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1.
Seven day old wheat and maize seedlings were exposed to 1300 or 2000 microeinsteins per square meter per second photosynthetically active radiation in CO 2-free air for 3 hours with either 1% O 2 in N 2 or N 2-only and then returned to normal air of 340 microliters per liter CO 2, 21% O 2 in N 2. Activity of the ribulose bisphosphate carboxylase and amount of the substrate, ribulose 1,5-bisphosphate, were measured during and following the CO 2-free treatments as was photosynthetic CO 2 fixation. Photoinhibition of photosynthesis was observed only with wheat seedlings following the N 2 only treatment. During the CO 2-free treatments, the levels of RuBP rose during all experiments except when wheat was photoinhibited. The activity of the ribulose bisphophate carboxylase, measured directly upon grinding the leaves, declined during the CO 2-free conditions. The carboxylase total activity increased in minutes in the leaf during and following the CO 2-free treatments. The specific activities of the wheat carboxylase went from 0.16 to 1.06 micromoles CO 2 fixed per milligram protein per minute while the maize carboxylase varied from 0.05 to 0.36 micromole CO 2 fixed per millogram protein per minute. This suggests that in these seedlings considerable inactive carboxylase must be stored in a form not activatable in extracts by CO 2 and Mg 2+. Possible mechanisms of regulation of photosynthesis by the ribulose bisphosphate carboxylase must consider not only the amount of active enzyme, but the amount of enzyme which the plant can make activatable upon demand. 相似文献
2.
The course of respiration of attached maize ( Zea mays L.) leaves was measured by infrared gas analysis of CO 2 efflux in the dark following illumination in atmospheres of 300 microliters of CO 2 per liter of air, CO 2-free air, and CO 2-free N 2 containing 400 microliters of O 2 per liter. CO 2 efflux from control leaves started 3 to 4 minutes after darkening, increased to a maximum after about 20 minutes, and returned to a steady minimum after 2 to 3 hours. Respiration was quantitatively related to prior illumination, independent of net CO 2 fixation in the light, and depressed by N 2. Light, but not air, was required to produce a substrate for respiration in the subsequent dark period; air was required for oxidation of the substrate to CO 2. The stimulation of respiration by prior illumination in maize leaves differs in its slower onset and greater duration from the postillumination burst of photorespiration. 相似文献
3.
Summary The photosynthetic products of Portulaca oleracea differ greatly depending on leaf age and length of exposure to 14CO 2. Mature leaves of P. oleracea fix 14CO 2 primarily into organic and amino acids during a 10-s exposure period. Less than 2% of the 14CO 2 fixed appears in phosphorylated compounds. In contrast, incorporation into amino acids can account for over 60% of the total 14CO 2 fixed by young leaves in an equal time period, and incorporation into alanine alone can account for up to one half of this amount. Senescent leaves display a quantitative shift of primary products toward phosphorylated compounds with a concomitant reduction of the label residing in malate and asparate. About 8 times more phosphoglyceric acid is produced in senescent leaves than in mature leaves. The aspartate/ malate ratio is not constant and depends on the length of time the leaves are exposed to 14CO 2 and the age of the leaves under study. It appears as if the stage of leaf development is one of the most important factors determining the operation of a particular enzyme system in C 4 plants. 相似文献
4.
