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 t o a controlled basal bending, had a reduced terminal primary elongation, in dicating mechanosensing and intra plant signalling. The 'intensity' of the growth response, as measured by the time to recover an elongation rate simi lar to the control, varied hugely between plants. However, no relation was found between the intensity of this response and the mechanical variables c haracterizing the global mechanical state of the stem. In this paper, a loc al analysis of mechanical state of each bent stem is performed in the conte xt of beam theory. The spatial distributions of local variables all along t he stem (curvature, bending moment, strains and stresses) are established. The validity of hypotheses underlying the mechanical analysis is demonstrat ed. To investigate the relationships between the mechanical stimulus and th e growth response, a novel biomechanical analysis based on spatial integrat ion of the mechanical stimulus is presented. It revealed that the mechanose nsing is local and scattered through the stem and that the variability of t he growth response is only explained by the integrals of the longitudinal s train field.