scholarly journals Activation Energy Analysis and Limiting Factors in Photosynthesis

1972 ◽  
Vol 25 (2) ◽  
pp. 419 ◽  
Author(s):  
RM Gifford ◽  
RB Musgrave
Keyword(s):  
Activation Energy ◽  
Temperature Response ◽  
Co2 Concentration ◽  
Co2 Exchange ◽  
Photochemical Reactions ◽  
High Light ◽  
Limiting Factors ◽  
Grass Species ◽  
Low Co2 ◽  
Rate Limiting

It has been proposed that activation energies of CO2 exchange obtained from Arrhenius plots of the temperature response of leaf CO2 exchange rates (or the equivalent QIO analysis) should elucidate the rate-limiting processes. Chmora and Oya (1967), for example, suggest that a QlO (15-25�0) of about 1 for maize photo-synthesis at low light and low CO2 concentration implies photochemical reactions are limiting, at high light and high CO2 a QIO of 1 �6 implies enzyme reactions are limiting, whilst at high light and low CO2 a QlO of 1� 25 suggests diffusion is limiting. Bjorkman, Nobs, and Hiesey (1969) surmise that for Mimulus sp. at 0�07% CO2 the coincidence of QIO (15-30�0) for both CO2 exchange (at 1'5% oxygen and saturating light) and extracted carboxydismutase (QlO = 2�7-3�3) could reflect a causal relationship. Charles-Edwards and Charles-Edwards (1970) find that for clones of three grass species there is a clustering of the determinations of activation energy around certain values. It is suggested that each such value may be characteristic of a certain rate-limiting process.

Assimilate Movement in Lolium and Sorghum Leaves. Iii. Carbon Dioxide Concentration Effects on the Metabolism and Translocation of Photosynthate.

1982 ◽  
Vol 9 (6) ◽  
pp. 705 ◽  
Author(s):  
IF Wardlaw
Keyword(s):  
Water Stress ◽  
Stomatal Closure ◽  
Carbon Dioxide Concentration ◽  
Co2 Concentration ◽  
Co2 Exchange ◽  
Co2 Uptake ◽  
Concentration Effects ◽  
Low Light ◽  
Low Co2 ◽  
Before And After

Raising the CO2 concentration of air to 720 �l I-� increased the rate of net CO2 uptake by the leaf of Lolium temulentum, a C*3 species, more than in Sorghum sudanense, a C*4 species. In Lolium, but not in Sorghum, high CO2 over a 6 h period resulted in relatively more of the additional leaf photosynthate being partitioned into storage rather than to translocation. Removing CO2 from the air passing over a 5 cm length of leaf before and after a pulse application of 14CO2 resulted in a reduced labelling of sucrose and a slower rate of export of 14C-labelled photosynthate in both species. With the fall in net CO2 exchange by the leaf section deprived of CO2 there was a compensating increase within this section in retention of photosynthate derived from the distal part of the leaf. Evidence provided by 14CO2 pulse chase experiments and CO2 exchange studies confirmed the relative enhancement of photorespiration under low CO2 concentrations in Lolium, but not in Sorghum. The CO2 depletion experiments provide a useful base for comparison with the effect of low light and water stress on photosynthate metabolism and translocation in that both these conditions reduce CO2 uptake. There is support for the suggestion that the change in photosynthate metabolism under water stress in C*3 species may result from reduced CO2 entry into the leaf due to stomatal closure.

The Effect of CO2 Enrichment and Irradiance on the Growth, Morphology and Gas Exchange of a C3 (Panicum laxum) and a C4 (Panicum antidotale) Grass

1997 ◽  
Vol 24 (3) ◽  
pp. 407 ◽  
Author(s):  
Oula Ghannoum ◽  
Susanne von Caemmerer ◽  
Edward W. R. Barlow ◽  
Jann P. Conroy
Keyword(s):  
Gas Exchange ◽  
Co2 Enrichment ◽  
Fold Increase ◽  
Dry Weight ◽  
Co2 Concentration ◽  
High Light ◽  
High Co2 ◽  
Low Co2 ◽  
C4 Species ◽  
C3 Species

