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1.
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
2.
The degree of C 4 photosynthesis was assessed in four hybrids among C 4, C 4-like, and C 3-C 4 species in the genus Flaveria using 14C labeling, CO 2 exchange, 13C discrimination, and C 4 enzyme activities. The hybrids incorporated from 57 to 88% of the 14C assimilated in a 10-s exposure into C 4 acids compared with 26% for the C 3-C 4 species Flaveria linearis, 91% for the C 4 species Flaveria trinervia, and 87% for the C 4-like Flaveria brownii. Those plants with high percentages of 14C initially fixed into C 4 acids also metabolized the C 4 acids quickly, and the percentage of 14C in 3-phosphoglyceric acid plus sugar phosphates increased for at least a 30-s exposure to 12CO 2. This indicated a high degree of coordination between the carbon accumulation and reduction phases of the C 4 and C 3 cycles. Synthesis and metabolism of C 4 acids by the species and their hybrids were highly and linearly correlated with discrimination against 13C. The relationship of 13C discrimination or 14C metabolism to O 2 inhibition of photosynthesis was curvilinear, changing more rapidly at C 4-like values of 14C metabolism and 13C discrimination. Incorporation of initial 14C into C 4 acids showed a biphasic increase with increased activities of phosphoe nolpyruvate carboxylase and NADP-malic enzyme (steep at low activities), but turnover of C 4 acids was linearly related to NADP-malic enzyme activity. Several other traits were closely related to the in vitro activity of NADP-malic enzyme but not phosphoe nolpyruvate carboxylase. The data indicate that the hybrids have variable degrees of C 4 photosynthesis but that the carbon accumulation and reduction portions of the C 4 and C 3 cycles are well coordinated. 相似文献
3.
The effect of 3,3-dichloro-2-(dihydroxyphosphinoylmethyl)-propenoate (DCDP), an analog of phosphoe nolpyruvate (PEP), on PEP carboxylase activity in crude leaf extracts and on photosynthesis of excised leaves was examined. DCDP is an effective inhibitor of PEP carboxylase from Zea mays or Panicum miliaceum; 50% inhibition was obtained at 70 or 350 micromolar, respectively, in the presence of 1 millimolar PEP and 1 millimolar HCO 3−. When fed to leaf sections via the transpiration stream, DCDP at 1 millimolar strongly inhibited photosynthesis in C 4 species (79-98% inhibition for a range of seven C 4 species), but only moderately in C 3 species (12-46% for four C 3 species), suggesting different mechanisms of inhibition for each photosynthetic type. The response of P. miliaceum (C 4) net photosynthesis to intercellular pCO 2 showed that carboxylation efficiency, as well as the CO 2 saturated rate, are lowered in the presence of DCDP and supported the view that carboxylation efficiency in C 4 species is directly related to PEP carboxylase activity. A fivefold increase in intercellular pCO 2 over that occurring in P. miliaceum under normal photosynthesis conditions only increased net photosynthesis rate in the presence of 1 millimolar DCDP from zero to about 5% of the maximal uninhibited rate. Therefore, it seems unlikely that direct fixation of atmospheric CO 2 by the bundle sheath cells makes any significant contribution to photosynthetic CO 2 assimilation in C 4 species. The results support the concept that C 4-selective herbicides may be developed based on inhibitors of C 4 pathway reactions. 相似文献
4.
Leaves of Flaveria brownii exhibited slightly higher amounts of oxygen inhibition of photosynthesis than the C 4 species, Flaveria trinervia, but considerably less than the C 3 species, Flaveria cronquistii. The photosynthetic responses to intercellular CO 2, light and leaf temperature were much more C 4-like than C 3-like, although 21% oxygen inhibited the photosynthetic rate, depending on conditions, up to 17% of the photosynthesis rate observed in 2% O 2. The quantum yield for CO 2 uptake in F. brownii was slightly higher than that for the C 4 species F. trinervia in 2% O 2, but not significantly different in 21% O 2. The quantum yield was inhibited 10% in the presence of 21% O 2 in F. brownii, yet no significant inhibition was observed in F. trinervia. An inhibition of 27% was observed for the quantum yield of F. cronquistii in the presence of 21% O 2. The photosynthetic response to very low intercellular CO 2 partial pressures exhibited a unique pattern in F. brownii, with a break in the linear slope observed at intercellular CO 2 partial pressure values between 15 and 20 μbar when analyzed in 21% O 2. No significant break was observed when analyzed in 2% O 2. When taken collectively, the gas-exchange results reported here are consistent with previous biochemical studies that report incomplete intercellular compartmentation of the C 3 and C 4 enzymes in this species, and suggest that F. brownii is an advanced, C 4-like C 3-C 4 intermediate. 相似文献
5.
