High photosynthetic rate of a chlorophyll mutant of cotton

In a chlorophyll mutant (virescent) and wild-type cotton (Gossypium hirsutum L.), a number of photosynthetic parameters have been measured and compared with those published for other chlorophyll mutants. (a) The photosynthetic rates at 230 w/m² (400-700 nm) from a tungsten lamp were 36.8 mg CO₂ fixed/dm²·hr (virescent) and 39.5 mg CO₂ fixed/dm²·hr (wild-type). On a chlorphyll basis, the photosynthetic rates were 36.8 and 12.1 mg CO₂ fixed/mg chl·hr, respectively. (b) The photosynthetic rates at 13 w/m² (400-700 nm) from a tungsten source were 7.1 mg CO₂ fixed/dm²·hr (virescent) and 7.4 mg CO₂ fixed/dm²·hr (wild-type). On a chlorophyll basis, the photosynthetic rates were 6.0 and 1.4 mg CO₂ fixed/mg chl·hr, respectively. (c) The chlorophyll a/b ratios of the virescent and wild-type leaves were 3.3 and 4.1 (d) The chlorophyll/carotenoid ratios for the virescent and wild-type leaves were 3.2 and 7.3, respectively. (e) The photosynthetic carbon metabolism of the chlorophyll mutant was through the reductive pentose phosphate cycle. (f) The CO₂ compensation points for the virescent and wild-type plants were similar. (g) The mutant and wild-type leaves have the same quantum yield in the red part of the visible spectrum, but the virescent leaves have a lower quantum yield in the blue part of the spectrum. (h) Virescent and wild-type leaves contain similar levels on a protein basis of several reductive pentose phosphate cycle enzymes.     

Ribulose bisphosphate carboxylase: altered genetic expression in tall fescue

A decaploid tall fescue (Festuca arundinacea Schreb) genotype has been found which exhibits net photosynthetic rates of 32 to 41 mg CO₂/dm²·hour as opposed to a mean of 22 mg CO₂/dm²·hour for 10 hexaploid genotypes. The decaploid genotype exhibited a ribulose 1,5-bisphosphate (RuBP) carboxylase specific activity 1.3- to 2-fold higher than typical tall fescue genotypes. Specific activities of photorespiratory enzymes and nitrate reduction enzymes were lower in the decaploid than the hexaploid genotypes. Results suggest that genetic expression of RuBP carboxylase activity may have been altered to increase the net photosynthesis rate in the decaploid genotype.     

Rapid isolation of mesophyll cells from leaves of soybean for photosynthetic studies

Mesophyll cells were rapidly isolated from soybean (Glycine max [L.]) leaves using a combined Macerase enzyme-stirring technique. About 50% to 70% of the leaf cells on a chlorophyll basis from 3 grams of leaves could be isolated in 15 minutes. The cells obtained by this method were capable of high rates of photosynthesis even after storage in the dark for periods of up to 9 hours. The CO₂-saturated rate of photosynthesis increased from 5 μm CO₂/mg Chl·hour at 5 C to 170 μm CO₂/mg Chl·hour at 40 C. At atmospheric CO₂ concentration, the rate varied from 5 to 55 μm CO₂/mg Chl·hour over this temperature range. The reduced temperature response of photosynthesis at low CO₂ concentration was due to an increased Km(CO₂) of the cells with increasing temperature. The products of photosynthesis in the isolated cells were similar to the products of leaf photosynthesis.     

Effects of Light, Carbon Dioxide, and Temperature on Photosynthesis, Oxygen Inhibition of Photosynthesis, and Transpiration in Solanum tuberosum

Individual leaves of potato (Solanum tuberosum L. W729R), a C₃ plant, were subjected to various irradiances (400-700 nm), CO₂ levels, and temperatures in a controlled-environment chamber. As irradiance increased, stomatal and mesophyll resistance exerted a strong and some-what paralleled regulation of photosynthesis as both showed a similar decrease reaching a minimum at about 85 neinsteins·cm⁻²·sec⁻¹ (about ½ of full sunlight). Also, there was a proportional hyperbolic increase in transpiration and photosynthesis with increasing irradiance up to 85 neinsteins·cm⁻²·sec⁻¹. These results contrast with many C₃ plants that have a near full opening of stomata at much less light than is required for saturation of photosynthesis.     

