scholarly journals A Model Describing the Regulation of Ribulose-1,5-Bisphosphate Carboxylase, Electron Transport, and Triose Phosphate Use in Response to Light Intensity and CO2 in C3 Plants

1990 ◽  
Vol 94 (4) ◽  
pp. 1728-1734 ◽  
Author(s):  
Rowan F. Sage
Keyword(s):  
Electron Transport ◽  
Light Intensity ◽  
C3 Plants ◽  
Bisphosphate Carboxylase ◽  
Triose Phosphate

Ribulose bisphosphate carboxylase—oxygenase: its role in photosynthesis

1986 ◽  
Vol 313 (1162) ◽  
pp. 305-324 ◽  
Keyword(s):  
Electron Transport ◽  
Carbon Assimilation ◽  
Kinetic Properties ◽  
Ribulose Bisphosphate Carboxylase ◽  
Ribulose Bisphosphate ◽  
Rubp Carboxylase ◽  
Bisphosphate Carboxylase ◽  
Triose Phosphate ◽  
Ribulose Bisphosphate Carboxylase Oxygenase

Synthesis of triose phosphate by the chloroplast requires three substrates: light, CO 2 and orthophosphate (P i ). In the response of the rate of carbon assimilation to the concentration of CO 2 , the kinetic properties of RuBP carboxylase-oxygenase (Rubisco) constitute the main limitation at low CO 2 concentrations, while at higher concentrations of CO 2 the limitation is shifted towards the reactions leading to the regeneration of the substrate, RuBP, driven by electron transport. In these circumstances, light or P i or both, can become limiting. The characteristics of Rubisco that can affect photosynthesis fall under three main headings: (1) amount and kinetic constants; (2) activation state; and (3) regulation of catalysis (including the role of effectors, such as Pt and glycerate 3-phosphate (PGA)). These characteristics are analysed, and the role of changes in activity of the enzyme is discussed in the context of limitation and regulation of the photosynthetic process. Other factors considered are the regeneration of RuBP and its relation to electron transport, P i supply, and photorespiration. The influence that expected increases in atmospheric CO 2 concentration, and/or genetic improvements in the characteristics of the enzyme, may have on the present balance between the partial processes of photosynthesis, is discussed.

scholarly journals A cyanobacterial photorespiratory bypass model to enhance photosynthesis by rerouting photorespiratory pathway in C3 plants

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Ghazal Khurshid ◽  
Anum Zeb Abbassi ◽  
Muhammad Farhan Khalid ◽  
Mahnoor Naseer Gondal ◽  
Tatheer Alam Naqvi ◽  
...  
Keyword(s):  
Kinetic Model ◽  
Inorganic Phosphate ◽  
Elevated Level ◽  
Photosynthetic Efficiency ◽  
C3 Plants ◽  
Simultaneous Increase ◽  
Photosynthetic Pathway ◽  
Bisphosphate Carboxylase ◽  
Toxic Compound ◽  
Overall Efficiency

AbstractPlants employ photosynthesis to produce sugars for supporting their growth. During photosynthesis, an enzyme Ribulose 1,5 bisphosphate carboxylase/oxygenase (Rubisco) combines its substrate Ribulose 1,5 bisphosphate (RuBP) with CO2 to produce phosphoglycerate (PGA). Alongside, Rubisco also takes up O2 and produce 2-phosphoglycolate (2-PG), a toxic compound broken down into PGA through photorespiration. Photorespiration is not only a resource-demanding process but also results in CO2 loss which affects photosynthetic efficiency in C3 plants. Here, we propose to circumvent photorespiration by adopting the cyanobacterial glycolate decarboxylation pathway into C3 plants. For that, we have integrated the cyanobacterial glycolate decarboxylation pathway into a kinetic model of C3 photosynthetic pathway to evaluate its impact on photosynthesis and photorespiration. Our results show that the cyanobacterial glycolate decarboxylation bypass model exhibits a 10% increase in net photosynthetic rate (A) in comparison with C3 model. Moreover, an increased supply of intercellular CO2 (Ci) from the bypass resulted in a 54.8% increase in PGA while reducing photorespiratory intermediates including glycolate (− 49%) and serine (− 32%). The bypass model, at default conditions, also elucidated a decline in phosphate-based metabolites including RuBP (− 61.3%). The C3 model at elevated level of inorganic phosphate (Pi), exhibited a significant change in RuBP (+ 355%) and PGA (− 98%) which is attributable to the low availability of Ci. Whereas, at elevated Pi, the bypass model exhibited an increase of 73.1% and 33.9% in PGA and RuBP, respectively. Therefore, we deduce a synergistic effect of elevation in CO2 and Pi pool on photosynthesis. We also evaluated the integrative action of CO2, Pi, and Rubisco carboxylation activity (Vcmax) on A and observed that their simultaneous increase raised A by 26%, in the bypass model. Taken together, the study potentiates engineering of cyanobacterial decarboxylation pathway in C3 plants to bypass photorespiration thereby increasing the overall efficiency of photosynthesis.

