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PubMed2004

Dark chilling inhibition of photosynthesis and symbiotic nitrogen fixation in soybean during pod filling.

The growth stage of a soybean [Glycine max (L.) Merrill] plant may influence its physiological response to dark chilling. Opposed to vegetative development, the intense nutrient and energy requirements of the developing seeds during pod filling could cause additional chilling damage and decreased recovery capacity. Previously, we investigated dark chilling tolerance during vegetative development in two soybean genotypes, 'Maple Arrow' and 'Fiskeby V' and consistently found that photosynthesis and symbiotic nitrogen fixation (SNF) was less affected by dark chilling in 'Maple Arrow'. In this study we describe the dark chilling response of the same genotypes during pod filling. Our aim was to establish whether the potential selection criteria for dark chilling tolerance, identified during vegetative development, was equally sensitive during pod filling. The results indicate that photosynthesis is less affected by dark chilling in 'Maple Arrow' than in 'Fiskeby V', not only during vegetative development, but also during the critical reproductive stage of pod filling. 'Fiskeby V' also lacks the ability to restore normal photosynthetic capacity during an extended recovery treatment. The decrease of nodule ureide content indicates that SNF was inhibited to a similar extent in both genotypes. Nodule ureide content was reduced more than stem ureide content, suggesting that the former is a more sensitive indicator of chilling stress effects on SNF. The results indicate that certain photosynthetic and fluorescence parameters are sensitive indicators of dark chilling tolerance throughout plant development and should prove valuable in future breeding programmes aimed at increasing the chilling tolerance of soybean.

Carbon Dioxide↗
PubMed2003

Evidence for recycling of inorganic phosphate by wheat chloroplasts during photosynthesis at air levels of CO2 and O2.

Phosphate recycling under photorespiratory conditions was investigated using intact wheat chloroplasts from Triticum aestivum (cv. Maris dove). A decline in the optimal Pi level needed to support steady-state photosynthesis was observed (a) as the bicarbonate supply became limiting, or (b) as oxygen concentrations were increased. Further, at subsaturating CO2 and elevated O2 (52%), photosynthetic induction periods were shortest in the absence of exogenous Pi, and severely extended by its addition. Thus, photosynthesis under low CO2 levels which favor ribulose 1,5 bisphosphate (RuBP) oxygenase activity and glycolate synthesis by chloroplasts decreases their dependency on exogenous Pi from the initial illumination of chloroplasts through to the attainment of steady state rates of O2 evolution. Uptake of phosphate (Pi) was directly measured at ambient O2 concentrations and showed the stoichiometry of O2 evolved to Pi consumed at 10 mmol/L bicarbonate (saturating) had a mean value of 3.0, and was increased to 5.4 at 2.5 mmol/L bicarbonate and to > 8.0 at 1.0 mmol/L bicarbonate. The observation is consistent with enhanced stromal recycling of Pi released during hydrolysis of phosphoglycolate produced in greater quantities as the ratio of RuBP carboxylase relative to oxygenase activities (vc/vo) declines. The theoretical relationship between vc/vo and O2/Pi stoichiometries was derived and compared favorably to experimental data obtained.

Carbon Dioxide↗
PubMed1981

Effect of acetone on the toxicity of atrazine towards photosynthesis in Anabaena.

The effect of acetone on the toxicity of atrazine towards photosynthesis in the blue-green algae Anabaena inaequalis, A. variabilis and A. cylindrica was investigated. The order of sensitivity to atrazine was A. inaequalis greater than A. variabilis greater than A. cylindrica. Acetone and atrazine interacted additively, antagonistically, and synergistically, depending upon the concentrations of acetone and atrazine used. The EC50 of atrazine towards photosynthesis was dependent upon the type of solvent-pesticide interaction.

Acetone↗
PubMed1967

The circadian rhythm in photosynthesis in Acetabularia in the presence of actinomycin D, puromycin, and chloramphenicol.

