Despite having beneficial effects, selenium is not an essential element for plants and its action mechanisms are still unclear. In this context, we evaluated effects of selenium, considering possible modulations of the photosynthetic apparatus of Billbergia zebrina plants during in vitro culture. Lateral shoots of B. zebrina were grown in a medium with different concentrations of selenium (0, 2, 4, and 16 μM). After 75 d, concentrations of photosynthetic pigments, growth traits, and chlorophyll a fluorescence were evaluated. In low concentrations, selenium increased the potential energy conservation capacity of the photosynthetic apparatus, maintained the PSII energy transport reaction stability, and improved the electron transport dynamics between the intersystem and PSI. In addition, B. zebrina showed physiological disturbances at Se concentrations equal or greater than 16 μM, presenting reduced growth and photosynthetic pigment contents and impaired photosynthetic apparatus. Abbreviations: ABS/RC -absorption flux per RC; Chl -chlorophyll; Chltotal -total chlorophyll; DI0/RC -dissipated energy flux per RC; ET0/RC -electron transport flux per RC; F0 -minimal fluorescence yield of the dark-adapted state; FI -fluorescence intensity at 30 ms; FJ -fluorescence intensity at 2 ms; FK -fluorescence intensity at 0.3 ms; Fm -maximal fluorescence yield of the dark-adapted state; FM -fresh mass; FP -fluorescence intensity at 300 ms; OCE -oxygen-evolving complex; Pheo -pheophytin; PI(ABS) -performance index based on absorption; PI(Total) -overall performance index, which measures the performance up until the final electron acceptors of PSI; RC -reaction center; RC/ABS -total number of active reaction center per absorption; RE0/RC -reduction of end acceptors at PSI electron acceptor side per RC; ROS -reactive oxygen species; TR0/RC -trapping flux per RC; VI -relative variable fluorescence at 30 ms (point I); VJ -relative variable fluorescence at 2 ms (point J); δR0 -efficiency/probability with which an electron from the intersystem electron carriers moves to reduce end electron acceptors at the PSI acceptor side; φD0 -quantum yield of energy dissipation; φE0 -quantum yield of electron transport; φP0 -maximum quantum yield of primary photochemistry; φR0 -quantum yield of reduction of end electron acceptors at the PSI acceptor side; ρR0 -efficiency with which a trapped exciton can move an electron into the electron transport chain from QA − to the PSI end electron acceptors; ψE0 -probability that a trapped exciton moves an electron into the electron transport chain beyond QA − . Acknowledgments: The authors would like to acknowledge the scholarship awarded by the CNPq (Brazilian National Council for Scientific and Technological Development) and the FAPES (Espírito Santo State Research Foundation).

Deleterious effects induced by high zinc (Zn) concentrations can be alleviated with selenium (Se) co-exposure. Therefore, we analyzed the morphophysiological changes of Billbergia zebrina in response to Zn and Se co-exposure. Plants were cultured in media containing three Zn concentrations (0, 30, and 300 μM) combined with two Se concentrations (0 and 4 μM), for a total of six treatments. At 75 d of culture, the leaf anatomy, chlorophyll (Chl) a fluorescence, and contents of photosynthetic pigments (Chl) and nutrients were analyzed. The total Chl content declined with rising Zn concentrations. Plants cultured with Se presented a decrease in the Chl a/b ratio and greater total Chl content. Positive L-and K-bands were verified under Se absence and with 30 and 300 μM Zn. Plants showed bioaccumulation capacity and tolerance to excess Zn. Se acted as a modulator to alleviate the Zn stress.

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