Quantitative analysis of State 1–State 2 transitions in intact leaves using modulated fluorimetry — evidence for changes in the absorption cross-section of the two photosystems during state transitions

The changes in the light-harvesting antenna size of photosystem I were investigated in the green alga Chiamydobotrys stellata during transition from autotrophic to photoheterotrophic nutrition by measuring the light-saturation behavior of hydrogen evolution following single turnover flashes. It was found that during autotrophic-to-photoheterotrophic transition the antenna size of photosystem I increased from 180 to 250 chlorophyll. The chlorophyll (a + b)/P700 ratio decreased from 800 to 550. The electron transport of photosystem I measured from reduced 2,6-dichlorophenolindophenol to methylviologen was accelerated 1.4 times. In the 77K fluorescence spectra, the photosystem II fluorescence yield was considerably lowered relative to the photosystem I fluorescence yield. It is suggested that the increased light-harvesting capacity and redistribution of absorbed excitation energy in favor of photosystem I is a response of photoheterotrophic algae to meet the ATP demand for acetate metabolism by efficient photosystenr. I cyclic electron transport when the noncyclic photophosphorylation is inhibited by CO2 deficiency.In the green alga Chlamydobotrys stellata, the ultrastructure and photosynthetic activities of chloroplast membranes depend on the nutritional conditions. Autotrophically grown cells evolve oxygen and utilize CO2 as a carbon source, like other unicellular green algae (25). Under heterotrophic culture conditions when CO2 is replaced by acetate, 02 evolution is abolished and only PSI activity is necessary for acetate metabolism (26,27). In the photoheterophic cells, the membrane structure of the chloroplasts is almost grana free (28) and the amount of

Section: Resultsmentioning

confidence: 95%

Hydrogen Photoevolution Indicates an Increase in the Antenna Size of Photosystem I in Chlamydobotrys stellata during Transition from Autotrophic to Photoheterotrophic Nutrition

Boichenko¹,

Wießner²,

Klimov³

et al. 1992

“…Modulated Chl fluorescence was used to follow state transitions as described previously (21). Modulated green light at 540 nm was chopped at 20 Hz (Stanford Research Systems model SR540) and transmitted to the sample via one branch ofa trifurcated light guide.…”

Section: Fluorescence Measurementsmentioning

confidence: 99%

“…Two extreme possibilities may be considered. In the first case, which is described as the 'separate 60 package' model (25), the two photosystems do not interact excitonically, and the distribution ratios are then calculated as described previously (21). In the second case, which is described as the 'spillover' model (25) Assuming again a + = 1, it follows that: B= 2 and a =2fi7.…”

Section: Light Distribution Measured By Fluorescencementioning

confidence: 99%

Light Energy Distribution in the Brown Alga Macrocystis pyrifera (Giant Kelp)

Fork

Herbert²,

Malkin³

1991

The brown alga Macrocystis pyrifera (giant kelp) was studied by a combination of fluorescence spectroscopy at 77 kelvin, room temperature modulated fluorimetry, and photoacoustic techniques to determine how light energy is partitioned between photosystems I and 11 in states 1 and 2. Preillumination with farred light induced the high fluorescence state (state 1) as determined by fluorescence emission spectra measured at 77K and preillumination with green light produced a low fluorescence state (state 2). Upon transition from state 1 to state 2, there was an almost parallel decrease of all of the fluorescence bands at 693, 705, and 750 nanometers and not the expected decrease of fluorescence of photosystem 11 and increase of fluorescence in photosystem 1. The momentary level of room temperature fluorescence (fluorescence in the steady state, Fj), as well as the fluorescence levels corresponding to all closed (Fm) or all open (Fo) reaction-center states were measured following the kinetics of the transition between states 1 and 2. Calculation of the distribution of light 2 (540 nanometers) between the two photosystems was done assuming both the 'separate package' and 'spill-over' models. Unlike green plants, red algae, and cyanobacteria, the changes here of the light distribution were rather small in Macrocystis so that there was approximately an even distribution of the photosystem 11 light at 540 nanometers to photosystem I and photosystem 11 in both states 1 and 2. Photoacoustic measurements confirmed the conclusions reached as a result of fluorescence measurements, i.e. an almost equal distribution of light-2 quanta to both photosystems in each state. This conclusion was reached by analyzing the enhancement phenomenon by light 2 of the energy storage measured in far red light. The effect of light 1 in decreasing the energy storage measured in light 2 is also consistent with this conclusion. The photoacoustic experiments showed that there was a significant energy storage in light 1 which could be explained by cyclic electron transport around photosystem 1 antennae of PSI and PSII differ significantly in their absorption so that excitation can be quite unequal depending upon the spectrum of the incident light. Unbalanced excitation in favor of PSI occurs, for example, under illumination with farred light (and also in blue light for cyanobacteria and red algae). At wavelengths below about 670 nm, PSII absorbs more light than does PSI in higher plants and algae. In brown algae, diatoms, and dinoflagellates, the photosynthetically active carotenoids, such as fucoxanthin and peridinin, are the dominant absorbing pigments ofgreen light. It was concluded from fluorescence action spectra measurements that these pigments serve mainly as antennae for PSII (13).A mechanism exists, however, in many organisms, by which an initial unequal light distribution in favor of PSII creates an adaptation process that drives the photosynthetic apparatus slowly (usually within minutes) toward a more balanced light distribution ...