Anucleate Acetabularia crenulata shows a circadian rhythm in photosynthesis. In this study, an oxygen electrode was employed to measure this photosynthetic rhythm in the presence and absence of the inhibitors, actinomycin D, chloramphenicol, and puromycin. High concentrations of the inhibitors were used: actinomycin D, 20-40 micrograms ml-1; puromycin, 30 and 100 micrograms ml-1; and chloramphenicol, 250 micrograms ml-1. The effectiveness of these inhibitors on protein synthesis was also measured under the same conditions used for the determination of rhythmicity. In spite of large effects of all three inhibitors on the incorporation of 14C leucine, no effect on the period or the phase of the photosynthetic rhythm was observed. The higher concentration of puromycin and chloramphenicol produced toxic effects which were expressed as a reduction in the amount of photosynthesis, but rhythmicity was still apparent. After 3 or 4 days' exposure to actinomycin, Acetabularia became resistant to its effect. Recovery was also observed in the ability to incorporate leucine. The implications of these results for theories of the basic oscillator responsible for circadian rhythmicity are discussed.

Acetabularia↗
PubMed2003

A model of dynamics of leaves and nitrogen in a plant canopy: an integration of canopy photosynthesis, leaf life span, and nitrogen use efficiency.

A model of dynamics of leaves and nitrogen is developed to predict the effect of environmental and ecophysiological factors on the structure and photosynthesis of a plant canopy. In the model, leaf area in the canopy increases by the production of new leaves, which is proportional to the canopy photosynthetic rate, with canopy nitrogen increasing with uptake of nitrogen from soil. Then the optimal leaf area index (LAI; leaf area per ground area) that maximizes canopy photosynthesis is calculated. If leaf area is produced in excess, old leaves are eliminated with their nitrogen as dead leaves. Consequently, a new canopy having an optimal LAI and an optimal amount of nitrogen is obtained. Repeating these processes gives canopy growth. The model provides predictions of optimal LAI, canopy photosynthetic rates, leaf life span, nitrogen use efficiency, and also the responses of these factors to changes in nitrogen and light availability. Canopies are predicted to have a larger LAI and a higher canopy photosynthetic rate at a steady state under higher nutrient and/or light availabilities. Effects of species characteristics, such as photosynthetic nitrogen use efficiency and leaf mass per area, are also evaluated. The model predicts many empirically observed patterns for ecophysiological traits across species.

Ecosystem↗
PubMed2003

Effects of leaf ascorbate content on defense and photosynthesis gene expression in Arabidopsis thaliana.

Ascorbate deficiency in the Arabidopsis thaliana vtc1 mutant had no effect on photosynthesis, but modified defense pathways. The ascorbate content of vtc1 leaves was increased 14-fold after 10 mM ascorbate was supplied, without a concomitant change in redox state. High ascorbate modified the abundance of 495 transcripts. Transcripts encoding dehydroascorbate reductase, pathogenesis-related protein 1, and a peroxiredoxin were decreased, whereas those encoding salicylate induction-deficient protein 1, Cu,Zn superoxide dismutase, iron superoxide dismutase, metallothionein, and glutathione transferases were increased. Catalase transcripts were unaffected, but ascorbate peroxidase isoforms APX1 and tAPX were slightly decreased and sAPX transcripts increased. A number of nuclear encoded transcripts for photosynthetic electron transport components were repressed as a result of ascorbate accumulation, whereas those that were chloroplast-encoded were increased. High ascorbate caused decreases in mRNAs encoding chloroplast enzymes such as fructose-1,6-bisphosphatase and sedoheptulose-1,7-bisphosphatase that are activated by reduced thioredoxin. In contrast, others, such as glucose 6-phosphate dehydrogenase, whose activity is inactivated by reduced thioredoxin, were repressed. Together, these results show that ascorbate is involved in metabolic cross-talk between redox-regulated pathways. The abundance of this antioxidant provides information on redox buffering capacity that coordinates redox processes associated with the regulation of photosynthesis and plant defense.

