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

Abstract

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 Use and Characteristics of the Photoacoustic Method in the Study of Photosynthesis

“…One example is the state I-state 2 transition, resulting from slow adaptation to an initial unequal light distribu tion of light-2, which in higher plants ends in a more equal distribution (43a). (43,73,75). This effect allows determina tion of the ratio a/� for the modulated light-l (75).…”

“…This effect allows determina tion of the ratio a/� for the modulated light-l (75). In red and brown marine algae (43,73) the situation is more complex, with modulated light-l measuring substantial ES, which was attributed to independent PS I activity (most likely cyclic electron flow, cfbelow). An analytical approach was developed to obtain light distribution and energy transfer parameters from the PA energy storage data (43,73).…”

“…For example, when PS I is saturated by excessive background light-I, the resulting modulated signal arises solely from PS II (22), which is proportional to the fraction of the modulated light absorption in PS II. Another example is the use of modulated light-I, distributed almost exclusively to PS I, where addition of background light with a better distribution to PS II removes the limitation in PS I and gives rise to a change in the PS I signal (43,73,75), marking an increase of its photoactivity. In such experiments one may use all the different aspects of the PA signal [oxygen evolution (22), energy storage (43,73,75), or oxygen uptake (which has not yet been used)] to obtain different information.…”

A photoacoustic study of water infiltrated leaves

“…This is consistent with previous estimations (cf. Malkin et al 1990, Fork et al 1991) that energy storage is composed of roughly equal contributions from PSI and PS II (weighed also by the light distribution and the opening degree of each photosystem) and that P.S I contribution to energy storage is essentially non-variable. This is also consistent with the previous section on the photosynthetic induction transient, where at its initial moments energy storage is again roughly 1/2 (more accurately about 0.6) of the maximum, corresponding to the contribution of PSI 49 only.…”

Fluorescence as a Tool to Understand Changes in Photosynthetic Electron Flow Regulation

“…Nevertheless, within the diatoms (see Chapter 7) as well as higher plants (Johnson et al 1993) there are clear differences in qE amplitude that have been highlighted. Whereas, qT is currently unknown in diatoms (Owens 1986) and brown macroalgae (Fork et al 1991), and of only moderate importance in higher plants and dinoflagellates (Hill et al 2005), yet highly developed in some green microalgae and cyanobacteria (Finazzi 2005;Mullineaux and Emlyn-Jones 2005). Amongst the three components of NPQ, qE has a major influence on the Chl a fluorescence signal under normal growth conditions (Logan et al 2007; see also Chapter 7).…”