The effect of CO2 enrichment and irradiance on the growth and gas exchange of two tropical grasses, Panicum laxum (C3) and Panicum antidotale (C4) were investigated. The two species were grown at either 350 (low) or 700 (high) µL L-1 CO2 concentration, under 40% (low) or 100% (high) of direct sunlight and supplied with ample water and nutrition. Elevated CO2 enhanced plant dry weight at both irradiances in the C3 species (1.41-fold and 1.71-fold increase at low and high light, respectively) but only at high light in the C4 species (1.28 fold increase). CO2 enrichment had no effect on the dry weight of P. antidotale, when stem development was suppressed by growth under artificial lighting. When measured at the CO2 concentration at which they were grown, assimilation rates were similar in the low and high CO2 grown plants, for both species. However, when measurements made at low CO2 were compared, CO2 assimilation rates of the high light, high CO2 grown C3 and C4 species were lower than those of their low CO2 grown counterparts. High CO2 strongly reduced the stomatal conductance of both species, while it affected the Rubisco content (30% decrease) of the high light C3 species only. This work shows clearly that C4 species can respond to CO2 enrichment under favourable growth conditions, and that acclimation to elevated CO2 in pasture grasses does not necessarily involve accumulation of non-structural carbohydrates or reduction of total N or soluble proteins in source leaves.

CO2 and Temperature-dependent Induction in C4 Photosynthesis: an Approach to the Hierarchy of Rate-limiting Processes

1997 ◽  
Vol 24 (4) ◽  
pp. 505 ◽  
Author(s):  
Agu Laisk ◽  
Gerald E. Edwards
Keyword(s):  
C4 Photosynthesis ◽  
Co2 Concentration ◽  
Temperature Dependent ◽  
Co2 Response ◽  
Amaranthus Cruentus ◽  
Low Co2 ◽  
Phosphoglyceric Acid ◽  
Rate Of Photosynthesis ◽  
Rate Limiting ◽  
Kinetics Of

Rate-limiting processes for C4 photosynthesis were examined in Sorghum bicolor, an NADP-ME type species, and Amaranthus cruentus, an NAD-ME type C4 species, by studying the kinetics of transient changes in photosynthetic rates following rapid changes in CO2 or temperature. Primary responses (faster than 15 s) to increasing CO2 or temperature are considered direct effects on the turnover rate of the C4 cycle, whereas medium transient changes (2–3 min) are considered due to build-up of C4 cycle intermediates, and the slowest transient changes (20–30 min) are thought to be related to end product synthesis. Reciprocal plot of carboxylation rates versus cell wall (dissolved) CO2 concentration (Cw) gives an apparent Km (CO2) of 8 µM and a Vm of 200 µmol m-2 s-1 for PEP carboxylase, which is about 4 times higher than the maximum rate of photosynthesis. Under strictly limiting CO2, the rate of PEP carboxylation in C4 photosynthesis is independent of temperature (20–35°C), suggesting a physical rather than a biochemical limitation. It is suggested that the rates of C3 and C4 cycles are coordinated through the pool sizes of the C4 cycle, which are in equilibrium with the pool of 3-phosphoglyceric acid. At low CO2, the C4 pools decrease and are slowly regenerated at elevated CO2, restricting the CO2 response of C4 photosynthesis.

The Effect of CO2 Enrichment and Irradiance on the Growth, Morphology and Gas Exchange of a C3 (Panicum laxum) and a C4 (Panicum antidotale) Grass

1997 ◽  
Vol 24 (2) ◽  
pp. 227 ◽  
Author(s):  
Oula Ghannoum ◽  
Susanne von Caemmerer ◽  
Edward W. R. Barlow ◽  
Jann P. Conroy
Keyword(s):  
Gas Exchange ◽  
Co2 Enrichment ◽  
Fold Increase ◽  
Dry Weight ◽  
Co2 Concentration ◽  
High Light ◽  
High Co2 ◽  
Low Co2 ◽  
C4 Species ◽  
C3 Species

The effect of CO2 enrichment and irradiance on the growth and gas exchange of two tropical grasses, Panicum laxum (C3) and Panicum antidotale (C4) were investigated. The two species were grown at either 350 (low) or 700 (high) µL L-1 CO2 concentration, under 40% (low) or 100% (high) of direct sunlight and supplied with ample water and nutrition. Elevated CO2 enhanced plant dry weight at both irradiances in the C3 species (1.41-fold and 1.71-fold increase at low and high light, respectively) but only at high light in the C4 species (1.28 fold increase). CO2 enrichment had no effect on the dry weight of P. antidotale, when stem development was suppressed by growth under artificial lighting. When measured at the CO2 concentration at which they were grown, assimilation rates were similar in the low and high CO2 grown plants, for both species. However, when measurements made at low CO2 were compared, CO2 assimilation rates of the high light, high CO2 grown C3 and C4 species were lower than those of their low CO2 grown counterparts. High CO2 strongly reduced the stomatal conductance of both species, while it affected the Rubisco content (30% decrease) of the high light C3 species only. This work shows clearly that C4 species can respond to CO2 enrichment under favourable growth conditions, and that acclimation to elevated CO2 in pasture grasses does not necessarily involve accumulation of non-structural carbohydrates or reduction of total N or soluble proteins in source leaves.

