A better understanding of the microalgal basic biology is still required to improve the feasibility of algal bio-products. The photosynthetic capability is one of the parameters that need further ...progress in research. A superior PSII activity was previously described in the green alga Neochloris oleoabundans. In this study, N. oleoabundans was grown in a glucose-supplied culture medium, in order to provide new information on the organisation and interaction of thylakoid protein complexes under mixotrophy. Fluorescence measurements suggested a strong association of light harvesting complex II (LHCII) to PSII in mixotrophic samples, confirmed by the lack of LHCII phosphorylation under growth light and the presence of PSI-PSII-LHCII megacomplexes in Blue-Native gel profile. The chloroplast ultrastructure was accordingly characterised by a higher degree of thylakoid appression compared to autotrophic microalgae. This also affected the capability of mixotrophic microalgae to avoid photodamage when exposed to high-light conditions. On the whole, it emerged that the presence of glucose affected the photosynthetic performance of mixotrophic samples, apparently limiting the dynamicity of thylakoid protein complexes. As a consequence, PSII is preserved against degradation and the PSI:PSII is lowered upon mixotrophic growth. Apparent increase in PSII photochemical activity was attributed to a down-regulated chlororespiratory electron recycling.
•Mixotrophy influences the photosynthetic performance of Neochloris oleoabundans.•High FV/FM values are linked to a down-regulated chlororespiration under mixotrophy.•A stronger association of thylakoid complexes is promoted in mixotrophic cells.•Lower dynamicity of complexes allows PSII preservation under growth light.
Baldisserotto C., Ferroni L., Giovanardi M., Boccaletti L., Pantaleoni L. and Pancaldi S. 2012. Salinity promotes growth of freshwater Neochloris oleoabundans UTEX 1185 (Sphaeropleales, Chlorophyta): ...morphophysiological aspects. Phycologia 51: 700-710. DOI: 10.2216/11-099.1
Neochloris oleoabundans was described as a freshwater unicellular green microalga; however, some literature suggested that it was an edaphic and halotolerant alga. Neochloris oleoabundans was studied so far for its high lipid content, especially under nitrogen starvation, for possible industrial applications. Information on the morphophysiological characteristics of the alga and its photosynthetic apparatus in different culture conditions still remained incomplete. In the present work, its growth was compared using low-salinity and brackish media with increasing nitrogen supply. The morphophysiological aspects, with a special attention on its photosynthetic apparatus, were analysed through light and transmission electron microscopy, photosynthetic pigment quantification, PSII maximum quantum yield measurements and evaluations of the chlorophyll-protein assembly state. In contrast to what has been reported in previous work on the positive effect of nitrate on N. oleobundans growth, we found negative or negligible effects in our samples cultivated in low-salinity or brackish media, respectively. Brackish conditions induced a better growth of the alga, which showed some morphological variations (cell volume enlargement, cell wall thickening, increased stromatic starch and polyphosphate grains). Furthermore, brackish cultured algae were characterized by a strong increase in cellular chlorophylls and carotenoids. Fluorimetric analyses pointed to the absence of disturbance to the photosynthetic apparatus and to a higher photosynthetic efficiency in brackish cultured samples with respect to controls in the low-salinity medium, indicating a somehow better photosynthetic performance. Interestingly, the behaviour of the F680/F685+694 ratio pointed to a possible positive correlation between nitrogen supply and PSII core stability. On the whole, morphological, biochemical and biophysical results confirmed the higher acclimatized growth of N. oleoabundans in brackish media, which seem more suitable for algal growth than low-salinity ones.
Room temperature (RT) microspectrofluorimetry in vivo of single cells has a great potential in photosynthesis studies. In order to get new information on RT chlorophyll fluorescence bands, we ...analyzed the spectra of
Chlamydomonas reinhardtii
mutants lacking fundamental proteins of the thylakoid membrane and spectra of photoinhibited WT cells. RT spectra of single living cells were characterized thorough derivative analyses and Gaussian deconvolution. The results obtained suggest that the dynamism in LHCII assembly could be sufficient to explain the variations in amplitudes of F680 (free LHCII), F694 (LHCII-PSII) and F702 (LHCII aggregates); F686 was assigned to the PSII core. Based on the revised assignments and on the variations observed, we discuss the meaning of the two fluorescence emission ratios F680/(F686 + F694) and F702/(F686 + F694), showing that these are sensitive parameters under moderate photoinhibition. In the most photoinhibited samples, the RT spectra tended to degenerate, showing characteristics of mutants that are partly depleted in PSII.
