Carbon dioxide compensation—its relation to photosynthetic carboxylation reactions, systematics of the Gramineae, and leaf anatomy

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A bstract. Some previous studies of photorespiration and glycolate oxidation were reexamined and correlated by infra-red CO, analysis. Data about rate of photosynthesis and oxygen sensitivity indicated that complete inhibition of photosynthesis with 3. (3,4-dichlorophenyl) -1,1 dimethyl urea (DCMU) allowed dark respiration to continue in the light. Photorespiration was also inhibited. The oxygen senisitivity of glycolate-stimulated CO2 production was found to be compatible with the proposal that glycolate is a substrate of photorespiration. B-oth 'in vivo' and 'in vitro' studies of the alga Nitella flexilis have revealed a pathway of glycolate oxidation similar to that of higher plants. DCMU inhibition of photosynthesis by Nitella gave results similar to those for the monocotyledons tested. Under very low light intensity, carbon dioxide compensation in corn was measurable but was not sensitive to high oxygen concentration. It appears that the lack of photorespiration in this plant is not the end result of efficient internal recycling of CO, to photosynthesis.Photorespiration has been described as a CO, producing process that operates during photosynthesis in some leaves and algae. The newer evidence supporting this concept is based on the response of photorespiration to 0. concentration. It has been shown that dark respiration in leaves is saturated by about 2 % 02 whereas photorespiration has a much higher 0., requirement (7,25). 'Much recent literature also implicates glycolic acid as a substrate of photorespiration. The correlation which we have studied is the O., requirement for glycolate-stimulated CO, production. These results led to another studv of whether corn leaves produce CO., by photorespiration during photosynthesis.A recent paper by El-Sharkawy et al. (6) has provided data on CO. production in the light and dark when C0, source-sink relationships were changed by inhibiting photosynthesis with DCM\IU.Under these conditions the rates in light and dark were identical and these data were used as evidence for a common source of CO, evolved both during photosynthesis and in the dark. We re-examined this work and extended it with information about the effect of 02 tension on rates of CO., production.As a check against the possibility that the gas exchange results from the DCMU-treated monocotyledons were an artifact of stomatal behavior, the gas exchange of a DCMU-treated alga, Nitella flexilis, was studied. This alga has been shown to have a photorespiratory mechanism similar to that of some land plants (3). Results obtained by inhibiting photosynthesis by non-chemical means have

Section: Resultsmentioning

confidence: 99%

“…These plants also have photorespiration (5). Corn and many tropical grasses, which lack photorespiration, have a different carboxylation sequence in which C-4 compounds are labeled first (5,10). This appears to be true also for low compensation members of the Amaranthaceae and Chenopodiaceae (27, unpublished data).…”

Section: Resultsmentioning

confidence: 99%

Photorespiration and Glycolate Metabolism: A Re-examination and Correlation of Some Previous Studies

Downton

Tregunna

1968

Self Cite

“…Monocots and dicots were classed as photosynthetically efficient or inefficient from published comparisons of the response of photosynthesis to 02 concentration (4,9) or of the CO, compensation concentration among species (3,5,13). Triticale, the interspecific hybrid of wheat and rye, was classed inefficient by the characteristics of its parents.…”

Section: Methodsmentioning

confidence: 99%

“…Growth of Phaseolus vulgaris, Mimulus cardinalis, and the liverwort Marchantia polymorpha increased when aerial portions of the plants were maintained in low 02 compared with ambient air (1,2). Photosynthesis in the leaves of efficient species is not enhanced by low 02 (4, 9) nor is growth stimulated (1,2); this is not surprising since these species have either no photorespiration or show quite low rates (5,14).…”

mentioning

confidence: 99%

Dark Germination and Seedling Growth in Monocots and Dicots of Different Photosynthetic Efficiencies in 2% and 20.9% O₂

