Frequently asked questions about chlorophyll fluorescence, the sequel

[EN] Using chlorophyll (Chl) a fluorescence many aspects of the photosynthetic apparatus can be studied, both in vitro and, noninvasively, in vivo. Complementary techniques can help to interpret changes in the Chl a fluorescence kinetics. Kalaji et al. (Photosynth Res 122: 121-158, 2014a) addressed several questions about instruments, methods and applications based on Chl a fluorescence. Here, additionalChl a fluorescence-related topics are discussed again in a question and answer format. Examples are the effect of connectivity on photochemical quenching, the correction of F-V/F-M values for PSI fluorescence, the energy partitioning concept, the interpretation of the complementary area, probing the donor side of PSII, the assignment of bands of 77 K fluorescence emission spectra to fluorescence emitters, the relationship between prompt and delayed fluorescence, potential problems when sampling tree canopies, the use of fluorescence parameters in QTL studies, the use of Chl a fluorescence in biosensor applications and the application of neural network approaches for the analysis of fluorescence measurements. The answers draw on knowledge fromdifferent Chl a fluorescence analysis domains, yielding in several cases new insights.Kalaji, H.; Schansker, G.; Brestic, M.; Bussotti, F.; Calatayud, A.; Ferroni, L.; Goltsev, V.... (2017). Frequently asked questions about chlorophyll fluorescence, the sequel. 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Light absorption and scattering by high light-tolerant, fast-growing Chlorella vulgaris IPPAS C-1 cells

Algal cells are highly complex optical systems that can dynamically change their structure. Consequently, absorption and scattering properties of algae change, while the cells are acclimating to different light conditions or during growth and division in a cell cycle. This may be particularly important in algal species that can grow rapidly under very high-light such as Chlorella vulgaris IPPAS C-1 that is studied here. From cell transmittance measured conventionally and using integrating sphere, we evaluated absorption and scattering coefficients and cross sections per cell dry weight and chlorophyll content. This was done for asynchronous cell culture grown in low-light (LL; 220 μmol (photons) m−2 s−1) or high-light (HL; 1760 μmol (photons) m−2 s−1) light, as well as during cell cycle of synchronous culture grown in HL. During the cell cycle, we also determined cell ultrastructural organization by transmission electron microscopy, and correlated its parameters with absorption and scattering cross sections per cell dry weight. We found that the IPPAS C-1 cells of asynchronous culture scatter light more than other cells, however, internal organization of the cells that is decisive for scattering is less sensitive to HL and LL treatment than the cell pigment content that controls absorption. The light scattering and absorption were dynamically changed during cell cycle of synchronous cells grown in the HL. Changes in ratio of chloroplast to protoplast area, reflecting amount of scattering chloroplast membrane (outer, inner) interfaces, best correlated with changes in light scattering. We suggest that the increased light scattering by the HL-acclimated IPPAS C-1 cells might be responsible for increased HL resilience reported in the literature. Biotechnological aspect of this study is that the scattering and absorption properties of phytoplankton cells ought to be calibrated for each particular growth phase or irradiance to which the cells are acclimated. © 2020 Elsevier B.V

Ecophysiological and Anatomical Mechanisms behind the Nurse Effect: Which Are More Important? A Multivariate Approach for Cactus Seedlings

BACKGROUND: Cacti establish mostly occurs under the canopy of nurse plants which provide a less stressful micro-environment, although mechanisms underlying this process are unknown. The impact of the combination of light and watering treatments on Opuntia streptacantha (Cactaceae) seedlings was examined. METHODS/PRINCIPAL FINDINGS: Ecophysiological [titratable acidity, osmotic potential (‘solute potential’, Ψ(s)), relative growth rate (RGR) and their components (NAR, SLA, and LWR)], anatomical (chloroplast density, chloroplast frequency, and cell area), and environmental [photosynthetic photon flux density (PPFD) and air temperature] sets of variables were analyzed, assessing relationships between them and measuring the intensity of the relationships. Three harvests were carried out at days 15, 30, and 45. Ψ(s) and acidity content were the most important responses for seedling establishment. The main anatomical and environmental variables were chloroplast density and water availability, respectively. Opuntia streptacantha seedlings establish better in the shade-watering treatment, due to higher Ψ(s) and acidity, unaffected chloroplasts, and lower PPFD. In addition, the chloroplasts of cells under high-light and non-watering treatment were clumped closer to the center of the cytosol than those under shade-drought, to avoid photoinhibition and/or to better distribute or utilize the penetrating light in the green plant tissue. CONCLUSIONS: Opuntia seedlings grow better under the shade, although they can tolerate drought in open spaces by increasing and moving chloroplasts and avoiding drastic decreases in their Ψ(s). This tolerance could have important implications for predicting the impact of climate change on natural desert regeneration, as well as for planning reforestation-afforestation practices, and rural land uses