Structural and Functional Characteristics of Ajuga reptansPhotosynthesis under Cold Climate Conditions

Structural, functional, and biochemical characteristics of the photosynthetic apparatus of a nemoral herbaceous perennial plant Ajuga reptansL. inhabiting the middle taiga subzone were investigated. Plant leaves were characterized by a high content of green (3.1 mg/dm²) and yellow (0.64 mg/dm²) pigments and contained moderate-sized chloroplasts with grana consisting of ten thylakoids or more. The maximum rate of photosynthesis in summergreen leaves (5–8 mg CO₂/(dm²h)) was observed at 14–16°C under a saturating photosynthetically active radiation of 50 W/m². At 6–7°C, the rate of CO₂assimilation was reduced to 60–80% of the maximum one. The temperature optimum of photosynthesis was not constant and shifted by 2–6°C depending on the changes in the ambient temperature. Wintergreen leaves were capable of photosynthesis in late autumn after heavy freezes and in early spring after a long winter. The accumulation of soluble carbohydrates and free amino acids in leaves helps to maintain the functional activity of the photosynthetic apparatus.     

Photosynthesis and Respiration of Developing Populus tremuloides Internodes

The photosynthetic and respiratory performance of developing internodes of Populus tremuloides was evaluated by infrared gas analysis. Anatomical and morphological transitions were related to metabolic activity. Photosynthetic rates ranged from 6.0 to 10.0 milligrams CO₂ per decimeter squared per hour in the youngest internodes to 2.5 to 3.8 milligrams CO₂ per decimeter squared per hour in internodes with fully developed bark tissues. Respiration exceeded the rate of photosynthesis on the average by a factor of two. Stem photosynthesis increased with temperature up to 40°C and declined steeply between 40 and 50°C. Stem respiration increased nearly linearly to temperatures as high as 50°C.     

The effect of light on the tricarboxylic Acid cycle in green leaves: I. Relative rates of the cycle in the dark and the light

Excised green leaves of mung bean (Phaseolus aureus L. var. Mungo) were used to determine the effect of light on the rate of endogenous respiration via the tricarboxylic acid cycle. Illumination with white light at an intensity of 0.043 gram calories cm⁻²min⁻¹ (approximately 8600 lux) of visible radiation (400-700 nm) gave a rate of apparent photosynthesis, measured as net CO₂ uptake, of 21 mg CO₂ dm⁻²hr⁻¹ which was about 11-fold greater than the rate of dark respiration. The feeding of ¹⁴CO₂ or ¹⁴C-labeled acids of the tricarboxylic acid cycle in the dark for 2 hours was established as a suitable method for labeling mitochondrial pools of cycle intermediates.     

Induction of Acid Metabolism in Portulacaria afra

Portulacaria afra, a succulent plant, shifts from a predominantly C₃ mode of gas exchange to a typical Crassulacean acid metabolism type CO₂ uptake in response to water or NaCl stress. Control plants in the absence of water stress assimilated CO₂ during the light (about 7-8 mg CO₂ dm⁻² hr⁻¹), transpiration (about 1.5 g dm⁻² hr⁻¹) was predominantly during the day, stomates were open during the day, and there was little diurnal organic acid fluctuation. Stressed plants showed only dark CO₂ uptake and dark water loss, nocturnal stomatal opening, and an increased diurnal fluctuation of titratable acidity. Within 2 weeks after rewatering, stressed plants returned to the control acid fluctuation levels indicating that the response to stress was reversible.     