Antioxidants↗
PubMed2002

Regulation of photosynthesis of C3 plants in response to progressive drought: stomatal conductance as a reference parameter.

We review the photosynthetic responses to drought in field-grown grapevines and other species. As in other plant species, the relationship between photosynthesis and leaf water potential and/or relative water content in field-grown grapevines depends on conditions during plant growth and measurements. However, when light-saturated stomatal conductance was used as the reference parameter to reflect drought intensity, a common response pattern was observed that was much less dependent on the species and conditions. Many photosynthetic parameters (e.g. electron transport rate, carboxylation efficiency, intrinsic water-use efficiency, respiration rate in the light, etc.) were also more strongly correlated with stomatal conductance than with water status itself. Moreover, steady-state chlorophyll fluorescence also showed a high dependency on stomatal conductance. This is discussed in terms of an integrated down-regulation of the whole photosynthetic process by CO2 availability in the mesophyll. A study with six Mediterranean shrubs revealed that, in spite of some marked interspecific differences, all followed the same pattern of dependence of photosynthetic processes on stomatal conductance, and this pattern was quite similar to that of grapevines. Further analysis of the available literature suggests that the above-mentioned pattern is general for C3 plants. Even though the patterns described do not necessarily imply a cause and effect relationship, they can help our understanding of the apparent contradictions concerning stomatal vs. non-stomatal limitations to photosynthesis under drought. The significance of these findings for the improvement of water-use efficiency of crops is discussed.

Biological Transport↗
PubMed2006

Effects of the fungal endophyte, Neotyphodium lolii, on net photosynthesis and growth rates of perennial ryegrass (Lolium perenne) are independent of In Planta endophyte concentration.

BACKGROUND AND AIMS: Neotyphodium lolii is a fungal endophyte of perennial ryegrass (Lolium perenne), improving grass fitness through production of bioactive alkaloids. Neotyphodium species can also affect growth and physiology of their host grasses (family Poaceae, sub-family Pooideae), but little is known about the mechanisms. This study examined the effect of N. lolii on net photosynthesis (P(n)) and growth rates in ryegrass genotypes differing in endophyte concentration in all leaf tissues. METHODS: Plants from two ryegrass genotypes, Nui D and Nui UIV, infected with N. lolii (E+) differing approx. 2-fold in endophyte concentration or uninfected clones thereof (E-) were grown in a controlled environment. For each genotype x endophyte treatment, plant growth rates were assessed as tillering and leaf extension rates, and the light response of P(n), dark respiration and transpiration measured in leaves of young (30-45 d old) and old (>90 d old) plants with a single-chamber open infrared gas-exchange system. KEY RESULTS: Neotyphodium lolii affected CO(2)-limited rates of P(n), which were approx. 17 % lower in E+ than E- plants (P < 0.05) in the young plants. Apparent photon yield and dark respiration were unaffected by the endophyte (P > 0.05). Neotyphodium lolii also decreased transpiration (P < 0.05), but only in complete darkness. There were no endophyte effects on P(n) in the old plants (P > 0.05). E+ plants grew faster immediately after replanting (P < 0.05), but had approx. 10 % lower growth rates during mid-log growth (P < 0.05) than E- plants, but there was no effect on final plant biomass (P > 0.05). The endophyte effects on P(n) and growth tended to be more pronounced in Nui UIV, despite having a lower endophyte concentration than Nui D. CONCLUSIONS: Neotyphodium lolii affects CO(2) fixation, but not light interception and photochemistry of P(n). The impact of N. lolii on plant growth and photosynthesis is independent of endophyte concentration in the plant, suggesting that the endophyte mycelium is not simply an energy drain to the plant. However, the endophyte effects on P(n) and plant growth are strongly dependent on the plant growth phase.