The activities of key C 4 enzymes in gel-filtered, whole-leaf extracts and the photosynthetic characteristics for reciprocal F 1 hybrids of Flaveria pringlei (C 3) and F. brownii (C 4-like species) were measured to determine whether any inherited C 4-photosynthetic traits are responsible for their reduced CO 2 compensation concentration values (AS Holaday, S Talkmitt, ME Doohan Plant Sci 41: 31-39). The activities of phosphoenolpyruvate carboxylase, pyruvate, orthophosphate dikinase, and NADP-malic enzyme (ME) for the reciprocal hybrids are only about 7 to 17% of those for F. brownii, but are three- to fivefold greater than the activities for F. pringlei. The low activities of these enzymes in the hybrids appear to be the result of a partial dominance of F. pringlei genes over certain F. brownii genes. However, no such dominance occurs with respect to the expression of genes for NADP-malate dehydrogenase, which is as active in the hybrids as in F. brownii. In contrast to the situation with the enzymes above, cytoplasmic factors appear to determine the inheritance of NAD-ME. The NAD-ME activity in each hybrid is comparable to that in the respective maternal parent. Pulse-chase 14CO 2 incorporation analyses at ambient CO 2 levels indicate that the hybrids initially assimilate 7 to 9% of the total assimilated CO 2 into C 4 acids as compared to 3.5% for F. pringlei. In the hybrids, the percentage of 14C in malate decreases from an average of 6.5 to 2.1% after a 60-second chase in 12CO 2/air. However, this apparent C 4-cycle activity is too limited or inefficient to substantially alter CO 2 exchange from that in F. pringlei, since the values of net photosynthesis and O 2 inhibition of photosynthesis are similar for the hybrids and F. pringlei. Also, the ratio of the internal to the external CO 2 concentration and the initial slopes of the plot of CO 2 concentration versus net photosynthesis are essentially the same for the hybrids and F. pringlei. At 45 micromoles CO 2 per mole and 0.21 mole O 2 per mole, the hybrids assimilate nearly fivefold more CO 2 into C 4 acids than does F. pringlei. Some turnover of the malate pool occurs in the hybrids, but the labelling of the photorespiratory metabolites, glycine and serine, is the same in these plants as it is in F. pringlei. Thus, although limited C 4-acid metabolism may operate in the hybrids, we conclude that it is not effective in altering O 2 inhibition of CO 2 assimilation. The ability of the hybrids to assimilate more CO 2 via phosphoenolpyruvate carboxylase at low levels of CO 2 than does F. pringlei may result in an increased rate of reassimilation of photorespiratory CO 2 and CO 2 compensation concentrations below that of their C 3 parent. If the hybrids do possess a limited C 4 cycle, it must operate intracellularly. They are not likely to have inherited an intercellular compartmentation of C 4 enzymes, since F. brownii has incomplete compartmentation of key C 3 and C 4 enzymes. 相似文献
6.
Photosynthesis was examined in leaves of Flaveria brownii A. M. Powell, grown under either 14% or 100% full sunlight. In leaves of high light grown plants, the CO 2 compensation point and the inhibition of photosynthesis by 21% O 2 were significantly lower, while activities of ribulose 1,5-bisphosphate carboxylase/oxygenase and various C 4 cycle enzymes were considerably higher than those in leaves grown in low light. Both the CO 2 compensation point and the degree of O 2 inhibition of apparent photosynthesis were relatively insensitive to the light intensity used during measurements with plants from either growth conditions. Partitioning of atmospheric CO 2 between Rubisco of the C 3 pathway and phosphoenolpyruvate carboxylase of the C 4 cycle was determined by exposing leaves to 14CO 2 for 3 to 16 seconds, and extrapolating the labeling curves of initial products to zero time. Results indicated that ~94% of the CO 2 was fixed by the C 4 cycle in high light grown plants, versus ~78% in low light grown plants. Thus, growth of F. brownii in high light increased the expressed level of C 4 photosynthesis. Consistent with the carbon partitioning patterns, photosynthetic enzyme activities (on a chlorophyll basis) in protoplasts from leaves of high light grown plants showed a more C 4-like pattern of compartmentation. Pyruvate, Pi dikinase and phosphoenolpyruvate carboxylase were more enriched in the mesophyll cells, while NADP-malic enzyme and ribulose 1,5-bisphosphate carboxylase/oxygenase were relatively more abundant in the bundle sheath cells of high light than of low light grown plants. Thus, these results indicate that F. brownii has plasticity in its utilization of different pathways of carbon assimilation, depending on the light conditions during growth. 相似文献
7.
