Plants growing in nature often experience fluctuating irradiance. However, in the laboratory, the dynamics of photosynthesis are usually explored by instantaneously exposing dark-adapted plants to constant light and examining the dark-to-light transition, which is a poor approximation of natural phenomena. With the aim creating a better approximation, we exposed leaves of pea (Pisum sativum) to oscillating light and measured changes in the functioning of PSI and PSII, and of the proton motive force at the thylakoid membrane. We found that the dynamics depended on the oscillation period, revealing information about the underlying regulatory networks. As demonstrated for a selected oscillation period of 60 s, the regulation tries to keep the reaction centers of PSI and PSII open. We present an evaluation of the data obtained, and discuss the involvement of particular processes in the regulation of photosynthesis. The forced oscillations provided an information-rich fingerprint of complex regulatory networks. We expect future progress in understanding these networks from experiments involving chemical interventions and plant mutants, and by using mathematical modeling and systems identification and control tools.

• Keywords
• Pisum sativum, Fluctuating light, forced oscillations, pea, photosynthesis, photosystem I and II, proton motive force, regulation,
• MeSH
• Photosynthesis physiology   MeSH
• Photosystem I Protein Complex metabolism   MeSH
• Photosystem II Protein Complex * metabolism   MeSH
• Pisum sativum * metabolism   MeSH
• Plant Leaves metabolism   MeSH
• Plants metabolism   MeSH
• Light MeSH
• Electron Transport physiology   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Photosystem I Protein Complex MeSH
• Photosystem II Protein Complex * MeSH

A microscope for imaging of chlorophyll fluorescence kinetics was equipped with a chamber that allows the growth of an immobilised population of algae and their study under well-defined conditions. Single cells of the chlorococcal alga Scenedesmus quadricauda were grown and recorded for periods of whole cell cycles (up to 48 h) displaying a normal course of cell development. Heterogeneity in fluorescence yield among individual coenobia in the population and among different cells in one coenobium were analysed. Differences were observed both in the shape of Kautsky transients and in the modulation of fluorescence parameter values during the progress of the cell cycle. The extent of heterogeneity in fluorescence parameters was cell cycle dependent - in some phases of the cycle, the population was almost homogeneous, while distinct heterogeneity was observed, in particular between the protoplast division and the release of the daughter coenobia. The heterogeneity was not random but reflected developmental processes.

• MeSH
• Cell Cycle physiology   MeSH
• Chlorophyll metabolism   MeSH
• Chlorophyta cytology   metabolism   MeSH
• Microscopy, Fluorescence MeSH
• Photosynthesis physiology   MeSH
• Kinetics MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Chlorophyll MeSH