Biomass↗
PubMed1995

WIMOVAC: a software package for modelling the dynamics of plant leaf and canopy photosynthesis.

The ability to predict net carbon exchange and production of vegetation in response to predicted atmospheric and climate change is critical to assessing the potential impacts of these changes. Mathematical models provide an important tool in the study of whole plant, canopy and ecosystem responses to global environmental change. Because this requires prediction beyond experience, mechanistic rather than empirical models are needed. The uniformity and strong understanding of the photosynthetic process, which is the primary point of response of plant production to global atmospheric change, provides a basis for such an approach. Existing modelling systems have been developed primarily for expert modellers and have not been easily accessible to experimentalists, managers and students. Here we describe a modular modelling system operating within Windows to provide this access. WIMOVAC (Windows Intuitive Model of Vegetation response to Atmosphere and Climate Change) is designed to facilitate the modelling of various aspects of plant photosynthesis with particular emphasis on the effects of global climate change. WIMOVAC has been designed to run on IBM PC-compatible computers running Microsoft Windows. The package allows the sophisticated control of the simulation processes for photosynthesis through a standardized Windows user interface and provides automatically formatted results as either tabulated data or as a range of customizable graphs. WIMOVAC has been written in Microsoft Visual Basic, to facilitate the rapid development of user-friendly modules within the familiar Windows framework, while allowing a structured development. The highly interactive nature of controls adopted by WIMOVAC makes it suitable for research, management and educational purposes.

Algorithms↗
PubMed2000

An overnight chill induces a delayed inhibition of photosynthesis at midday in mango (Mangifera indica L.).

The effect of a cold night on photosynthesis in herbaceous chilling-sensitive crops, like tomato, has been extensively studied and is well characterized. This investigation examined the behaviour of the sub-tropical fruit tree, mango, to enable comparison with these well-studied systems. Unlike tomato, chilling between 5 degrees C and 7 degrees C overnight produced no significant inhibition of light-saturated CO(2) assimilation (A:) during the first hours following rewarming, measured either under controlled environment conditions or in the field. By midday, however, there was a substantial decline in A:, which could not be attributed to photoinhibition of PSII, but rather was associated with an increase in stomatal limitation of A: and lower Rubisco activity. Overnight chilling of tomato can cause severe disruption in the circadian regulation of key photosynthetic enzymes and is considered to be a major factor underlying the dysfunction of photosynthesis in chilling-sensitive herbaceous plants. Examination of the gas exchange of mango leaves maintained under constant conditions for 2 d, demonstrated that large depressions in A: during the subjective night were primarily the result of stomatal closure. Chilling did not disrupt the ability of mango leaves to produce a circadian rhythm in stomatal conductance. Rather, the midday increase in stomatal limitation of A: appeared to be the result of altered guard cell sensitivity to CO(2) following the dark chill.

Circadian Rhythm↗
PubMed2000

Modelling the role of Rubisco activase in limiting non-steady-state photosynthesis.

The roles of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and Rubisco activase in limiting the approach of photosynthesis to steady-state following a step increase from a low to a saturating value of photon flux density (PFD) are reviewed. This information, along with the effect of Rubisco on steady-state photosynthetic rate and the effect of Rubisco activase on maximum Rubisco activation state, is then used to construct a model to predict the optimum allocation of protein between Rubisco and Rubisco activase for plants exposed to different light environments. The model predicts that the distribution of protein that produces the maximum steady-state rate of photosynthesis does not produce the maximum activation rate for Rubisco or the maximum steady-state activation state. The latter conclusion may explain why Rubisco is rarely found to be fully activated in leaves, even at saturating PFD values. The former suggests that plants exposed to fluctuating PFD should allocate more protein to Rubisco activase than plants exposed to constant PFD. This aspect of the model is explored in more detail for lightflecks of differing duration.

Carbon Dioxide↗
PubMed2001

Low sink demand limits photosynthesis under P(i) deficiency.

