Exposure times in rapid light curves affect photosynthetic parameters in algae (original) (raw)
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Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1968
I. Synchronous ChIorellafusca was exposed to light for periods of o.I sec-I5 rain. Subsequent to the illumination, the rate of 02 exchange passes through a series of transient phenomena. These transients vary greatly with cellular age and depend also upon conditions prior to and during the experiment. However, the individual maxima and minima of O 2 exchange specified as T1, T 2, T 3 .... occur at reproducible times provided that algae of the same developmental stage and pretreatment are used. 2. At least 5 individual components are involved in the complex changes: (a) A sudden photosynthetic O 2 evolution (T1) which, after darkening, declines rapidly and without oscillations. (b) A brief and distinct 02 uptake (T~) immediately after switching off the light, which is only observed under special conditions. (c) The next maxima and minima Ta, T4, Ts, and partly also T 6 obviously are damped oscillations of the respiratory 02 uptake, started by an inhibition of some respiratory step by photosynthesis. (d) A slow declining stimulation of 02 uptake superimposed on the foregoing transients occurs after longer light exposures. (e) A very strong stimulation of respiratory 02 consumption (Ts), culminating not until 6 to 8 rain after the start of illumination, is induced only by irradiation with shortwave light (< 54 ° nm) after longer dark periods. 3. The individual components differ with respect to their dependence on intensity, wavelength and duration of the light exposure and their sensitivity to several inhibitors. According to their characteristics all transients except T 8 depend on, but in different ways, the function of the photosynthetic apparatus. The components b and c seem to be closely connected with System I.
Rapid light curves: a new fluorescence method to assess the state of the photosynthetic apparatus
Photosynthesis Research, 1999
Photosynthetic electron transport rates (ETR), calculated from chlorophyll fluorescence parameters, were compared in long term light and dark adapted as well as photoinhibited Pisum sativum leaves using a novel chlorophyll fluorescence method and a new instrument: rapid light curves (RLC) generated with the MINI-PAM. RLCs are plots of ETRs versus actinic irradiances applied for 10 s. Large changes in maximum electron transport rates (ETR max ) were observed when leaves were shifted from dark to moderate light, or from dark to photoinhibitory light and vice versa. Maximum ETRs were very low following long term dark adaptation, but increased to maximum levels within 8 to 15 minutes of illumination. It took more than 3 hours, however, to return irradiance-exposed leaves to the fully dark adapted state. Quenching analysis of RLCs revealed large q E development in long-term dark adapted leaves accounting for the low ETRs. Leaves photoinhibited for 3 hours had similarly reduced ETRs. In these leaves, however, q I was largely responsible for this reduction. Actinic irradiance exposures and saturating flashes affected leaves with different irradiance histories differently.
Effects of high light stress on photosynthesis of polar macroalgae in relation to depth distribution
Marine Ecology Progress Series, 1997
The capability of several polar macroalgal s p e c~e s to protect photosynthesis against excesslve irradiation by dynamic photoinhibition was investigated and related to the specific depth distribu-t~o n of the species. Photoinhibition of photosynthesis was induced by exposure of the algae to a photon fluence rate of 500 pm01 m-2 S-' for 2 h. Changes in the oxygen production rate and in v~v o chlorophyll fluorescence were recorded. For oxygen measurements gross P, , , and the slope (alpha) of the fluence rate-response curve were detel-m~ned before and after photoinhibitory treatment and after recovery of photosynthesis in dim light. In fluorescence measurements the kinetics of change of the variable fluorescence during the inhibitory time phase and the recovery phase were determined. Significant differences in the reactions dunng exposure and recovery were found in the different algal classes. With~n each class a correlation between species depth distnbution and the ability to cope with high light stress was found. Algae growing in nature close to the water surface or in the Intertidal were generally not severely stressed. Algae growing in the rn~ddle and upper subtidal zone showed a decrease In photosynthetic activity during high l~g h t stress with full recovery of photosynthesis In subsequent d~m light. Fluorescence measurements showed that the reaction kinetics of photoinhibition and recovery were slower than in algae growing close to the water surface or in the intertidal. Algae growing in the lower subtidal also showed a decrease in the photosynthetic parameters due to high light stress; however, photosynthesis recovered only slightly and very slowly d u r~n g subsequent dim light conditions. In these algae the decrease in the photosynthetic activity was caused by photodamage rather than by dynamic photoinhibition. In conclusion these experiments indicate that algae already cultured for a long time in the laboratory, retain a certain genetic adaptation to the natural light environment. This is true not only for the lower light limit, but also for the upper light limit.
