photosynthetic production
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2021 ◽  
Author(s):  
◽  
Michael Doherty

<p>Ocean acidification has the potential to drastically alter the coral reef ecosystem by reducing the calcification rate of corals and other reef-builders, and hence a considerable amount of research is now focused on this issue. It also is conceivable that acidification may affect other physiological processes of corals. In particular, acidification may alter photosynthetic physiology and hence the productivity of the coraldinoflagellate symbiosis that is pivotal to the reef's survival and growth. However, very little is known about the impacts of acidification on the photophysiology of corals or, indeed, other invertebrate-algal symbioses. This gap in our knowledge was addressed here by measuring the impacts of acidification (pH 7.6 versus pH 8.1) on the photophysiology and health of the tropical coral Stylophora pistillata and its isolated dinoflagellate symbionts ('zooxanthellae'), and the temperate sea anemone Anthopleura aureoradiata. The comparative nature of this study allowed for any differences between tropical and temperate symbioses, and zooxanthellae in a symbiotic or free-living state, to be assessed. Corals, anemones and cultured zooxanthellae were maintained in flowthrough seawater systems, and treated either with non-acidified (control) seawater at pH 8.1, or seawater acidified with CO2 or HCl to pH 7.6. A variety of parameters, including zooxanthellar density, chlorophyll content, photosynthetic health (Yi), and the ratio of gross photosynthetic production to respiration (P:R) were measured via cell counts, spectrophotometry, respirometry and PAM fluorometry, at a series of time-points up to a maximum of 42 days. Acidification generated by the addition of CO2 had no discernible effect on Yi of either the corals or anemones. However, in the coral, chlorophyll content per zooxanthella cell increased by 25%, which was countered by a near-significant decline (22%) in the rate of gross photosynthesis per unit chlorophyll; as zooxanthellar density remained unchanged, this led to a constant P:R ratio. When acidified via CO2, the isolated zooxanthellae exhibited no impacts in recorded Yi or chlorophyll levels. The response of the anemone to acidification via CO2 was different to that observed in the coral, as the density of zooxanthellae increased, rather than the chlorophyll content per cell, leading to an increased rate of gross photosynthesis. However P:R again remained constant as the increased photosynthesis was matched by an increased rate of respiration. In contrast to the impacts of CO2, HCl adversely impacted the chlorophyll content per cell in both the isolated zooxanthellae and sea anemone, and Yi, gross photosynthesis per cell, and overall gross photosynthesis in the sea anemone; however, despite the decline in gross photosynthesis, P:R remained constant due to the concurrent decline in respiration. Unfortunately, the corals in the HCl experiment died due to technical issues. There are two plausible reasons for this difference between CO2 and HCl. Firstly, HCl may have caused intracellular acidosis which damaged chloroplast structure and photosynthetic function. Secondly, the increased levels of aqueous CO2 stimulated photosynthetic function and hence mitigated for the effects of lowered pH. In addition, evidence is presented for a pH threshold for A. aureoradiata of between pH 6 and pH 6.75 (acidified with HCl), at which point photosynthesis 'shuts-down'. This suggests that, even without the potentially beneficial effects from increased CO2 levels, it is likely that oceanic pH would need to decrease to less than pH 6.75 for any acidosis effects to compromise the productivity of this particular symbiosis. Since acidification will have the benefits of increased CO2 and will reach nowhere near such low pH levels as those extremes tested here, it is proposed that ocean acidification via increased dissolution of CO2 into our oceans will have no impact on the photosynthetic production of symbiotic cnidarians. Indeed, it is entirely likely that increased CO2 will add some benefit to the usually carbon-limited symbiotic zooxanthellae. Ocean acidification is not likely to benefit corals however, with compromised calcification rates likely to undermine the viability of the coral. Symbiotic sea anemones, which do not bio-mineralise CaCO3, are better placed to take advantage of the increased CO2 as we move toward more acidic oceans.</p>


