Giant fluctuations in strain rate as part of normal leaf growth

We report the effects of abrupt transitions of light intensity on the growth patterns and mechanical properties of young tobacco leaves. Changes in light intensity induce large variations in the leaf strain rate, which can be an order of magnitude larger than the average growth rates, and include both tissue expansion and shrinkage. These are accompanied by large changes in the tissue’s mechanical properties. Similar effects are observed in response to wind. We show evidence supporting the hypothesis that these effects originate from hydraulic mechanisms, i.e., variations in turgor pressure. In the context of growth patterns and growth regulation, we show giant fluctuations in strain rate to be a normal part of the growth process of leaves, which should be taken into account as a means for redistributing the stresses accumulated during the process of growth.