Oxygen Evolution Induction Research Articles

Quenching of chlorophyllafluorescence by oxygen in normal air in higher plant leaves

Abstract The influence of oxygen removal on chlorophyll fluorescence induction was studied in higher plant leaves. Removal of oxygen from the air surrounding maize leaves led to the increase of the fluorescence intensity and to a delay of the time at which the P-peak and M1-maximum appeared. The oxygen removal also led to the increase of the fluorescence intensity and induction period in C3 plants including soybean, reed, sasa, and Maackia amurensis. The slow quenching of fluorescence induction in these C3 plants was more sensitive to oxygen removal than in the case of maize. Simultaneous measurement of fluorescence and oxygen evolution induction in closed leaf discs showed that a greater part of the slow quenching, including the appearance of M1-maximum, takes place without oxygen evolution or CO2-dependent electron transport. Therefore, it is concluded that oxygen in normal air is the main fluorescence quencher during the fluorescence induction in higher plant leaves; near the P-peak and M1-maximum oxyg...

Carotenoid transformations underlying the blue absorbance change in flashed leaves during the induction of oxygen evolution

The blue absorbance change occurring in flashed bean (Phaseolus vulgaris L.) leaves when exposed to continuous light (first observed by Strasser; Strasser, R.J. (1973) Arch. Int. Physiol. Biochem. 81, 935–955) is caused by the conversion of the following xanthophylls: violaxanthine → antheraxanthine → zeaxanthine. This conclusion is derived from the simultaneous occurrence of both reactions: (a) In flashed leaves, blue absorbance change and xanthophyll conversion take place under strong (2 mW · cm−2) but not under weak (0.02 mW · cm−2) white light. (b) In chloroplasts isolated from flashed leaves, the blue absorbance change occurs in the dark under conditions that also induce the xanthophyll conversion. (c) Blue absorbance change and xanthophyll conversion are both inhibited by dithiothreitol. In addition, the light-induced blue absorbance change is reversed in the dark if aerobic conditions are maintained, i.e. under conditions that in normal leaves favor the reversal of the above reaction sequence.The significance of the xanthophyll conversion is discussed in relation to other phenomena occurring in flashed leaves after exposure to continuous illumination.

Correlation of Absorbance Changes and Thylakoid Fusion with the Induction of Oxygen Evolution in Bean Leaves Greened by Brief Flashes

Dark-grown bean leaves (Phaseolus vulgaris) which had been greened for several days in a repetitive series of brief xenon flashes were studied during the initial induction period when O(2) evolution first appears. The induction of O(2) evolution requires actinic irradiation (e.g. 2 mw/cm(2) of red light) and goes to completion in about 8 minutes with a half-time just under 3 minutes. Absorbance measurements on the intact leaves showed that a change of a carotenoid pigment, monitored at 505 nm, was closely correlated with the rate of O(2) evolution during the induction period. Inhibitor studies, however, showed that the absorbance change persisted in the presence of a number of inhibitors which blocked O(2) evolution. Electron microscopy revealed that the primary thylakoids which were unfused in the flashed leaves before induction became fused in pairs or groups of three during the 8-minute induction period. It is postulated that the 505-nm absorbance change of the carotenoid pigment is correlated more directly with the fusion process than with O(2) evolution. Heat treatment (45 C for 5 min) or infiltration with 0.8 m tris, which prevented the fusion process, also prevented the absorbance change.If the leaves were preilluminated for 8 minutes with very weak red light (20 muw/cm(2)) which induced no O(2) evolution, absorbance change, or thylakoid fusion, there was an immediate burst of O(2) evolution at the onset of actinic irradiation and the induction period, as noted by O(2) evolution or by the 505-nm absorbance change, was reduced to 2 minutes (half-time of 40 seconds). It is concluded that the electron transport system in the flashed leaves is blocked at the Mn site between water and photosystem II and that the photoactivation of Mn into the thylakoid membranes occurs during the low light, photoactivation process. After the electron transport chain is thus repaired, ion-pumping mechanisms driven by actinic light may lead to steady-state photosynthesis as well as to thylakoid fusion.

Correlation between the induction of oxygen evolution and of variable fluorescence in flashed bean leaves

Beans grown under intermittent light (1 msec polychromatic intense light flash every 15 min during cultivation in darkness) do not show photosynthetic oxygen production and variable fluorescence emission immediately after the administration of continuous light for the first time. However, a weak light preillumination is enough to sensitize the leaf in such a way that an actinic illumination then provokes quite normal oxygen production behaviour, as well as variable fluorescence emission. Kinetic studies show that both oxygen production criteria (oxygen outburst and induction kinetics of oxygen production) and variable fluorescence emission criteria (position and intensity of the emission peaks) change in the same way as a function of the amount of light given during the preillumination period. We conclude that the induction of oxygen evolution and the induction of variable fluorescence in flashed leaves are correlated phenomena regulated by a weak light intensity multiquantum mechanism.