The role of the demand for carbon assimilates (the 'sink') in regulating photosynthetic carbon assimilation (Pn: the 'source') in response to phosphate (P(i)) deficiency was examined in tobacco (Nicotiana tabacum L.). P(i) supply was maintained or withdrawn from plants, and in both treatments the source/sink ratio was decreased in some plants by darkening all but two source leaves (partially darkened plants). The remaining plants were kept fully illuminated. P(i)-sufficient plants showed little variation in rate of Pn, amounts of P(i) or phosphorylated intermediates. Withdrawal of P(i) decreased Pn by 75% under the growing conditions and at both low and high internal CO2 concentration. Concomitantly, P(i), phosphorylated intermediates and ATP contents decreased and starch increased. RuBP and activity of phosphoribulokinase closely matched the changes in Pn, but Rubisco activity remained high. Partial darkening P(i)-deficient plants delayed the loss of photosynthetic activity; Rubisco and phosphoribulokinase activities and amounts of sucrose and metabolites, particularly RuBP and G6P, were higher than in fully illuminated Pi-deficient plants. Rates of sucrose export from leaves were more than 2-fold greater than in fully illuminated P(i)-deficient plants. Greater sucrose synthesis, facilitated by increased G6P content, an activator of SPS, would recycle P(i) from the cytosol back to the chloroplast, maintaining ATP, RuBP and hence Pn. It is concluded that low sink strength imposes the primary limitation on photosynthesis in P(i)-deficient plants which restricts sucrose export and sucrose synthesis imposing an end-product synthesis limitation of photosynthesis.

Adenosine Triphosphate↗
PubMed2000

Effects of drought on photosynthesis in Mediterranean plants grown under enhanced UV-B radiation.

The effects of drought on the photosynthetic characteristics of three Mediterranean plants (olive, Olea europea L.; rosemary, Rosmarinus officinalis L.; lavender, Lavandula stoechas L.) exposed to elevated UV-B irradiation in a glasshouse were investigated over a period of weeks. Drought conditions were imposed on 2-year-old plants by withholding water. During the onset of water stress, analyses of the response of net carbon assimilation of leaves to their intercellular CO2 concentration were used to examine the potential limitations imposed by stomata, carboxylation velocity and capacity for regeneration of ribulose 1,5-bisphosphate on photosynthesis. Measurements of chlorophyll fluorescence were used to determine changes in the efficiency of light utilization for electron transport, the occurrence of photoinhibition of photosystem II photochemistry and the possibility of stomatal patchiness across leaves. The first stages of water stress produced decreases in the light-saturated rate of CO2 assimilation which were accompanied by decreases in the maximum carboxylation velocity and the capacity for regeneration of ribulose 1,5-bisphosphate in the absence of any significant photodamage to photosystem II. Leaves of rosemary and lavender were more sensitive than those of olive during the first stages of the drought treatment and also exhibited increases in stomatal limitation. With increasing water stress, significant decreases in the maximum quantum efficiency of photosystem II photochemistry occurred in lavender and rosemary, and stomatal limitation was increased in olive. No indication of any heterogeneity of photosynthesis was found in any leaves. Drought treatment significantly decreased leaf area in all species, an important factor in drought-induced decreases in photosynthetic productivity. Exposure of plants to elevated UV-B radiation (0.47 W m(-2)) prior to and during the drought treatment had no significant effects on the growth or photosynthetic activities of the plants. Consequently, it is predicted that increasing UV-B due to future stratospheric ozone depletion is unlikely to have any significant impact on the photosynthetic productivity of olive, lavender and rosemary in the field.

Carbon Dioxide↗
PubMed2003

Gas exchange measurements, what can they tell us about the underlying limitations to photosynthesis? Procedures and sources of error.