The Lycophyte Selaginella martensii efficiently acclimates to diverse light environments, from deep shade to full sunlight. The plant does not modulate the abundance of the Light Harvesting Complex ...II, mostly found as a free trimer, and does not alter the maximum capacity of thermal dissipation (NPQ). Nevertheless, the photoprotection is expected to be modulatable upon long‐term light acclimation to preserve the photosystems (PSII, PSI). The effects of long‐term light acclimation on PSII photoprotection were investigated using the chlorophyll fluorometric method known as “photochemical quenching measured in the dark” (qPd). Singularly high‐qPd values at relatively low irradiance suggest a heterogeneous antenna system (PSII antenna uncoupling). The extent of antenna uncoupling largely depends on the light regime, reaching the highest value in sun‐acclimated plants. In parallel, the photoprotective NPQ (pNPQ) increased from deep‐shade to high‐light grown plants. It is proposed that the differences in the long‐term modulation in the photoprotective capacity are proportional to the amount of uncoupled LHCII. In deep‐shade plants, the inconsistency between invariable maximum NPQ and lower pNPQ is attributed to the thermal dissipation occurring in the PSII core.
In plants, the non-photochemical quenching of chlorophyll fluorescence (NPQ) induced by high light reveals the occurrence of a multiplicity of regulatory processes of photosynthesis, primarily ...devoted to photoprotection of photosystem I and II (PSI and PSII). The study of NPQ relaxation in darkness allows the separation of three kinetically distinct phases: the fast relaxing high-energy quenching qE, the intermediate relaxing phase and the nearly non-relaxatable photoinhibitory quenching. Several processes can underlie the intermediate phase. In the ancient vascular plant Selaginella martensii (Lycopodiophyta) this component, here termed qX, was previously proposed to reflect mainly a photoprotective energy-spillover from PSII to PSI. It is hypothesized that qX is induced by an over-reduced photosynthetic electron transport chain from PSII to final acceptors. To test this hypothesis the leaves were treated with the reductant dithiothreitol (DTT) and the chlorophyll fluorescence changes were analysed during the induction with high irradiance and the subsequent relaxation in darkness. DTT treatment caused the well-known decrease in NPQ induction and expectedly resulted in a disturbed photosynthetic electron flow. The relaxation curves of Y(NPQ), formally representing the quantum yield of the regulatory thermal dissipation, revealed a DTT dose-dependent decrease in amplitude not only of qE, but also of qX, up to the complete disappearance of the latter. Modelling of the relaxation curves under alternative scenarios led to the conclusion that DTT is permissive with respect to qX induction but suppresses its dark relaxation. The strong dependence of qX on the chloroplast redox state is discussed with respect to its proposed energy-spillover photoprotective significance in a lycophyte.
•In Selaginella martensii, the reductant DTT inhibits NPQ induction by ca. 50%.•DTT causes a disturbance of the photosynthetic electron flow from PSII to final acceptors.•DTT causes a dose-dependent strong decrease in the amplitude of the intermediate phase qX of NPQ dark relaxation.•Modelled Y(NPQ) relaxation curves allowed disentangling between alternative options about DTT effect on qX.•A reduced stroma is permissive to qX induction but suppresses its relaxation.
Plants differ in their ability to tolerate salt stress. In aquatic ecosystems, it is important to know the responses of microalgae to increased salinity levels, especially considering that global ...warming will increase salinity levels in some regions of the Earth, e.g., Ethiopia. A green microalga, Kirchneriella sp. (Selenastraceae, Chlorophyta), isolated from freshwater Lake Awasa in the Rift Valley, Ethiopia, was cultured in media amended with 0, 0.4, 1.9, 5.9, and 19.4 g NaCl·L⁻¹ adjusted with NaCl to five salinity levels adjusted with NaCl. Growth was monitored for 3 mo, then samples were collected for photosynthetic pigment determinations, microspectrofluorimetric analyses, and micro- and submicroscopic examinations. The best growth was found at 1.9 g NaCl·L⁻¹. In the chloroplast, excess NaCl affected the coupling of light harvesting complex II and photosystem II (LHCII-PSII), but changes in thylakoid architecture and in the PSII assembly state allowed sufficient integrity of the photosynthetic membrane. The mucilaginous capsule around the cell probably provided partial protection against NaCl excess. On the whole, the microalga is able to acclimate to a range of NaCl concentrations, and this plasticity indicates that Kirchneriella sp. may survive future changes in water quality.
As major primary producers in marine environments, diatoms are considered a valuable feedstock of biologically active compounds for application in several biotechnological fields. Due to their ...metabolic plasticity, especially for light perception and use and in order to make microalgal production more environmentally sustainable, marine diatoms are considered good candidates for the large-scale cultivation. Among physical parameters, light plays a primary role. Even if sunlight is cost-effective, the employment of artificial light becomes a winning strategy if a high-value microalgal biomass is produced. Several researches on marine diatoms are designed to study the influence of different light regimens to increase biomass production enriched in biotechnologically high-value compounds (lipids, carotenoids, proteins, polysaccharides), or with emphasised photonic properties of the frustule.
