature, bending moment, strains and stresses) are established. The validity of hypotheses underlying the mechanical analysis is demonstrated. To investigate the relationships between the mechanical stimulus and the growth response, a novel biomechanical analysis based on spatial integration of the mechanical stimulus is presented. It revealed that the mechanosensing is local and scattered through the stem and that the variability of the growth response is only explained by the integrals of the longitudinal strain field.