Lycophyte division is composed of ancient vascular plants that diverged from euphyllophyte lineage ca. 400 million years ago. Among these, Selaginella martensii Spring has evolved to inhabit shade environments of tropical-equatorial rainforests. However, this plant is also able to acclimate efficiently to light regimes as different as deep shade and full sunlight (Ferroni et al. 2016, 2021). Such characteristic reveals a marked flexibility of the photosynthetic machinery in response to the light availability, but the underlying structural and dynamic acclimation features have been clarified only partially. In fact, differently from most seed plants, S. martensii is unable to modulate the content of Photosystem II antenna complexes (LHCII), which remains constant from deep shade to full sunlight regime, while the ratio between PSII and PSI decreases. In order to clarify the light acclimation features in S. martensii under deep-shade (L), intermediate shade (M) and full sunlight (H), we analyzed some functional aspects of light harvesting and electron transport after the plants' exposure to dark for 20 minutes, far red (FR) light for 20 minutes and moderate light for 1 hour. The analysis was performed using a HandyPEA (Hansatech, UK) fluorometer, which allowed us to calculate the JIP-test parameters. Among these, we particularly focused on ABS/RC, i.e. the functional antenna size of a PSII unit (Stirbet and Govindjee 2011). We also used the fluorescence transients to calculate the PSII excitonic connectivity parameters, which describe the probability of excitation transfer between different PSII units (Stirbet 2013). Our results suggest that the acclimation to different light regimes influences both PSII functional antenna size and PSII connectivity, but the direction of changes apparently contrasted with expectations. On one hand, the PSII antenna size was only slightly variable from L to H plants. On the other hand, PSII connectivity was in general far lower when compared to common values reported for seed plants. Especially H plants reported connectivity values close to 0, suggesting a "puddle" organization of PSII.
Effects of long-term light acclimation on Photosystem II functional antenna size and excitonic connectivity in Selaginella martensii.
Colpo A.;Baldisserotto C.;Pancaldi S.;Ferroni L.
2021
Abstract
Lycophyte division is composed of ancient vascular plants that diverged from euphyllophyte lineage ca. 400 million years ago. Among these, Selaginella martensii Spring has evolved to inhabit shade environments of tropical-equatorial rainforests. However, this plant is also able to acclimate efficiently to light regimes as different as deep shade and full sunlight (Ferroni et al. 2016, 2021). Such characteristic reveals a marked flexibility of the photosynthetic machinery in response to the light availability, but the underlying structural and dynamic acclimation features have been clarified only partially. In fact, differently from most seed plants, S. martensii is unable to modulate the content of Photosystem II antenna complexes (LHCII), which remains constant from deep shade to full sunlight regime, while the ratio between PSII and PSI decreases. In order to clarify the light acclimation features in S. martensii under deep-shade (L), intermediate shade (M) and full sunlight (H), we analyzed some functional aspects of light harvesting and electron transport after the plants' exposure to dark for 20 minutes, far red (FR) light for 20 minutes and moderate light for 1 hour. The analysis was performed using a HandyPEA (Hansatech, UK) fluorometer, which allowed us to calculate the JIP-test parameters. Among these, we particularly focused on ABS/RC, i.e. the functional antenna size of a PSII unit (Stirbet and Govindjee 2011). We also used the fluorescence transients to calculate the PSII excitonic connectivity parameters, which describe the probability of excitation transfer between different PSII units (Stirbet 2013). Our results suggest that the acclimation to different light regimes influences both PSII functional antenna size and PSII connectivity, but the direction of changes apparently contrasted with expectations. On one hand, the PSII antenna size was only slightly variable from L to H plants. On the other hand, PSII connectivity was in general far lower when compared to common values reported for seed plants. Especially H plants reported connectivity values close to 0, suggesting a "puddle" organization of PSII.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