The principles, equipment and procedures for measuring leaf and canopy gas exchange have been described previously as has chlorophyll fluorescence. Simultaneous measurement of the responses of leaf gas exchange and modulated chlorophyll fluorescence to light and CO2 concentration now provide a means to determine a wide range of key biochemical and biophysical limitations on photo synthesis in vivo. Here the mathematical frameworks and practical procedures for determining these parameters in vivo are consolidated. Leaf CO2 uptake (A) versus intercellular CO2 concentration (Ci) curves may now be routinely obtained from commercial gas exchange systems. The potential pitfalls, and means to avoid these, are examined. Calculation of in vivo maximum rates of ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (Rubisco) carboxylation (Vc,max), electron transport driving regeneration of RuBP (Jmax), and triose-phosphate utilization (VTPU) are explained; these three parameters are now widely assumed to represent the major limitations to light-saturated photosynthesis. Precision in determining these in intact leaves is improved by the simultaneous measurement of electron transport via modulated chlorophyll fluorescence. The A/Ci response also provides a simple practical method for quantifying the limitation that stomata impose on CO2 assimilation. Determining the rate of photorespiratory release of oxygen (Rl) has previously only been possible by isotopic methods, now, by combining gas exchange and fluorescence measurements, Rl may be determined simply and routinely in the field. The physical diffusion of CO2 from the intercellular air space to the site of Rubisco in C3 leaves has long been suspected of being a limitation on photosynthesis, but it has commonly been ignored because of the lack of a practical method for its determination. Again combining gas exchange and fluorescence provides a means to determine mesophyll conductance. This method is described and provides insights into the magnitude and basis of this limitation.

Botany↗
PubMed2005

Strategies to maintain redox homeostasis during photosynthesis under changing conditions.

Plants perform photosynthesis and assimilatory processes in a continuously changing environment. Energy production in the various cell compartments and energy consumption in endergonic processes have to be well adjusted to the varying conditions. In addition, dissipatory pathways are required to avoid any detrimental effects caused by over-reduction. A large number of short-term and long-term mechanisms interact with each other in a flexible way, depending on intensity and the type of impact. Therefore, all levels of regulation are involved, starting from energy absorption and electron flow events through to post-transcriptional control. The simultaneous presence of strong oxidants and strong reductants during oxygenic photosynthesis is the basis for regulation. However, redox-dependent control also interacts with other signal transduction pathways in order to adapt metabolic processes and redox-control to the developmental state. Examples are given here for short-term and long-term control following changes of light intensity and photoperiod, focusing on the dynamic nature of the plant regulatory systems. An integrating network of all these mechanisms exists at all levels of control. Cellular homeostasis will be maintained as long as the mechanisms for acclimation are present in sufficiently high capacities. If an impact is too rapid, and acclimation on the level of gene expression cannot occur, cellular damage and cell death are initiated.

Adaptation, Physiological↗
PubMed2006

Evolution of glutamine synthetase in heterokonts: evidence for endosymbiotic gene transfer and the early evolution of photosynthesis.

