Experimental and theoretical study on high temperature induced changes in chlorophyll a fluorescence oscillations in barley leaves upon 2 % CO₂

Abstract

Oscillations in many of photosynthetic quantities with a period of about 1 min can be routinely measured with higher plant leaves after perturbation of the steady state by sudden change in gas phase. Among all hypotheses suggested so far to explain the oscillations, an effect of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) activation status to control the oscillations is highly probable, at least upon high temperature (HT) treatment when in vivo RuBPCO activity controlled by RuBPCO activase (RuBPCO-A) decreases. Therefore, we measured the oscillations in fluorescence signal coming from barley leaves (Hordeum vulgare L. cv. Akcent) after their exposure for various time intervals to different HTs in darkness. We also evaluated steady state fluorescence and CO 2 exchange parameters to have an insight to functions of electron transport chain within thylakoid membrane and Calvin cycle before initiation of the oscillations. The changes in period of the oscillations induced by moderate HT (up to 43 °C) best correlated with changes in non-photochemical fluorescence quenching (q N ) that in turn correlated with changes in gross photosynthetic rate (P G ) and rate of RuBPCO activation (k act ). Therefore, we suggest that changes in period of the oscillations caused by moderate HT are mainly controlled by RuBPCO activation status. For more severe HT (45 °C), the oscillations disappeared which was probably caused by an insufficient formation of NADPH by electron transport chain within thylakoid membrane as judged from a decrease in photochemical fluorescence quenching (q P ). Suggestions made on the basis of experimental data were verified by theoretical simulations of the oscillations based on a model of Calvin cycle and by means of a control analysis of the model.Additional key words: Hordeum vulgare; model; NADPH; ribulose-1,5-bisphosphate carboxylase/oxygenase and its activase.

Modelling of light-induced chlorophyll a fluorescence rise (O-J-I-P transient) and changes in 820 nm-transmittance signal of photosynthesis

“…Values of the rate constants (after the normalization) used in the model are listed in Table A1. Values of some of the rates constant were found by trail-and-error approach (Lazár et al 2005) to obtain a satisfactory shape of the FLR and I 820 signal curves. However, the values of the rate constants are "comparable" with values of "similar" rate constants in the model (k f B , k b B ) and hence represent a reasonable estimate.…”

Temperature sensitivity of photosystem II in isolated thylakoid membranes from fluridone-treated pea leaves

“…Taking into account the strong influence of the redox state of cyt. b559 on the F m fluorescence level (Lazar et al, 2005), as . Polarographic sensitivity is 3 V/µA.…”

Function of mitochondria during the transition of barley protoplasts from low light to high light

“…Oscillations in photosynthesis following a perturbation in light intensity or gas phase composition has been studied for a long time but the underlying mechanism(s) explaining these oscillations are still not clearly resolved (Laza´r et al 2005). However, a number of possibilities have been suggested such as insufficiency of ATP or inorganic phosphate (Sivak and Walker 1987;Walker 1992).…”

“…It has, however, been difficult to establish cause-consequence relationships between the changing factors and consequently the driving forces for the fluctuations are not well known (Laza´r et al 2005).…”