Microalgae are studied as innovative sources of a wide range of highly valuable products, including proteins for the food/feed sectors. However, protein content varies depending on algal species, ...culture conditions and harvesting period. The Phylum Chlorophyta includes most of the described species of green algae. Due to their remarkable peculiarities, four Chlorophyta species belonging to two distinct classes were selected for the research:
Chlorella vulgaris
and
Chlorella protothecoides
as Trebouxiophyceae, and
Neochloris oleoabundans
and
Scenedesmus acutus
as Chlorophyceae. The algae were studied to obtain comparative results about their growth performance, and total protein content and profile under the same culture conditions. Since photosynthetic process directly influences biomass production, photosynthetic pigment, PSII maximum quantum yield and thylakoid protein content and profile were analysed. SDS-PAGE and 2D BN/SDS-PAGE were performed to expand information on the organization and assembly of the resolved thylakoid complexes of samples. Despite the algal species showed similar growth rates and photosynthetic efficiency,
S. acutus
showed the highest capability to accumulate proteins and photosynthetic pigments. Regarding the thylakoid protein profile, the two Trebouxiophyceae showed very similar pattern, whereas different amounts of LHCII occurred within the two Chlorophyceae. Finally, the separation of thylakoid protein complexes in 2D BN/SDS-PAGE revealed a more complex pattern in
S. acutus
as compared to the other species. Overall, it is suggested that a higher stability of the photosynthetic membranes can result in higher biomass and protein production. Altogether, results have highlighted the metabolic uniqueness of each strain, resulting in a non-obvious comparison with the other species.
The current understanding of photosynthesis across land plant phylogeny strongly indicates that ancient vascular plants are mainly limited by strong constitutive CO2 diffusional constraints, ...particularly low stomatal and mesophyll conductance. Considering that the lycophyte Selaginella martensii can demonstrate long-term light acclimation, this study addresses the regulation extent of CO2 assimilation in this species cultivated under contrasting light regimes of deep shade, medium shade and high light. Comparative analyses of photosynthetic traits, CO2 conductance and leaf morpho-anatomy revealed acclimation plasticity similar to that of seed plants, though occurring in the context of an inherently low photosynthetic capacity typical of lycophytes. Specific modulations of the stomatal density and aperture, chloroplast surface exposed to mesophyll airspaces and cell wall thickness sustained a marked improvement in CO2 diffusion from deep shade to high light. However, the maximum carboxylation rate was comparatively less effectively upregulated, leading to a greater incidence of biochemical limitations of photosynthesis. Because of a low carboxylation capacity under any light regime, a lycophyte prevents potential photodamage to the chloroplast by not only exploiting the thermal dissipation of excess absorbed energy but also diverting a large fraction of photosynthetic electrons to sinks alternative to carboxylation.
•In a lycophyte the CO2 diffusion into the leaf is strongly regulated based on growth light environment.•Changes in CO2 diffusion depend on stomatal density and size, and on chloroplast surface facing the intercellular spaces.•Under high light, photosynthesis is more limited by biochemical than diffusional constraints.•Safety valves are thermal dissipation of excess absorbed light and electron flow to alternative sinks.•Acclimation plasticity of photosynthesis in a lycophyte is overall similar to that of seed plants.
Using chlorophyll (Chl)
a
fluorescence many aspects of the photosynthetic apparatus can be studied, both in vitro and, noninvasively, in vivo. Complementary techniques can help to interpret changes ...in the Chl
a
fluorescence kinetics. Kalaji et al. (Photosynth Res 122:121–158,
2014a
) addressed several questions about instruments, methods and applications based on Chl
a
fluorescence. Here, additional Chl
a
fluorescence-related topics are discussed again in a question and answer format. Examples are the effect of connectivity on photochemical quenching, the correction of
F
V
/
F
M
values for PSI fluorescence, the energy partitioning concept, the interpretation of the complementary area, probing the donor side of PSII, the assignment of bands of 77 K fluorescence emission spectra to fluorescence emitters, the relationship between prompt and delayed fluorescence, potential problems when sampling tree canopies, the use of fluorescence parameters in QTL studies, the use of Chl
a
fluorescence in biosensor applications and the application of neural network approaches for the analysis of fluorescence measurements. The answers draw on knowledge from different Chl
a
fluorescence analysis domains, yielding in several cases new insights.
PDF