CO2-induced ion and fluid transport in human retinal pigment epithelium

In the intact eye, the transition from light to dark alters pH, [Ca²⁺], and [K] in the subretinal space (SRS) separating the photoreceptor outer segments and the apical membrane of the retinal pigment epithelium (RPE). In addition to these changes, oxygen consumption in the retina increases with a concomitant release of CO₂ and H₂O into the SRS. The RPE maintains SRS pH and volume homeostasis by transporting these metabolic byproducts to the choroidal blood supply. In vitro, we mimicked the transition from light to dark by increasing apical bath CO₂ from 5 to 13%; this maneuver decreased cell pH from 7.37 ± 0.05 to 7.14 ± 0.06 (n = 13). Our analysis of native and cultured fetal human RPE shows that the apical membrane is significantly more permeable (≈10-fold; n = 7) to CO₂ than the basolateral membrane, perhaps due to its larger exposed surface area. The limited CO₂ diffusion at the basolateral membrane promotes carbonic anhydrase–mediated HCO₃ transport by a basolateral membrane Na/nHCO₃ cotransporter. The activity of this transporter was increased by elevating apical bath CO₂ and was reduced by dorzolamide. Increasing apical bath CO₂ also increased intracellular Na from 15.7 ± 3.3 to 24.0 ± 5.3 mM (n = 6; P < 0.05) by increasing apical membrane Na uptake. The CO₂-induced acidification also inhibited the basolateral membrane Cl/HCO₃ exchanger and increased net steady-state fluid absorption from 2.8 ± 1.6 to 6.7 ± 2.3 µl × cm⁻² × hr⁻¹ (n = 5; P < 0.05). The present experiments show how the RPE can accommodate the increased retinal production of CO₂ and H₂O in the dark, thus preventing acidosis in the SRS. This homeostatic process would preserve the close anatomical relationship between photoreceptor outer segments and RPE in the dark and light, thus protecting the health of the photoreceptors.     

C(4) Photosynthesis: Light-dependent CO(2) Fixation by Mesophyll Cells, Protoplasts, and Protoplast Extracts of Digitaria sanguinalis

Mesophyll cells, protoplasts, and protoplast extracts of Digitaria sanguinalis were used for comparative studies of light-dependent CO₂ fixation. CO₂ fixation was low without the addition of organic substrates. Pyruvate, oxaloacetate, and 3-phosphoglycerate induced relatively low rates (10 to 90 μmoles/mg chlorophyll·hr) of CO₂ fixation when added separately. However, a highly synergistic relationship was found between pyruvate + oxaloacetate and pyruvate + 3-phosphoglycerate for inducing light-dependent CO₂ fixation in the mesophyll preparations. Highest rates of CO₂ fixation were obtained with protoplast extracts. Pyruvate, in combination with oxaloacetate or 3-phosphoglycerate induced light-dependent rates from 150 to 380 μmoles of CO₂ fixed/mg chlorophyll·hr which are equivalent to or exceed reported rates of whole leaf photosynthesis in C₄ species. Concentrations of various substrates required to give half-maximum velocities of CO₂ fixation were determined, with the protoplast extracts generally saturating at the lowest substrate concentrations. Chloroplasts separated from protoplast extracts showed little capacity for CO₂ fixation. The results suggest that CO₂ fixation in C₄ mesophyll cells is dependent on chloroplasts and extrachloroplastic phosphoenolpyruvate carboxylase.     

The effect on net photosynthesis of pedigree selection for low and high rates of photorespiration in tobacco

A normal appearing plant with a low rate of photorespiration (ratio of ¹⁴CO₂ released light/dark = 1.6) was found in an unselected tobacco (Nicotiana tabacum) cultivar. The plant was self-pollinated, and further selections were made on several successive generations. Excised leaves from the progeny of the selections were examined for photorespiration and net CO₂ assimilation in normal air during photosynthesis. Similar measurements were made of plants derived from selfed parents with high rates of photorespiration (ratio of ¹⁴CO₂ released light/dark = 3.0 or greater). Efficient photosynthetic plants (greater than 22.0 mg of CO₂ dm⁻² hr⁻¹) with low rates of photorespiration produced a larger proportion of efficient progeny (about 25%) than did selfing inefficient plants (about 6%), but this proportion did not increase in successive generations.     

