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1.
Thirty-three grass species were examined in two experiments in an attempt to locate plants with photosynthetic responses to O 2, CO 2 compensation concentrations, and leaf anatomy intermediate to those of C 3 and C 4 species. Species examined included seven from the Laxa group in the Panicum genus, one of which, P. milioides Nees ex Trin., has been reported earlier to have intermediate characteristics. The species with O 2-sensitive photosynthesis typical of C 3 plants showed more than 37% increase in apparent photosynthesis at 2% O 2 compared to 21% O 2 at 25 C and 335 microliters per liter CO 2, whereas in Panicum milioides, P. schenckii Hack., and P. decipiens Nees ex Trin., members of the Laxa group of Panicum, increases ranged from 25 to 30%. The remainder of the species did not respond to O 2. Species with O 2 responses characteristic of C 3 plants exhibited CO 2 compensation concentrations of 44 microliters per liter or higher at 21% O 2 and 25 to 27.5 C and species characterized as O 2-insensitive had values of microliters per liter or less. The CO 2 compensation concentration (Г) values of P. milioides, P. schenckii, and P. decipiens ranged from 10.3 to 23.3 microliters per liter. Other species of the Laxa group of Panicum exhibited O 2 response and Г values of either C 3 ( P. laxum Sw., P. hylaeicum Mez., and P. rivulare Trin.) or C 4 ( P. prionitis Griseb.) plants. Leaves of species with O 2 response and CO 2 compensation values typical of C 3 plants had poorly developed or nearly empty bundle sheath cells, and much larger distances and mesophyll cell numbers between veins than did the O 2-insensitive ones. Vein spacings in P. milioides, P. schenckii, and P. decipiens ranged from 0.18 to 0.28 millimeter and mesophyll cell number between veins from 5.2 to 7.8. While these vein spacings are closer than those of most C 3 grasses, two O 2-sensitive species of Dactylis had vein spacings similar to these Panicums and veins in Glyceria striata, another O 2-sensitive plant, were separated by only four mesophyll cells and 0.12 millimeter. Bundle sheath cells of the three intermediate Panicums contained greater quantities of organelles than are typical for C 3 grasses. 相似文献
2.
The quantum requirement (QR) for photosynthesis in Sedum praealtum, a Crassulacean acid metabolism plant, was compared with that of wheat, a C 3 plant, and maize, a C 4 plant, at 30 C. During the deacidification phase in S. praealtum, approximately 16 moles quanta were absorbed per mole malate consumed. This is equivalent to 16 moles quanta per mole CO 2 fixed, assuming 1 mole CO 2 is assimilated per mole malate decarboxylated. This QR for Crassulacean acid metabolism is similar to that of the C 3 or C 4 plant under atmospheric conditions, even though there are considerable differences in the biochemistry of photosynthesis. During late-afternoon C 3-like fixation of atmospheric CO 2 in S. praealtum, the QR was relatively high with values of 41 under 21% O 2 and 19 under 2% O 2. During the deacidification phase in S. praealtum, the relatively low QR can be accounted for by the repression of photorespiration and saturation of photosynthesis from the elevated CO 2 concentration in the leaves during malate decarboxylation. 相似文献
3.
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
4.
