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1.
A ventilated diffusion porometer was modified and adapted for simultaneous measurements of leaf resistance and photosynthesis (using 14C). The system enables measurements to be made under field and laboratory conditions with different concentrations of CO 2 and vapor pressure gradients between the evaporating surfaces inside the leaf and the external atmosphere. The leaf is subjected to the porometer's atmosphere only for short periods (up to 30 seconds) and it is assumed that stomata are not affected. Establishing the linear regression of the effect of CO 2 concentration on net photosynthesis makes it possible to extrapolate for CO 2 compensation point, to calculate the overall resistance to CO 2 and the mesophyll resistance to CO 2. 相似文献
2.
The rate of net CO 2 assimilation (A), the stomatal ( gs) and residual ( gr) conductances to CO 2, the intercellular CO 2 concentration, the CO 2 compensation points at 21% O 2 (Γ 21) and at 2% O 2 (Γ 2), and the amounts of dry matter, nitrogen, and carbohydrates were determined, from anthesis through grain filling, in the flag leaf blade and sheath of spring wheat ( Triticum aestivum L. cv Kolibri). The nitrogen content and the rate of net CO 2 assimilation declined slowly until the onset of senescence in both organs, about 3 weeks after anthesis. During senescence the reduction of A in both organs was not primarily caused by a decrease in gs; the main factor is the decrease in gr. From values of Γ 21 and Γ 2 it is suggested that the rate of respiration in the light contributing to the CO 2 compensation point is higher in sheaths than in blades irrespective of the O 2 level considered. The role of sheaths storing and later transporting assimilates to the developing grains seems to be more important for shoot yield than that of sheaths functioning as photosynthetic organs after the onset of senescence occurs. It is suggested that accumulation of carbohydrates in leaves might somehow trigger senescence in the flag leaf blade and sheath simultaneously. 相似文献
3.
A comprehensive developmental survey of leaf area, chlorophyll, photosynthetic rate, leaf resistance, transpiration ratio, CO 2 compensation point and photorespiration was conducted in apple. The largest changes in each of the photosynthetic characteristics studied took place during the earliest stages of leaf development, coinciding with the period of greatest leaf expansion and chlorophyll synthesis. During early development, photosynthesis increased 5-fold, reaching a maximum rate of 40 mg CO 2 dm -2 hr -1 at a leaf plastochron index (LPI) of 10. During this same period, leaf resistance, transpiration ratio, CO 2 compensation point and mesophyll resistance decreased, while carboxylation efficiency increased. Two especially interesting aspects of the data discussed are simultaneous changes that occur at a LPI of 10 and 12 in all of the photosynthetic characteristics examined and an apparent decrease in photorespiration as leaves age. From our results it is clear that stage of leaf development is an important factor affecting the rate of photosynthesis and photorespiration.Scientific Paper No. 5687, College of Agriculture, Washington State University, Pullman. This work is supported by the National Science Foundation Grant 80-10958 and the Columbia River Orchards Foundation. 相似文献
4.
The gas exchange characteristics of 24 genotypes of Lycopersicon esculentum Mill. and one of L. minutum were measured with an infrared gas analyzer and dew point hygrometer in an open system. Net carbon exchange (NCE) and transpiration rate were measured at 50, 100, 150, and 300 μ1 1 −1 CO 2, and a regression of NCE versus internal lead [CO 2] estimates was calculated. The slope of the regression curve at the CO 2 compensation point was used as the measure of carboxylation efficiency (CE). Significant genotypic differences for CE were obtained. Differences in CE did not appear to be due to differences in diffusive resistance defined as the sum of the boundary layer resistance ( ra) and the stomatal plus cuticular resistance ( r1). There was no correlation ( r = -0.07) between ( ra + r1) and CE. Within groups with nonsignificantly different means for ( ra + r1) there were genotypes with extremes for CE. 相似文献
5.