Journal of Phycology, 2004
The photosynthesis-irradiance (PE) relationship links indices of phytoplankton biomass (e.g. chl) to rates of primary production. The PE curve can be characterized by two variables: the light-limited slope (a b) and the light-saturated rate (P b max) of photosynthesis. Variability in PE curves can be separated into two categories: that associated with changes in the light saturation index, E k (5 P b max /a b) and that associated with parallel changes in a b and P b max (i.e. no change in E k). The former group we refer to as ''E k-dependent'' variability, and it results predominantly from photoacclimation (i.e. physiological adjustments in response to changing light). The latter group we refer to as ''E k-independent'' variability, and its physiological basis is unknown. Here, we provide the first review of the sporadic field and laboratory reports of E k-independent variability, and then from a stepwise analysis of potential mechanisms we propose that this important yet largely neglected phenomenon results from growth rate-dependent variability in the metabolic processing of photosynthetically generated reductants (and generally not from changes in the oxygenevolving PSII complexes). Specifically, we suggest that as growth rates decrease (e.g. due to nutrient stress), reductants are increasingly used for simple ATP generation through a fast (o1s) respiratory pathway that skips the carbon reduction cycle altogether and is undetected by standard PE methodologies. The proposed mechanism is consistent with the field and laboratory data and involves a simple new ''twist'' on established metabolic pathways. Our conclusions emphasize that simple reductants, not reduced carbon compounds, are the central currency of photoautotrophs.
Regulation of Photosynthetic Induction State by the Magnitude and Duration of Low Light Exposure
Plant physiology
Alocasia (Alocasia macrorrhiza [L.] C . Don) and soybean (Clycine max [L.]) were grown under high or low photon flux density (PFD) conditions to achieve a range of photosynthetic capacities and light-adaptation modes. The COz assimilation rate and in vivo linear electron transport rate (If) were determined over a range of PFDs and under saturating 1-s-duration lightflecks applied at a range of frequencies. At the same mean PFD, the assimilation rate and the Jf were lower under the lightfleck regimes than under constant light. The activation state of two, key enzymes of the photosynthetic carbon reduction cycle pathway, ribulose-l,5bisphosphate carboxylase/oxygenase (Rubisco) and fructose-l,6bisphosphatase, and the photosynthetic induction states (ISs) were also found to be lower under flashing as compared to continuous PFD. Under all conditions, the IS measured 120 s after an increase in PFD to constant and saturating values was highly correlated with the Rubisco activation state and stomatal conductances established in the light regime before the increase. Both the fructose-1,6bisphosphatase and Rubisco activities estabiished in a particular light regime were highly correlated with the mean If in that regime.
Marine Biology, 2009
The effects of light exposure on the photosynthetic activity of kleptoplasts were studied in the sacoglossan mollusc Elysia viridis. The photosynthetic activity of ingested chloroplasts was assessed in vivo by non-destructively measuring photophysiological parameters using pulse amplitude modulation (PAM) fluorometry. Animals kept under starvation were exposed to two contrasting light conditions, 30 lmol photons m -2 s -1 (low light, LL), and 140 lmol photons m -2 s -1 (high light, HL), and changes in photosynthetic activity were monitored by measuring the maximum quantum yield of photosystem II (PSII), F v /F m , the minimum fluorescence, F o , related to chlorophyll a content, and by measuring rapid light-response curves (RLC) of relative electron transport rate (rETR). RLCs were characterised by the initial slope of the curve, a RLC , related to efficiency of light capture, and the maximum rETR level, rETR m,RLC , determined by the carbon-fixation metabolism. Starvation induced the decrease of all photophysiological parameters. However, the retention of photosynthetic activity (number of days for F v /F m [ 0), as well as the rate and the patterns of its decrease over time, varied markedly with light exposure. Under HL conditions, a rapid, exponential decrease was observed for F v /F m , a RLC and rETR m,RLC , F o not showing any consistent trend of variation, and retention times ranged between 6 and 15 days. These results suggested that the retention of chloroplast functionality is limited by photoinactivation of PSII reaction center protein D1. In contrast, under LL conditions, a slower decrease in all parameters was found, with retention times varying from 15 to 57 days. F v /F m , a RLC and rETR m,RLC exhibited a bi-phasic pattern composed by a long phase of slow decrease in values followed by a rapid decline, whilst F o decayed exponentially. These results were interpreted as resulting from lower rates of D1 photoinactivation under low light and from the gradual decrease in carbon provided by photosynthesis due to reduction of functional photosynthetic units.