Respiratory CO(2) as Carbon Source for Nocturnal Acid Synthesis at High Temperatures in Three Species Exhibiting Crassulacean Acid Metabolism

Temperature effects on nocturnal carbon gain and nocturnal acid accumulation were studied in three species of plants exhibiting Crassulacean acid metabolism: Mamillaria woodsii, Opuntia vulgaris, and Kalanchoë daigremontiana. Under conditions of high soil moisture, nocturnal CO₂ gain and acid accumulation had temperature optima at 15 to 20°C. Between 5 and 15°C, uptake of atmospheric CO₂ largely accounted for acid accumulation. At higher tissue temperatures, acid accumulation exceeded net carbon gain indicating that acid synthesis was partly due to recycling of respiratory CO₂. When plants were kept in CO₂-free air, acid accumulation based on respiratory CO₂ was highest at 25 to 35°C. Net acid synthesis occurred up to 45°C, although the nocturnal carbon balance became largely negative above 25 to 35°C. Under conditions of water stress, net CO₂ exchange and nocturnal acid accumulation were reduced. Acid accumulation was proportionally more decreased at low than at high temperatures. Acid accumulation was either similar over the whole temperature range (5-45°C) or showed an optimum at high temperatures, although net carbon balance became very negative with increasing tissue temperatures. Conservation of carbon by recycling respiratory CO₂ was temperature dependent. At 30°C, about 80% of the dark respiratory CO₂ was conserved by dark CO₂ fixation, in both well irrigated and water stressed plants.     

Estimating Bacterioplankton Production by Measuring [3H]thymidine Incorporation in a Eutrophic Swedish Lake

Bacterioplankton abundance, [³H]thymidine incorporation, ¹⁴CO₂ uptake in the dark, and fractionated primary production were measured on several occasions between June and August 1982 in eutrophic Lake Norrviken, Sweden. Bacterioplankton abundance and carbon biomass ranged from 0.5 × 10⁹ to 2.4 × 10⁹ cells liter⁻¹ and 7 to 47 μg of C liter⁻¹, respectively. The average bacterial cell volume was 0.185 μm³. [³H]thymidine incorporation into cold-trichloroacetic acid-insoluble material ranged from 12 × 10⁻¹² to 200 × 10⁻¹² mol liter⁻¹ h⁻¹. Bacterial carbon production rates were estimated to be 0.2 to 7.1 μg of C liter⁻¹ h⁻¹. Bacterial production estimates from [³H]thymidine incorporation and ¹⁴CO₂ uptake in the dark agreed when activity was high but diverged when activity was low and when blue-green algae (cyanobacteria) dominated the phytoplankton. Size fractionation indicated negligible uptake of [³H]thymidine in the >3-μm fraction during a chrysophycean bloom in early June. We found that >50% of the ³H activity was in the >3-μm fraction in late August; this phenomenon was most likely due to Microcystis spp., their associated bacteria, or both. Over 60% of the ¹⁴CO₂ uptake in the dark was attributed to algae on each sampling occasion. Algal exudate was an important carbon source for planktonic bacteria. Bacterial production was roughly 50% of primary production.     

Investigation on photorespiration with a sensitive C-assay

A leaf disk assay for photorespiration has been developed based on the rate of release of recently fixed ¹⁴CO₂ in light in a rapid stream of CO₂-free air at 30° to 35°. In tobacco leaves (Havana Seed) photorespiration with this assay is 3 to 5 times greater than the ¹⁴CO₂ output in the dark. In maize, photorespiration is only 2% of that in tobacco.

The importance of open leaf stomata, rapid flow rates of CO₂-free air, elevated temperatures, and oxygen in the atmosphere in order to obtain release into the air of a larger portion of the ¹⁴CO₂ evolved within the tissue in the light was established in tobacco. Photorespiration, but not dark respiration, was inhibited by α-hydroxy-2-pyridinemethanesulfonic acid, an inhibitor of glycolate oxidase, and by 3-(4-chlorophenyl)-1,1-dimethylurea (CMU), an inhibitor of photosynthetic electron transport, under conditions which did not affect the stomata. These experiments show that the substrates of photorespiration and dark respiration differ and also provide additional support for the role of glycolate as a major substrate of photorespiration. It was also shown that at 35° the quantity of ¹⁴CO₂ released in the assay may represent only 33% of the gross ¹⁴CO₂ evolved in the light, the remainder being recycled within the tissue.