This study aims to elucidate the molecular mechanism for the transient increase in the O 2‐uptake rate in tobacco ( Nicotiana tabacum cv Xanthi) leaves after turning off actinic lights (ALs). The photosynthetic O 2 evolution rate reaches a maximum shortly after the onset of illumination with ALs and then decreases to zero in atmospheric CO 2/O 2 conditions. After turning off the ALs, tobacco leaves show a transient increase in the O 2‐uptake rate, the post‐illumination transient O 2‐uptake, and thereafter, the O 2‐uptake rate decreases to the level of the dark‐respiration rate. Photosynthetic linear electron flow, evaluated as the quantum yield of photosystem II [Y(II)], maintained a steady‐state value distinct from the photosynthetic O 2‐evolution rate. In high‐[CO 2] conditions, the photosynthetic O 2‐evolution rate and Y(II) showed a parallel behavior, and the post‐illumination transient O 2‐uptake was suppressed. On the other hand, in maize leaves (a C4 plant), even in atmospheric CO 2/O 2 conditions, Y(II) paralleled the photosynthetic O 2‐evolution rate and the post‐illumination transient O 2‐uptake was suppressed. Hypothesizing that the post‐illumination transient O 2‐uptake is driven by C3 plant photorespiration in tobacco leaves, we calculated both the ribulose 1,5‐bisphosphate carboxylase‐ and oxygenase‐rates (Vc and Vo) from photosynthetic O 2‐evolution and the post‐illumination transient O 2‐uptake rates. These values corresponded to those estimated from simultaneous chlorophyll fluorescence/O 2‐exchange analysis. Furthermore, the H +‐consumption rate for ATP synthesis in both photosynthesis and photorespiration, calculated from both Vc and Vo that were estimated from chlorophyll fluorescence/CO 2‐exchange analysis, showed a positive linear relationship with the dissipation rate of the electrochromic shift signal. Thus, these findings support our hypothesis. 相似文献
5.
The effect of leaf temperature on the post-illumination burst of CO 2 (PIB) in 15 day-old primary bean leaves ( Phaseolus vulgaris L.) was studied by means of infrared gas analysis in a closed gas exchange system. The amplitude and kinetic of PIB was different
with its own characteristic course for different temperature steps. The temperature optimum for the PIB at 21% O 2 near the carbon dioxide compensation concentration Λ (150 mg m -3) was 33 °C while that for net photosynthetic rate ( P
N) at 21% O 2 and 600 mg m -3 CO 2 was 24.5 °C. The PIB was observed to 12…33 s after the darkening of leaves. No PIB was observed at 2% O 2. The applicability of PIB as an estimate of photorespiration rate R
p has been proved by comparing it with extrapolation of the relationship between P
n and CO 2 concentration to zero. 相似文献
6.
To study the effect of O 2 on the photosynthetic and glycolate pathways, maize leaves were exposed to 14CO 2 during steady-state photosynthesis in 21 or 1% O 2. At the two O 2 concentrations after a 14CO 2 pulse (4 seconds) followed by a 12CO 2 chase, there was a slight difference in CO 2 uptake and in the total amount of 14C fixed, but there were marked changes in 14C distribution especially in phosphoglycerate, ribulose bisphosphate, glycine, and serine. The kinetics of 14C incorporation into glycine and serine indicated that the glycolate pathway is inhibited at low O 2 concentrations. In 1% O 2, labeling of glycine was reduced by 90% and that of serine was reduced by 70%, relative to the control in 21% O 2. A similar effect has been observed in C 3 plants, except that, in maize leaves, only 5 to 6% of the total 14C fixed under 21% O 2 was found in glycolate pathway intermediates after 60 seconds chase. This figure is 20% in C 3 plants. Isonicotinyl hydrazide did not completely block the conversion of glycine to serine in 21% O 2, and the first carbon atom of serine was preferentially labeled during the first seconds of the chase. These results supported the hypothesis that the labeled serine not only derives from glycine but also could be formed from phosphoglycerate, labeled in the first carbon atom during the first seconds of photosynthesis. 相似文献
7.
Prior illumination in CO 2-free air enhances a respiration from maize ( Zea mays L.) leaves different in onset and duration from the postillumination burst of photorespiration. The course of respiration after brief illumination of attached leaves was measured as CO 2 efflux in darkness into CO 2-free atmospheres with four O 2 concentrations. The peak of CO 2 efflux following illumination was suppressed by 2.23% O 2, was completely eliminated by 0.04% O 2, and was not stimulated by 40% O 2 compared with air. Compared with air, steady dark respiration was suppressed by 0.04% O 2 but was not affected by 2.23% nor 40% O 2. Excision and subsequent uptake of distilled water through the vascular system nearly eliminated the enhanced respiration. 相似文献
8.