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
8.
Four species of the genus Flaveria, namely F. anomala, F. linearis, F. pubescens, and F. ramosissima, were identified as intermediate C 3-C 4 plants based on leaf anatomy, photosynthetic CO 2 compensation point, O 2 inhibition of photosynthesis, and activities of C 4 enzymes. F. anomala and F. ramosissima exhibit a distinct Kranz-like leaf anatomy, similar to that of the C 4 species F. trinervia, while the other C 3-C 4 intermediate Flaveria species possess a less differentiated Kranz-like leaf anatomy. Photosynthetic CO 2 compensation points of these intermediates at 30°C were very low relative to those of C 3 plants, ranging from 7 to 14 microliters per liter. In contrast to C 3 plants, net photosynthesis by the intermediates was not sensitive to O 2 concentrations below 5% and decreased relatively slowly with increasing O 2 concentration. Under similar conditions, the percentage inhibition of photosynthesis by 21% O 2 varied from 20% to 25% in the intermediates compared with 28% in Lycopersicon esculentum, a typical C 3 species. The inhibition of carboxylation efficiency by 21% O 2 varied from 17% for F. ramosissima to 46% for F. anomala and were intermediate between the C 4 (2% for F. trinervia) and C 3 (53% for L. esculentum) values. The intermediate Flaveria species, especially F. ramosissima, have substantial activities of the C 4 enzymes, phosphoenolpyruvate carboxylase, pyruvate, orthophosphate dikinase, NADP-malic enzyme, and NADP-malate dehydrogenase, indicating potential for C 4 photosynthesis. It appears that these Flaveria species may be true biochemical C 3-C 4 intermediates. 相似文献
9.
Hybrids between the C 4-like species, Flaveria brownii, A. M. Powell and the C 3-C 4 intermediate species Flaveria linearis Lag., Flaveria floridana Johnston, and Flaveria oppositifolia (DC.) Rydb. exhibited bivalent chromosome pairing during meiosis and stainability of pollen was high, ranging from 51 to 95%. An F 2 population produced from an F. brownii × F. linearis F 1 hybrid, exhibited bivalent chromosome pairing and high pollen stainability indicating a high degree of fertility in the hybrid. Oxygen inhibition of apparent photosynthesis averaged 6.8% for F. brownii and 22.2% for the C 3-C 4 species (in two experiments), and F 1 hybrids exhibited inhibitions which were intermediate to their parents. Values of carbon dioxide compensation concentration determined at low irradiance were 4.0, 34.0, and 6.5 microliters per liter for F. brownii, F. linearis and their F 1 hybrid, respectively. The mean value at low irradiance for 33 F 1 plants was 6.8 microliters per liter, and individual values ranged only from 3.7 to 11.7 microliters per liter. Anatomical characteristics for the F 1 hybrid leaves were intermediate to those of the parents, and there was considerable variation among F 2 plants derived from F. brownii × F. linearis. In the F 2 population δ 13C values ranged from −27‰ to −20‰. The expression of more C 4-like characteristics by the F 1 hybrids in this study and their apparent high fertility make them promising specimens for producing segregating populations for use in C 4 inheritance studies. 相似文献
10.