2021 ◽  
Author(s):  
◽  
Michael Doherty

<p>Ocean acidification has the potential to drastically alter the coral reef ecosystem by reducing the calcification rate of corals and other reef-builders, and hence a considerable amount of research is now focused on this issue. It also is conceivable that acidification may affect other physiological processes of corals. In particular, acidification may alter photosynthetic physiology and hence the productivity of the coraldinoflagellate symbiosis that is pivotal to the reef's survival and growth. However, very little is known about the impacts of acidification on the photophysiology of corals or, indeed, other invertebrate-algal symbioses. This gap in our knowledge was addressed here by measuring the impacts of acidification (pH 7.6 versus pH 8.1) on the photophysiology and health of the tropical coral Stylophora pistillata and its isolated dinoflagellate symbionts ('zooxanthellae'), and the temperate sea anemone Anthopleura aureoradiata. The comparative nature of this study allowed for any differences between tropical and temperate symbioses, and zooxanthellae in a symbiotic or free-living state, to be assessed. Corals, anemones and cultured zooxanthellae were maintained in flowthrough seawater systems, and treated either with non-acidified (control) seawater at pH 8.1, or seawater acidified with CO2 or HCl to pH 7.6. A variety of parameters, including zooxanthellar density, chlorophyll content, photosynthetic health (Yi), and the ratio of gross photosynthetic production to respiration (P:R) were measured via cell counts, spectrophotometry, respirometry and PAM fluorometry, at a series of time-points up to a maximum of 42 days. Acidification generated by the addition of CO2 had no discernible effect on Yi of either the corals or anemones. However, in the coral, chlorophyll content per zooxanthella cell increased by 25%, which was countered by a near-significant decline (22%) in the rate of gross photosynthesis per unit chlorophyll; as zooxanthellar density remained unchanged, this led to a constant P:R ratio. When acidified via CO2, the isolated zooxanthellae exhibited no impacts in recorded Yi or chlorophyll levels. The response of the anemone to acidification via CO2 was different to that observed in the coral, as the density of zooxanthellae increased, rather than the chlorophyll content per cell, leading to an increased rate of gross photosynthesis. However P:R again remained constant as the increased photosynthesis was matched by an increased rate of respiration. In contrast to the impacts of CO2, HCl adversely impacted the chlorophyll content per cell in both the isolated zooxanthellae and sea anemone, and Yi, gross photosynthesis per cell, and overall gross photosynthesis in the sea anemone; however, despite the decline in gross photosynthesis, P:R remained constant due to the concurrent decline in respiration. Unfortunately, the corals in the HCl experiment died due to technical issues. There are two plausible reasons for this difference between CO2 and HCl. Firstly, HCl may have caused intracellular acidosis which damaged chloroplast structure and photosynthetic function. Secondly, the increased levels of aqueous CO2 stimulated photosynthetic function and hence mitigated for the effects of lowered pH. In addition, evidence is presented for a pH threshold for A. aureoradiata of between pH 6 and pH 6.75 (acidified with HCl), at which point photosynthesis 'shuts-down'. This suggests that, even without the potentially beneficial effects from increased CO2 levels, it is likely that oceanic pH would need to decrease to less than pH 6.75 for any acidosis effects to compromise the productivity of this particular symbiosis. Since acidification will have the benefits of increased CO2 and will reach nowhere near such low pH levels as those extremes tested here, it is proposed that ocean acidification via increased dissolution of CO2 into our oceans will have no impact on the photosynthetic production of symbiotic cnidarians. Indeed, it is entirely likely that increased CO2 will add some benefit to the usually carbon-limited symbiotic zooxanthellae. Ocean acidification is not likely to benefit corals however, with compromised calcification rates likely to undermine the viability of the coral. Symbiotic sea anemones, which do not bio-mineralise CaCO3, are better placed to take advantage of the increased CO2 as we move toward more acidic oceans.</p>


2021 ◽  
Author(s):  
Guoyi Feng ◽  
Qian Zhang ◽  
Chitao Sun ◽  
Xiaopeng Lei ◽  
Shulin Wang ◽  
...  

