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ABSTRACT

Plants are permanently exposed to rapidly changing environments, therefore it is evident that they had to evolve mechanisms enabling them to dynamically adapt to such fluctuations. Here we study how plants can be trained to enhance their photoprotection and elaborate on the concept of the short-term illumination memory in Arabidopsis thaliana. By monitoring fluorescence emission dynamics we systematically observe the extent of non-photochemical quenching (NPQ) after previous light exposure to recognise and quantify the memory effect. We propose a simplified mathematical model of photosynthesis that includes the key components required for NPQ activation, which allows us to quantify the contribution to photoprotection by those components. Due to its reduced complexity, our model can be easily applied to study similar behavioural changes in other species, which we demonstrate by adapting it to the shadow-tolerant plant Epipremnum aureum. Our results indicate that a basic mechanism of short-term light memory is preserved. The slow component, accumulation of zeaxanthin, accounts for the amount of memory remaining after relaxation in darkness, while the fast one, antenna protonation, increases quenching efficiency. With our combined theoretical and experimental approach we provide a unifying framework describing common principles of key photoprotective mechanisms across species in general, mathematical terms.

5. Concluding remarks

We have demonstrated that our current understanding of quenching processes can be converted into more general, mathematical terms and with the implemented theory we can reproduce the most critical behavioural features of short-term illumination memory. This memory is generated by the interaction of two components of NPQ, that were previously identified by many others. The slower one, accumulation of zeaxanthin, accounts for the amount of memory lasting after relaxation in darkness, while the fast one increases the efficiency of quenching. However, our experiments do not provide evidence for an acceleration of quenching activity by previous light exposure. Rather, we propose to explain the consistently lower F M in the first seconds of the second light period by accumulation of Zx only. Therefore, plants with active short-term memory of previously experienced light initiate their photoprotection with some head-start, but at the same speed. Moreover, our computational model supports hypotheses on why shadow-tolerant plants exhibit a higher quenching capacity. Together with this manuscript we provide all necessary files to repeat and perform further experiments in silico, therefore we encourage our readers to treat this adaptation as an example of how our model can be used to test hypotheses regarding NPQ in other, also less studied organisms. Further, because of its simplicity and easy adaptability, the model has the potential to support knowledge transfer from lab to field. Especially in combination with cheap and easy-to-use devices to measure photosynthetic parameters outdoors (such as MultispeQ designed by the PhotosynQ project [66]), our model provides a theoretical framework in which the multitude of data can be interpreted in a sophisticated way. Thus, it can serve as a bridge to understand in how far observations obtained under controlled lab conditions allow deriving conclusions about the behaviour in real, highly fluctuating, outdoor conditions. Therefore, its real usefulness will depend on the creativity of its users.