Light microscopic examination of leaf cross-sections showed that Flaveria brownii A. M. Powell exhibits Kranz anatomy, in which distinct, chloroplast-containing bundle sheath cells are surrounded by two types of mesophyll cells. Smaller mesophyll cells containing many chloroplasts are arranged around the bundle sheath cells. Larger, spongy mesophyll cells, having fewer chloroplasts, are located between the smaller mesophyll cells and the epidermis. F. brownii has very low CO 2 compensation points at different O 2 levels, which is typical of C 4 plants, yet it does show about 4% inhibition of net photosynthesis by 21% O 2 at 30°C. Protoplasts of the three photosynthetic leaf cell types were isolated according to relative differences in their buoyant densities. On a chlorophyll basis, the activities of phosphoenolpyruvate carboxylase and pyruvate, Pi dikinase (carboxylation phase of C 4 pathway) were highest in the larger mesophyll protoplasts, intermediate in the smaller mesophyll protoplasts, and lowest, but still present, in the bundle sheath protoplasts. In contrast, activities of ribulose 1,5-bisphosphate carboxylase, other C 3 cycle enzymes, and NADP-malic enzyme showed a reverse gradation, although there were significant activities of these enzymes in mesophyll cells. As indicated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the banding pattern of certain polypeptides of the total soluble proteins from the three cell types also supported the distribution pattern obtained by activity assays of these enzymes. Analysis of initial 14C products in whole leaves and extrapolation of pulse-labeling curves to zero time indicated that about 80% of the CO 2 is fixed into C 4 acids (malate and aspartate), whereas about 20% of the CO 2 directly enters the C 3 cycle. This is consistent with the high activity of enzymes for CO 2 fixation by the C 4 pathway and the substantial activity of enzymes of the C 3 cycle in the mesophyll cells. Therefore, F. brownii appears to have some capacity for C 3 photosynthesis in the mesophyll cells and should be considered a C 4-like species. 相似文献
11.
The initial products of photosynthesis by the C 3 species Flaveria cronquistii, the C 4 species F. trinervia, and the C 3-C 4 intermediate species F. ramosissima were determined using a pulse-chase technique with 14CO 2- 12CO 2. The intermediate species F. ramosissima incorporated at least 42% of the total soluble 14C fixed into malate and aspartate after 10 seconds of photosynthesis in 14CO 2, as compared with 90% for the C 4 species F. trinervia and 5% for the C 3 species F. cronquistii. In both F. ramosissima and F. trinervia, turnover of labeled malate and aspartate occurred during a chase period in 12CO 2, although the rate of turnover was slower in the intermediate species. Relative to F. cronquistii, F. ramosissima showed a reduced incorporation of radioactivity into serine and glycine during the pulse period. These results indicate that a functional C 4 pathway of photosynthesis is operating in F. ramosissima which can account for its reduced level of photorespiration, and that this species is a true biochemical intermediate between C 3 and C 4 plants. 相似文献
12.
Photosynthesis rates of detached Panicum miliaceum leaves were measured, by either CO 2 assimilation or oxygen evolution, over a wide range of CO 2 concentrations before and after supplying the phosphoenolpyruvate (PEP) carboxylase inhibitor, 3,3-dichloro-2-(dihydroxyphosphinoyl-methyl)-propenoate (DCDP). At a concentration of CO 2 near ambient, net photosynthesis was completely inhibited by DCDP, but could be largely restored by elevating the CO 2 concentration to about 0.8% (v/v) and above. Inhibition of isolated PEP carboxylase by DCDP was not competitive with respect to HCO 3−, indicating that the recovery was not due to reversal of enzyme inhibition. The kinetics of 14C-incorporation from 14CO 2 into early labeled products indicated that photosynthesis in DCDP-treated P. miliaceum leaves at 1% (v/v) CO 2 occurs predominantly by direct CO 2 fixation by ribulose 1,5-bisphosphate carboxylase. From the photosynthesis rates of DCDP-treated leaves at elevated CO 2 concentrations, permeability coefficients for CO 2 flux into bundle sheath cells were determined for a range of C 4 species. These values (6-21 micromoles per minute per milligram chlorophyll per millimolar, or 0.0016-0.0056 centimeter per second) were found to be about 100-fold lower than published values for mesophyll cells of C 3 plants. These results support the concept that a CO 2 permeability barrier exists to allow the development of high CO 2 concentrations in bundle sheath cells during C 4 photosynthesis. 相似文献
13.