scholarly journals Physiological Characteristics of Photosynthesis in Yellow-Green, Green and Dark-Green Chinese Kale (Brassica oleracea L. var. alboglabra Musil.) under Varying Light Intensities

Plants ◽  
2020 ◽  
Vol 9 (8) ◽  
pp. 960
Author(s):  
Kuan-Hung Lin ◽  
Feng-Chi Shih ◽  
Meng-Yuan Huang ◽  
Jen-Hsien Weng
Keyword(s):  
Electron Transport ◽  
Energy Dissipation ◽  
Light Intensity ◽  
Thermal Energy ◽  
Electron Transport Rate ◽  
Transport Rate ◽  
Physiological Characteristics ◽  
Chinese Kale ◽  
Thermal Energy Dissipation ◽  
Dark Green

The objective of this work was to study physiological characteristics and photosynthetic apparatus in differentially pigmented leaves of three Chinese kale cultivars. Chlorophyll (Chl) fluorescence and photochemical reflectance index (PRI) measurements in green, yellow-green, and dark-green cultivars in response to varying light intensities. As light intensity increased from 200 to 2000 photosynthetic photon flux density (PPFD), fraction of light absorbed in photosystem (PS) II and PRI values in all plants were strongly lowered, but fraction of light absorbed in PSII dissipated via thermal energy dissipation and non-photochemical quenching (NPQ) values in all plants wereremarkably elevated.When plants were exposed to 200 PPFD, the values of fraction of light absorbed in PSII, utilized in photosynthetic electron transport(p), andfraction of light absorbed excitation energy in PSII dissipated via thermal energy dissipation (D), remained stable regardless of the changes in levels of Chla + b. Under 800 and 1200 PPFD, the values of p and electron transport rate (ETR) decreased, but D and NPQ increased as Chla + bcontent decreased, suggesting that decrease inChla + bcontent led to lower PSII efficiency and it became necessary to increase dissipate excess energy. On the contrary, in 2000 PPFD, leaves with lower Chla + bcontent had relatively higher p and electron transport rate (ETR) values and lower D level, as well as tended to increase more in NPQ but decrease more in PRI values. The consistent relations between PRI and NPQ suggest that NPQ is mainly consisted ofthe xanthophyll cycle-dependentenergy quenching.Yellow-green cultivar showed lower Chla + bcontent but high carotenoids/Chla + b ratio and had high light protection ability under high PPFD. The precise management of photosynthetic parameters in response to light intensity can maximize the growth and development of Chinese kale plants.

Photoinhibitory Damage to Chloroplasts under Phosphate Deficiency and Alleviation of Deficiency and Damage by Photorespiratory Reactions

1989 ◽  
Vol 44 (5-6) ◽  
pp. 524-536 ◽  
Author(s):  
U. Heber ◽  
J. Viil ◽  
S. Neimanis ◽  
T. Mimura ◽  
K.-J. Dietz
Keyword(s):  
Electron Transport ◽  
Light Intensity ◽  
Oxygen Evolution ◽  
High Light Intensity ◽  
High Light ◽  
Phosphate Deficiency ◽  
Loss Of Function ◽  
Low Light ◽  
Chloroplast Stroma ◽  
Pi Deficiency

