Absorption spectrum and oxygen evolution measurements
To monitor the contents of AsA which could directly protect
photosystems, AsA levels in chloroplasts were monitored by using vitamin
C assay kit (A009, Nanjing Jiancheng Bioengineering Institute, Nanjing,
China).1O2in chloroplasts contents were measured by using plant ROS singlet oxygen
assay kit
(GMS10150.4,
GENMED, Boston, MA, USA). Chloroplasts were isolated from Z.
marina leaves, which were dark-adapted and exposed to 300 µE for 3
h, by using the plants leaf
chloroplast rude divide kit (GMS16004.1, GENMED).
To monitor change in
carbon fixation ability during 300
µE light exposure, the Rubisco
carboxylase activity was determined
by using ribulose bisphosphate carboxylase/oxygenase (Rubisco) activity
detection kit (BC0440, Solarbio, Beijing, China). Absorption
measurements were performed using a multifunctional enzyme-labeled
instrument (Tecan, Männedorf,
Switzerland).
O2evolution rate used to reflect the
leaves photosynthetic rate was measured at 15 °C
with a liquid-phase oxygen
electrode system (Chlorolab2+, Hansatech, Norfolk, UK).
Chlorophyll a fluorescence
and 820 nm modulated reflection (MR820nm) measurements
A pulse-amplitude modulated fluorometer (Mini-PAM;
Walz, Germany) was used to
measure NPQ. During the course of
measurements, the PAM fiber was placed in a fixed position at 60° in
relation to Z. marina leaves to avoid shading or darkening.
Multi-function plant efficiency analyzer 2 (M-PEA-2; Hansatech,
Hercules, UK) was used to simultaneously detect the kinetics of prompt
fluorescence (PF), delayed
fluorescence (DF), and
MR820nm and thus to monitor photochemical activity and
dissect events in the electron transfer chain (Strasser et al., 2010;
Gururani et al.,
2015)10,62.
Changes in the OJIP fluorescence
rise kinetics were assessed by calculating the difference value of
variable fluorescence curves as ΔV t =
Δ[(F t - F O) /
(F m - F O)]. The relative
variable fluorescence at the K-step (W K) was an
indicator of the PSII electron donation capacity (Strasser, 1997;
Brestic et al., 2012){Brestic, 2012 #265;Strasser, 1997 #269}. The
decay kinetics of DF at maximum I 1 were fitted
with the function DF(t ) = L 1 × exp(-t /τ 1) + L 2 × exp(-t /τ 2) + L 3, whereL 1 and L 2represent the amplitudes of the
decay kinetics component and τ 1 andτ 2 represent their lifetimes (in ms),
respectively. L 1 corresponded to the electron
transport capacity at PSII donor side
(Goltsev
et al., 2009; Gao et al., 2013). MR820nm obtained by a
modulated measuring light at 820 nm was measured
after far-red light was closed
(Zhang et al.,
2011).V re-red, the initial rate of
P700+re-reduction, was calculated to
quantify PSI-CEF activity. Detailed calculations and physiological
explanations of parameters are listed in Table S2.