“…The energy redistribution between PSI and PSII has been studied by monitoring changes in fluorescence characteristics of photosystems and photosynthetic 02 evolution (6,12,16,22,27). Although fluorescence studies gave convincing evidence for the changes in the absorption cross-section of photosystems during state transitions, they are considered to be equivocal.…”

Section: Introductionmentioning

confidence: 99%

“…Although fluorescence studies gave convincing evidence for the changes in the absorption cross-section of photosystems during state transitions, they are considered to be equivocal. Several (9,(20)(21)(22) (15,20). In the present study, we measured Sugar maple (Acer saccharum Marsh.)…”

mentioning

confidence: 96%

Photoacoustic Study of Changes in the Energy Storage of Photosystems I and II during State 1-State 2 Transitions

Veeranjaneyulu¹,

Charland²,

Charlebois³

et al. 1991

Using photoacoustic spectroscopy, state 1-state 2 transitions were demonstrated in vivo in intact sugar maple leaves (Acer saccharum Marsh.) by following the changes in energy storage of photosystems (PS) I and 11. Energy storage measured with 650 nm modulated light (light 2) in the presence of background white light indicated the total energy stored by both photosystems (EST), and in the presence of background far-red light showed the energy stored by PSI (ESPS,) In 02-evolving photosynthetic organisms, electron transfer from water to NADP requires the balanced excitation of PSI and PSII to achieve maximal photochemical efficiency. The distribution of absorbed energy between both photosystems depends on the wavelength of excitation and is initially unbalanced under light limiting conditions (6, 23) inasmuch as the composition of the pigment pools of PSI and PSII differs significantly (5). Plants possess a regulatory mechanism to balance the excitation energy distribution between both photosystems to maximize the quantum yield of photochemistry (see reviews in refs. 4, 14, 25, and 29). This phenomenon of excitation redistribution is referred to as state transition and was first observed in algae by studying fluorescence and photosynthetic 02 evolution (6, 23).In accessory pigment, PSII absorbs more light at short wavelength region (X < 670 nm) than PSI (14, 26). PSI alone absorbs in the far-red region of the spectrum (X > 715 nm) (15,20). Exposure of an intact leaf to short wavelength light leads to the adaptation of its photosynthetic apparatus to state 2 by redistributing the energy in favor of PSI to have balanced excitation of both photosystems. This is reversible in the presence of far-red light, leading to state 1, where short wavelength light largely excites PSII.These state 1-state 2 transitions are explained by two different models: (a) a spillover mechanism, which implies an unidirectional transfer of excitation energy from PSII to PSI and requires the physical proximity of the two photosystems (13, 24); (b) another mechanism involves a change in the absorption cross-section of the photosystems brought by the physical relocation of LHC.2 The migration of this pigmentprotein complex is effected by the reversible protein phosphorylation controlled by the redox state ofthe plastoquinone pool and Cyt b6-fcomplex (2,3,10,17). This latter model is widely accepted to be operative in higher plants, despite the persistent claims on the occurrence of the spillover mechanism (13).The energy redistribution between PSI and PSII has been studied by monitoring changes in fluorescence characteristics of photosystems and photosynthetic 02 evolution (6,12,16,22,27). Although fluorescence studies gave convincing evidence for the changes in the absorption cross-section of photosystems during state transitions, they are considered to be equivocal. Several