The Genetic and Physiological Characteristics of the Symbiodinium spp. in the Endemic Anemone Anthopleura Aureoradiata

<p>Photosynthetic dinoflagellates of the genus Symbiodinium form symbiotic relationships with many marine hosts, including cnidarian corals and sea anemones. This partnership is extremely successful in tropical waters leading to a great diversity of coral species and Symbiodinium types. Environmental condition in the tropics are stable, changes to which can lead to destabilization of the symbiotic interactions between the host and symbiont, which in turn can lead to total breakdown of the partnership and expulsion of the symbiont. Temperate symbiotic cnidarian species, especially sea anemones, are less common but locally abundant. Environmental conditions are highly variable with extreme differences in light and temperature. Adaptation to these conditions has led to the success of resilient partnerships, but also to less diversity of Symbiodinium types. This study looked at the relationship between the endemic New Zealand anemone, Anthopleura aureoradiata, and its symbiotic relationship with the Symbiodinium cells it harbours. The aim was to determine why and how this symbiotic relationship is so resilient to the temperate conditions by 1) determining the molecular identity of the Symbiodinium spp. within the anemone, throughout its latitudinal range and through the seasons, and whether any seasonal changes differed between two habitats, the rocky shore and mudflats; 2) comparing the identity of the Symbiodinium spp. in New Zealand with those from four species of anemones from Europe (Cereus pedunculatus, Anthopleura ballii and Anemonia viridis from the south-west of England and Aiptasia mutabilis from Brittany (France)) to establish any differences or similarities between the northern and southern hemispheres; 3) determining whether resilience to environmental conditions is attributed to the Symbiodinium photoprotective mechanisms. A. aureoradiata were collected in early autumn in five sites from the top (Parengarenga Harbour) to the bottom (Stewart Island) of New Zealand for the latitudinal study. Seasonal anemones were collected from a rocky shore in Wellington Harbour (Point Halswell, Kau Bay) and a mudflat at Pauatahanui Inlet. Symbiodinium types were identified to subcladal level using ITS2 sequencing. A low diversity of types was found, with all anemones harbouring algal cells identified as being similar, or identical to, Symbiodinium sp. Mediterranean clade A (Med clade A) and Symbiodinium sp. Amed (Amed). 96.55% of the anemones from the latitudinal study, all the winter anemones, 87.50% of the summer anemones and almost 78% of the autumn anemones harboured Symbiodinium cells most similar or identical to Med clade A. All Symbiodinium sequences from the European anemones also were identified as being similar or identical to Med clade A or Amed, suggesting that the Symbiodinium in A. aureoradiata are likely not endemic. It is not known whether anemones harbour both types simultaneously and whether a change in dominant symbiont type occurs with seasons within anemones by “shuffling”. The photophysiology of the Symbiodinium cells isolated from the anemones was studied using an Imaging-PAM fluorometer whilst being maintained in six light and temperature treatments. The photosynthetic rate of PSII, energy quenching by NPQ, and photosystem recovery were measured to determine whether the Symbiodinium cells had a strong capacity for photoprotection and were able to down-regulate quickly to reduce photodamage to the chloroplast. The main outcome of this study is that the Symbiodinium cells within A. aureoradiata are very effective in protecting themselves against photo-damage by activating an efficient NPQ system. Down-regulation of the quantum efficiency of PSII under high light conditions appeared to cease altogether. Whether this was a true measurement of down-regulation to stop photodamage, or whether these clade A types use an alternative electron transport that bypasses PSII, and can therefore not be measured with the I-PAM fluorometer technique used, needs to be addressed in future studies.</p>

The Genetic and Physiological Characteristics of the Symbiodinium spp. in the Endemic Anemone Anthopleura Aureoradiata

