Fig. 8. Heat at 40°C induced transthylakoid proton motive force, NPQ, CEF, but reduced O2 evolution and respiration rates in Chlamydomonas cells.
a, b Heat treatment of 40°C increased the transthylakoid proton motive force (pmf). ECSt, measured by electrochromic shift (ECS), represents the transthylakoid pmf. c, d NPQ was more sensitive to ECSt (or pmf) during both heat treatments, with higher NPQ produced at a given pmf. NPQ, non-photochemical quenching, measured using room temperature chlorophyll fluorescence. e Both 35°C and 40°C induced the activity of cyclic electron flow around PSI (CEF) although with different dynamics and reversibility. P700+ reduction to measure CEF in the presence of 10 µmol DCMU to block PSII activity; the smaller P700+ reduction time constant indicates faster P700+ reduction and higher CEF activity. The red shaded area depicts the duration of the high temperature. f, g, h Gross O2 evolution rates and respiration rates were reduced during the 40°C heat treatment, measured using a Hansatech Chlorolab 2 Clark-type oxygen electrode. Mean ± SE, n = 5 biological replicates. Statistical analyses were performed using two-tailed t-test assuming unequal variance by comparing treated samples with the pre-heat samples under the same light (a, b, f, g, h, *) or constant 25°C samples at the same time point (e, *), or by comparing samples between 35°C and 40°C at the same time point (e, #). a, b, e, f, g P values were corrected by FDR. *, p < 0.05, the colors and positions of asterisks match the treatment conditions and time points, respectively. (e) #, p < 0.05, the positions of pound signs match the time points. Not significant, ns.