Circadian characterization of non-structural carbohydrate dynamics in the Caatinga pioneer tree Erythrina velutina during late seedling establishment

We carried out a circadian characterization of non-structural carbohydrate dynamics in the different organs of Erythrina velutina seedlings at late establishment. Seeds were incubated under controlled conditions for 9 days and then seedlings were hydroponically grown in a greenhouse for 8 days. Carbon dioxide uptake was measured in the cordiform leaves every 2 h during the daytime (12 h) and every 4 h during the night-time (12 h); seedlings were harvested every 4 h during the day-night cycle (24 h) to assess the contents of non-structural carbohydrates and the activities of amylases and invertases. Diel patterns of non-structural carbohydrate content were identified in the photosynthetic organs, in which the turnover of starch operated far from its depletion at dawn. In the heterotrophic organs, however, changes in the starch content over 24 h may have maintained the supply of soluble sugars, buffering transient fluctuations in carbon availability. Although it seems that amylase activity was not influenced by the circadian rhythm in the different seedling organs, diel patterns of invertase activity were recognized in the photosynthetic organs.