Flaveria cronquistii (C 3), F. chloraefolia (C 3-C 4), F. floridana (C 3-C 4), F. pubescens (C 3-C 4), F. anomala (C 3-C 4), F. linearis (C 3-C 4), F. brownii (C 4), F. palmeri (C 4), F. trinervia (C 4) and F. australasica (C 4), comprising 10 out of the 21 known species of the genus Flaveria (Asteraceae), were included in a comparative study of the kinetic and regulatory properties of green leaf phosphoenolpyruvate (PEP) carboxylase. At least three kinetically distinct enzyme-forms were identified on the basis of their affinities for PEP and the degree of allosterism with respect to this substrate. The kinetic properties of PEP carboxylase of most of the species seemingly were modified in vivo depending on the growth conditions of the plants. Km(PEP free)-values of the enzyme from the five C 3-C 4 intermediate species ranged from 6 micromolar ( F. chloraefolia, low light-grown) to 38 micromolar ( F. pubescens, high light-grown). In contrast, the Km for PEP of PEP carboxylase from the C 3 species F. cronquistii (13 micromolar) apparently was not influenced by growth conditions. The response of the enzyme from the C 3 and C 3-C 4 species was hyperbolic in all cases. A second isoform with a lower affinity for PEP (88-100 micromolar), but also hyperbolic kinetics was found in the C 4 species F. brownii, whereas in the three other C 4 species examined a PEP carboxylase with a still lower affinity for PEP (187-221 micromolar) and sigmoidal kinetics was present. These isozyme-related kinetic data were supported by analyses of the elution behavior of the enzyme during anion-exchange chromatography on DEAE-Trisacryl M. The results are discussed with respect to the evolution of C 4 photosynthesis in the Flaveria genus. 相似文献
14.
The potential for C 4 photosynthesis was investigated in five C 3-C 4 intermediate species, one C 3 species, and one C 4 species in the genus Flaveria, using 14CO 2 pulse- 12CO 2 chase techniques and quantum-yield measurements. All five intermediate species were capable of incorporating 14CO 2 into the C 4 acids malate and aspartate, following an 8-s pulse. The proportion of 14C label in these C 4 products ranged from 50–55% to 20–26% in the C 3-C 4 intermediates F. floridana Johnston and F. linearis Lag. respectively. All of the intermediate species incorporated as much, or more, 14CO 2 into aspartate as into malate. Generally, about 5–15% of the initial label in these species appeared as other organic acids. There was variation in the capacity for C 4 photosynthesis among the intermediate species based on the apparent rate of conversion of 14C label from the C 4 cycle to the C 3 cycle. In intermediate species such as F. pubescens Rydb., F. ramosissima Klatt., and F. floridana we observed a substantial decrease in label of C 4-cycle products and an increase in percentage label in C 3-cycle products during chase periods with 12CO 2, although the rate of change was slower than in the C 4 species, F. palmeri. In these C 3-C 4 intermediates both sucrose and fumarate were predominant products after a 20-min chase period. In the C 3-C 4 intermediates, F. anomala Robinson and f. linearis we observed no significant decrease in the label of C 4-cycle products during a 3-min chase period and a slow turnover during a 20-min chase, indicating a lower level of functional integration between the C 4 and C 3 cycles in these species, relative to the other intermediates. Although F. cronquistii Powell was previously identified as a C 3 species, 7–18% of the initial label was in malate+aspartate. However, only 40–50% of this label was in the C-4 position, indicating C 4-acid formation as secondary products of photosynthesis in F. cronquistii. In 21% O 2, the absorbed quantum yields for CO 2 uptake (in mol CO 2·[mol quanta] -1) averaged 0.053 in F. cronquistii (C 3), 0.051 in F. trinervia (Spreng.) Mohr (C 4), 0.052 in F. ramosissima (C 3-C 4), 0.051 in F. anomala (C 3-C 4), 0.050 in F. linearis (C 3-C 4), 0.046 in F. floridana (C 3-C 4), and 0.044 in F. pubescens (C 3-C 4). In 2% O 2 an enhancement of the quantum yield was observed in all of the C 3-C 4 intermediate species, ranging from 21% in F. ramosissima to 43% in F. pubescens. In all intermediates the quantum yields in 2% O 2 were intermediate in value to the C 3 and C 4 species, indicating a co-function of the C 3 and C 4 cycles in CO 2 assimilation. The low quantum-yield values for F. pubescens and F. floridana in 21% O 2 presumably reflect an ineffcient transfer of carbon from the C 4 to the C 3 cycle. The response of the quantum yield to four increasing O 2 concentrations (2–35%) showed lower levels of O 2 inhibition in the C 3-C 4 intermediate F. ramosissima, relative to the C 3 species. This indicates that the co-function of the C 3 and C 4 cycles in this intermediate species leads to an increased CO 2 concentration at the site of ribulose-1,5-bisphosphate carboxylase/oxygenase and a concomitant decrease in the competitive inhibition by O 2.Abbreviations PEP
phosphoenolpyruvate
- PGA
3-phosphoglycerate
- RuBP
ribulose-1,5-bisphosphate 相似文献
15.
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
16.