A systems-wide understanding of photosynthetic acclimation in algae and higher plants
The ability of phototrophs to colonise different environments relies on robust protection against oxidative stress, a critical requirement for the successful evolutionary transition from water to land. Photosynthetic organisms have developed numerous strategies to adapt their photosynthetic apparatus to changing light conditions in order to opti-mise their photosynthetic yield, which is crucial for life on Earth to exist. Photosynthetic acclimation is an excellent example of the complexity of biological systems, where highly diverse processes, ranging from electron excitation over protein protonation to enzymatic processes coupling ion gradients with biosynthetic activity, interact on drastically different timescales from picoseconds to hours. Efficient functioning of the photosynthetic apparatus and its protection is paramount for efficient downstream processes, including metabolism and growth. Modern experimental techniques can be successfully integrated with theoretical and mathematical models to promote our understanding of underlying mechanisms and principles. This review aims to provide a retrospective analysis of multidisciplinary photosynthetic acclimation research carried out by members of the Marie Curie Initial Training Project, AccliPhot, placing the results in a wider context. The review also highlights the applicability of photosynthetic organisms for
Marine Biology, 2005
Short-term variability in the photosynthetic activity of microphytobenthos assemblages was studied by measuring chlorophyll fluorescence rapid light curves (RLC), using pulse amplitude modulated (PAM) fluorometry. Measurements carried out on undisturbed samples under dark–light cycles revealed large diel oscillations in both the initial slope of the RLC (α) and in the maximum relative electron transport rate (ETRm). Short-term variations in RLC parameters were also observed, closely following changes in incident photon irradiance (E). Increases in irradiance were followed by decreases in α and increases in ETRm, resulting in significant correlations between the light-saturation parameter E k and E. These results were interpreted as resulting from the onset of reversible energy-dissipating, non-photochemical quenching mechanisms and of compensatory high light-induced activation of carbon metabolism activity. Short-term RLC variability was shown to result mainly from physiological causes and to be detectable only by using short (10–20 s) light steps during RLC construction. Dark-adapted samples kept under constant conditions exhibited apparently endogenous rhythms in RLC parameters and in the maximum quantum yield, F v/F m, coincident with vertical migratory movements occurring during subjective photoperiods. These fluctuations appeared to result from the interaction between migratory rhythms and the physiological responses, and from the endogenous activation of processes affecting both the efficiency of energy transfer from light-harvesting antennae to the photosystem II (PSII) reaction centres or from non-radiative pathways (F v/F m, α) and the reactions downstream of PSII (ETRm).
Aquatic Biology, 2009
The quantum yield of photosystem II (φ II , also termed ΔF /F m ' or F v /F m in light-or darkacclimated plants, respectively) of the tropical seagrass Halophila stipulacea was measured in situ using modulated fluorescence techniques over diel periods at a range of depths. Photosynthetic electron transport rates (ETRs), as derived from φ II values at specific ambient photosynthetically available radiation (PAR) irradiances, increased in direct proportion to increasing irradiance in the morning and, at shallow sites (7 to 10 m), reached saturating rates and then declined in the afternoon with lower PAR-specific ETRs. On the other hand, plants at 32 to 33 m showed no saturation even at midday, and the percentage reduction in PAR-specific afternoon ETRs was less than that of the shallower plants. The use of an automated shutter in the measuring device enabled non-photochemical quenching due to down-regulation and basal intrinsic non-radiative decay to be distinguished. While midday values of down-regulation were lower in deeper water, basal intrinsic non-radioactive decay remained fairly constant at 30 to 40% at all depths, with more variation in shallow waters. The maximal φ II (i.e. F v /F m ) reached similar values at midnight regardless of depth. H. stipulacea acclimates to the widely varying irradiances across this depth gradient by regularly modulating down-regulationbased non-photochemical quenching processes, while dissipating a large proportion of light energy through intrinsic decay regardless of depth.