The possibility of altering CO 2 exchange of C 3-C 4 species by growing them under various CO 2 and O 2 concentrations was examined. Growth under CO 2 concentrations of 100, 350, and 750 micromoles per mole had no significant effect on CO 2 exchange characteristics or leaf anatomy of Flaveria pringlei (C 3), Flaveria floridana (C 3-C 4), or Flaveria trinervia (C 4). Carboxylation efficiency and CO 2 compensation concentrations in leaves of F. floridana developed under the different CO 2 concentrations were intermediate to F. pringlei and F. trinervia. When grown for 12 days at an O 2 concentration of 20 millimoles per mole, apparent photosynthesis was strongly inhibited in Panicum milioides (C 3-C 4) and to a lesser degree in Panicum laxum (C 3). In P. milioides, acute starch buildup was observed microscopically in both mesophyll and bundle sheath cells. Even after only 4 days exposure to 20 millimoles per mole O 2, the presence of starch was more pronounced in leaf cross-sections of P. milioides compared to those at 100 and 210 millimoles per mole. Even though this observation suggests that P. milioides has a different response to low O 2 with respect to translocation of photosynthate or sink activity than C 3 species, the concentration of total available carbohydrate increased in shoots of all species by 33% or more when grown at low O 2. This accumulation occurred even though relative growth rates of Festuca arundinacea (C 3) and P. milioides grown for 4 days at 210 millimoles per mole O 2, were inhibited 83 and 37%, respectively, when compared to plants grown at 20 millimoles per mole O 2. 相似文献
5.
A method was devised to quantify short-term photorespiratory rates in terrestrial plants using 18O-intermediates of the glycolate pathway, specifically glycolate, glycine, and serine. The pathway intermediates were isolated and analyzed on a GC/MS to determine molecular percent 18O-enrichment. Rates of glycolate synthesis were determined from 18O-labeling kinetics of the intermediates, derived rate equations, and nonlinear regression techniques. Glycolate synthesis in wheat ( Triticum aestivum L.), a C 3 plant, and maize ( Zea mays L.), a C 4 plant, was stimulated by high O 2 concentrations and inhibited by high CO 2 concentrations. The synthesis rates were 7.3, 2.1, and 0.7 micromoles per square decimeter per minute under a 21% O 2 and 0.035% CO 2 atmosphere for leaf tissue of wheat, maize seedlings, and 3-month-old maize, respectively. Photorespiratory CO 2 evolution rates were estimated to be 27, 6, and 2%, respectively, of net photosynthesis for the three groups of plants under the above atmosphere. The results from maize tissue support the hypothesis that C 4 plants photorespire, albeit at a reduced rate in comparison to C 3 plants, and that the CO 2/O 2 ratio in the bundle sheath of maize is higher in mature tissue than in seedling tissue. The pool size of the three photorespiratory intermediates remained constant and were unaffected by changes in either CO 2 or O 2 concentrations throughout the 10-minute labeling period. This suggests that photorespiratory metabolism is regulated by other mechanism besides phosphoglycolate synthesis by ribulose-1,5-bisphosphate carboxylase/oxygenase, at least under short-term conditions. Other mechanisms could be alternate modes of synthesis of the intermediates, regulation of some of the enzymes of the photorespiratory pathway, or regulation of carbon flow between organelles involved in photorespiration. The glycolate pool became nearly 100% 18O-labeled under an atmosphere of 40% O 2. This pool failed to become 100% 18O-enriched under lower O 2 concentrations. 相似文献
6.
Net photosynthetic rates of Spirodela polyrrhiza turions, at low O 2 levels, were 6.2 and 38.8 micromoles O 2 per gram fresh weight per hour at 1 millimolar HCO 3− and CO 2 saturation, respectively, and much lower in a regular low-pH growth solution. Air equilibration O 2 concentrations decreased rates considerably, except at CO 2 saturation. The surfacing rate of turions in various inorganic carbon surroundings correlated positively with their photosynthetic rates, but were the same at high and low O 2 levels. The relevance of these findings in relation to environmental conditions conductive to germination of autotrophically growing turions is discussed. 相似文献
7.
