Electron Transport Rate

For the first time, the photosynthetic performance of field-grown macroalgae from the Magellan Strait was evaluated with respect to their photoadaptation in the field and acclimation potential to ultraviolet radiation. Five macroalgal species were collected in the eulittoral and the upper sublittoral: Ulva intestinalis, Porphyra columbina, Adenocystis utricularis, Desmarestia confervoides and D. ligulata. Photosynthesis vs. irradiance (P-I) curves of macroalgae

To study the response of tomato (Solanum lycopersicum cv. Rio Grande) to salinity, the effect on plant growth, water relations, stomatal conductance and Chlorophyll fluorescence was investigated. Tomato plants were grown in peat culture under controlled conditions ...

A poplar plantation has been exposed to an elevated CO2 concentration for 5 years using the free air CO2 enrichment (FACE) technique. Even after such a long period of exposure, leaves of Populus x euramericana have not shown clear signs of photosynthetic acclimation. Only at the end of the growing season for shade leaves was a decrease of maximum velocity

Rapid light-response curves (RLC) of variable chlorophyll fluorescence were measured on estuarine benthic microalgae with the purpose of characterising its response to changes in ambient light, and of investigating the relationship to steady-state light-response curves (LC). The response of RLCs to changes in ambient light (E, defined as the irradiance level to which a sample is acclimated to prior to the start of the RLC) was characterised by constructing light-response curves for the RLC parameters α RLC, the initial slope, ETRm,RLC, the maximum relative electron transport rate, and E k,RLC, the light-saturation parameter. Measurements were carried out on diatom-dominated suspensions of benthic microalgae and RLC and LC parameters were compared for a wide range of ambient light conditions, time of day, season and sample taxonomic composition. The photoresponse of RLC parameters was typically bi-phasic, consisting of an initial increase of all parameters under low ambient light (E < 21–181 μmol m−2 s−1), and of a phase during which α RLC decreased significantly with E, and the increase of ETRm,RLC and E k,RLC was attenuated. The relationship between RLC and LC parameters was dependent on ambient irradiance, with significant correlations being found between α RLC and α, and between ETRm,RLC and ETRm, for samples acclimated to low and to high ambient irradiances, respectively. The decline of α RLC under high light (Δα RLC) was strongly correlated (P < 0.001 in all cases) with the level of non-photochemical quenching (NPQ) measured before each RLC. These results indicate the possibility of using RLCs to characterise the steady-state photoacclimation status of a sample, by estimating the LC parameter E k, and to trace short-term changes in NPQ levels without dark incubation.

Conventional fossil fuels are facing a global challenge which lead scientists to explore alternative fuel production from biological sources. The algae-based fuels are gaining rapid attention as it has potential to replace petroleum-based fuels. An indigenous high lipid producing microalgae was isolated from a freshwater pond in the KwaZulu-Natal province of South Africa. The isolate was later identified as Chlorella

The steady-state chlorophyll fluorescence (Fs) presented different diurnal variation patterns in irrigated and water-stressed plants, the latter showing a midday depression, which was more pronounced as more severe was the stress. Here we address the possible causes of such variations and discuss the applicability of Fs for stress assessment. In water stress experiments with several C3 plants, the ratio of Fs normalised to dark-adapted intrinsic fluorescence (Fo) was negatively and exponentially correlated with non-photochemical quenching (NPQ). The relationship was abolished by treatment with DTT, an inhibitor of xanthophyll de-epoxidation. These and other evidences suggest that increased non-radiative dissipation under drought was responsible for Fs variations. Interestingly, the ratio Fs/Fo fixed at a given high light intensity directly correlated with CO2 assimilation in air, with electron transport rate and with stomatal conductance. Therefore, the ratio Fs/Fo, which can be mea...