Relationship between the inhibition of leaf respiration by light and enhancement of leaf dark respiration following light treatment

1998 ◽  
Vol 25 (4) ◽  
pp. 437 ◽  
Author(s):  
Owen K. Atkin ◽  
John R. Evans ◽  
Katharina Siebke
Keyword(s):  
Dark Respiration ◽  
Intercellular Co2 Concentration ◽  
Co2 Concentration ◽  
Fast Response ◽  
Co2 Exchange ◽  
Common Mechanism ◽  
Low Co2 ◽  
Leaf Dark Respiration ◽  
Co2 Release ◽  
Intercellular Co2

Respiration (R, non-photorespiratory mitochondrial CO2 release) in leaves is inhibited by light. However, exposure to darkness after a period of illumination can also result in R being temporarily stimulated (termed ‘light enhanced dark respiration’, LEDR). We used a fast-response CO2 exchange system to investigate these observations in tobacco leaves. After switching off the light, there were two peaks of CO2 release, the first at 15–20 s (the photorespiratory post-illumination burst) and the second at 180–250 s (LEDR). LEDR occurred in all post-illumination experiments, independent of O2 or CO2 concentration. However, LEDR increased with increasing irradiance during the pre-dark period, suggesting some dependency on prior photosynthesis. We investigated the inhibition of R by light at low CO2 concentrations (?*): ?* is the intercellular CO2 concentration at which net CO2 release represents R in the light. The inhibition of R in the light took about 50 s and was even evident at 3 mmol photons m-2 s-1, regardless of the light quality (red, blue or white). The inhibition of R by light showed similar dependency on irradiance as LEDR, such that the degree of inhibition was positively correlated with the level of LEDR. In the light, switching from 350 ppm to a low CO2 concentration that resulted in the intercellular CO2 concentration being at ?*, resulted in R initially increasing and then stabilising. Maintaining the leaf at ?* did not, therefore, lead to an underestimation of R. Our data suggest that a common mechanism may be responsible for both the inhibition of R by light and LEDR.

Kinetic model of hybridoma cultures for the identification of rate limiting factors and process optimisation

1996 ◽  
Vol 42 (2-3) ◽  
pp. 197-205
Author(s):  
A. Lourenço da Silva ◽  
A. Marc ◽  
J.M. Engasser ◽  
J.L. Goergen
Keyword(s):  
Kinetic Model ◽  
Limiting Factors ◽  
Process Optimisation ◽  
Rate Limiting

Is Cognitive Psychopathology Plausible? Illustrations from Memory Research

1996 ◽  
Vol 41 (7) ◽  
pp. S5-S13 ◽  
Author(s):  
Jean-Marie Danion ◽  
Herbert Weingartner ◽  
Leonard Singer
Keyword(s):  
Cognitive Remediation ◽  
Preliminary Evidence ◽  
Limiting Factors ◽  
Specific Rate ◽  
Memory Impairments ◽  
Central Processing ◽  
Elementary Computation ◽  
The One ◽  
Functional Mechanisms ◽  
Rate Limiting

Objective: To examine the strengths and weaknesses of cognitive psychopathology through the specific examples of the memory impairments associated with the administration of benzodiazepines, with schizophrenia, and with depression. Method: These examples are analyzed with reference to a model of memory based on the principle of division between specialized and central processing structures. A basic contention is that it is useful to consider 2 broad classes of processes—automatic, associative, or sensory/perceptual processes on the one hand and intentional, strategic, or reflective processes on the other hand—as being separate. Results: The functional mechanisms of the memory impairments associated with these conditions are beginning to be identified, and there is preliminary evidence that a deficit in an elementary computation may have dramatic consequences on highest cognitive functions. There is also evidence that certain memory impairments are linked to specific dysfunctional outcomes in everyday life. By showing that specific rate-limiting factors of cognitive performance can be identified and are amenable to cognitive interventions, existing data open the door for theoretically and empirically based cognitive remediation of mental disorders. Conclusion: The bulk of available evidence (albeit limited) makes the enterprise of cognitive psychopathology quite plausible and convincing.

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