Photoinhibition of photosynthesis in chilled potato leaves is not correlated with a loss of Photosystem-II activity

Abstract

When 23 °C-grown potato leaves (Solanum tuberosum L.) were irradiated at 23 °C with a strong white light, photosynthetic electron transport and Photosystem-II (PS II) activity were inhibited in parallel. When the light treatment was given at a low temperature of 3 °C, the photoinhibition of photosynthesis was considerably enhanced, as expected. Surprisingly, no such stimulation of photoinhibition was observed with respect to the PS II function. A detailed functional analysis of the photosynthetic apparatus, using in-vivo fluorescence, absorbance, oxygen and photoacoustic measurements, and artificial electron donors/acceptors, showed a pronounced alteration of PS I activity during light stress at low temperature. More precisely, it was observed that both the pool of photooxidizeable reaction center pigment (P700) of PS I and the efficiency of PS I to oxidize P700 were dramatically reduced. Loss of P700 activity was shown to be essentially dependent on atmospheric O2 and to require a continued flow of electrons from PS II, suggesting the involvement of the superoxide anion radical which is produced by the interaction of O2 and the photosynthetic electron-transfer chain through the Mehler reaction. Mass spectrometric measurements of O2 exchange by potato leaves under strong illumination did not reveal, however, any stimulation of the Mehler reaction at low temperature, thus leading to the conclusion that O2 toxicity mainly resulted from a chilling-induced inhibition of the scavenging system for O2-radicals. Support for this interpretation was provided by the light response of potato leaves infiltrated with an inhibitor (diethyldithiocarbamate) of the chloroplastic Cu-Zn superoxide dismutase. It was indeed possible to simulate the differential inhibition of the PS II photochemical activity and the linear electron transport observed during light stress at low temperature by illuminating at 23 °C diethyldithiocarbamate-poisoned leaves. The experimental data presented here suggests that (i) the previously reported resistance of PS I to photoinhibition damage in-vivo is not an intrinsic property of PS I but results from efficient protective systems against O2 toxicity, (ii) PS I is photoinhibited in chilled potato leaf due to the inactivation of this PS I defence system and (iii) PS I is more sensitive to superoxide anion radicals than PS II.

The protective function of the xanthophyll cycle in photosynthesis

“…1: light-induced loss of electron transport at 23°C proceeded independently of lipid peroxidation whereas chilling stress in the light simultaneously caused photosynthesis inhibition and lipid photooxidation. Moreover, strong light stress at 3°C was previously observed to cause an O2-dependent selective loss of PSI function which was mimicked at 230C by illuminating leaves infiltrated with a SOD inhibitor [8], suggesting that 02-is involved in the lipid peroxidation phenomena reported here. The present study (Table 1, Fig.…”

“…A previous study of light-treated potato leaves [8] has shown that photoinhibition of photosynthetic electron transport at 23°C (growth temperature) and at 3°C are different phenom- ena. This is confirmed by the data of Fig.…”

“…Haig) were used. Plants were grown in a growth chamber under controlled conditions of temperature, light and air humidity, as described in [8]. Detached leaves placed on moist filter paper were exposed at 23 Abbreviations: 0p, quantum yield of photosynthetic electron transport; V, A and Z, violaxanthin, antheraxanthin and zeaxanthin, respectively; DTT, dithiothreitol; PS, photosystem; SOD, superoxide dismutase; LHC(II), light harvesting chlorophyll a/b-protein complexes (of PSII).…”

“…This report provides experimental evidences supporting hypothesis (v): the presence of A and Z was observed to determine the lipid peroxidation status of illuminated potato leaves. thermistor thermometer, was maintained constant during the light treatment as previously described [8]. In some experiments, leaves were pretreated with dithiothreitol (DTT) as described by Bilger et al [9]: cut leaves were kept at a photon flux density of 40/IE.m-2-s -~ for 2 or 3 h with their petiole in a solution of 3 mM DTT or in distilled water (controls).…”

Alterações fisiológicas após aplicação de silício em cacau e sua influência na preferência por pulgões

“…Tais mudanças podem representar perda de eficiência fotoquí-mica pelas plantas e, como consequência, a diminuição da fotossíntese. Além disso, o maior desempenho das reações de oxi-redução do FSI [R 0 /(1-R 0 )] no Catongo pode ser explicado pelo fato de o FSI ser mais tolerante ao excesso de radiação do que o FSII (Havaux & Davaud, 1994), o que permite a este genótipo utilizar a pequena quantidade de energia absorvida para redução da ferredoxina e do NADP + . Por outro lado, a fotoinibição, nesse genótipo, também pode estar relacionada com a ausência de antocianinas em suas folhas (Figueira & Cascardo, 2001), pigmentos que conferem efeito fotoprotetor ao aparato fotossintético (Close & Beadle, 2003).…”