Ribulose Bisphosphate Carboxylase-oxygenase Activity Research Articles

The cost of photoinhibition

Photoinhibition is an inevitable consequence of oxygenic photosynthesis. However, the concept of a 'photoinhibition-proof' plant in which photosystem II (PSII) is immune to photodamage is useful as a benchmark for considering the performances of plants with varying mixes of mechanisms which limit the extent of photodamage and which repair photodamage. Some photodamage is bound to occur, and the energy costs of repair are the direct costs of repair plus the photosynthesis foregone during repair. One mechanism permitting partial avoidance of photodamage is restriction of the number of photons incident on the photosynthetic apparatus per unit time, achieved by phototactic movement of motile algae to places with lower incident photosynthetically active radiation (PAR), by phototactic movement of plastids within cells to positions that minimize the incident PAR and by photonastic relative movements of parts of photolithotrophs attached to a substrate. The other means of avoiding photodamage is dissipating excitation of photosynthetic pigments including state transitions, non-photochemical quenching by one of the xanthophyll cycles or some other process and photochemical quenching by increased electron flow through PSII involving CO₂ and other acceptors, including the engagement of additional electron transport pathways. These mechanisms inevitably have the potential to decrease the rate of growth. As well as the decreased photosynthetic rates as a result of photodamage and the restrictions on photosynthesis imposed by the repair, avoidance, quenching and scavenging mechanisms, there are also additional energy, nitrogen and phosphorus costs of producing and operating repair, avoidance, quenching and scavenging mechanisms. A comparison is also made between the costs of photoinhibition and those of other plant functions impeded by the occurrence of oxygenic photosynthesis, i.e. the competitive inhibition of the carboxylase activity of ribulose bisphosphate carboxylase-oxygenase by oxygen via the oxygenase activity, and oxygen damage to nitrogenase in diazotrophic organisms.

Water stress inhibits plant photosynthesis by decreasing coupling factor and ATP

Water stress substantially alters plant metabolism, decreasing plant growth and photosynthesis1,2,3,4 and profoundly affecting ecosystems and agriculture, and thus human societies5. There is controversy over the mechanisms by which stress decreases photosynthetic assimilation of CO2. Two principal effects are invoked2,4: restricted diffusion of CO2 into the leaf, caused by stomatal closure6,7,8, and inhibition of CO2 metabolism9,10,11. Here we show, in leaves of sunflower (Helianthus annuus L.), that stress decreases CO2 assimilation more than it slows O2 evolution, and that the effects are not reversed by high concentrations of CO212,13. Stress decreases the amounts of ATP9,11 and ribulose bisphosphate found in the leaves, correlating with reduced CO2 assimilation11, but the amount and activity of ribulose bisphosphate carboxylase-oxygenase (Rubisco) do not correlate. We show that ATP-synthase (coupling factor) decreases with stress and conclude that photosynthetic assimilation of CO2 by stressed leaves is not limited by CO2 diffusion but by inhibition of ribulose biphosphate synthesis, related to lower ATP content resulting from loss of ATP synthase.

Responses of the Spring Ephemeral Claytonia virginica L. to Light and Nutrient Manipulations and Implications for the "Vernal-Dam" Hypothesis

EICKMEIER, W. G. AND E. E. SCHUSSLER (Department of Biology, Vanderbilt University, Nashville, TN 37235). Responses of the spring ephemeral Claytonia virginica L. to light and nutrient manipulations and implications for the vernal-dam hypothesis. Bull. Torrey Bot. Club 120: 157-165. 1993.-The effects of shading and fertilization on the ecophysiology of the spring ephemeral Claytonia virginica L. (Portulacaceae) were examined in the field. A two-way factorial design with main factors of light treatment (ambient control irradiance vs. 90% attenuation) and nutrient treatment (unfertilized control vs. 192 kg ha- i total N, P205, and K20 equivalents added) was employed at Radnor Lake, TN. Plant shading reduced biomass development, enhanced tissue nutrient concentration, and reduced both specific leaf weight and ribulose bisphosphate carboxylase/oxygenase (RUBISCO) activity relative to unshaded controls. Fertilization enhanced aboveground nonreproductive biomass, elevated tissue nutrient concentration for N and P but not K, and increased the leaf width/length index relative to controls. Of greatest ecophysiological importance were significant light by nutrient interactions where the stimulation of both aboveground productivity and RUBISCO activity in response to fertilization occurred only for plants in unshaded, high-irradiance conditions. These results suggest that C. virginica may be nutrient limited under ambient field conditions, is not capable of acclimation to low-irradiance, that irradiance and nutrient availability interact synergistically to affect the magnitude of short-term nutrient sequestering in C. virginica biomass, and imply that total nutrient capture by the vernal dam may adjust to variation in early-season nutrient conditions to affect forest-wide nutrient conservation.