Heichel

Day

1972

The stimulation of net photosynthesis by 1 to 4% 02 in socalled "inefficient" plants is well established and is believed to result from the suppression of photorespiration (16) Growth in darkness of the embryo of imbibed seeds can occur only if respiration releases energy and produces intermediates for synthesis of new tissue. We tested our hypotheses by observing growth in darkness soon after germination in 2% and 20.9% 02 of seedlings of 28 monocots and dicots classified as inefficient or efficient by photosynthetic characteristics. MATERIALS AND METHODSMonocots and dicots were classed as photosynthetically efficient or inefficient from published comparisons of the response of photosynthesis to 02 concentration (4, 9) or of the CO, compensation concentration among species (3, 5, 13). Triticale, the interspecific hybrid of wheat and rye, was classed inefficient by the characteristics of its parents. All the species tested had no specific requirements for germination, such as light, stratification, scarification, or alternating temperatures.The seed of Coix was removed from the fruit case and the seed of A vena was removed from the glumes prior to the experiments.In each experiment, 15 to 100 seeds of each species were placed on a 7.5 cm square of standard germination blotter in a 200 cm' plastic germination box fitted with input and exit ports for a gas stream. The blotter was moistened with sterile distilled water, and the box was sealed. The boxes were placed in a darkened growth cabinet (E.G.C. type M3) at 27 C and attached to gas streams containing either atmospheric concentrations of 02 (20.9%) and CO2 (0.032%) or 2%02 and 0.0315% CO, in N2. The gas streams were bubbled through washing bottles, humidified to saturation at 27 C, and passed through the germination boxes at a constant flow of 40 cm' min-'. The low 02 boxes were initially purged at 2 1 min-' for 5 min.Depending upon the rapidity of germination the experiments were continued for 72, 96, or 120 hr. Seeds not germinating after 120 hr in low 02 were maintained in low 02 for 144 hr and then transferred to air to determine if germination would ensue. The percentage germination of each species was measured using radicle emergence of 1 mm as the criterion. The seeds were not surface-sterilized and experiments were discarded if fungal growth occurred.Growth at each 02 concentration was estimated by measuring the length of the radicle or the total length of roots when branching occurred and the length of the hypocotyl or coleoptile on 10 randomly selected seedlings of each species. Lengths of roots and coleoptile or hypocotyl in 2% 02 were compared with those in 20.9%02 and summed for total growth comparisons.Although mass might have been a more precise measurement of growth than length, the differences in growth were easily scored by eye. Therefore the linear estimate of growth was adopted. Reproducibility was checked by replicating eight of 30 experiments a second time. The ratio of growth in 2% 02 compared with 20.9% 02 was not significantly differen...

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mentioning

confidence: 98%

Relation of CO₂ Compensation Concentration to Apparent Photosynthesis in Maize

Heichel

Musgrave

1969

,1u CO2/l air) for species with inefficient photosynthesis and high photorespiration, and low (<10 pI CO2/l air) for species with efficient photosynthesis and negligi-ble photorespiration (4,16,25,26).Maize belongs to this latter group (14, 16), and has a rCO2L, independent of°2 concentration (15,20).Recent models demonstrate that the magnitude of the [CO2], depends upon the diffusive resistance of the leaf to CO2, the efficiency of CO2 fixation in the chloroplasts, and the respiration rate of the leaf (1,21,24).A second, lesser used, method exists for predicting the photosynthetic efficiency of leaves. The Michaelis constant (Km) of a leaf has been postulated (7) as "the external CO2 concentration which enables the leaf, at saturating light intensity, to fix CO2 at half the maximal velocity". The Km depends upon the affinity of the carboxylating enzymes for CO2, the diffusive resistance of the leaf, and the rate of respiration. Thus Zelitch (27), whose convention we adopt, designates the Km for a leaf as an "overall Michaelis constant". Goldsworthy (7) and Zelitch (27) found that the Km for photosynthesis of maize was only 10 to 15 % lower than tobacco