Fluorescence Induction From Photosystem II: Analytical Equations for the Yields of Photochemistry and Fluorescence Derived From Analysis of a Model Including Exciton-Radical Pair Equilibrium and Restricted Energy Transfer Between Photosynthetic Units

1995 ◽  
Vol 22 (2) ◽  
pp. 183 ◽  
Author(s):  
HW Trissl ◽  
J Lavergne
Keyword(s):  
Photosystem Ii ◽  
Radical Pair ◽  
Fluorescence Induction ◽  
Reaction Centre ◽  
Continuous Transition ◽  
Reaction Centres ◽  
Induction Kinetics ◽  
Lake Model ◽  
Time Courses ◽  
Analytical Relations

The theoretical relationships between the fluorescence and photochemical yields of photosystem II (PSII) and the fraction of open reaction centres are examined in a model based on the following assumptions: (a) a homogeneous, infinite PSII domain; (b) exciton-radical pair equilibrium; and (c) different rates of exciton transfer between 'core' and 'peripheral' antenna beds. Simple analytical relations are examined for the yields and their time-courses in induction experiments. Variation of the inter-unit transfer rate allows continuous transition from the case of 'separated units' to the pure 'lake' model. Widely used relations for estimating the fraction of closed reaction centres from the complementary area of the fluorescence, or the photochemical yield from fluorescence levels are derived. An experimental induction curve is analysed, considering its composition of 'α' and 'β' centres. The sigmoidicity of the induction kinetics is characterised by a single parameter J (corresponding to Joliots' 'p'), that is shown to depend on both the connectivity of the photosynthetic units and on reaction centre parameters. On the other hand, the relation between J and the extreme fluorescence levels (or the deviation from the linear Stern-Volmer dependence of 1 /Φf, on the fraction of open traps) is only controlled by antenna connectivity. Experimental data are more consistent with a model of 'connected units' for PSIIα than with the pure 'lake' model.

In vivo Changes in Chloroplast ThylakoidMembrane Activity during Viable and Non-viable Dehydration of a Drought-tolerant Plant, Borya nitida

1982 ◽  
Vol 9 (5) ◽  
pp. 611 ◽  
Author(s):  
SE Hethzerington ◽  
RM Smillie ◽  
ND Hallam
Keyword(s):  
Photosystem Ii ◽  
Photosystem I ◽  
Fluorescence Induction ◽  
Cytochrome F ◽  
Chlorophyll Fluorescence Induction ◽  
Reaction Centre ◽  
Partial Recovery ◽  
Induction Kinetics ◽  
Slow Development

Expanded leaves of Borya nitida Labill. were detached and placed in atmospheres of 100, 96, 88, 53 or 13% relative humidity at 25°C. In vivo chlorophyll fluorescence induction kinetics and the photooxidation of cytochrome f were measured before and after dehydration and again after rehydration by floating on water. In contrast to slow dehydration at 96% R.H., which resulted in an initial stimulation of photosystem II activity, the slow development of a partial block on the photoreducing side of photosystem II and the eventual degreening of leaves to a yellow viable condition, fast dehydration at 13% R.H. induced rapid loss of photosystem I activity and a slower development of a block on the photooxidizing side of photosystem . Although the leaves remained green, photo- system activity did not recover upon rehydration. Charge separation in the photosystem II complex still took place in the dehydrated leaves but upon rehydration the photosystem II reaction centre appeared to be disassociated from the light harvesting system. Dehydration at intermediate relative humidities (88 and 53%) led to a partial block on the photoreducing side of photosystem II and, more slowly, inhibition of photosynthetic electron transfer on the photooxidizing side of photosystem II. Following rehydration there was partial recovery of reactions associated with photosystem I but the leaves were unable to return to their original condition.

Humidity-sensitive Degreening and Regreening of Leaves of Borya nitida Labill. As Followed by Changes in Chlorophyll Fluorescence

1982 ◽  
Vol 9 (5) ◽  
pp. 587 ◽  
Author(s):  
SE Hethzerington ◽  
RM Smillie
Keyword(s):  
Chlorophyll Fluorescence ◽  
Relative Humidity ◽  
Photosystem Ii ◽  
Photosystem I ◽  
Fluorescence Induction ◽  
Physiological Age ◽  
Chlorophyll Fluorescence Induction ◽  
Induction Kinetics ◽  
Mediated Electron Transfer

Fast and slow chlorophyll fluorescence induction kinetics were used to follow changes in photosynthetic activity during humidity-sensitive degreening and regreening of leaves of Borya nidita Labill. During dry periods the leaves of this desiccation-tolerant plant lose chlorophyll, becoming yellow-brown and upon rehydration turn green again. This degreening process can be simulated in detached leaves by slow dehydration at 96% relative humidity. Under these conditions changes in chlorophyll fluorescence in vivo and the activities of photosystems I and II in chloroplasts isolated from dehydrated leaves indicated that degreening was accompanied initially by a stimulation of photosystem II activity and a gradual decrease in photosystem I-mediated electron transfer, while at advanced stages of degreening both photosystems were lost. Control leaves detached and kept at 100% relative humidity remained green and showed little change in chlorophyll fluorescence kinetics. During the rehydration and subsequent regreening of dry yellow leaves, photosystem I activity appeared to recover faster than photosystem II. The ability of the leaves to recover and regreen from the dried state, either on the plant or after detachment, depended upon the physiological age of the leaves at the time of dehydration.

Inhibition of quantum yield of PS II electron transport in Spirulina platensis by osmotic stress may be explained mainly by an increase in the proportion of the QB-non-reducing PS II reaction centres

1998 ◽  
Vol 25 (6) ◽  
pp. 689 ◽  
Author(s):  
Congming Lu ◽  
Jianhua Zhang ◽  
Avigad Vonshak
Keyword(s):  
Electron Transport ◽  
Quantum Yield ◽  
Osmotic Stress ◽  
Spirulina Platensis ◽  
Fluorescence Induction ◽  
Photochemical Quenching ◽  
Ps Ii ◽  
Reaction Centres ◽  
Induction Kinetics ◽  
Fluorescence Induction Kinetics

Modulated chlorophyll fluorescence and fluorescence induction kinetics were used to evaluate the PS II photochemistry in Spirulina platensis exposed to osmotic stress (0–0.8 M mannitol). Osmotic stress decreased the efficiency of excitation energy capture by open PS II reaction centres (Fv′/Fm′) and more significantly, decreased photochemical quenching (qP). Osmotic stress also decreased the maximal efficiency of PS II photochemistry (Fv/Fm). There was no significant change in non-photochemical quenching (qN), indicating that the decreased Fv′/Fm′ was not due to an increase in qN. Analyses of the fast fluorescence induction kinetics indicated that osmotic stress caused a significant increase in the proportion of the QB-non-reducing PS II reaction centres. Based on the results in this study, we suggest that a substantial increase in the proportion of the QB-non-reducing PS II reaction centres may be responsible for the decrease in qP and Fv′/Fm′, of which both resulted in the decrease in the quantum yield of PS II electron transport (ΦPSII ).

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