<p>Photosynthetic dinoflagellates of the genus Symbiodinium form symbiotic relationships with many marine hosts, including cnidarian corals and sea anemones. This partnership is extremely successful in tropical waters leading to a great diversity of coral species and Symbiodinium types. Environmental condition in the tropics are stable, changes to which can lead to destabilization of the symbiotic interactions between the host and symbiont, which in turn can lead to total breakdown of the partnership and expulsion of the symbiont. Temperate symbiotic cnidarian species, especially sea anemones, are less common but locally abundant. Environmental conditions are highly variable with extreme differences in light and temperature. Adaptation to these conditions has led to the success of resilient partnerships, but also to less diversity of Symbiodinium types. This study looked at the relationship between the endemic New Zealand anemone, Anthopleura aureoradiata, and its symbiotic relationship with the Symbiodinium cells it harbours. The aim was to determine why and how this symbiotic relationship is so resilient to the temperate conditions by 1) determining the molecular identity of the Symbiodinium spp. within the anemone, throughout its latitudinal range and through the seasons, and whether any seasonal changes differed between two habitats, the rocky shore and mudflats; 2) comparing the identity of the Symbiodinium spp. in New Zealand with those from four species of anemones from Europe (Cereus pedunculatus, Anthopleura ballii and Anemonia viridis from the south-west of England and Aiptasia mutabilis from Brittany (France)) to establish any differences or similarities between the northern and southern hemispheres; 3) determining whether resilience to environmental conditions is attributed to the Symbiodinium photoprotective mechanisms. A. aureoradiata were collected in early autumn in five sites from the top (Parengarenga Harbour) to the bottom (Stewart Island) of New Zealand for the latitudinal study. Seasonal anemones were collected from a rocky shore in Wellington Harbour (Point Halswell, Kau Bay) and a mudflat at Pauatahanui Inlet. Symbiodinium types were identified to subcladal level using ITS2 sequencing. A low diversity of types was found, with all anemones harbouring algal cells identified as being similar, or identical to, Symbiodinium sp. Mediterranean clade A (Med clade A) and Symbiodinium sp. Amed (Amed). 96.55% of the anemones from the latitudinal study, all the winter anemones, 87.50% of the summer anemones and almost 78% of the autumn anemones harboured Symbiodinium cells most similar or identical to Med clade A. All Symbiodinium sequences from the European anemones also were identified as being similar or identical to Med clade A or Amed, suggesting that the Symbiodinium in A. aureoradiata are likely not endemic. It is not known whether anemones harbour both types simultaneously and whether a change in dominant symbiont type occurs with seasons within anemones by “shuffling”. The photophysiology of the Symbiodinium cells isolated from the anemones was studied using an Imaging-PAM fluorometer whilst being maintained in six light and temperature treatments. The photosynthetic rate of PSII, energy quenching by NPQ, and photosystem recovery were measured to determine whether the Symbiodinium cells had a strong capacity for photoprotection and were able to down-regulate quickly to reduce photodamage to the chloroplast. The main outcome of this study is that the Symbiodinium cells within A. aureoradiata are very effective in protecting themselves against photo-damage by activating an efficient NPQ system. Down-regulation of the quantum efficiency of PSII under high light conditions appeared to cease altogether. Whether this was a true measurement of down-regulation to stop photodamage, or whether these clade A types use an alternative electron transport that bypasses PSII, and can therefore not be measured with the I-PAM fluorometer technique used, needs to be addressed in future studies.</p>

