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1.
Photosynthetic characteristics were studied in several F 1 hybrids between C 4 and C 3-C 4 species of Flaveria. Stable carbon isotope ratios, O 2 inhibition of apparent photosynthesis, and phosphoenolpyruvate carboxylase activities in the hybrids were similar to the means for the parents. Values of CO 2 compensation concentrations were nearer to those of the C 4 parent and apparent photosynthesis was below that of both parents, being only 60 and 74% of that of the lowest (C 3-C 4) parent in two experiments. Reductions of CO 2 compensation concentration and O 2 inhibition of apparent photosynthesis as well as increases in carbon isotope ratios and phosphoenolpyruvate carboxylase activities compared to values in C 3-C 4 species suggest transfer of a limited degree of C 4 photosynthesis to the F 1 hybrids. However, the lower apparent photosynthesis of the hybrids suggests that transfer of C 4 characteristics to non-C 4 species is detrimental unless characteristics associated with C 4 photosynthesis are fully developed. There was a highly significant negative correlation ( r = −0.90) between CO 2 compensation concentration and the logarithm of phosphoenolpyruvate carboxylase activity in the parents and hybrids, suggesting involvement of this enzyme in controlling the CO 2 compensation concentration. Although bundle-sheath cells were more developed in leaves of hybrids than in C 3-C 4 parents, they appeared to contain lower quantities of organelles than those of the C 4 parent. Reduced quantities of organelles in bundle-sheath cells could indicate incomplete compartmentation of partial pathways of the C 4 cycle in the hybrids. This may mean that the reduction of CO 2 compensation and O 2 inhibition of apparent photosynthesis relative to the C 3-C 4 parents is less dependent on fully developed Kranz anatomy than is increased apparent photosynthesis. 相似文献
2.
The action spectrum of apparent photosynthesis for attached radish ( Raphanus sativus L. var. Early Scarlet Globe) and corn ( Zea mays L. var. Pride V.) leaves was measured at 300 μl/l CO 2 and both 21% and 2% O 2. The spectra were measured at light intensities where apparent photosynthesis was proportional to intensity. For radish, a high compensation point plant, oxygen had an inhibiting effect on photosynthesis at all wavelengths from 402 to 694 mμ. If a constant rate of photosynthesis at 21% O 2 for the different wavelengths was chosen, then the percent increase in net CO 2 fixation at 2% O 2 was constant. For corn, a low compensation point plant, no inhibitory effect of oxygen concentration from 2% to 21% O 2 was found over the visible spectrum. The CO 2 compensation point for light intensities greater than the light compensation point was found to be constant and independent of wavelength for both radish and corn leaves. For radish, the lowering of the oxygen concentration from 21% to 2% at these intensities was found to reduce the CO 2 compensation point by the same amount for the wavelengths studied. 相似文献
3.
Measurements of CO 2 exchange at varying O 2 concentrations in seven grass species of the Laxa group of Panicum and activities of five photosynthetic enzymes were compared to values obtained for these characters in a cool season C 3 grass, tall fescue ( Festuca arundinacea Schreb.) and a C 4 grass, P. maximum Jacq. Plants were divided into three groups on the basis of the inhibition of apparent photosynthesis by 21% O 2. Rates of apparent photosynthesis in P. prionitis Griseb. and P. maximum were virtually unaffected by changes in O 2 concentration. In another group consisting of P. hylaeicum Mez., P. rivulare Trin., P. laxum Sw., and tall fescue apparent photosynthesis was inhibited by 28.2 to 36.0% at 21% O 2. An intermediate inhibition of 20.6 to 23.3% at 21% O 2 was exhibited by P. milioides Nees ex Trin., P. schenckii Hack., and P. decipiens Nees ex Trin. The CO 2 compensation concentration for P. prionitis and P. maximum was low (≤6 microliters per liter CO 2 at 21% O 2) and affected little by O 2, whereas values for P. hylaeicum, P. rivulare, P. laxum, and tall fescue were much greater, and increased almost linearly from 2 to 48% O 2. Values for P. milioides, P. schenckii, and P. decipiens were intermediate to the other two groups. The effect of O 2 on total leaf conductance to CO 2 was similar to the C 3 grasses and the intermediate Panicums. However, estimates of photorespiration in the intermediate species were low and changed little with O 2 in comparison to estimates for the C 3 species which were higher and increased greatly with increased O 2. 相似文献
4.