Some factors influencing dark respiration, photorespiration, and photosynthesis were examined for their effect on the CO 2 compensation point (70 μl/l) of detached soybean ( Glycine max) leaf discs. A higher compensation point in young leaves decreased to the constant value after leaf expansion and maturation, but increased again during senescence. The compensation point was 40 to 50% higher in plants grown in the summer than in the winter. The compensation point and dark respiration increased with temperatures above 17 C. Below 17 C dark respiration continued to decrease, but the compensation point did not decrease further. Increasing light intensities did not affect the compensation point. 相似文献
6.
Summary Carbon dioxide and oxygen gas exchange of illuminated Amaranthus and Phaseolus leaves was measured from 0–600 ppm of CO 2 in an open system.At low oxygen concentration (2% O 2) the ratio of CO 2 uptake to O 2 evolution came close to 1.At high oxygen partial pressure (42% O 2) the O 2 compensation point of an Amaranthus leaf was increased and oxygen evolution was depressed. Accordingly the CO 2/O 2 quotients were variable; the lowest value of 1,9 differed significantly from 1,0.The oxygen and carbon dioxide compensation points of a Phaseolus leaf were increased at high oxygen concentration (42% O 2) and oxygen evolution as well as carbon dioxide uptake were reduced. Therefore the ratios CO 2 over O 2 varied and differed greatly from 1,0.It was concluded that the nature of photosynthates is regulated by the gas composition around the leaves. 相似文献
7.
Glycolate and ammonia excretion plus oxygen exchanges were measured in the light in l-methionine- dl-sulfoximine treated air-grown Chlamydomonas reinhardii. At saturating CO 2 (between 600 and 700 microliters per liter CO 2) neither glycolate nor ammonia were excreted, whereas at the CO 2 compensation concentration (<10 microliters per liter CO 2) treated algae excreted both glycolate and ammonia at rates of 37 and 59 nanomoles per minute per milligram chlorophyll, respectively. From the excretion values we calculate the amount of O 2 consumed through the glycolate pathway. The calculated value was not significantly different from the component of O 2 uptake sensitive to CO 2 obtained from the difference between O 2 uptake of the CO 2 compensation point and at saturating CO 2. This component was about 40% of stationary O 2 uptake measured at the CO 2 compensation point. From these data we conclude that glyoxylate decarboxylation in air-grown Chlamydomonas represents a minor pathway of metabolism even in conditions where amino donors are deficient and that processes other than glycolate pathway are responsible for the O 2 uptake insensitive to CO 2. 相似文献
8.
Water hyacinth ( Eichhornia crassipes [Mart.] Solms) plants were grown in environmental chambers at ambient and enriched CO 2 levels (330 and 600 microliters CO 2 per liter). Daughter plants (ramets) produced in the enriched CO 2 gained 39% greater dry weight than those at ambient CO 2, but the original mother plants did not. The CO 2 enrichment increased the number of leaves per ramet and leaf area index, but did not significantly increase leaf size or the number of ramets formed. Flower production was increased 147%. The elevated CO 2 increased the net photosynthetic rate of the mother plants by 40%, but this was not maintained as the plants acclimated to the higher CO 2 level. After 14 days at the elevated CO 2, leaf resistance increased and transpiration decreased, especially from the adaxial leaf surface. After 4 weeks in elevated as compared to ambient CO 2, ribulose bisphosphate carboxylase activity was 40% less, soluble protein content 49% less, and chlorophyll content 26% less; whereas starch content was 40% greater. Although at a given CO 2 level the enriched CO 2 plants had only half the net photosynthetic rate of their counterparts grown at ambient CO 2, they showed similar internal CO 2 concentrations. This suggested that the decreased supply of CO 2 to the mesophyll, as a result of the increased stomatal resistance, was counterbalanced by a decreased utilization of CO 2. Photorespiration and dark respiration were lower, such that the CO 2 compensation point was not altered. The photosynthetic light and CO 2 saturation points were not greatly changed, nor was the O 2 inhibition of photosynthesis (measured at 330 microliters CO 2 per liter). It appears that with CO 2 enrichment the temporary increase in net photosynthesis produced larger ramets. After acclimation, the greater total ramet leaf area more than compensated for the lower net photosynthetic rate on a unit leaf area basis, and resulted in a sustained improvement in dry weight gain. 相似文献
9.
