Relative functional and optical absorption cross-sections of PSII and other photosynthetic parameters monitored in situ, at a distance with a time resolution of a few seconds, using a prototype light induced fluorescence transient (LIFT) device

The prototype light-induced fluorescence transient (LIFT) instrument provides continuous, minimally intrusive, high time resolution (similar to 2 s) assessment of photosynthetic performance in terrestrial plants from up to 2m. It induces a chlorophyll fluorescence transient by a series of short flashes in a saturation sequence (180 similar to 1 mu s flashlets in <380 mu s) to achieve near-full reduction of the primary acceptor Q(A), followed by a relaxation sequence (RQ(A); 90 flashlets at exponentially increasing intervals over similar to 30 ms) to observe kinetics of Q(A) re-oxidation. When fitted by the fast repetition rate (FRR) model (Kolber et al. 1998) the Q(A) flash of LIFT/FRR gives smaller values for F(m)Q(A) from dark adapted leaves than F(m)PAM from pulse amplitude modulated (PAM) assays. The ratio F(m)Q(A)/F(m)PAM resembles the ratio of fluorescence yield at the J/P phases of the classical O-J-I-P transient and we conclude that the difference simply is due to the levels of PQ pool reduction induced by the two techniques. In a strong PAM-analogous WL pulse in the dark monitored by the Q(A) flash of LIFT/FRR phi PSIIWL approximate to phi(PSII)PAM. The Q(A) flash also tracks PQ pool reduction as well as the associated responses of ETRQ(A) -> PQ and PQ -> PSI, the relative functional (sigma(PSII)) and optical absorption (alpha(PSII)) cross-sections of PSII in situ with a time resolution of similar to 2 s as they relax after the pulse. It is impractical to deliver strong WL pulses at a distance in the field but a longer PQ flash from LIFT/FRR also achieves full reduction of PQ pool and delivers phi(PSII)PQ approximate to phi(PSII)PAM to obtain PAM-equivalent estimates of ETR and NPQ at a distance. In situ values of sPSII and aPSII from the Q(A) flash with smaller antenna barley (chlorina-f2) and Arabidopsis mutants (asLhcb2-12, ch1-3 Lhcb5) are proportionally similar to those previously reported from in vitro assays. These direct measurements are further validated by changes in antenna size in response to growth irradiance. We illustrate how the Q(A) flash facilitates our understanding of photosynthetic regulation during sun flecks in natural environments at a distance, with a time resolution of a few seconds.