The weedy species Parthenium hysterophorus (Asteraceae) possesses a Kranz-like leaf anatomy. The bundle sheath cells are thick-walled and contain numerous granal chloroplasts, prominent mitochondria, and peroxisomes, all largely arranged in a centripetal position. Both mesophyll and bundle sheath chloroplasts accumulate starch. P. hysterophorus exhibits reduced photorespiration as indicated by a moderately low CO 2 compensation concentration (20-25 microliters per liter at 30°C and 21% O 2) and by a reduced sensitivity of net photosynthesis to 21% O 2. In contrast, the related C 3 species P. incanum and P. argentatum (guayule) lack Kranz anatomy, have higher CO 2 compensation concentrations (about 55 microliters per liter), and show a greater inhibition of photosynthesis by 21% O 2. Furthermore, in P. hysterophorus the CO 2 compensation concentration is relatively less sensitive to changes in O 2 concentrations and shows a biphasic response to changing O 2, with a transition point at about 11% O 2. Based on these results, P. hysterophorus is classified as a C 3-C 4 intermediate. The activities of diagnostic enzymes of C 4 photosynthesis in P. hysterophorus were very low, comparable to those observed in the C 3 species P. incanum ( e.g. phosphoenolpyruvate carboxylase activity of 10-29 micromoles per milligram of chlorophyll per hour). Exposures of leaves of each species to 14CO 2 (for 8 seconds) in the light resulted in 3-phosphoglycerate and sugar phosphates being the predominant initial 14C products (77-84%), with ≤4% of the 14C-label in malate plus aspartate. These results indicate that in the C 3-C 4 intermediate P. hysterophorus, the reduction in leaf photorespiration cannot be attributed to C 4 photosynthesis. 相似文献
5.
The effect of 21% O 2 and 3% O 2 on the CO 2 exchange of detached wheat leaves was measured in a closed system with an infrared carbon dioxide analyzer. Temperature was varied between 2° and 43°, CO 2 concentration between 0.000% and 0.050% and light intensity between 40 ft-c and 1000 ft-c. In most conditions, the apparent rate of photosynthesis was inhibited in 21% O 2 compared to 3% O 2. The degree of inhibition increased with increasing temperature and decreasing CO 2 concentration. Light intensity did not alter the effect of O 2 except at light intensities or CO 2 concentrations near the compensation point. At high CO 2 concentrations and low temperature, O 2 inhibition of apparent photosynthesis was absent. At 3% O 2, wheat resembled tropical grasses in possessing a high rate of photosynthesis, a temperature optimum for photosynthesis above 30°, and a CO 2 compensation point of less than 0.0005% CO 2. The effect of O 2 on apparent photosynthesis could be ascribed to a combination of stimulation of CO 2 production during photosynthesis, and inhibition of photosynthesis itself. 相似文献
6.
Two naturally occurring species of the genus Alternanthera, namely A. ficoides and A. tenella, were identified as C 3-C 4 intermediates based on leaf anatomy, photosynthetic CO 2 compensation point (Γ), O 2 response of г, light intensity response of г, and the activities of key enzymes of photosynthesis. A. ficoides and A. tenella exhibited a less distinct Kranz-like leaf anatomy with substantial accumulation of starch both in mesophyll and bundle sheath cells. Photosynthetic CO 2 compensation points of these two intermediate species at 29°C were much lower than in C 3 plants and ranged from 18 to 22 microliters per liter. Although A. ficoides and A. tenella exhibited similar intermediacy in г, the apparent photorespiratory component of O 2 inhibition in A. ficoides is lower than in A. tenella. The г progressively decreases from 35 microliters per liter at lowest light intensity to 18 microliters per liter at highest light intensity in A. tenella. It was, however, constant in A. ficoides at 20 to 25 microliters per liter between light intensities measured. The rates of net photosynthesis at 21% O 2 and 29°C by A. ficoides and A. tenella were 25 to 28 milligrams CO 2 per square decimeter per hour which are intermediate between values obtained for Tridax procumbens and A. pungens, C 3 and C 4 species, respectively. The activities of key enzymes of C 4 photosynthesis, phosphoenolpyruvate carboxylase, pyruvate Pi dikinase, NAD malic enzyme, NADP malic enzyme and phosphoenolpyruvate carboxykinase in the two intermediates, A. ficoides and A. tenella are very low or insignificant. Results indicated that the relatively low apparent photorespiratory component in these two species is presumably the basis for the C 3-C 4 intermediate photosynthesis. 相似文献
7.
