Measurements of photosynthetic activities
Gas exchange analysis, Chl fluorescence and P700+ were
simultaneously measured using a combined system of GFS-3010 and
Dual-PAM-100 (Heinz WalzGmbH, Germany). Ambient air (40 Pa
CO2, 21 kPa O2) and gases with pure
CO2 were mixed to determine the CO2concentration during measurements. The gases were saturated with water
vapor at 18.0±0.1 °C, and the leaf temperature was maintained at 25 °C.
The following Chl fluorescence parameters were calculated as described
by Baker (2008): Fo, minimum fluorescence yield; Fm, maximum
fluorescence yield; Fm’, maximum fluorescence yield under the
illumination; and Fs, steady-state fluorescence yield. A measuring light
(0.1 µE m-2 s-1) and a saturated
pulse (20,000 µE m-2 s-1, 600 ms)
were applied to determine Fo, Fm, and Fm’. The oxidation-reduction state
of P700 in photosystem (PS) I was determined according to the method of
Klughammer & Schreiber (1994). The maximum oxidation level of P700 (Pm)
was obtained using a saturated pulse under far-red light illumination.
The oxidation–reduction state of P700 was determined using the
oxidation level of P700 at the steady-state (P) and the maximum
oxidation level of P700 under illumination (Pm’). For determining theproton motive force (pmf ), H+-efflux
conductance (gH+), and H+-efflux
rate (V H+) in leaves, the
electrochromic shift (ECS) was measured using the dark interval
relaxation kinetics-analysis (Sacksteder & Kramer, 2000). The value ofpmf was normalized by the ECS-signal obtained by a
single-turnover flash (10 µs) (Takagi et al., 2017). Actinic red light
(AL) was used to measure the photosynthetic parameters.