The chlorophyll a fluorescence induction curve in the green microalga Haematococcus pluvialis: further insight into the nature of the P–S–M fluctuation and its relationship with the “low-wave” phenomenon at steady-state

Abstract

Chlorophyll fluorescence is an information-rich signal which provides an access to the management of light absorbed by PSII. A good example of this is the succession of fast fluorescence fluctuations during light-induced photosynthetic induction after dark-adaptation. During this period, the fluorescence trace exhibits several inflexion points: O-J-I-P-S-M-T. Whereas the OJIP part of this kinetics has been the subject of many studies, the processes that underly the PSMT transient are less understood. Here, we report an analysis of the PSMT phase in the green microalga Haematococcus pluvialis in terms of electron acceptors and light use by photochemistry, fluorescence and non-photochemical quenching (NPQ). We identify additional sub-phases between P and S delimited by an inflexion point, that we name Q, found in the second time scale. The P-Q phase expresses a transient photochemical quenching specifically due to alternative electron transport to oxygen. During the transition from Q to S, the NPQ increases and then relaxes during the S-M phase in about 1 min. It is suggested that this transient NPQ observed during induction is a high energy state quenching (qE) dependent on the alternative electron transport to molecular oxygen. We further show that this NPQ is of the same nature than the NPQ, known as the low-wave phenomenon, which is transiently observed after a saturating light pulse given at steady-state. In both cases, the NPQ is oxygen-dependent. This NPQ is observed at external pH 6.0, but not at pH 7.5, which seems correlated with faster saturation of the PQ pool at pH 6.0.

Monitoring the photosynthetic activity at single-cell level in Haematococcus lacustris

“…Although the post-illumination fluorescence rise could not be unequivocally identified at single-cell level, the low-wave phenomenon was visible in individual green cells after a saturation pulse in the dark following the actinic illumination [in agreement with previous studies obtained in bulk cultures (Larcher and Neuner 1989, Xyländer and Hagen 2002, Tsuyama et al 2004, Fratamico et al 2016], but not in red cells (Figs. 1, 2).…”

“…More strikingly, Chl fluorescence kinetics occurring after saturation pulses or dark-to-light transitions revealed specific features. The so-called low wave fluorescence transient is manifested by a brief reversible lowering (dip) of Chl fluorescence yield after saturating multi-turnover pulses given either in the darkadapted state or during actinic illumination (Larcher and Neuner 1989, Xyländer and Hagen 2002, Tsuyama et al 2004, Fratamico et al 2016. Such low waves were observed in Haematococcus and were suggested to arise either from transiently increased nonphotochemical quenching, as a result of the formation of a trans-thylakoid proton gradient due to cyclic electron flow around PSI (Fratamico et al 2016), or from an imbalance between the charge separation capacity of the photosystems and the electron buffering capacity of the intersystem electron transport pool (Hagen et al 1992).…”

“…Various aspects of the fast and slow fluorescence induction phenomena have been assessed, and it was found that the slow phase of the fluorescence transient, the so-called P-S-M-T phase is associated with transient activation of the energy-dependent q E component of NPQ. In addition, after a saturation light pulse, the so-called low wave effect appeared, manifested by a transient drop of Chl fluorescence yield below the steady-state level, which effect was associated with the qE component of NPQ (Fratamico et al 2016). However, these mechanisms have not been investigated at the singlecell level and during the entire transformation process of green cells to red cells (and reversal of red to green cells).…”

Membrane Inlet Mass Spectrometry: A Powerful Tool for Algal Research

“…To limit noise on the exchange rates graphic, data shown in (D) are integrated with a sliding average of 30 s wide. study the link between CO 2 fixation and non-photochemical quenching of chlorophyll fluorescence (Sültemeyer et al, 1989;Fratamico et al, 2016;Ware et al, 2020). Furthermore, in conditions where the use of 18 O 2 is not possible (e.g.…”

“…Indeed, fluorescence measurements have often been used together with MIMS CO 2 and O 2 exchange measurements to study the link between CO 2 fixation and non-photochemical quenching of chlorophyll fluorescence ( Sültemeyer et al., 1989 ; Fratamico et al., 2016 ; Ware et al., 2020 ). Furthermore, in conditions where the use of 18 O 2 is not possible ( e.g.…”