The relative magnitudes of ( a) CO 2 compensation concentration, ( b) zero CO 2 intercept of the CO 2 response curve, ( c) O 2 suppression of net photosynthesis, ( d) differential 12CO 2 and 14CO 2 uptake, and ( e) 14CO 2 efflux into CO 2-free air were determined in the dry bean ( Phaseolus vulgaris L.) varieties Michelite-62 (M-62) and Red Kidney (RK). In comparing the two varieties for each of the above processes, there were three categories of response, M-62 > RK, M-62 = RK, and M-62 < RK. Since these processes did not give the same relative difference for the two varieties being studied, it was concluded that these phenomena cannot validly be used to estimate the magnitude of photorespiration, although they do identify its presence. The results suggest that photorespiration is but one component of O 2 inhibition of net photosynthesis and that photorespiration itself has two or more component metabolic pathways. 相似文献
8.
The genus Flaveria shows evidence of evolution in the mechanism of photosynthesis as its 21 species include C 3, C 3-C 4, C 4-like, and C 4 plants. In this study, several physiological and biochemical parameters of photosynthesis and photorespiration were measured in 18 Flaveria species representing all the photosynthetic types. The 10 species classified as C 3-C 4 intermediates showed an inverse continuum in level of photorespiration and development of the C 4 syndrome. This ranges from F. sonorensis with relatively high apparent photorespiration and lacking C 4 photosynthesis to F. Among the intermediates, the photosynthetic CO2 compensation points at 30°C and 1150 micromoles quanta per square meter per second varied from 9 to 29 microbars. The values for the three C 4-like species varied from 3 to 6 microbars, similar to those measured for the C 4 species. The activities of the photorespiratory enzymes glycolate oxidase, hydroxypyruvate reductase, and serine hydroxymethyltransferase decreased progressively from C 3 to C 3-C 4 to C 4-like and C 4 species. On the other hand, most intermediates had higher levels of phosph enolpyruvate carboxylase and NADP-malic enzyme than C 3 species, but generally lower activities compared to C 4-like and C 4 species. The levels of these C 4 enzymes are correlated with the degree of C 4 photosynthesis, based on the initial products of photosynthesis. Another indication of development of the C 4 syndrome in C 3-C 4 Flaveria species was their intermediate chlorophyll a/b ratios. The chlorophyll a/b ratios of the various Flaveria species are highly correlated with the degree of C 4 photosynthesis suggesting that the photochemical machinery is progressively altered during evolution in order to meet the specific energy requirements for operating the C 4 pathway. In the progression from C 3 to C 4 species in Flaveria, the CO 2 compensation point decreased more rapidly than did the decrease in O 2 inhibition of photosynthesis or the increase in the degree of C 4 photosynthesis. These results suggest that the reduction in photorespiration during evolution occurred initially by refixation of photorespired CO 2 and prior to substantive reduction in O 2 inhibition and development of the C 4 syndrome. However, further reduction in O 2 inhibition in some intermediates and C 4-like species is considered primarily due to the development of the C 4 syndrome. Thus, the evolution of C 3-C 4 intermediate photosynthesis likely occurred in response to environmental conditions which limit the intercellular CO 2 concentration first via refixation of photorespired CO 2, followed by development of the C 4 syndrome. 相似文献
9.