采用盆栽试验方法,探讨了香樟( Cinnamomum camphora)凋落叶不同土壤添加水平(0 g/盆为CK、25 g/盆、50 g/盆,100 g/盆)对受体作物小白菜( Brassica chinensis)、莴笋( Lactuca sativa)幼苗生长和光合特性的影响。结果显示:(1)香樟凋落叶分解对两种作物的地径、株高、生物量、叶片数和叶面积均有明显的抑制作用,且抑制效应随凋落叶添加量的增加而增强,但随着分解时间的延长其抑制作用逐渐减弱甚至表现为促进作用。(2)香樟凋落叶分解对两种作物的光合色素含量均有明显的抑制效应,并随凋落叶添加量的增加抑制作用增强,且持续时间延长。(3)经凋落叶处理的两种作物叶片净光合速率( Pn)、气孔导度( Gs)、蒸腾速率( Tr)、水分利用率(WUE)总体上均低于CK,而胞间CO 2浓度( Ci)在各凋落叶处理下均高于CK。(4)随着土壤中凋落叶量的增加,两种作物在光饱和以及CO 2饱和状态下的最大净光合速率( Pn max)、表观量子效率(AQY)、羧化速率(CE)、光呼吸速率( Rp)和暗呼吸速率( Rd)均不断下降,而光补偿点(LCP)、光饱和点(LSP)、CO 2饱和点(CSP)、CO 2补偿点(CCP)因受体作物的不同,表现出不同的变化趋势。研究表明,土壤中香樟凋落叶分解释放的化感物质,能通过降低受体作物的光合色素合成和光合能力,限制其营养生长,最终影响生物量积累;相对于莴笋,小白菜对香樟凋落叶分解产生的化感胁迫效应具有更强的耐受性,可能更适宜在香樟林间种植。 相似文献
10.
Four self-pollinated, doubled-haploid tobacco, ( Nicotiana tabacum L.) lines (SP422, SP432, SP435, and SP451), selected as haploids by survival in a low CO 2 atmosphere, and the parental cv Wisconsin-38 were grown from seed in a growth room kept at high CO 2 levels (600-700 parts per million). The selected plants were much larger (especially SP422, SP432, and SP451) than Wisconsin-38 nine weeks after planting. The specific leaf dry weight and the carbon (but not nitrogen and sulfur) content per unit area were also higher in the selected plants. However, the chlorophyll, carotenoid, and alkaloid contents and the chlorophyll a/b ratio varied little. The net CO 2 assimilation rate per unit area measured in the growth room at high CO 2 was not higher in the selected plants. The CO 2 assimilation rate versus intercellular CO 2 curve and the CO 2 compensation point showed no substantial differences among the different lines, even though these plants were selected for survival under CO 2 compensation point conditions. Adult leaf respiration rates were similar when expressed per unit area but were lower in the selected lines when expressed per unit dry weight. Leaf respiration rates were negatively correlated with specific leaf dry weight and with the carbon content per unit area and were positively correlated with nitrogen and sulfur content of the dry matter. The alternative pathway was not involved in respiration in the dark in these leaves. The better carbon economy of tobacco lines selected for low CO 2 survival was not apparently related to an improvement of photosynthesis rate but could be related, at least partially, to a significantly reduced respiration (mainly cytochrome pathway) rate per unit carbon. 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.
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
13.
