Transient winter leaf reddening in Cistus creticus characterizes weak (stress-sensitive) individuals, yet anthocyanins cannot alleviate the adverse effects on photosynthesis

Abstract

Under apparently similar field conditions individual plants of Cistus creticus turn transiently red during winter, while neighbouring plants remain green. These two phenotypes provide a suitable system for comparing basic photosynthetic parameters and assessing critically two hypotheses, i.e. anthocyanins afford photoprotection and anthocyanins induce shade characteristics on otherwise exposed leaves. With that aim, pigment levels and in vivo chlorophyll fluorescence parameters were monitored in dark-acclimated (JIP-test) and light-acclimated (saturation pulse method) leaves during both the green and the red period of the year. No evidence for actual photoprotection by anthocyanins was obtained. On the contrary, all fluorescence parameters related to yields and probabilities of photochemical energy conversion and electron flow, from initial light trapping to final reduction of ultimate electron acceptors in PSI, declined in the red phenotype after leaf reddening. Moreover, the pool sizes of final electron acceptors of PSII diminished, indicating that both photosystems were negatively affected. Vulnerability to winter stress was also indicated by sustained chlorophyll loss, inability to increase the levels of photoprotective xanthophylls and increased quantum yield of non-regulated energy loss during reddening. However, during the same period, the relative PSII antenna size increased, indicating an apparent shade acclimation after anthocyanin accumulation, while changes in the photosynthetic pigment ratios were also compatible to the shade acclimation hypothesis. All parameters recovered to pre-reddening values upon re-greening. It is concluded that the photosynthetic machinery of the red leaf phenotype has an inherently low capacity for winter stress tolerance, which is not alleviated by anthocyanin accumulation.

Fig. 1.

Pigment levels and their ratios in green (closed circles) and red (open circles) phenotypes of C. creticus sampled on the dates indicated. The arrows denote the start and the end of the ‘red’ period. Leaves senesce and fall from mid-April to mid-May in parallel with new leaf emergence. During April, when old and new leaves co-occur, only old leaves (green and red, respectively) were sampled. The May sampling concerns new green leaves for both phenotypes. Values are means from two independent extractions per sampling date. Differences in each parameter between the two phenotypes are not significant during the ‘green’ period, but they are during the ‘red’ period, with the exception of the epoxidation state (EPS). P-values for the red period are inserted. VAZ=violaxanthin+antheraxanthin+zeaxanthin; EPS=(V+0.5A)/VAZ.

Fig. 2.

Quantum yields of energy capture and electron flow as well as probabilities for trapped excitation energy to move electrons along the linear electron transport in green (closed circles) and red (open circles) phenotypes of C. creticus sampled on the dates indicated; φ_P0 (equivalent to F_V/F_M), maximum quantum yield of primary photochemistry; φ_E0, quantum yield of electron transfer to intermediate carriers; φ_R0, quantum yield of reduction of electron acceptors of PSI; ψ_E0, efficiency to conserve trapped excitation energy to electron transfer; δ_R0, efficiency of electron transfer between reduced intermediate carriers to final electron acceptors of PSI. The arrows denote the start and the end of the ‘red’ period. Values are means ±standard deviation from five plants (six leaves per plant). The asterisks denote statistically significant (P <0.05) differences between the two phenotypes in the parameter indicated for each sampling date.

Fig. 3.

Fast chlorophyll fluorescence transients of green (closed circles) and red (open circles) phenotypes sampled before (08/12/2007) and after (15/03/2008) leaf reddening of the red phenotype. Note the logarithmic time scale. On the vertical axis the relative variable fluorescence is given as V_t=(F_t–F₀)/(F_M–F₀), i.e. after double normalization at F₀ and F_M. F₀ is the fluorescence yield at 20 μs. Values are means from five plants (six leaves per plant).

Fig. 4.

Specific energy fluxes per active (i.e. Q_A-reducing) PSII reaction centre (RC) in green (closed circles) and red (open circles) phenotypes sampled on the dates indicated. The arrows denote the start and the end of the ‘red’ period. ABS, TR₀, ET₀, and DI₀ stand for absorbed energy, trapped energy, electron transport, and dissipated energy, respectively. Values are means ±standard deviation from five plants (six leaves per plant). The asterisks denote statistically significant (P <0.05) differences between the two phenotypes in the indicated parameter for each sampling date.

Fig. 5.

Fluorescence rise kinetics of the I–P phase in green (closed circles) and red (open circles) phenotypes before (08/12/2007) and after (15/03/2008) leaf reddening of the red phenotype. On the vertical axis fluorescence is given as (F_t–F₀)/(F_I–F₀), after normalization at F_I. F₀ and F_I stand for fluorescence yield at 20 μs and at 30 ms, respectively. Values are means from five plants (six leaves per plant).

Fig. 6.

Changes in light-acclimated PSII effective yield, Φ_PSII, and non-photochemical energy quenching (either regulated, Φ_NPQ, or non-regulated, Φ_NO), versus incident light level, in green (closed circles) or red (open circles) leaves. The experiment was performed during the ‘red’ period (5 March 2008) and the left and right panels refer to values obtained from the upper and lower leaf side, respectively. The leaves remained under the indicated PAR until stable values for each parameter were obtained. Values are means ±standard deviation from five plants (four leaves per plant). The asterisks denote statistically significant (P <0.05) differences between the two phenotypes in the parameter indicated for each PAR level.

Fig. 7.

Linear electron transport rates (ETR) along PSII in the lower leaf side of green (closed circles) and red (open circles) phenotypes. The experiment was performed during the ‘red’ period (5 March 2008). The leaves remained under the indicated PAR until stable values for each parameter were obtained. Values are means ±standard deviation from five plants (four leaves per plant). The asterisks denote statistically significant (P <0.05) differences between the two phenotypes in the parameter indicated for each PAR level.