Photosynthetic O 2 production and photorespiratory O 2 uptake were measured using isotopic techniques, in the C 3 species Hirschfeldia incana Lowe., Helianthus annuus L., and Phaseolus vulgaris L. At high CO 2 and normal O 2, O 2 production increased linearly with light intensity. At low O 2 or low CO 2, O 2 production was suppressed, indicating that increased concentrations of both O 2 and CO 2 can stimulate O 2 production. At the CO 2 compensation point, O 2 uptake equaled O 2 production over a wide range of O 2 concentrations. O 2 uptake increased with light intensity and O 2 concentration. At low light intensities, O 2 uptake was suppressed by increased CO 2 concentrations so that O 2 uptake at 1,000 microliters per liter CO 2 was 28 to 35% of the uptake at the CO 2 compensation point. At high light intensities, O 2 uptake was stimulated by low concentrations of CO 2 and suppressed by higher concentrations of CO 2. O 2 uptake at high light intensity and 1000 microliters per liter CO 2 was 75% or more of the rate of O 2 uptake at the compensation point. The response of O 2 uptake to light intensity extrapolated to zero in darkness, suggesting that O 2 uptake via dark respiration may be suppressed in the light. The response of O 2 uptake to O 2 concentration saturated at about 30% O 2 in high light and at a lower O 2 concentration in low light. O 2 uptake was also observed with the C 4 plant Amaranthus edulis; the rate of uptake at the CO 2 compensation point was 20% of that observed at the same light intensity with the C 3 species, and this rate was not influenced by the CO 2 concentration. The results are discussed and interpreted in terms of the ribulose-1,5-bisphosphate oxygenase reaction, the associated metabolism of the photorespiratory pathway, and direct photosynthetic reduction of O 2. 相似文献
8.
The gas exchange of spinach plants, salt-stressed by adding NaCl to the nutrient solution in increments of 25 millimolar per day to a final concentration of 200 millimolar, was studied 3 weeks after starting NaCl treatment. Photosynthesis became light saturated at 1100 to 1400 micromoles per square meter per second in salt-treated plants and at approximately 2000 micromoles per square meter per second in control plants. Photosynthetic capacity of the mesophyll measured as a function of intercellular partial pressure of CO 2 at the light intensity prevailing during growth and at light saturation were both decreased in the salttreated plants. The CO 2 compensation points and relative enhancements of photosynthesis at low O 2 were not affected by salinity. The lower photosynthetic rates in salt-treated leaves at 450 micromoles per square meter per second were associated with a 70% reduction in stomatal conductance and low intercellular CO 2 (219 microbars; cf. 285 microbars for controls). Increasing photon flux density to light saturation extended the linear portions of the CO 2 response curves, increased stomatal conductances, increased intercellular CO 2 in the salt-treated plants, but lowered it in controls, and accentuated differences in photosynthetic rate (area basis) between the treatments. Leaves from salt-treated plants were thicker but contained about 73% of the chlorophyll per unit area of control plants. When photosynthetic rates were expressed on a chlorophyll basis there was no difference in initial slope of assimilation versus intercellular CO2 between treatments. Photosynthetic rates (chlorophyll basis) at light saturation differed only by 20% which was also observed earlier with isolated, intact chloroplasts (Robinson et al. 1983 Plant Physiol 73: 238-242). Measurement of carbon isotope ratio revealed less discrimination against 13C with salt treatment and confirmed the persistence of low intercellular partial pressures of CO2 during plant growth. The development of a thicker leaf with less chlorophyll per unit area during salt treatment permitted stomatal conductance and intercellular partial pressure of CO2 to decline without restricting photosynthesis and had the benefit of greatly increasing water use efficiency. 相似文献
9.
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
10.
Diffusion of inorganic carbon into isolated bundle sheath cells from a variety of C 4 species was characterized by coupling inward diffusion of CO 2 to photosynthetic carbon assimilation. The average permeability coefficient for CO 2 ( PCO2) for five representatives from the three decarboxylation types was approximately 20 micromoles per minute per milligram chlorophyll per millimolar, on a leaf chlorophyll basis. The average value for the NAD-ME species Panicum miliaceum (10 determinations) was 26 with a standard deviation of 6 micromoles per minute per milligram chlorophyll per millimolar, on a leaf chlorophyll basis. A PCO2 of at least 500 micromoles per minute per milligram chlorophyll per millimolar was determined for cells isolated from the C 3 plant Xanthium strumarium. It is concluded that bundle sheath cells are one to two orders of magnitude less permeable to CO 2 than C 3 photosynthetic cells. These data also suggest that CO 2 diffusion in bundle sheath cells may be made up of two components, one involving an apoplastic path and the other a symplastic (plasmodesmatal) path, each contributing approximately equally. 相似文献
11.