The effects of various chemical treatments upon photosynthesis, soluble leaf protein, CO 2 compensation point, and leaf light transmission in soybean, Glycine max (L.) Merr., seedlings were examined following varying response periods after application at 14 to 17 days postemergence. The compounds N 6-benzyladenine (BA), 2-(4-chlorophenoxy)-2-methylpropanoic acid (CPMP), (4-chlorophenoxy)acetic acid (CPA), rhodanine- N-acetic acid (RAA), and 2,3,5-triiodobenzoic acid (TIBA) significantly increased soluble protein and decreased senescence, measured by leaf light transmission, at CO 2 concentrations below the compensation point in a survival chamber. All compounds except BA significantly decreased transmission values under ambient atmospheric conditions. In statistically significant experiments, applications of 3.49 millimolar CPMP increased net photosynthesis on a leaf area basis by an average of 14.4% at all trifoliolate positions with increases generally requiring response periods of 12 days or longer. RAA at 1.31 and 2.61 millimolar increased net photosynthesis by 19 to 36% following 13-day response periods. CPMP and other compounds tested had no effect upon the CO 2 compensation point after 4- to 8-day response periods. The effects of CPMP and RAA upon net photosynthesis and soluble protein appeared to involve a combined stimulation of protein synthesis and an antisenescent effect. There were no indications that any of the photosynthetic changes observed resulted from direct differential effects upon ribulose bisphosphate carboxylase-oxygenase. The assays for soluble protein and light transmission responded more consistently to the chemicals than did photosynthesis. 相似文献
14.
The CO 2 compensation points of Coccochloris peniocystis, a blue-green alga and Chlamydomonas reinhardtii, a green alga, were determined at pH 8.0 in a closed system by a gas chromatographic technique. The compensation point of Chlamydomonas increased markedly with temperature, rising from 0.79 microliter per liter CO 2 at 15 C to 2.5 microliters per liter CO 2 at 35 C. In contrast, the compensation point of Coccochloris at 20 C was 0.71 microliter per liter CO 2 and rose to only 0.95 microliter per liter CO 2 at 40 C. 相似文献
15.
Constructs containing the cDNAs encoding the primary leaf catalase in Nicotiana or subunit 1 of cottonseed ( Gossypium hirsutum) catalase were introduced in the sense and antisense orientation into the Nicotiana tabacum genome. The N. tabacum leaf cDNA specifically overexpressed CAT-1, the high catalytic form, activity. Antisense constructs reduced leaf catalase specific activities from 0.20 to 0.75 times those of wild type (WT), and overexpression constructs increased catalase specific activities from 1.25 to more than 2.0 times those of WT. The NADH-hydroxypyruvate reductase specific activity in transgenic plants was similar to that in WT. The effect of antisense constructs on photorespiration was studied in transgenic plants by measuring the CO 2 compensation point (Γ) at a leaf temperature of 38°C. A significant linear increase was observed in Γ with decreasing catalase (at 50% lower catalase activity Γ increased 39%). There was a significant temperature-dependent linear decrease in Γ in transgenic leaves with elevated catalase compared with WT leaves (at 50% higher catalase Γ decreased 17%). At 29°C, Γ also decreased with increasing catalase in transgenic leaves compared with WT leaves, but the trend was not statistically significant. Rates of dark respiration were the same in WT and transgenic leaves. Thus, photorespiratory losses of CO 2 were significantly reduced with increasing catalase activities at 38°C, indicating that the stoichiometry of photorespiratory CO 2 formation per glycolate oxidized normally increases at higher temperatures because of enhanced peroxidation. 相似文献
16.
Using iron stress to reduce the total amount of light-harvesting and electron transport components per unit leaf area, the influence of light-harvesting and electron transport capacity on photosynthesis in sugar beet ( Beta vulgaris L. cv F58-554H1) leaves was explored by monitoring net CO 2 exchange rate ( P) in relation to changes in the content of Chl. In most light/CO2 environments, and especially those with high light (≥1000 microeinsteins photosynthetically active radiation per square meter per second) and high CO2 (≥300 microliters CO2 per liter air), P per area was positively correlated with changes in Chl (a + b) content (used here as an index of the total amount of light-harvesting and electron transport components). This positive correlation of P per area with Chl per area was obtained not only with Fe-deficient plants, but also over the normal range of variation in Chl contents found in healthy, Fe-sufficient plants. For example, light-saturated P per area at an ambient CO2 concentration close to normal atmospheric levels (300 microliters CO2 per liter air) increased by 36% with increase in Chl over the normal range, i.e. from 40 to 65 micrograms Chl per square centimeter. Iron deficiency-mediated changes in Chl content did not affect dark respiration rate or the CO2 compensation point. The results suggest that P per area of sugar beet may be colimited by light-harvesting and electron transport capacity (per leaf area) even when CO2 is limiting photosynthesis as occurs under field conditions. 相似文献
17.
