Leaf movements and Darwin - A novel adaptive perspective on an old conundrum

Darwin (1880) proposed a role for nyctinastic circadian driven leaf movements in the conservation of meristemic heat. We have shown that in Arabidopsis thaliana, a highly r-strategist weed, such movements may play a novel role facilitating competition for light between individual plants through an action characterized by leaf overtopping. Experiments have been conducted investigating the adaptive role of this mechanism, in which wild type was put into direct spatial competition with the arrhythmic circadian clock mutant, lhy-1. Two different light regimes (16 hour day, 8 hour night and continuous light) were used in an effort to determine under which conditions competition, as measured by image analysis of leaf area from an aerial view, was maximized. It was found that the day/night cycle regime conferred a selective advantage on wild type. It consistently out-competed lhy-1, acquiring a total leaf exposure area that was at least 25% greater than lhy-1. Under continuous light conditions the advantage was gained by lhy-1 indicating that such an environment is negatively-selective with respect to circadian leaf movements. These experimental results compliment the findings of similar experiments conducted using arrhythmic circadian mutants of the cyanobacterium, Synechococcus elongates (Woelfle et al., 2004). These data are indicative of an adaptive role for circadian driven leaf movements in A. thaliana as a resource-seeking aid in competition.

Darwin, C.R., 1880. The Power of Movement in Plants. John Murray, London.

Woelfle, M.A., Ouyang, Y., Phanvijhitsiri, K., Johnson, C.H., 2004. Current Biology, 14, 1481–1486.