Assessments of photosynthetic activity in marine plants can now be made in situ using a newly developed, submersible, pulse-amplitude modulated (PAM) fluorometer: Diving-PAM. PAM fluorometry provides a measure of chlorophyll a fluorescence using rapid-light curves in which the electron-transport rate can be determined for plants exposed to ambient light conditions. This technique was used to compare the photosynthetic responses of seagrasses near Rottnest Island, Western Australia. Several fluorescence parameters were measured as a function of time of day and water depth; electron-transport rate (ETR), quantum yield, photochemical quenching and non-photochemical quenching and Photosystem II (PSII) photochemical efficiency (F v :F m ratio) were measured. Results indicate that recent light-history plays a crucial role in seagrass photosynthetic responses. Maximum ETR of Posidonia australis, Amphibolis antarctica and Halophila ovalis is influenced by the irradiance during the diurnal cycle, with low rates at dawn and dusk (<10 μmol electron m−2 s−1), highest rates in late morning (40 to 60 μmol electron m−2 s−1) and a mid-day depression. Maximum ETR and PSII photochemical efficiency varied widely between seagrass species and were not correlated. A comparison of photochemical to non-photochemical quenching indicated that seagrasses in shallow water receiving high light have a high capacity for non-photochemical quenching (e.g. light protection) compared to seagrasses in deep water. These results indicate that in situ measurements of photosynthesis will provide new insights into the mechanisms and adaptive responses of marine plants.

The effects of the motility inhibitors 2,3-butanedione monoxime (BDM) and latranculin A (Lat A) on the motility, photosynthetic activity and pigment composition of the benthic diatoms Cylindrotheca closterium and Pleurosigma angulatum were studied. BDM inhibited diatom gliding, preventing motility at concentrations of 12.5 mM and 50 mM for C. closterium and P. angulatum, respectively. For both species, the quantum yield of PSII (ΔF/Fm′) decreased with increasing concentrations of BDM. Reduced excitation at PSII reaction centres were caused by BDM-induced conversion of the pigment diadinoxanthin to diatoxanthin, through the activation of the xanthophyll cycle. Lat A inhibited diatom gliding, preventing motility at concentrations of 0.1 μM and 0.25 μM for C. closterium and P. angulatum, respectively. Concentrations of Lat A as high as 1 μM showed no significant effects on the PSII quantum yield, on the light-response curves of relative electron transport rate (initial slope of light curve, a, and maximum relative electron transport rate, ETRm), or on the pigment composition of treated diatom cells. These results indicate that BDM has unavoidable effects on the photosynthetic activity by affecting the xanthophyll cycle, which hamper its use as a motility inhibitor in diatom studies. On the other hand, the absence of effects of Lat A on the photosynthetic activity makes this motility inhibitor a useful tool for the study of the ecological and photophysiological relevance of benthic diatom migration.

The operation of photosynthetic energy-dissipating processes is commonly characterized by measuring the light response of the nonphotochemical quenching (NPQ) of chlorophyll fluorescence, or NPQ versus E curves. This study proposes a mathematical model for the quantitative description of the generic NPQ versus E curve. The model is an adaptation of the Hill equation and is based on the close dependence of NPQ on the xanthophyll cycle (XC). The model was tested on NPQ versus E curves measured in the plant Arabidopsis thaliana and the diatom Nitzschia palea, representing the two main types of XC, the violaxanthin–antheraxanthin–zeaxanthin (VAZ) type and the diadinoxanthin–diatoxanthin (DD–DT) type, respectively. The model was also fitted to a large number of published light curves, covering the widest possible range of XC types, taxa, growth conditions, and experimental protocol of curve generation. The model provided a very good fit to experimental and published data, coping with the large variability in curve characteristics. The model was further used to quantitatively compare the light responses of NPQ and of PSII electron transport rate, ETR, through the use of indices combining parameters of the models describing the two types of light–response curves. Their application to experimental and published data showed a systematic large delay of the buildup of NPQ relatively to the saturation of photochemistry. It was found that when ETR reaches saturation, NPQ is on average still below one fifth of its maximum attainable level, which is only reached at irradiances about three times higher. It was also found that organisms having the DD–DT type of XC appeared to be able to start operating the XC at lower irradiances than those of the VAZ type.