Species in the Laxa group of Panicum have C 3 or C 3/C 4 photosynthesis based on leaf anatomical and CO 2 exchange characteristics. Hybrids were previously made between C 3/C 4 and C 3 species in this group (RH Brown et al. 1985 Plant Physiol 77: 653-658). In this paper, CO 2 exchange, morphological, and leaf anatomical characteristics of F 2 or F 5 progeny from colchicine-induced amphiploids of C 3/C 4 × C 3 hybrids ( Panicum milioides Nees ex Trin. [C 3/C 4] × Panicum laxum Mez [C 3] and Panicum spathellosum Doell [C 3/C 4] × Panicum boliviense Hack. [C 3]) were studied. There were no differences found in morphology or physiology between the amphiploids and the F1 hybrids from which they were produced. In the segregating progeny, CO2 compensation concentration and photorespiration values typical of C3, but not of C3/C4 plants, were recovered. Progeny were found from both crosses which possessed O2 inhibition of apparent photosynthesis typical of the parents, and in the case of the P. milioides × P. laxum cross, leaf anatomy and overall plant morphology typical of the parents were observed in some progeny. The progeny were found to possess recombinations of various traits associated with reduced photorespiration, so that no correlation existed among O2 inhibition of apparent photosynthesis, CO2 compensation concentration, and leaf anatomical traits. One plant was especially noteworthy in possessing leaf anatomy typical of C3/C4 plants, but with CO2 exchange characteristics of C3 plants. 相似文献
10.
The Laxa group of the Panicum genus contains species which have CO 2 exchange and anatomical characteristics intermediate to C 3 and C 4 photosynthetic types (C 3/C 4), and also species characterized as C 3. Hybrids were made between two of the C 3/C 4 species and two C 3 species. Carbon dioxide exchange and morphological, leaf anatomical, and cytogenetic characteristics of F 1 hybrids between Panicum milioides Nees. ex Trin (C 3/C 4) and P. laxum Mez. (C 3), P. spathellosum Doell (C 3/C 4) and P. boliviense Hack. (C 3), and P. spathellosum and P. laxum were studied. There were no consistent differences in apparent photosynthesis, although two of the three hybrids had higher net CO 2 uptake than the C 3 parent. Values of inhibition of apparent photosynthesis by 21% O 2, CO 2 loss in the light, and CO 2 compensation concentration for the hybrids were between those of the parents. All three hybrids showed leaf anatomical traits, especially organelle quantities in the bundle sheath cells, between those of their respective parents. Linear regression of CO 2 compensation concentration on the percentage of mitochondria and chloroplasts in vascular bundle sheaths of the parents and hybrids gave correlation coefficients of −0.94. This suggests that the reduction in CO 2 loss in the C 3/C 4 species, and to a lesser degree in the F 1 hybrids, was due to development of organelles and perhaps a higher proportion of leaf photorespiration in bundle sheaths. The overall morphology of the hybrids was so different from the parents that they could be described as new taxonomic forms. The chromosomes in the hybrids were mainly unpaired or paired as bivalents indicating possible homology between some parental genomes. 相似文献
11.
Photosynthetic CO 2 and O 2 exchange was studied in two moss species, Hypnum cupressiforme Hedw. and Dicranum scoparium Hedw. Most experiments were made during steady state of photosynthesis, using 18O 2 to trace O 2 uptake. In standard experimental conditions (photoperiod 12 h, 135 micromoles photons per square meter per second, 18°C, 330 microliters per liter CO 2, 21% O 2) the net photosynthetic rate was around 40 micromoles CO 2 per gram dry weight per hour in H. cupressiforme and 50 micromoles CO 2 per gram dry weight per hour in D. scoparium. The CO 2 compensation point lay between 45 and 55 microliters per liter CO 2 and the enhancement of net photosynthesis by 3% O 2versus 21% O 2 was 40 to 45%. The ratio of O 2 uptake to net photosynthesis was 0.8 to 0.9 irrespective of the light intensity. The response of net photosynthesis to CO 2 showed a high apparent Km (CO 2) even in nonsaturating light. On the other hand, O 2 uptake in standard conditions was not far from saturation. It could be enhanced by only 25% by increasing the O 2 concentration (saturating level as low as 30% O 2), and by 65% by decreasing the CO 2 concentration to the compensation point. Although O 2 is a competitive inhibitor of CO 2 uptake it could not replace CO 2 completely as an electron acceptor, and electron flow, expressed as gross O 2 production, was inhibited by both high O 2 and low CO 2 levels. At high CO 2, O 2 uptake was 70% lower than the maximum at the CO 2 compensation point. The remaining activity (30%) can be attributed to dark respiration and the Mehler reaction. 相似文献
12.