Abstract Effects of Pi deficiency on photosynthesis ot isolated spinach chloroplasts were examined. The following observations were made: (1) Chloroplasts isolated in Pi-free media evolved oxygen in the light in the absence of added Pi until acid-extractable Pi in the chloroplasts had decreased to 1 to 2.5 m M . This Pi was unavailable for photophosphorylation as shown by the inability of the chloroplasts to respond by oxygen evolution to the addition of PGA. In the state of Pi-deficiency, stromal ATP to A DP ratios were in the light close to or below ratios observed in the dark. In the presence of 2 mᴍ PGA, addition of 20 μm Pi was insufficient to increase ATP to ADP ratios, but sufficient for appreciable oxygen evolution. (2) More Pi was available for oxygen evolution of phosphate-deficient chloroplasts at low levels of C02 than at high levels. This was due mainly to the suppression of oxygenation of RuBP by high C02 levels which prevented formation of phosphoglycolate and the subsequent release of Pi into the chloroplast stroma. (3) More oxygen was produced by phosphate-deficient chloroplasts at a low light intensity than at a high light intensity. This was due to increased availability of endogenous Pi under low light and to photoinhibition of the chloroplasts by high light. The main product of photosynthesis of phosphate-deficient chloroplasts in the presence of a high bicarbonate concentration was starch, and the main soluble product was PGA. (4) After phosphate-deficient chloroplasts had ceased to evolve oxygen in the light, they be­ came photosensitive. Part of the loss of the capacity for oxygen evolution is attributed to leakage of PGA, but the main reason for loss of function is photoinactivation of electron transport. Both photosystems of the electron transport chain were damaged by light. (5) Protection against photoinactivation was provided by coupled electron transport. Photo­ inactivation of phosphate-deficient chloroplasts was less extensive in the presence of low C02 concentrations which permitted oxygenation of RuBP than at high CO2 concentrations. Electron transport to C02 and other physiological electron acceptors and to the herbicide methylviologen was also protective. However, electron transport to oxygen in the Mehler reaction failed to provide appreciable protection against high light intensities, because oxygen reduction is slow and reactive oxygen species produced in the light contribute to photoinactivation.

scholarly journals Photochemical Acclimation of Three Contrasting Species to Different Light Levels: Implications for Optimizing Supplemental Lighting

2017 ◽  
Vol 142 (5) ◽  
pp. 346-354 ◽  
Author(s):  
Shuyang Zhen ◽  
Marc W. van Iersel
Keyword(s):  
Electron Transport ◽  
Light Intensity ◽  
Photochemical Efficiency ◽  
Light Response ◽  
High Light ◽  
Photon Flux ◽  
Ambient Light ◽  
Response Curves ◽  
Low Light ◽  
Supplemental Lighting

Photosynthetic responses to light are dependent on light intensity, vary among species, and can be affected by acclimation to different light environments (e.g., light intensity, spectrum, and photoperiod). Understanding how these factors affect photochemistry is important for improving supplemental lighting efficiency in controlled-environment agriculture. We used chlorophyll fluorescence to determine photochemical light response curves of three horticultural crops with contrasting light requirements [sweetpotato (Ipomea batatas), lettuce (Lactuca sativa), and pothos (Epipremnum aureum)]. We also quantified how these responses were affected by acclimation to three shading treatments-full sun, 44% shade, and 75% shade. The quantum yield of photosystem II (ΦPSII), a measure of photochemical efficiency, decreased exponentially with increasing photosynthetic photon flux (PPF) in all three species. By contrast, linear electron transport rate (ETR) increased asymptotically with increasing PPF. Within each shading level, the high-light-adapted species sweetpotato used high light more efficiently for electron transport than light-intermediate lettuce and shade-tolerant pothos. Within a species, plants acclimated to high light (full sun) tended to have higher ΦPSII and ETR than those acclimated to low light (44% or 75% shade). Nonphotochemical quenching (NPQ) (an indicator of the amount of absorbed light energy that is dissipated as heat) was upregulated with increasing PPF; faster upregulation was observed in pothos as well as in plants grown under 75% shade. Our results have implications for supplemental lighting: supplemental light is used more efficiently and results in a greater increase in ETR when provided at low ambient PPF. In addition, high-light-adapted crops and crops grown under relatively high ambient light can use supplemental light more efficiently than low-light-adapted crops or those grown under low ambient light.

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