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

Abstract

. (2017). 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. Functional Plant Biology: an international journal of plant function, 44 (10), 985-1006 See next page for additional authorsRelative 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 AbstractThe prototype light-induced fluorescence transient (LIFT) instrument provides continuous, minimally intrusive, high time resolution (~2 s) assessment of photosynthetic performance in terrestrial plants from up to 2 m. It induces a chlorophyll fluorescence transient by a series of short flashes in a saturation sequence (180 1μs flashlets inμs) to achieve near-full reduction of the primary acceptor QA, followed by a relaxation sequence (RQA; 90 flashlets at exponentially increasing intervals over ~30 ms) to observe kinetics of QA reoxidation. When fitted by the fast repetition rate (FRR) model (Kolber et al. 1998) the QA flash of LIFT/ FRR gives smaller values for FmQA from dark adapted leaves than FmPAM from pulse amplitude modulated (PAM) assays. The ratio FmQA/FmPAM 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 QA flash of LIFT/FRR φPSIIWL ≈ φPSIIPAM. The QA flash also tracks PQ pool reduction as well as the associated responses of ETR QA → PQ and PQ → PSI, the relative functional (σPSII) and optical absorption (aPSII) cross-sections of PSII in situ with a time resolution of ~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 φPSIIPQ ≈ φPSIIPAM to obtain PAM-equivalent estimates of ETR and NPQ at a distance. In situ values of σPSII and aPSII from the QA flash with smaller antenna barley (chlorinaf2) 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 QA flash facilitates our understanding of photosynthetic regulation during sun flecks in natural environments at a distance, with a time resolution of a few seconds. A new approach to monitoring leaf photosynthesis in situ using 30 ms chlorophyll fluorescence transients at ~ 2 s intervals at distances up to 2 m is described. By monitoring fluorescence with near full reduction of Q A (the primary quinone acceptor of PSII) these transients deliver parameters not directly av...

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“…All parameters and symbols in this study match the conventional PAM terminology, with the LIFT data being marked by a Q A or PQ to denote the source of the fluorescence data from either the Q A or PQ flashes described previously [22]. Maximum photochemical yield of photosystem II was calculated as:…”

“…The LIFT instrument was operated with a non-invasive flash cycle (termed Q A flash) [22] with an SQ A phase consisting of 300 flashlets separated by a 1.6 µs delay (~3 ms) and an RQ A phase consisting of 90 flashlets with an exponential increase in the 1.6 µs delay described by an exponential term of 0.5 (~300 ms). To obtain dark adapted reference Fm values, for the calculation of YNPQ and YNO, a modified flash cycle (termed PQ flash) with an SQ A phase consisting of 6000 flashlets with a 20 µs delay and an RQ A phase identical to the Q A flash (~700 ms) was used [22]; see supplementary material, Figure S1 for comparison of the Q A and PQ flash to PAM.…”

“…To obtain dark adapted reference Fm values, for the calculation of YNPQ and YNO, a modified flash cycle (termed PQ flash) with an SQ A phase consisting of 6000 flashlets with a 20 µs delay and an RQ A phase identical to the Q A flash (~700 ms) was used [22]; see supplementary material, Figure S1 for comparison of the Q A and PQ flash to PAM. To facilitate automatic targeting and monitoring of measured leaves, the LIFT and QE Pro were mounted on a computer controlled motorized tripod (Celestron advanced VX; Celestron, Rouse Hill, NSW, Australia) and operated through custom designed software.…”

“…In a typical LIFT excitation protocol, up to 300 flashlets are delivered at high duty cycle (SQ A phase), resulting in a gradual saturation of the observed fluorescence yield, roughly proportional to the increasing level of Q A reduction. The next 90-120 flashlets are delivered at exponentially decreasing duty cycle (RQ A phase), where the fluorescence yield relaxes, with kinetics defined by the rates of photosynthetic electron transport [22]. The entire fluorescence transient is then fitted using the fast repetition rate (FRR) model to determine maximum (Fm in dark or F'm in the light) and minimum fluorescence (Fo in dark or F' in the light) [23].…”

“…The leaf absorbance (α) was determined for each leaf from regression of leaf SPAD measurements against the PAR absorbance (400 to 700 nm) of leaves measured in an integrating sphere (see supplementary material; Figure S2). Partitioning of the yields of non-photochemical quenching (YNPQ) and constitutive heat dissipation (YNO) [22] were calculated according to the formulas of Klughammer et al [30]:…”