Low-Cost Chlorophyll Fluorescence Imaging for Stress Detection

Plants naturally contain high levels of the stress-responsive fluorophore chlorophyll. Chlorophyll fluorescence imaging (CFI) is a powerful tool to measure photosynthetic efficiency in plants and provides the ability to detect damage from a range of biotic and abiotic stresses before visible symptoms occur. However, most CFI systems are complex, expensive systems that use pulse amplitude modulation (PAM) fluorometry. Here, we test a simple CFI system, that does not require PAM fluorometry, but instead simply images fluorescence emitted by plants. We used this technique to visualize stress induced by the photosystem II-inhibitory herbicide atrazine. After applying atrazine as a soil drench, CFI and color images were taken at 15-minute intervals, alongside measurements from a PAM fluorometer and a leaf reflectometer. Pixel intensity of the CFI images was negatively correlated with the quantum yield of photosystem II (ΦPSII) (p < 0.0001) and positively correlated with the measured reflectance in the spectral region of chlorophyll fluorescence emissions (p < 0.0001). A fluorescence-based stress index was developed using the reflectometer measurements based on wavelengths with the highest (741.2 nm) and lowest variability (548.9 nm) in response to atrazine damage. This index was correlated with ΦPSII (p < 0.0001). Low-cost CFI imaging can detect herbicide-induced stress (and likely other stressors) before there is visual damage.

Evidence for variable chlorophyll fluorescence of photosystem I in vivo

Room temperature fluorescence in vivo and its light-induced changes are dominated by chlorophyll a fluorescence excited in photosystem II, F(II), peaking around 685 nm. Photosystem I fluorescence, F(I), peaking around 730 nm, so far has been assumed to be constant in vivo. Here, we present evidence for significant contributions of F(I) to variable fluorescence in the green unicellular alga Chlorella vulgaris, the cyanobacterium Synechococcus leopoliensis and a light-green ivy leaf. A Multi-Color-PAM fluorometer was applied for measurements of the polyphasic fluorescence rise (O-I1-I2-P) induced by strong 440 nm light in a dilute suspension of Chlorella, with detection alternating between emission above 700 nm (F > 700) and below 710 nm (F < 710). By averaging 10 curves each of the F > 700 and F < 710 recordings even small differences could be reliably evaluated. After equalizing the amplitudes of the O-I1 phase, which constitutes a specific F(II) response, the O-I1-I2 parts of the two recordings were close to identical, whereas the I2-P phase was larger in F > 700 than in F < 710 by a factor of 1.42. In analogous measurements with Synechococcus carried out in the dark state 2 using strong 625 nm actinic light, after O-I1 equalization the I2-P phase in F > 700 exceeded that in F < 710 even by a factor of 1.99. In measurements with Chlorella, the I2-P phase and with it the apparent variable fluorescence of PS I, Fv(I), were suppressed by moderate actinic background light and by the plastoquinone antagonist DBMIB. Analogous measurements with leaves are rendered problematic by unavoidable light intensity gradients and the resulting heterogenic origins of F > 700 and F < 710. However, a light-green young ivy leaf gave qualitatively similar results as those obtained with the suspensions, thus strongly suggesting the existence of Fv(I) also in leaves.

Modification of a gas exchange system to measure active and passive chlorophyll fluorescence simultaneously under field conditions

Solar-induced fluorescence (SIF) is a promising tool to estimate photosynthesis across scales; however, there has been limited research done at the leaf-level to investigate the relationship between SIF and photosynthesis. To help bridge this gap, a LI-COR LI-6800 gas exchange instrument was modified with a visible-near-infrared (VIS-NIR) spectrometer to measure active and passive fluorescence simultaneously. The system was adapted by drilling a hole into the bottom plate of the leaf chamber and inserting a fiber-optic to measure passive steady-state fluorescence (Ft,λ, analogous to SIF) from the abaxial surface of a leaf. This new modification can concurrently measure gas exchange, passive fluorescence, and active fluorescence over the same leaf area and will allow researchers to measure leaf-level Ft,λ in the field to validate tower-based and satellite measurements. To test the modified instrument, measurements were performed on leaves of well-watered and water stressed walnut plants at three light-levels and a constant air temperature. Measurements on these same plants were also conducted using a similarly modified Walz GFS-3000 gas exchange instrument to compare results. We found a positive linear correlation between Ft,λ measurements from the modified LI-6800 and GFS-3000 instruments. We also report a positive linear relationship between Ft,λ and normalized steady-state chlorophyll fluorescence (Ft/Fo) from the pulse-amplitude modulation (PAM) fluorometer of the LI-6800 system. Accordingly, this modification will inform the link between spectrally resolved Ft,λ and gas-exchange – leading to improved interpretation of how remotely sensed SIF tracks changes in the light reactions of photosynthesis.

