Abstract
BackgroundLight/dark cycles are probably the most important environmental signals that regulate plant development. Light is essential for photosynthesis, but an excess, in combination with the unavoidable presence of atmospheric oxygen inside the chloroplast, leads to excessive reactive oxygen species production. Among the defense mechanisms that activate plants to cope with environmental stress situations, it is worth noting the ascorbate-glutathione cycle, a complex metabolic pathway in which a variety of photochemical, chemical and enzymatic steps are involved.ResultsWe herein studied the dynamic behavior of this pathway under light/dark conditions and for several consecutive days. For this purpose, a mathematical model was developed including a variable electron source with a rate law proportional to the intensity of solar irradiance during the photoperiod, and which is continuously turned off at night and on again the next day. The model is defined by a nonlinear system of ordinary differential equations with an on/off time-dependent input, including a parameter to simulate the fact that the photoperiod length is not constant throughout the year, and which takes into account the particular experimental kinetics of each enzyme involved in the pathway. Unlike previous models, which have only provided steady-state solutions, the present model is able to simulate diurnal fluctuations in the metabolite concentrations, fluxes and enzymatic rates involved in the network.ConclusionsThe obtained results are broadly consistent with experimental observations and highlight the key role played by ascorbate recycling for plants to adapt to their surrounding environment. This approach provides a new strategy to in vivo studies to analyze plant defense mechanisms against oxidative stress induced by external changes, which can also be extrapolated to other complex metabolic pathways to constitute a useful tool to the scientific community in general.Electronic supplementary materialThe online version of this article (doi:10.1186/s12918-015-0239-y) contains supplementary material, which is available to authorized users.
Highlights
Light/dark cycles are probably the most important environmental signals that regulate plant development
ASC and reduced glutathione (GSH) consumption was more meaningful, which led to higher levels of MDA, DHA and oxidized glutathione (GSSG) at noon. All these results indicate that plants displaying increased activity in the Calvin-Benson cycle will better resist excessive light, i.e., the Calvin-Benson cycle, besides providing sugars, is regenerating electron acceptors (NADP+ in the model) to represent chloroplast self-protection
In this paper, a mathematical model able to simulate the distribution of the electron flow from photosystem I (PSI) in the chloroplast, and the dynamics of the chemical and enzymatic reactions involved in the ASC-GSH pathway has been developed, which takes into account for the first time the succession of days and nights
Summary
Light/dark cycles are probably the most important environmental signals that regulate plant development. Light is essential for photosynthesis, but an excess, in combination with the unavoidable presence of atmospheric oxygen inside the chloroplast, leads to excessive reactive oxygen species production. The amount of sunlight that reaches the surface of our planet is not constant, but varies according to different factors such as time of day, season, altitude, latitude and atmospheric composition. When the light absorbed/light used for CO2 fixation ratio is above 1, the generation of reactive oxygen species (ROS) is greatly accelerated, which will lead to the inhibition of photosynthetic machinery. Under such conditions, plants can activate different protective mechanisms to Valero et al BMC Systems Biology (2016) 10:11
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