Summary The influence of water stress on photosynthesis of drought hardened, and non-hardened, Eucalyptus socialis plants was examined. Particular attention was given to the effects of low leaf water potential on stomatal and intracellular resistance to CO 2 transport and on the CO 2 compensation point. Though the hardening treatment had a pronounced influence on leaf morphology, there was no apparent difference in the photosynthetic response to drought stress between hardened and non-hardened treatments, or with repeated drought cycles. These results suggest a high degree of genetic preconditioning to drought in this species. 相似文献
18.
The response of net photosynthesis and apparent light respiration to changes in [O 2], light intensity, and drought stress was determined by analysis of net photosynthetic CO 2 response curves. Low [O 2] treatment resulted in a large reduction in the rate of photorespiratory CO 2 evolution. Lightintensity levels influenced the maximum net photosynthetic rate at saturating [CO 2]. These results indicate that [CO 2], [O 2] and light intensity affect the levels of substrates involved in the enzymatic reactions of photosynthesis and photorespiration. Intracellular resistance to CO 2 uptake decreased in low [O 2] and increased at low leaf water potentials. This response reflects changes in the efficiency with which photosynthetic and photorespiratory substrates are formed and utilized. Water stress had no effect on the CO 2 compensation point or the [CO 2] at which net photosynthesis began to saturate at high light intensity. The relationship between these data and recently published in-vitro kinetic measurements with ribulose-diphosphate carboxylase is discussed.Abbreviations
C
w
intracellular CO 2 concentration
-
F
gross
gross photosynthesis
-
F
net
net photosynthesis
-
I
light intensity
-
R
L
light respiration rate
-
r
c
carboxylation resistance
-
r
8
leaf gas-phase resistance
-
r
i
intracellular resistance; to CO 2 uptake
-
r
t
resistance to CO 2 flux between the intercellular spaces and the carboxylation sites
-
T
L
leaf temperature
-
t
leaf water potential
-
CO 2 compensation point 相似文献
19.
Significant differences in CO 2 compensation concentration measured in the field among varieties of the species Zea mays L. are reported for the first time. CO 2 compensation concentrations were significantly (P≤ 0.01) and negatively correlated with apparent photosynthesis at 300 μl CO 2/liter air. The Michaelis constant (as defined) for a leaf was significantly (P≤ 0.01) and positively correlated with apparent photosynthesis among varieties. While the first correlation is similar to behavior of CO 2 compensation among species of different photosynthetic efficiency, the latter correlation is the converse of the behavior of K m among species. 相似文献
20.
The losses in chloroplast capacity to fix CO 2 when photosynthesis is reduced at low leaf water potential (ψ 1) have been proposed to result from photoinhibition. We investigated this possibility in soil-grown sunflower ( Helianthus annuus L. cv IS894) using gas exchange techniques to measure directly the influence of light during dehydration on the in situ chloroplast capacity to fix CO 2. The quantum yield for CO 2 fixation as well as the rate of light- and CO 2-saturated photosynthesis were strongly inhibited at low ψ 1. The extent of inhibition was the same whether the leaves were exposed to high or to low light during dehydration. When intercellular partial pressures of CO 2 were decreased to the compensation point, which was lower than the partial pressures resulting from stomatal closure, the inhibition of the quantum yield was also unaffected. Photoinhibition could be observed only after high light exposures were imposed under nonphysiological low CO 2 and O 2 where both photosynthesis and photorespiration were suppressed. The experiments are the first to test whether gas exchange at low ψ 1 is affected by potentially photoinhibitory conditions and show that the loss in chloroplast capacity to fix CO 2 was entirely the result of a direct effect of water availability on chloroplast function and not photoinhibition. 相似文献
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