Inactivation of H+-ATPase Participates in the Influence of Variation Potential on Photosynthesis and Respiration in Peas

Local damage (e.g., burning, heating, or crushing) causes the generation and propagation of a variation potential (VP), which is a unique electrical signal in higher plants. A VP influences numerous physiological processes, with photosynthesis and respiration being important targets. VP generation is based on transient inactivation of H+-ATPase in plasma membrane. In this work, we investigated the participation of this inactivation in the development of VP-induced photosynthetic and respiratory responses. Two- to three-week-old pea seedlings (Pisum sativum L.) and their protoplasts were investigated. Photosynthesis and respiration in intact seedlings were measured using a GFS-3000 gas analyzer, Dual-PAM-100 Pulse-Amplitude-Modulation (PAM)-fluorometer, and a Dual-PAM gas-exchange Cuvette 3010-Dual. Electrical activity was measured using extracellular electrodes. The parameters of photosynthetic light reactions in protoplasts were measured using the Dual-PAM-100; photosynthesis- and respiration-related changes in O2 exchange rate were measured using an Oxygraph Plus System. We found that preliminary changes in the activity of H+-ATPase in the plasma membrane (its inactivation by sodium orthovanadate or activation by fusicoccin) influenced the amplitudes and magnitudes of VP-induced photosynthetic and respiratory responses in intact seedlings. Decreases in H+-ATPase activity (sodium orthovanadate treatment) induced fast decreases in photosynthetic activity and increases in respiration in protoplasts. Thus, our results support the effect of H+-ATPase inactivation on VP-induced photosynthetic and respiratory responses.

Exogenous Abscisic Acid Can Influence Photosynthetic Processes in Peas through a Decrease in Activity of H+-ATP-ase in the Plasma Membrane

Abscisic acid (ABA) is an important hormone in plants that participates in their acclimation to the action of stressors. Treatment by exogenous ABA and its synthetic analogs are a potential way of controlling the tolerance of agricultural plants; however, the mechanisms of influence of the ABA treatment on photosynthetic processes require further investigations. The aim of our work was to investigate the participation of inactivation of the plasma membrane H+-ATP-ase on the influence of ABA treatment on photosynthetic processes and their regulation by electrical signals in peas. The ABA treatment of seedlings was performed by spraying them with aqueous solutions (10−5 M). The combination of a Dual-PAM-100 PAM fluorometer and GFS-3000 infrared gas analyzer was used for photosynthetic measurements; the patch clamp system on the basis of a SliceScope Pro 2000 microscope was used for measurements of electrical activity. It was shown that the ABA treatment stimulated the cyclic electron flow around photosystem I and decreased the photosynthetic CO2 assimilation, the amplitude of burning-induced electrical signals (variation potentials), and the magnitude of photosynthetic responses relating to these signals; in contrast, treatment with exogenous ABA increased the heat tolerance of photosynthesis. An investigation of the influence of ABA treatment on the metabolic component of the resting potential showed that this treatment decreased the activity of the H+-ATP-ase in the plasma membrane. Inhibitor analysis using sodium orthovanadate demonstrated that this decrease may be a mechanism of the ABA treatment-induced changes in photosynthetic processes, their heat tolerance, and regulation by electrical signals.