Partitioning and transport of recently fixed photosynthate was examined following 14CO 2 pulse-labeling of intact, attached leaves of Salvia splendens L. maintained in an atmosphere of 300 microliters per liter CO 2 and 20, 210, or 500 milliliters per liter O 2. Under conditions of increasing O 2 (210, 500 milliliters per liter), a smaller percentage of the recently fixed 14C in the leaf was allocated to starch, whereas a greater percentage of the fixed 14C appeared in amino acids, particularly serine. The increase in 14C in amino acids was reflected in material exported from source leaves. A higher percentage of 14C in serine, glycine, and glutamate was recovered in petiole extracts when source leaves were maintained under elevated O 2 levels. Although pool sizes of these amino acids were increased in both the leaves and petioles with increasing photorespiratory activity, no significant changes in either 14C distribution or concentration of transport sugars ( i.e. stachyose, sucrose, verbascose) were observed. The data indicate that, in addition to being recycled intracellularly into Calvin cycle intermediates, amino acids produced during photorespiration may also serve as transport metabolites, allowing the mobilization of both carbon and nitrogen from the leaf under conditions of limited photosynthesis. 相似文献
9.
The aim of this work was to investigate the mechanism of formation of triose phosphates and 3-phosphoglycerate during photosynthetic induction in leaves of Zea mays. Simultaneous measurements of gas exchange, chlorophyll a fluorescence and metabolite contents of maize leaves were made. Leaves illuminated in the absence of CO 2 showed a build-up of triose phosphates during the first 2 min of illumination which was comparable to the build-up observed in the presence of CO 2. Isolated mesophyll protoplasts, which lack the Calvin cycle, also showed a build-up of triose phosphates upon illumination. Leaves contained amounts of phosphoglycerate mutase and enolase adequate to account for the formation of triose phosphates and 3-phosphoglycerate from intermediates of the C 4 cycle and their precursors. 相似文献
10.
Primary leaves of bean ( Phaseolus vulgaris L.) seedlings cultivated for 14 days in a growth chamber on complete (control) and phosphate deficient (−P) Knop liquid medium
were used for measurements. The −P leaves were smaller and showed an increased specific leaf area (SLA). Their inorganic phosphate
(P i) concentration was considerably lowered. They did not show any significant changes in chlorophyll (Chl) ( a + b) concentration and in their net CO 2 assimilation rate when it was estimated under the conditions close to those of the seedlings growth. Light response curves
of photosynthetic net O 2 evolution ( P
NO 2) of the leaves for the irradiation range up to 500 μmol(photon) m −2 s −1 were determined, using the leaf-disc Clark oxygen electrode. The measurements were taken under high CO 2 concentration of about 1 % and O 2 concentrations of 21 % or lowered to about 3 % at the beginning of measurement. The results obtained at 21 % O 2 and the irradiations close to or higher than those used during the seedlings growth revealed the phosphorus stress suppressive
effect on the leaf net O 2 evolution, however, no such effect was observed at lower irradiations. Other estimated parameters of P
NO 2 such as: apparent quantum requirement (QR A) and light compensation point (LCP) for the control and −P leaves were similar. However, with a high irradiation and lowered
O 2 concentration the rate of P
NO 2 for the −P leaves was markedly higher than that for the control, in relation to both the leaf area and leaf fresh mass. This
difference also disappeared at low irradiations, but the estimated reduced QR A values indicate, under those conditions, the increased yield of photosynthetic light reaction, especially in the −P leaves.
The presented results confirm the suggestion that during the initial phase of insufficient phosphate feeding the acclimations
in the light phase of photosynthesis, both structural and functional appear. They correspond, probably, to the increased energy
costs of carbon assimilation under phosphorus stress, e.g. connected with raised difficulties in phosphate uptake and turnover and enhanced photorespiration. Under the experimental
conditions especially advantageous for the dark phase of photosynthesis (saturating CO 2 and PAR, low O 2 concentration), those acclimations may be manifested as an enhancement of photosynthetic net O 2 evolution. 相似文献
11.