Photosnythetic responses of rough lemon and sour orange to soil flooding, chilling, and short-term temperature fluctuations during growth

Soil flooding and cold temperature reduced leaf CO 2 exchange rate ( CER) and activity of ribulose bisphosphate carboxylase-oxygenase (Rubisco) of rough lemon (RL), Citrus jambhiri Lush., and sour orange (SO), C. aurantium L. At growth-chamber conditions of low temperature (LT, 10°C) or high temperature (HT, 30°C), inhibitions in CER were 61% for flooded SO and 43% for flooded RL. For non-flooded trees, CER at LT was only about 27% that at HT. These inhibitions in CER were at least partially due to lower stomatal conductance. Reductions in Rubisco activity under prolonged soil flooding were about 30% at HT and 16% at LT. As a result of soil flooding, starch was higher in leaves, but was drastically reduced in fibrous roots of flooded trees under both LT and HT regimes. For non-flooded trees maintained at HT, starch was higher in leaves, but lower in fibrous roots as compared with non-flooded trees grown at LT. For trees maintained under the LT regime, activity of phosphoenolpyruvate carboxylase and concentration of proline in leaves were three- and 15-fold higher, respectively, as compared with trees grown at HT. Data on responses of CER to short-term fluctuations of temperature indicate that RL was more sensitive to sharp temperature variations than SO. Under prolonged soil flooding, however, RL was more tolerant than SO.

Mechanisms of inorganic-carbon acquisition in marine phytoplankton and their implications for the use of other resources

Most of the marine phytoplankton species for which data are available are rate saturated for photosynthesis and probably for growth with inorganic C at normal seawater concentrations; 2 of the 17 species are not saturated. Photosynthesis in these two species can probably be explained by assuming that CO, reaches the site of its reaction with RUBISCO (ribulose bisphosphate carboxylase-oxygenase) by passive diffusion. The kinetics of CO, fixation by intact cells are explicable by RUBISCO kinetics typical of (eucaryotic) algae, and a CO,-saturated in vivo RUBISCO activity not more than twice the in vivo light- and inorganic-C-saturated rate of photosynthesis. For the other species, the high affinity in vivo for inorganic C (and several other attributes) could be explained by postulating active influx of inorganic C yielding a higher concentration of CO, available to RUBISCO during steady state photosynthesis than in the medium. Although such a higher concentration of internal CO, in cells with high affinity for inorganic C is found at low (subseawater) levels of external inorganic C, the situation is more equivocal at normal seawater concentrations. In theory, the occurrence of a CO,-concentrating mechanism rather than passive CO, entry (with consequent glycolate synthesis and metabolism or excretion) could reduce the photon, N, Fe, Mn, and MO costs of growth, but increase the Zn and Se costs. Thus far, data on costs are available only for photons and N; these data generally agree with the predicted lower costs for cells with high affinity for inorganic C. The ecological significance of these attributes is that most marine phytoplankters are not likely to have photosynthetic or growth rates reduced by the measured decreases in inorganic C in productive seawater, drawdown of inorganic C in productive seawater (or increase as atmospheric CO, increases) might alter the competitive balance between cells with low and high affinity for inorganic C, and differences in the effectiveness of use of other resources between cells with high and low affinity could cause differences in the rate and extent of resourcelimited growth for communities dominated by high-affinity or low-affinity cells.

Changes in Some Photosynthetic and Photorespiratory Properties in Barley Leaves after Treatment with Jasmonic Acid

The influence of jasmonic acid (JA) on photosynthesis, dark respiration, photorespiration, and the activities of ribulose bisphosphate carboxylase/oxygenase (RuBPCO) and phosphoenolpyruvate carboxylase in 7-day-old barley seedlings ( Hordeum vulgare L., var. Alfa) was investigated. Plants treated with JA showed a decrease of the rate of photosynthetic CO 2 fixation and the activity of RuBP carboxylase. The rate of dark respiration was increased two-fold, of photorespiration increased about 70 %, and the CO 2 -compensation point increased about 20 %. Stomatal resistance increased about 70 % over control plants. As a result of the inhibition of the carboxylase activity of RuBPCO, the carboxylase/oxygenase ratio decreased.

