Abstract
Rapid light curves are one of the most widely used methods for assessing the physiological state of photosynthetic organisms. While the method has been applied in a range of physiological studies over the last 20 years, little progress has been made in adapting it for the new age of multi-parametric phenotyping. In order to advance research that is aimed at evaluating the physiological impact of multiple factors, the Phenoplate was developed: a simultaneous assessment of temperature and light gradients. It was used to measure rapid light curves of three marine microalgae across a temperature gradient and altered phosphate availability. The results revealed that activation of photoprotective mechanisms occurred with high efficiency at lower temperatures, and relaxation of photoprotection was negatively impacted above a certain temperature threshold in Tetraselmis sp. It was observed that Thalassiosira pseudonana and Nannochloropsis oceanica exhibited two unique delayed non-photochemical quenching signatures: in combinations of low light with low temperature, and darkness with high temperature, respectively. These findings demonstrate that the Phenoplate approach can be used as a rapid and simple tool to gain insight into the photobiology of microalgae.
Highlights
Methods based on variable chlorophyll a fluorescence for assessment of physiological status in photosynthetic organisms have been the preferred techniques for over 50 years of research in plant and micro algal studies [1] The measurement directly probes the photosynthetic machinery of the cell, Photosystem II (PSII), as well as Photosystem I (PSI) to a certain extent [2]
Data generated by the rapid light curve were used to create surface plots to visualise the relationship between temperature and relative electron transfer rates (rETR) under P-replete conditions
For all three microalgal species, the highest rETR measured was observed at 30 ◦C, for at least one light intensity, but this light intensity varied between the species
Summary
Methods based on variable chlorophyll a fluorescence for assessment of physiological status in photosynthetic organisms have been the preferred techniques for over 50 years of research in plant and micro algal studies [1] The measurement directly probes the photosynthetic machinery of the cell, Photosystem II (PSII), as well as Photosystem I (PSI) to a certain extent [2]. The instruments used were initially built by the researchers themselves, but gradually commercial versions became available. One such instrument is the WALZ Imaging PAM [9], which measures chlorophyll a fluorescence via a charged-couple device (CCD) camera. Other commercial [10] and custom built instruments [11] that perform similar measurements are available. The advantage provided by the imaging system is that multiple samples, or multiple areas of larger photosynthetic organisms, can be measured simultaneously and sample heterogeneity can be evaluated
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