Although the endosymbiotic evolution of chloroplasts through primary and secondary associations is well established, the evolutionary timing and stability of the secondary endosymbiotic events is less well resolved. Heterokonts include both photosynthetic and nonphotosynthetic members and the nonphotosynthetic lineages branch basally in phylogenetic reconstructions. Molecular and morphological data indicate that heterokont chloroplasts evolved via a secondary endosymbiosis, involving a heterotrophic host cell and a photosynthetic ancestor of the red algae and this endosymbiotic event may have preceded the divergence of heterokonts and alveolates. If photosynthesis evolved early in this lineage, nuclear genomes of the nonphotosynthetic groups may contain genes that are not essential to photosynthesis but were derived from the endosymbiont genome through gene transfer. These genes offer the potential to trace the evolutionary history of chloroplast gains and losses within these lineages. Glutamine synthetase (GS) is essential for ammonium assimilation and glutamine biosynthesis in all organisms. Three paralogous gene families (GSI, GSII, and GSIII) have been identified and are broadly distributed among prokaryotic and eukaryotic lineages. In diatoms (Heterokonta), the nuclear-encoded chloroplast and cytosolic-localized GS isoforms are encoded by members of the GSII and GSIII family, respectively. Here, we explore the evolutionary history of GSII in both photosynthetic and nonphotosynthetic heterokonts, red algae, and other eukaryotes. GSII cDNA sequences were obtained from two species of oomycetes by polymerase chain reaction amplification. Additional GSII sequences from eukaryotes and bacteria were obtained from publicly available databases and genome projects. Bayesian inference and maximum likelihood phylogenetic analyses of GSII provided strong support for the monophyly of heterokonts, rhodophytes, chlorophytes, and plants and strong to moderate support for the Opisthokonts. Although the phylogeny is reflective of the unikont/bikont division of eukaryotes, we propose based on the robustness of the phylogenetic analyses that the heterokont GSII gene evolved via endosymbiotic gene transfer from the nucleus of the red-algal endosymbiont to the nucleus of the host. The lack of GSIII sequences in the oomycetes examined here further suggests that the GSIII gene that functions in the cytosol of photosynthetic heterokonts was replaced by the endosymbiont-derived GSII gene.

Amino Acid Sequence↗
PubMed2005

Comparative genomics analysis of NtcA regulons in cyanobacteria: regulation of nitrogen assimilation and its coupling to photosynthesis.

We have developed a new method for prediction of cis-regulatory binding sites and applied it to predicting NtcA regulated genes in cyanobacteria. The algorithm rigorously utilizes concurrence information of multiple binding sites in the upstream region of a gene and that in the upstream regions of its orthologues in related genomes. A probabilistic model was developed for the evaluation of prediction reliability so that the prediction false positive rate could be well controlled. Using this method, we have predicted multiple new members of the NtcA regulons in nine sequenced cyanobacterial genomes, and showed that the false positive rates of the predictions have been reduced on an average of 40-fold compared to the conventional methods. A detailed analysis of the predictions in each genome showed that a significant portion of our predictions are consistent with previously published results about individual genes. Intriguingly, NtcA promoters are found for many genes involved in various stages of photosynthesis. Although photosynthesis is known to be tightly coordinated with nitrogen assimilation, very little is known about the underlying mechanism. We postulate for the fist time that these genes serve as the regulatory points to orchestrate these two important processes in a cyanobacterial cell.

Algorithms↗
PubMed2002

Enhanced susceptibility of photosynthesis to low-temperature photoinhibition due to interruption of chill-induced increase of S-adenosylmethionine decarboxylase activity in leaves of spinach (Spinacia oleracea L.).

The possible involvement of polyamines in the chilling tolerance of spinach (Spinacia oleracea L.) was investigated focusing on photosynthesis. During chilling at 8/5C (day/night) for 6 d, S-adenosylmethionine decarboxylase (SAMDC) activity increased significantly in leaves in parallel with the increase in putrescine and spermidine (Spd) content in leaves and chloroplasts. Treatment of leaves with methylglyoxal-bis(guanylhydrazone) (MGBG), an SAMDC inhibitor, resulted in the deterioration of plant growth and photosynthesis under chilling conditions, which was reversed by the concomitant treatment with Spd through the roots. Plants treated with MGBG showed lower photochemical efficiency of PSII than either the control or plants treated with MGBG plus Spd during chilling and even after transfer to warm conditions, suggesting an increase of photoinhibition due to low Spd in chloroplasts. Indeed, MGBG-treated plants had much lower activities of thylakoid electron transport and enzymes in carbon metabolism as well as higher degrees of lipid peroxidation of thylakoid membranes compared to the control. These results indicate that the enhanced activity of SAMDC with a consequential rise of Spd in chloroplasts is crucial for the cold acclimation of the photosynthetic apparatus in spinach leaves.

Acclimatization↗