Transfer of C 4 photosynthetic traits was studied through hybridization of Flaveria trinervia (Spreng.) Mohr (C 4) and Flaveria brownii A.M. Powell (C 4-like) with Flaveria linearis Lag. (C 3-C 4) and the C 3 species Flaveria pringlei Gandoger (C 3). Fertility was low, based on irregular chromosome pairing and low pollen stainability, except in F. brownii × F. linearis which had bivalent pairing and 76% stainable pollen. Hybrids had apparent photosynthesis values of 71 to 148% of the midparental means, while the CO 2 compensation concentration was similar to the C 4 or C 4-like parent, except in hybrids having the C 3 species F. pringlei as a parent. Inhibition of apparent photosynthesis by O 2, and phospho enolpyruvate carboxylase and NADP-malic enzyme activities and subunit levels in the hybrids were closer to the C 3 or C 3-C 4 parent. The species F. brownii and F. trinervia were equal in their capacity to transfer reduced O 2 inhibition of AP and CO 2 compensation concentration values to hybrids with F. linearis (C 3-C 4), although hybrids with F. trinervia had higher PEPC activity. The O 2 inhibition of AP was correlated with the logarithm of activities of phospho enolpyruvate carboxylase ( r = −0.95) and NADP-malic enzyme ( r = −0.87). These results confirm that C 4 traits can be transferred by hybridization of C 3-C 4 and C 4 or C 4-like species, with a higher degree of C 4 photosynthesis than exists in C 3-C 4 species, and at least in F. brownii × F. linearis, fertile progeny are obtained. 相似文献
13.
The response of apparent photosynthesis to N nutrition was studied in the C 3 grass, tall fescue ( Festuca arundinacea Schreb.), in the C 4 species Panicum maximum Jacq., and in Panicum milioides Nees ex Trin., a species with characteristics intermediate between C 3 and C 4 photosynthetic types. Plants were grown in culture solution containing 1, 5, 50, and 200 milligrams N per liter. Apparent photosynthesis was measured on the youngest fully expanded leaves at 320 microliters of CO 2 per liter of air and 21% O 2. Leaf conductance was calculated from transpiration measurements, and CO 2 compensation concentrations were also estimated. Several leaf anatomical characteristics were studied on plastic-embedded material. Leaf N content was determined on leaves which were used in photosynthesis measurements. 相似文献
14.
Photosynthetic gas exchange and malic acid fluctuations were monitored in 69 well-watered plants from five morphologically similar species of Talinum in an investigation of the ecophysiological significance of the Crassulacean acid metabolism (CAM)-cycling mode of photosynthesis. Unlike CAM, atmospheric CO 2 uptake in CAM-cycling occurs exclusively during the day; at night, the stomata are closed and respiratory CO 2 is recaptured to form malic acid. All species showed similar patterns of day-night gas exchange and overnight malic acid accumulation, confirming the presence of CAM-cycling. Species averages for gas exchange parameters and malic acid fluctuation were significantly different such that the species with the highest daytime gas exchange had the lowest malic acid accumulation and vice versa. Also, daytime CO 2 exchange and transpiration were negatively correlated with overnight malic acid fluctuation for all individuals examined together, as well as within one species. This suggests that malic acid may effect reductions in both atmospheric CO 2 uptake and transpiration during the day. No significant correlation between malic acid fluctuation and water-use efficiency was found, although a nonsignificant trend of increasing water-use efficiency with increasing malic acid fluctuation was observed among species averages. This study provides evidence that CO 2 recycling via malic acid is negatively correlated with daytime transpirational water losses in well-watered plants. Thus, CAM-cycling could be important for survival in the thin, frequently desiccated soils of rock outcrops on which these plants occur. 相似文献
15.
Gas exchange of Eurasian watermilfoil ( Myriophyllum spicatum L.) indicated a near-zero CO 2 compensation point and a high temperature optimum for photosynthesis. These properties are characteristic of plants fixing CO 2 by a β-carboxylation mechanism. Operation of the Calvin cycle was shown and no evidence for β-carboxylation was obtained. These results indicate that near-zero CO 2 compensation points are not dependent on a β-carboxylation mechanism. 相似文献
16.