It was concluded that maize does not evolve appreciable quantities of CO₂ in the light and that this largely accounts for the greater efficiency of net photosynthesis exhibited by maize. Hence low rates of photorespiration may be expected to be correlated with a high rate of CO₂ uptake at the normal concentrations of CO₂ found in air and at higher light intensities.

     

Non-existence of an optimum leaf area index for the production rate of white clover grown under constant conditions

Single clover plants were grown in the vegetative state, at 20 ± 1°, 85 ± 5% relative humidity, 320 ± 10 ppm CO₂, 12-hour day, with Hoagland nutrient in Perlite, and 100 w · m⁻² of photosynthetically active radiation (0.4-0.7 μ) from mercury-fluorescent lamps. Each plant was confined within a circle 18 cm in diameter by means of a wire framework. The CO₂ exchange rate of the whole plant was measured every second day for 3 months. There was no optimum leaf area index for the net photosynthesis rate. The respiration rate was determined mainly by the gross photosynthesis rate and only partly by the amount of non-photosynthetic or heavily shaded tissue. At the maximum leaf area index, when leaves were dying as fast as they were being produced, both photosynthesis and respiration remained at or near their maximum rates. At the end of 3 months, the whole plant was harvested and the dry weight and carbon content determined. The measured dry weight was close to that calculated from the total CO₂ uptake and a constant ratio of carbon content to dry weight of 39%. Optimum leaf area indices observed in field experiments are attributed to the failure to include the material which dies between harvests, and to decreases in the gross photosynthesis rate caused by climate changes or lack of nutrient, for example. The difference between production rate and growth rate or yield is emphasized.     

Effect of carbon dioxide and temperature on photosynthetic CO2 uptake and photorespiratory CO2 evolution in sunflower leaves

Using an open gas-exchange system, apparent photosynthesis, true photosynthesis (TPS), photorespiration (PR) and dark respiration of sunflower (Helianthus annuus L.) leaves were determined at three temperatures and between 50 and 400 l/l external CO₂. The ratio of PR/TPS and the solubility ratio of O₂/CO₂ in the intercellular spaces both decreased with increasing CO₂. The rate of PR was not affected by the CO₂ concentration in the leaves and was independent of the solubility ratio of oxygen and CO₂ in the leaf cell. At photosynthesis-limiting concentrations of CO₂, the ratio of PR/TPS significantly increased from 18 to 30°C and the rate of PR increased from 4.3 mg CO₂ dm^-2 h^-1 at 18°C to 8.6 mg CO₂ dm^-2 h^-1 at 30°C. The specific activity of photorespired CO₂ was CO₂-dependent but temperature-independent, and the carbon traversing the glycolate pathway appeared to be derived both from recently fixed assimilate and from older reserve materials. It is concluded that PR as a percentage of TPS is affected by the concentrations of O₂ and CO₂ around the photosynthesizing cells, but the rate of PR may also be controlled by other factors.Abbreviations APS apparent photosynthesis (net CO₂ uptake) - PR photorespiration (CO₂ evolution in light) - RuBP ribulose-1,5-bisphosphate - TPS true photosynthesis (true CO₂ uptake)     

Role of Sulfate Reduction Versus Methanogenesis in Terminal Carbon Flow in Polluted Intertidal Sediment of Waimea Inlet, Nelson, New Zealand

An investigation of the terminal anaerobic processes occurring in polluted intertidal sediments indicated that terminal carbon flow was mainly mediated by sulfate-reducing organisms in sediments with high sulfate concentrations (>10 mM in the interstitial water) exposed to low loadings of nutrient (equivalent to <10² kg of N · day⁻¹) and biochemical oxygen demand (<0.7 × 10³ kg · day⁻¹) in effluents from different pollution sources. However, in sediments exposed to high loadings of nutrient (>10² kg of N · day⁻¹) and biochemical oxygen demand (>0.7 × 10³ kg · day⁻¹), methanogenesis was the major process in the mediation of terminal carbon flow, and sulfate concentrations were low (≤2 mM). The respiratory index [¹⁴CO₂/(¹⁴CO₂ + ¹⁴CH₄)] for [2-¹⁴C]acetate catabolism, a measure of terminal carbon flow, was ≥0.96 for sediment with high sulfate, but in sediments with sulfate as little as 10 μM in the interstitial water, respiratory index values of ≤0.22 were obtained. In the latter sediment, methane production rates as high as 3 μmol · g⁻¹ (dry weight) · h⁻¹ were obtained, and there was a potential for active sulfate reduction.     

