Does growth correlate with turgor-induced elastic strain in stems? A re-evaluation of de Vries' classical experiments

The correlation between growth and turgor-induced elastic expansion was stu died in hypocotyls of sunflower (Helianthus annuus) seedlings under various growth conditions. Turgor-induced elastic cell wall strain was greater in hypocotyls of faster growing seedlings, i.e. in etiolated versus light-grow n ones. It also was higher in rapidly growing young seedlings as compared w ith nongrowing mature ones. However, analysis of the spatial distribution o f elastic strain and growth demonstrated that their correspondence was only apparent. Profiles of elastic strain declined steadily from the top of the hypocotyls toward the basis, whereas the profiles of relative elemental gr owth rate along the hypocotyls showed maxima within the growing zones. In c ontrast to earlier hypotheses, we conclude that turgor-induced elastic cell wall strain and growth do not correlate precisely in growing hypocotyls.