A few species of Cymbopogon and Vetiveria are potentially important tropical grasses producing essential oils. In the present study, we report on the leaf anatomy and photosynthetic carbon assimilation in five species of Cymbopogon and Vetiveria zizanioides. Kranz-type leaf anatomy with a centrifugal distribution of chloroplasts and exclusive localization of starch in the bundle sheath cells were common among the test plants. Besides the Kranz leaf anatomy, these grasses displayed other typical C 4 characteristics including a low (0–5 µl/l) CO 2 compensation point, lack of light saturation of CO 2 uptake at high photon flux densities, high temperature (35°C) optimum of net photosynthesis, high rates of net photosynthesis (55–67 mg CO 2 dm -2 leaf area h -1), little or no response of net photosynthesis to atmospheric levels of O 2 and high leaf 13C/ 12C ratios. The biochemical studies with 14CO 2 indicated that the leaves of the above plant species synthesize predominantly malate during short term (5 s) photosynthesis. In pulse-chase experiments it was shown that the synthesis of 3-phosphoglycerate proceeds at the expense of malate, the major first formed product of photosynthesis in these plant species. 相似文献
17.
The rate of dark CO 2 efflux from mature wheat ( Triticum aestivum cv Gabo) leaves at the end of the night is less than that found after a period of photosynthesis. After photosynthesis, the dark CO 2 efflux shows complex dependence on time and temperature. For about 30 minutes after darkening, CO 2 efflux includes a large component which can be abolished by transferring illuminated leaves to 3% O 2 and 330 microbar CO 2 before darkening. After 30 minutes of darkness, a relatively steady rate of CO 2 efflux was obtained. The temperature dependence of steady-state dark CO 2 efflux at the end of the night differs from that after a period of photosynthesis. The higher rate of dark CO 2 efflux following photosynthesis is correlated with accumulated net CO 2 assimilation and with an increase in several carbohydrate fractions in the leaf. It is also correlated with an increase in the CO 2 compensation point in 21% O 2, and an increase in the light compensation point. The interactions between CO 2 efflux from carbohydrate oxidation and photorespiration are discussed. It is concluded that the rate of CO 2 efflux by respiration is comparable in darkened and illuminated wheat leaves. 相似文献
18.
The effect of O 2 on the CO 2 exchange of detached leaves of corn ( Zea mays), wheat ( Triticum vulgare), oats ( Avena sativa), barley ( Hordeum vulgare), timothy ( Phleum pratense) and cat-tail ( Typha angustifolia) was measured with a Clark oxygen electrode and infrared carbon dioxide analysers in both open and closed systems. Corn leaves did not produce CO2 in the light at any O2 concentration, as was shown by the zero CO2 compensation point and the absence of a CO2 burst in the first minute of darkness. The rate of photosynthesis was inhibited by O2 and the inhibition was not completely reversible. On the other hand, the steady rate of respiration after a few minutes in the dark was not affected by O2. These results were interpreted as indicating the absence of any measurable respiration during photosynthesis. Twelve different varieties of corn studied all responded to O2 in the same way. The other 5 monocotyledons studied did produce CO2 in the light. Moreover, the CO2 compensation point increased linearly with O2 indicating a stimulation of photorespiration. The implications of the lack of photorespiration in studies of primary productivity are discussed. 相似文献
19.
