The growth response of the stems of genetically modified tobacco plants (Nicotiana tabacum 'Samsun') to flexural stimulation

Genetically modified tobacco plants (Nicotiana tabacum 'Samsun') with antis ense cinnamyl alcohol dehydrogenase DNA, produce secondary xylem of a reduc ed tensile stiffness. These plants were grown alongside control plants. The stems of the plants were flexed or protected from flexing over a period of several weeks. The tensile moduli and second moments of areas of the diffe rent tissues inside the stems were measured and used to calculate the bendi ng stiffness of the plants. In tobacco, the cylinder of xylem was found to be the most important tissue in determining the bending stiffness of the pl ants. The thickness of the xylem tissue cylinder increased when plants were subjected to flexural stimulation. This increased the bending stiffness of the stems. The response to mechanical stimulation was found to be correlat ed with tissue strain and the genetically modified plants were able to exac tly compensate for the reduced modulus of their xylem tissue by increasing the thickness of the xylem tissue cylinder more than in control plants. (C) 1999 Annals of Botany Company.