Relation of Photochemical Reflectance Indices Based on Different Wavelengths to the Parameters of Light Reactions in Photosystems I and II in Pea Plants

Measurement and analysis of the numerous reflectance indices of plants is an effective approach for the remote sensing of plant physiological processes in agriculture and ecological monitoring. A photochemical reflectance index (PRI) plays an important role in this kind of remote sensing because it can be related to early changes in photosynthetic processes under the action of stressors (excess light, changes in temperature, drought, etc.). In particular, we previously showed that light-induced changes in PRIs could be strongly related to the energy-dependent component of the non-photochemical quenching in photosystem II. The aim of the present work was to undertake comparative analysis of the efficiency of using light-induced changes in PRIs (ΔPRIs) based on different wavelengths for the estimation of the parameters of photosynthetic light reactions (including the parameters of photosystem I). Pea plants were used in the investigation; the photosynthetic parameters were measured using the pulse-amplitude-modulated (PAM) fluorometer Dual-PAM-100 and the intensities of the reflected light were measured using the spectrometer S100. The ΔPRIs were calculated as ΔPRI(band,570), where the band was 531 nm for the typical PRI and 515, 525, 535, 545, or 555 nm for modified PRIs; 570 nm was the reference wavelength for all PRIs. There were several important results: (1) ∆PRI(525,570), ∆PRI(531,570), ∆PRI(535,570), and ∆PRI(545,570) could be used for estimation of most of the photosynthetic parameters under light only or under dark only conditions. (2) The combination of dark and light conditions decreased the efficiency of ∆PRIs for the estimation of the photosynthetic parameters; ∆PRI(535,570) and ∆PRI(545,570) had maximal efficiency under these conditions. (3) ∆PRI(515,570) and ∆PRI(525,570) mainly included the slow-relaxing component of PRI; in contrast, ∆PRI(531,570), ∆PRI(535,570), ∆PRI(545,570), and ∆PRI(555,570) mainly included the fast-relaxing component of PRI. These components were probably caused by different mechanisms.

Variable PSII functioning and bleaching conditions of tropical scleractinian corals pre-and post-bleaching event

Mattan-Moorgawa S, Rughooputh SDDV, Bhagooli R. 2017. Variable PSII functioning and bleaching conditions of tropical scleractinian corals pre-and post-bleaching event. Ocean Life 1: 1-10. This study compared pre-bleaching and post-bleaching conditions of eight reef-building corals, Acropora cytherea, Acropora hyacynthus, Acropora muricata, Acropora sp., Pocillopora damicornis, Pocillopora eydouxi, Galaxea fascicularis and Fungia sp., in terms of visual coloration (non-bleached (NB), pale (P), partially bleached (PB) and bleached (B)) and chlorophyll fluorescence yield at photosystem II (PSII)). A total of twenty colonies from twelve stations along four transects were surveyed at Belle-Mare, Mauritius, from October 2008 to October 2009, and compared to the CoralWatch Coral Health Chart. PSII functioning, measured as Fv/Fm, were recorded in coral samples using a pulse-amplitudemodulated (PAM) fluorometer. Physico-chemical parameters (sea surface temperature, dissolved oxygen, salinity and pH) were recorded in situ. An increase in SST up to 31.4ºC in February 2009 triggered the bleaching event observed in May 2009 at the site. Acroporids showed the first sign of bleaching and paling as from January 2009 when mean SST was at 30ºC. Branching coral (P. eydouxi) and solitary coral (Fungia sp.) exhibited only 15% of their colonies showing paling by April 2009. A. cytherea, A. hyacynthus, and A. muricata showed varying bleaching conditions [Pale (P), Partially-bleached (PB) and Bleached (B)] at onset of the bleaching event whilst Acropora sp. showed only a paling of its colonies. Post-bleaching data indicated a differential recovery in visual coloration and PSII functioning among the corals. P. eydouxi and Fungia sp. showed no bleaching conditions throughout the study. P. damicornis and G. fascicularis indicated a quick coloration recovery from P to NB after the bleaching event, although their maximum quantum yield at PSII did not show significant changes in P and NB samples. A. muricata recovered faster than A. hyacynthus and A. cytherea in terms of PSII functioning. A differential recovery was observed post-bleaching event among the eight coral species, in terms of recovery of color and PSII functioning. The order of recovery was as follows: massive-like/ solitary corals > branching and semi-bulbous corals > tabular corals.