Reduced photorespiration has been reported in Panicum milioides on the basis of lower CO 2 compensation concentrations than in C 3 species, lower CO 2 evolution in the light, and less response of apparent photosynthesis to O 2 concentration. The lower response to O 2 in P. milioides could be due to reduced O 2 competition with CO 2 for reaction with ribulose 1,5-bisphosphate, to a reduced loss of CO 2, or to an initial fixation of CO 2 by phosphoenolpyruvate carboxylase. Experiments were carried out with Panicum maximum Jacq., a C 4 species having no apparent photorespiration; tall fescue ( Festuca arundinacea Schreb.), a C 3 species; P. milioides Nees ex Trin.; and Panicum schenckii Hack. The latter two species are closely related and have low photorespiration rates. CO 2 exchange was measured at five CO 2 concentrations ranging from 0 to 260 microliters per liter at both 2 and 21% O 2. Mesophyll conductance or carboxylation efficiency was estimated by plotting substomatal CO 2 concentrations against apparent photosynthesis. In the C 4 species P. maximum, mesophyll conductance was 0.96 centimeters per second and was unaffected by O 2 concentration. At 21% O 2 mesophyll conductance of tall fescue was decreased 32% below the value at 2% O 2. Decreases in mesophyll conductance at 21% O 2 for P. milioides and P. schenckii were similar to that for tall fescue. On the other hand, loss of CO 2 in CO 2-free air, estimated by extrapolating the CO 2 response curve to zero CO 2, was increased from 1.8 to 6.5 milligrams per square decimeter per hour in tall fescue as O 2 was raised from 2-21%. Loss of CO 2 was less than 1 milligram per square decimeter per hour for P. milioides and P. schenckii and was unaffected by O 2. The results suggest that the reduced O 2 response in P. milioides and P. schenckii is due to a lower loss of CO 2 in the light rather than less inhibition of carboxylation by O 2, since the decrease in carboxylation efficiency at 21% O 2 was similar for P. milioides, P. schenckii, and tall fescue. The inhibition of apparent photosynthesis by 21% O 2 in these three species at low light intensities was similar at 31 to 36% which also indicates similar O 2 effects on carboxylation. Apparent photosynthesis at high light intensity was inhibited less by 21% O 2 in P. milioides (16.8%) and P. schenckii (23.8%) than in tall fescue (28.4%). This lower inhibition in the Panicum species may have been due to a higher degree of recycling of photorespired CO 2 in these species than in tall fescue. 相似文献
20.
The extent of photorespiration, the inhibition of apparent photosynthesis (APS) by 21% O 2, and the leaf anatomical and ultrastructural features of the naturally occurring C 3–C 4 intermediate species in the diverse Panicum, Moricandia, and Flaveria genera are between those features of representative C 3 and C 4 plants. The greatest differences between the photosynthetic/photorespiratory CO 2 exchange characteristics of the C 3–C 4 intermediates and C 3 plants occur for the parameters which are measured at low pCO 2 (i.e., the CO 2 compensation concentration and rates of CO 2 evolution into CO 2-free air in the light). The rates of APS by the intermediate species at atmospheric pCO 2 are similar to those of C 3 plants.The mechanisms which are responsible for reducing photorespiration in the C 3–C 4 intermediate species are poorly understood, but two proposals have been advanced. One emphasizes the importance of limited C 4 photosynthesis which reduces O 2 fixation by ribulose 1,5-bisphosphate carboxylase/oxygenase, and, thus, reduces photorespiration by a CO 2-concentrating mechanism, while the other emphasizes the importance of the internal recycling of photorespiratory CO 2 evolved from the chloroplast/mitochondrion-containing bundle-sheath cells. There is no evidence from recent studies that limited C 4 photosynthesis is responsible for reducing photorespiration in the intermediate Panicum and Moricandia species. However, preliminary results suggest that some, but not all, of the intermediate Flaveria species may possess a limited C 4 cycle. The importance of a chlorophyllous bundle-sheath layer in the leaves of intermediate Panicum and Moricandia species in a mechanism based on the recycling of photorespiratory CO 2 is uncertain.Therefore, although they have yet to be clearly delineated, different strategies appear to exist in the C 3–C 4 intermediate group to reduce photorespiration. Of major importance is the finding that some mechanism(s) other than Crassulacean acid metabolism or C 4 photosynthesis has (have) evolved in at least the majority of these terrestrial intermediate species to reduce the seemingly wasteful metabolic process of photorespiration.Abbreviations APS
apparent (net) photosynthesis
- CAM
Crassulacean acid metabolism
- CE
carboxylation efficiency
- T
CO 2 compensation concentration
- IRGA
infrared gas analysis
- P i
orthophosphate
- PEP
phosphoenolpyruvate
- RuBP
ribulose 1,5-bisphosphate
Published as Paper No. 7383, Journal Series, Nebraska Agricultural Experiment Station. 相似文献
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