Flaveria pringlei exhibits C 3 CO 2 compensation concentration (Г) values averaging 53 μl CO 2/l at 21% (v/v) O 2 and 25 ± 2°C. When this species is hybridized with the C 4 species, F. brownii (male) ( ), the F 1 hybrid plants exhibit an average Г value of 31 μl CO 2/l at 21% O 2.Although light micrographs of leaf cross-sections show that the leaves of the hybrid plants possess the mesophyll arrangement characteristic of F. pringlei leaves, the hybrid plants have some bundle-sheath chloroplasts. However, the numbers of these organelles do not appear to be intermediate with respect to the numbers in the parents and are closest to the small number present in the bundle-sheath cells of F. pringlei leaves. The activities of key C 4 enzymes (in μmol · mg Chl ?1 · h ?1) are: phospho enolpyruvate (PEP) carboxylase, 121; pyruvate, orthophosphate (P i) dikinase, 26; NADP-malate dehydrogenase, 2529; and NADP-malic enzyme, 82. All of these activities are substantially higher than in F. pringlei, but are only 7–10% of those in F. brownii (with the exception of the NADP-malate dehydrogenase activity). These data suggest that a C 4 cycle might be operating to a limited extent in the hybrid plants resulting in reduced photorespiration.Whether or not C 4 photosynthesis occurs in these hybrid plants, they represent the first reported C 3 × C 4 F 1 hybrids to exhibit reduced Γ-values. This cross and its reciprocal should be useful models for studying the anatomical and biochemical factors determining the development of limited C 4 photosynthesis in C 3 species. 相似文献
17.
The basis for O 2 sensitivity of C 4 photosynthesis was evaluated using a C 4-cycle-limited mutant of Amaranthus edulis (a phospho enolpyruvate carboxylase-deficient mutant), and a C 3-cycle-limited transformant of Flaveria bidentis (an antisense ribulose-1,5-bisphosphate carboxylase/oxygenase [Rubisco] small subunit transformant). Data obtained with the C 4-cycle-limited mutant showed that atmospheric levels of O 2 (20 kPa) caused increased inhibition of photosynthesis as a result of higher levels of photorespiration. The optimal O 2 partial pressure for photosynthesis was reduced from approximately 5 kPa O 2 to 1 to 2 kPa O 2, becoming similar to that of C 3 plants. Therefore, the higher O 2 requirement for optimal C 4 photosynthesis is specifically associated with the C 4 function. With the Rubisco-limited F. bidentis, there was less inhibition of photosynthesis by supraoptimal levels of O 2 than in the wild type. When CO 2 fixation by Rubisco is limited, an increase in the CO 2 concentration in bundle-sheath cells via the C 4 cycle may further reduce the oxygenase activity of Rubisco and decrease the inhibition of photosynthesis by high partial pressures of O 2 while increasing CO 2 leakage and overcycling of the C 4 pathway. These results indicate that in C 4 plants the investment in the C 3 and C 4 cycles must be balanced for maximum efficiency. 相似文献
18.
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
19.
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
20.
A plant was found in the C 3-C 4 intermediate species, Flaveria linearis, in which apparent photosynthesis is stimulated by atmospheric O 2 concentrations. A survey of 44 selfed progeny of the plant showed that the O 2 stimulation of apparent photosynthesis was passed on to the progeny. When leaves equilibrated at 210 milliliters per liter O 2 were transferred to 20 milliliters per liter O 2 apparent photosynthesis was initially stimulated, but gradually declined so that at 30 to 40 minutes the rate was only about 80 to 85% of that at 210 milliliters per liter O 2. Switching from 20 to 210 milliliters per liter caused the opposite transition in apparent photosynthesis. All other plants of F. linearis reached steady rates within 5 minutes after switching O 2 that were 20 to 24% lower in 210 than in 20 milliliters per liter O 2. At low intercellular CO 2 concentrations and low irradiances, O 2 inhibition of apparent photosynthesis of the aberrant plant was similar to that in normal plants, but at an irradiance of 2 millimoles quanta per square meter per second and near 300 microliters per liter CO 2 apparent photosynthesis was consistently higher at 210 than at 20 milliliters per liter O 2. In morphology and leaf anatomy, the aberrant plant is like the normal plants in F. linearis. The stimulation of apparent photosynthesis at air levels of O 2 in the aberrant plant is similar to other literature reports on observations with C 3 plants at high CO 2 concentrations, high irradiance and/or low temperatures, and may be related to limitation of photosynthesis by triose phosphate utilization. 相似文献
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