Rubisco: its role in photorespiration

The release of CO 2 during photosynthesis that is due to the production and metabolism of glycollic acid is usually regarded as outward evidence for the wasteful process of photorespiration in plants. In the light, glycollic acid is produced almost entirely as a result of the oxygenase activity of ribulose bisphosphate carboxylaseoxygenase (Rubisco). Metabolism of the glycollic acid not only releases recently assimilated carbon back into the atmosphere but also uses a considerable amount of energy to recycle remaining carbon from the glycollate to intermediates of the photosynthetic carbon reduction cycle. Furthermore, nitrogen from amino acids is released as ammonia during the metabolism of glycollate; some further energy is needed for this ammonia to be reassimilated. The oxygenation of ribulose bisphosphate is competitive with carboxylation and it appears to be the relative concentrations of oxygen and carbon dioxide present in cells containing the enzyme that mainly determine the relative rates of the two reactions in leaves. Systems which concentrate carbon dioxide in photosynthetic cells decrease the extent of photorespiration in C 4 species, certain algae and cyanobacteria. However, carboxylases from different species also vary considerably in their relative capacities to catalyse carboxylation and oxygenation of ribulose bisphosphate under standard conditions. This variation allows some hope that photorespiration might be decreased without recourse to energydependent systems for increasing cellular CO 2 concentrations.

Light Response of Photosynthesis and of RuBP Carboxylase Oxygenase Activity in Young, Mature, and Senescing Leaves of Red Clover ( Trifolium pratense L.)

The light response of the CO2 exchange rate (CER) and of the activity of ribulose bis-phosphate carboxylase/oxygenase (RuBPCO) after rapid extraction (activity in vivo) and after activation with CO2 and Mg++ (activity in vitro) was determined in leaves of red clover (Trifolium pratense L.) 1, 2 and 4 weeks after the petioles were first visible. They were referred to as young, mature, and senescent leaves, respectively. The age of the leaf affected CER at high but not at low photosynthetic photon flux density (PPFD) and thus influenced the shape of the light response curve. At high PPFD, CER was highest in mature leaves and lowest in those which were senescing. Responses to PPFD and to the age of the leaf were similar for CER and for in vivo activity of RuBPCO suggesting that, even at low PPFD, CER was controlled by RuBPCO activity. At PPFD higher than 400 °mol quanta m−2s-1, RuBPCO seemed to be fully activated in vivo. At high PPFD, differences in CER and in activity of RuBPCO in vivo between leaves of different ages were related to varying RuBPCO contents as estimated from the activity of RuBPCO after activation with CO2 and Mg++in vitro. At lower PPFD, CER and in vivo activity of RuBPCO were independent of the age of the leaf despite differences in RuBPCO content. This was due to an effect of age on the degree of activation of RuBPCO in vivo below 300 °mol quanta m-2s-1.

Changes in the net charge and subunit properties of ribulose bisphosphate carboxylase–oxygenase during cold hardening of Puma rye

Ribulose bisphosphate carboxylase--oxygenase (RUBPCase) from leaves of cold-hardened and unhardened Puma rye was purified by gel filtration and ion exchange chromatography. The specific activity of the hardened form was twice that of the unhardened form. A difference in charge between the two forms of this enzyme was proved by gel electrofocussing. The estimated isoelectric point (pI) values were 6.4 and 6.3 for the enzyme from the hardened and unhardened source respectively. The large subunit (55,000 molecular weight) of the enzyme from only the unhardened source formed at apparent dimer during sodium dodecyl sulfate (SDS) gel electrophoresis. At pH 6,8 it was also the source of an anomalous polypeptide with an apparent molecular weight of 47,000. This anomalous polypeptide appeared in both hardened and unhardened preparations after irreversible inactivation of RUBPCase activity by NaCl. It also appeared after preparation of the purified enzymes for SDS--PAGE in the absence of beta-mercaptoethanol, but this was reversible. The enzyme from the hardened source was less affected in the absence of reducing agent. Structural evidence was obtained for the previously reported cold hardening of the enzyme against freeze inactivation. A freeze-thaw cycle applied to the enzyme in vitro caused some polymerization of the large subunit and its anomalous polypeptide, in the absence of reducing agent, especially in the unhardened case. This increased with repeated cycles until the fifth cycle when the large subunit monomer and its satellite were abolished only in preparations from the unhardened source. These data indicate that the large subunit is a probable site of change that occurred in this enzyme during cold hardening.