Tissue Tensions during Cell Elongation in Wheat Roots and a Comparison with Contractile Roots

A study has been made of tissue tensions in growing Triticum roots. After the initial phase of elongation with both a lateral and an exponential longitudinal growth, the tissues are under strong longitudinal stress. Plasmolysis in situ or splitting of the root in the pericyclic region causes an increase in length of the perivascular part. Freed from the stele the perivascular part contracts on plasmolysis. During the following only longitudinal growth, the stress decreases under decreased root diameter. When elongation has ceased, the root in situ contracts on plasmolysis. It is suggested that during radial growth longitudinal stresses are built up, which are released when the stele catches up with the growth of the cortex. The similarity to conditions in contractile roots of Arum (Lamant and Heller 1967) is pointed out. A difference is found in the polarity of growth and thus in the mode of release of the stresses. The cause of the tensions and methodical difficulties are discussed.