Light quality affects photosynthesis and leaf anatomy of birch plantlets in vitro

Cultures in vitro of Betula pendula Roth were subjected to light of different spectral qualities. Photosynthetic capacity was highest when the plantlets were exposed to blue light (max recorded photosynthesis, 82 mol CO₂ dm^–2 h^–1) and lowest when irradiated with light high in red and/or far-red wave lengths (max recorded photosynthesis, 40 mol CO₂ dm^–2 h^–1). Highest chlorophyll content (2.2 mg dm^–2 leaf area) was found in cultures irradiated with blue light, which also enhanced the leaf area. Morphometric analysis of light micrographs showed that the epidermal cell areas were largest in plantlets subjected to blue light and smallest in those subjected to red light. Morphometric analysis of electron micrographs of palisade cells, showed that the functional chloroplast area was largest in chloroplasts of leaves subjected to blue light and smallest in those exposed to red light. We suggest that light quality affects photosynthesis both through effects on the composition of the photosynthetic apparatus and on translocation of carbohydrates from chloroplasts.     

Malate Metabolism in the Dark After CO(2) Fixation in the Crassulacean Plant Kalanchoë tubiflora

The metabolism of [¹³C]malate was studied in the Crassulacean plant Kalanchoë tubiflora following exposure to ¹³CO₂ for 2 hour intervals during a 16 hour dark cycle. Nuclear magnetic resonance spectroscopy of [¹³C]malate extracted from labeled tissue revealed that the transient flux of malate to the mitochondria, estimated by the randomization of [4-¹³C]malate to [1- ¹³C]malate by fumarase, varied substantially during the dark period. At both 15 and 25°C, the extent of malate label randomization in the mitochondria was greatest during the early and late parts of the dark period and was least during the middle of the night, when the rate of ¹³CO₂ uptake was highest. Randomization of labeled malate continued for many hours after malate synthesis had initially occurred. Internally respired ¹²CO₂ also served as a source of carbon for malate formation. At 15°C, 15% of the total malate was formed from respired ¹²CO₂, while at 25°C, 49% of the accumulated malate was derived from respired ¹²CO₂. Some of the malate synthesized from external ¹³CO₂ was also respired during the night. The proportion of the total [¹³C]malate respired during the dark period was similar at 15 and 25°C, and respiration of newly formed [¹³C]malate increased as the night period progressed. These data are discussed with regard to the relative fluxes of malate to the mitochondria and the vacuole during dark CO₂ fixation.     

A Comparison of the Effects of Chilling on Leaf Gas Exchange in Pea (Pisum sativum L.) and Cucumber (Cucumis sativus L.)

The effects of chilling on the photosynthesis of a chilling-resistant species, pea (Pisum sativum L. cv Alaska) and a chilling-sensitive species, cucumber (Cucumis sativus L. cv Ashley) were compared in order to determine the differences in the photosynthetic chilling sensitivity of these two species. For these experiments, plants were chilled (5°C) for different lengths of time in the dark or light. Following a 1 hour recovery period at 25°C, photosynthetic activity was measured by gas exchange (CO₂ uptake and H₂O release), quantum yield, and induced chlorophyll fluorescence. The results show that pea photosynthesis was largely unaffected by two consecutive nights of chilling in the dark, or by chilling during a complete light and dark cycle (15 hours/9 hours). Cucumber gas exchange was reduced by one night of chilling, but its quantum yield and variable fluorescence were unaffected by dark chilling. However, chilling cucumber in the light led to reduced CO₂ fixation, increased internal leaf CO₂ concentration, decreased quantum yield, and loss of variable fluorescence. These results indicate that chilling temperatures in conjunction with light damaged the light reactions of photosynthesis, while chilling in the dark did not.