Abscisic acid inhibited the rate of 14CO 2 fixation in leaves of Pennisetum typhoides (Burm. f.) Stapf & Hubbard seedlings, but increased the activities of phosphoenol-pyruvate-carboxylase and malic enzyme. The leaves of the seedlings grown in the presence of abscisic acid incorporated, in comparison to the control, more radioactivity in the fraction of organic acids, but less radioactivity was recorded in the amino acid fraction. On the other hand, gibberellic acid which also inhibits photosynthetic 14CO 2 assimilation and decreases the activities of photosynthetic enzymes, favours greater incorporation in alanine, and reduces that in malate. It is deduced that bio-regulants can greatly influence the flow of 14C into individual photosynthetic products. As in growth, abscisic and gibberellic acids in combination tended to antagonize each other in their effects on enzyme activity as well as in incorporation of 14CO 2 into photosynthetic products. 相似文献
12.
Photosynthesis and light O 2-uptake of the aerial portion of the CAM plant Ananas comosus (L.) merr. were studied by CO 2 and O 2 gas exchange measurements. The amount of CO 2 which was fixed during a complete day-night cycle was equal to the amount of total net O 2 evolved. This finding justifies the assumption that in each time interval of the light period, the difference between the rates of net O 2-evolution and of net light atmospheric CO 2-uptake give the rates of malate-decarboxylation-dependent CO 2 assimilation. Based upon this hypothesis, the following photosynthetic characteristics were observed: (a) From the onset of the light to midphase IV of CAM, the photosynthetic quotient (net O 2 evolved/net CO 2 fixed) was higher than 1. This indicates that malate-decarboxylation supplied CO 2 for the photosynthetic carbon reduction cycle during this period. (b) In phase III and early phase IV, the rate of CO 2 assimilation deduced from net O 2-evolution was 3 times higher than the maximum rate of atmospheric CO 2-fixation during phase IV. A conceivable explanation for this stimulation of photosynthesis is that the intracellular CO 2-concentration was high because of malate decarboxylation. (c) During the final hours of the light period, the photosynthetic quotient decreased below 1. This may be the result of CO 2-fixation by phosphoenolpyruvate-carboxylase activity and malate accumulation. Based upon this hypothesis, the gas exchange data indicates that at least 50% of the CO 2 fixed during the last hour of the light period was stored as malate. Light O 2-uptake determined with 18O 2 showed two remarkable characteristics: from the onset of the light until midphase IV the rate of O 2-uptake increased progressively; during the following part of the light period, the rate of O 2-uptake was 3.5 times higher than the maximum rate of CO 2-uptake. When malate decarboxylation was reduced or suppressed after a night in a CO 2-free atmosphere or in continuous illumination, the rate of O 2-uptake was higher than in the control. This supports the hypothesis that the low rate of O 2-uptake in the first part of the light period is due to the inhibition of photorespiration by increased intracellular CO 2 concentration because of malate decarboxylation. In view of the law of gas diffusion and the kinetic properties of the ribulose-1,5-bisphosphate carboxylase/oxygenase, O 2 and CO 2 gas exchange suggest that at the end of the light period the intracellular CO 2 concentration was very low. We propose that the high ratio of O 2-uptake/CO 2-fixation is principally caused by the stimulation of photorespiration during this period. 相似文献
13.
To assess photosynthesis and yield components’ response of field-grown wheat to increasing ozone (O 3) concentration (based on diurnal pattern of ambient O 3) in China, winter wheat ( Triticum aestivum L.) cv. Jia 403 was planted in open top chambers and exposed to three different O 3 concentrations: O 3-free air (CF), ambient air (NF), and O 3-free air with additional O 3 (CF+O 3). Diurnal changes of gas exchange and net photosynthetic rate ( P
N) in response to photosynthetic photon flux density (PPFD) of flag leaves were measured at the filling grain stage, and yield
components were investigated at harvest. High O 3 concentration altered diurnal course of gas exchange [ P
N, stomatal conductance ( g
s), and intercellular CO 2 concentration ( C
i)] and decreased significantly their values except for C
i. Apparent quantum yield (AQY), compensation irradiance (CI), and saturation irradiance (SI) were significantly decreased,
suggesting photosynthetic capacity was also altered, characterized as reduced photon-saturated photosynthetic rate ( P
Nmax). The limit of photosynthetic activity was probably dominated by non-stomatal factors in combination with stomatal closure.