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
12.
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
13.
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
14.
Photosynthetic characteristics at high measurement irradiance were analyzed for single leaves of two C 3 and one C 4 species grown under twenty one combinations of irradiance level, irradiance duration, and air temperature in order to test the idea that photosynthetic characteristies developed by leaves in different environments are controlled by the daily amount of photosynthesis. Photosynthetic rates per unit area and mesophyll conductances at 25°C and air levels of CO 2 and O 2, and parameters for two photosynthesis models were used to characterize the photosynthetic properties of the leaves. Leaves with highest values of the photosynthetic parameters for each species were often developed in environments with irradiance levels below saturation for photosynthesis, and with only 12 hours of irradiance per day. Lower air temperature during growth increased the photosynthetic characteristics for a given irradiance regime. Photosynthetic characteristics had higher correlation coefficients with daily photosynthesis of mature leaves divided by 24-hour leaf elongation rates of young leaves, than with daily photosynthesis alone, indicating that photosynthetic characteristics may be related to a balance between photosynthesis and leaf expansion. 相似文献
15.
Carbonic anhydrase (CA, EC 4.2.1.1) catalyses the first reaction in the C 4 photosynthetic pathway, the conversion of atmospheric CO 2 to bicarbonate in the mesophyll cytosol. To examine the importance of the enzyme to the functioning of the C 4 photosynthetic pathway, Flaveria bidentis (L.) Kuntze, a C 4 dicot, was genetically transformed with an antisense construct in which the cDNA encoding a putative cytosolic CA (CA3) was placed under the control of a constitutive promoter. Some of the primary transformants had impaired CO 2 assimilation rates and required high CO 2 for growth. The T 1 progeny of four primary transformants were used to examine the quantitative relationship between leaf CA activity and CO 2 assimilation rate. CA activity was determined in leaf extracts with a mass spectrometric technique that measured the rate of 18O exchange from doubly labelled 13C 18O 2. Steady‐state CO 2 assimilation rates were unaffected by a decrease in CA activity until CA activity was less than 20% of wild type when they decreased steeply. Transformants with less than 10% of wild‐type CA activity had very low CO 2 assimilation rates and grew poorly at ambient CO 2 partial pressure. Reduction in CA activity also increased the CO 2 partial pressure required to saturate CO 2 assimilation rates. The present data show that CA activity is essential for the functioning of the C 4 photosynthetic pathway. 相似文献
16.
Leaves of C 3 plants which exhibit a normal O 2 inhibition of CO 2 fixation at less than saturating light intensity were found to exhibit O 2-insensitive photosynthesis at high light. This behavior was observed in Phaseolus vulgaris L., Xanthium strumarium L., and Scrophularia desertorum (Shaw.) Munz. O 2-insensitive photosynthesis has been reported in nine other C 3 species and usually occurred when the intercellular CO 2 pressure was about double the normal pressure. A lack of O 2 inhibition of photosynthesis was always accompanied by a failure of increased CO 2 pressure to stimulate photosynthesis to the expected degree. O 2-insensitive photosynthesis also occurred after plants had been water stressed. Under such conditions, however, photosynthesis became O 2 and CO 2 insensitive at physiological CO 2 pressures. Postillumination CO 2 exchange kinetics showed that O 2 and CO 2 insensitivity was not the result of elimination of photorespiration. It is proposed that O2 and CO2 insensitivity occurs when the concentration of phosphate in the chloroplast stroma cannot be both high enough to allow photophosphorylation and low enough to allow starch and sucrose synthesis at the rates required by the rest of the photosynthetic component processes. Under these conditions, the energy diverted to photorespiration does not adversely affect the potential for CO2 assimilation. 相似文献
17.