Abstract Background In order to study the effects of spatial distribution and yearly migration variations of soil water and salt in coastal saline land on photosynthetic production and yield formation of cotton, spatial distribution characteristics of water content, salinity, and pH in soil at 0–200 cm depths in 3 cotton fields that were similar in locality but differed markedly in degree of salinization were determined in April through October, and photosynthetic characteristics and photosynthate accumulation of cotton were also determined. Results The study shows that, the slightly salinized cotton field had lower soil salinity and pH, where soil water content was lower in rainy season (July–August), and at the late reproductive stage (September–October), soil water content was markedly higher than that in the moderately salinized cotton field, where cotton suffered smaller salt-alkali stress, photosynthetic production matched well with hydrothermal resource, the sink organ had a long photosynthate accumulation time and was at the active material accumulation stage for a long time; salt-alkali stress to the moderately salinized cotton field was relieved in rainy season, but at the early reproductive stage (April–June) and the late reproductive stage of cotton, salt-alkali stress remained evident, and photosynthetic production fit more poorly with the rich photothermal resource stage; the severely salinized cotton field subjected to prolonged high salt-alkali stress resulted in low levels of photosynthetic production capacity and yield. Conclusions For the severely salinized cotton field, salt inhibition and other relevant agronomic actions should be taken with greater efforts; for the moderately salinized cotton field, water and fertilizer management should be tightened at the early reproductive stage of cotton; for the slightly salinized cotton field, high-quality efficient cotton production should be developed.


Author(s):  
Indrajeet . ◽  
Akhil Rautela ◽  
Sanjay Kumar

Cyanobacteria, photosynthetic prokaryotic microorganisms having a simple genetic composition are the prospective photoautotrophic cell factories for the production of a wide range of biofuel molecules. Simple genetic composition of cyanobacteria allows effortless genetic manipulation which leads to increased research endeavour from the synthetic biology approach. An improved development of synthetic biology tools, genetic modification methods and advancement in transformation techniques to construct a strain which can contain multiple target genes in single operon will vastly expand the functions that can be used for engineering photosynthetic cyanobacteria for the generation of biofuels. In this review, recent advancements and approaches in synthetic biology tools and biofuel production by metabolically engineered cyanobacteria have been discussed. Various fuel molecules like isoprene, limonene, α-farnesene, squalene, alkanes, butanol and fatty acids which can be a substitute of petroleum and fossil fuels in future have been elaborated.


AMB Express ◽  
2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Fan Yang ◽  
Junli Zhang ◽  
Zhen Cai ◽  
Jie Zhou ◽  
Yin Li

AbstractThe oxygenase activity of Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) converts ribulose-1,5-bisphosphate (RuBP) into 2-phosphoglycolate, which in turn channels into photorespiration, resulting in carbon and energy loss in higher plants. We observed that glycolate can be accumulated extracellularly when two genes encoding the glycolate dehydrogenase of cyanobacteria Synechocystis sp. PCC 6803 were inactivated. This inspired us to explore the oxygenase function of Rubisco for production of glycolate, an important industrial chemical, from CO2 by engineered cyanobacteria. Since the oxygenase activity of Rubisco is generally low in CO2-rich carboxysome of cyanobacteria, we introduced Form II Rubisco, which cannot be assembled in carboxysome, into the cytoplasm of cyanobacteria. Heterologous expression of a Form II Rubisco from endosymbiont of tubeworm Riftia pachyptila (RPE Rubisco) significantly increased glycolate production. We show that the RPE Rubisco is expressed in the cytoplasm. Glycolate production increased upon addition of NaHCO3 but decreased upon supplying CO2. The titer of glycolate reached 2.8 g/L in 18 days, a 14-fold increase compared with the initial strain with glycolate dehydrogenase inactivated. This is also the highest glycolate titer biotechnologically produced from CO2 ever reported. Photosynthetic production of glycolate demonstrated the oxygenase activity of Form II Rubisco can be explored for production of chemicals from CO2.


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