Variation of Diel Leaf Growth Cycles

For extreme situations it has been shown that alterations of the diel variation of carbohydrate metabolism can induce changes of the diel leaf growth pattern. In leaves of Populus deltoides that were exposed to a three-times elevated CO2-content, a strong, transient decay of growth rate was observed during the afternoon, which temporally coincided with a transient decrease of glucose content (Walter et al. 2005). An amplification of nocturnal growth activity was found in leaves of transgenic potato plants that showed an increased starch content at the end of the day (Kehr et al. 1998), indicating that the pool of transitory starch is of utmost relevance for nocturnal growth activity. A clear indication how carbohydrate metabolism affects diel leaf growth cycles was recently observed in Arabidopsis thaliana: Starch-free-mutant plants (stfl, Kofler et al. 2000) that do not possess a relevant pool of transitory starch showed much lower growth rates than wild-type plants at night, but were able to grow with comparable intensity to wild-type plants during the day (Wiese et al. 2007). Another hint at the important role of temporal availability of carbohydrates in the regulation of growth dynamics is given by the observation that CAM- and C4-plants mainly grow during the day when availability of carbohydrates is high due to the decarboxylation of malate, while C3-plants show growth maxima at night-day transition phases, when metabolites coming from transitory starch probably play an important role. The fact that the investigated C3-plants do not show an unequivocal diel leaf growth cycle demonstrates that a large number of factors affects the basic temporal pattern of leaf growth and shows the dimension of the challenge to come to a conclusive picture of the regulation of dicot leaf growth dynamics.

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