Photosynthetic characteristics at high measurement irradiance were analyzed for single leaves of two C 3 and one C 4 species grown under twenty one combinations of irradiance level, irradiance duration, and air temperature in order to test the idea that photosynthetic characteristics developed by leaves in different environments are controlled by the daily amount of photosynthesis. Photosynthetic rates per unit area and mesophyll conductances at 25°C and air levels of CO 2 and O 2, and parameters for two photosynthesis models were used to characterize the photosynthetic properties of the leaves. Leaves with highest values of the photosynthetic parameters for each species were often developed in environments with irradiance levels below saturation for photosynthesis, and with only 12 hours of iradiance per day. Lower air temperature during growth increased the photosynthetic characteristics for a given irradiance regime. Photosynthetic characteristics had higher correlation coefficients with daily photosynthesis of mature leaves divided by 24-hour leaf elongation rates of young leaves, than with daily photosynthesis alone, indicating that photosynthetic characteristics may be related to a balance between photosynthesis and leaf expansion. 相似文献
18.
We grew velvetleaf ( Abutilon theophrasti Medic.) and cotton ( Gossypium hirsutum L. var. Stoneville 213) at three irradiances and determined the photosynthetic responses of single leaves to a range of six irradiances from 90 to 2000 μeinsteins m −2sec −1. In air containing 21% O 2, velvetleaf and cotton grown at 750 μeinsteins m −2sec −1 had maximum photosynthetic rates of 18.4 and 21.9 mg of CO 2 dm −2hr −1, respectively. Maximum rates for leaves grown at 320 and 90 μeinsteins m −2sec −1 were 15.3 and 10.3 mg of CO 2 dm −2hr −1 in velvetleaf and 12 and 6.7 mg of CO 2 dm −2hr −1 in cotton, respectively. In 1 O 2, maximum photosynthetic rates were 1.5 to 2.3 times the rates in air containing 21% O 2, and plants grown at medium and high irradiance did not differ in rate. In both species, stomatal conductance was not significantly affected by growth irradiance. The differences in maximum photosynthetic rates were associated with differences in mesophyll conductance. Mesophyll conductance increased with growth irradiance and correlated positively with mesophyll thickness or volume per unit leaf area, chlorophyll content per unit area, and photosynthetic unit density per unit area. Thus, quantitative changes in the photosynthetic apparatus help account for photosynthetic adaptation to irradiance in both species. Net assimilation rates calculated for whole plants by mathematical growth analysis were closely correlated with single-leaf photosynthetic rates. 相似文献
19.
The photosynthetic gas-exchange has been assessed traditionally either as O 2 evolution or CO 2 consumption. In this study, we used a liquid-phase O 2 electrode combined with CO 2 optodes to examine simultaneously photosynthesis in intact leaves of mangrove Rhizophora mucronata. We verified suitable conditions for leaf photosynthetic rates by assessing pH levels and NaHCO 3 concentrations and compared these to the gas-exchange method at various PAR levels. The photosynthetic rate in response to pH exhibited a similar pattern both for O 2 evolution and CO 2 consumption, and higher rates were associated with intermediate pH compared with low and high pH values. The net photosynthetic quotient (PQ) of R. mucronata leaves ranged from 1.04–1.28. The PQ values, which were never lesser than 1, suggested that photorespiration did not occur in R. mucronata leaves under aqueous conditions. The similar maximum photosynthetic rates suggested that all measurements had a high capacity to adjust the photosynthetic apparatus under a light saturation condition. The simultaneous measurements of O 2 evolution and CO 2 consumption using the Clark oxygen electrode polarographic sensor with the CO 2 optode sensor provided a simple, stable, and precise measurement of PQ under aqueous and saturated light conditions. 相似文献
20.
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
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