The significant reduction in yield was observed in CF+O 3 treatment as a result of a marked decrease in the ear length and the number of grains per ear, and a significant increase
in the number of infertile florets per ear. Even though similar responses were also observed in plants exposed to ambient
O 3 concentration, no statistical difference was observed at current ambient O 3 concentration in China. 相似文献
14.
Onion ( Allium cepa L.) plants were examined to determine the photosynthetic role of CO 2 that accumulates within their leaf cavities. Leaf cavity CO 2 concentrations ranged from 2250 L L –1 near the leaf base to below atmospheric (<350 L L –1) near the leaf tip at midday. There was a daily fluctuation in the leaf cavity CO 2 concentrations with minimum values near midday and maximum values at night. Conductance to CO 2 from the leaf cavity ranged from 24 to 202 mol m –2 s –1 and was even lower for membranes of bulb scales. The capacity for onion leaves to recycle leaf cavity CO 2 was poor, only 0.2 to 2.2% of leaf photosynthesis based either on measured CO 2 concentrations and conductance values or as measured directly by 14CO 2 labeling experiments. The photosynthetic responses to CO 2 and O 2 were measured to determine whether onion leaves exhibited a typical C 3-type response. A linear increase in CO 2 uptake was observed in intact leaves up to 315 L L –1 of external CO 2 and, at this external CO 2 concentration, uptake was inhibited 35.4±0.9% by 210 mL L –1 O 2 compared to 20 mL L –1 O 2. Scanning electron micrographs of the leaf cavity wall revealed degenerated tissue covered by a membrane. Onion leaf cavity membranes apparently are highly impermeable to CO 2 and greatly restrict the refixation of leaf cavity CO 2 by photosynthetic tissue.Abbreviations C a
external CO 2 concentration
- C i
intercellular CO 2 concentration
-
CO 2 compensation concentration
- PPFR
photosynthetic photon fluence rate 相似文献
15.
A leaf disk assay for photorespiration has been developed based on the rate of release of recently fixed 14CO 2 in light in a rapid stream of CO 2-free air at 30° to 35°. In tobacco leaves (Havana Seed) photorespiration with this assay is 3 to 5 times greater than the 14CO 2 output in the dark. In maize, photorespiration is only 2% of that in tobacco. The importance of open leaf stomata, rapid flow rates of CO2-free air, elevated temperatures, and oxygen in the atmosphere in order to obtain release into the air of a larger portion of the 14CO2 evolved within the tissue in the light was established in tobacco. Photorespiration, but not dark respiration, was inhibited by α-hydroxy-2-pyridinemethanesulfonic acid, an inhibitor of glycolate oxidase, and by 3-(4-chlorophenyl)-1,1-dimethylurea (CMU), an inhibitor of photosynthetic electron transport, under conditions which did not affect the stomata. These experiments show that the substrates of photorespiration and dark respiration differ and also provide additional support for the role of glycolate as a major substrate of photorespiration. It was also shown that at 35° the quantity of 14CO2 released in the assay may represent only 33% of the gross 14CO2 evolved in the light, the remainder being recycled within the tissue. It was concluded that maize does not evolve appreciable quantities of CO2 in the light and that this largely accounts for the greater efficiency of net photosynthesis exhibited by maize. Hence low rates of photorespiration may be expected to be correlated with a high rate of CO2 uptake at the normal concentrations of CO2 found in air and at higher light intensities. 相似文献
16.
The effect of leaf temperature on stomatal conductance and net CO 2 uptake was studied on French bean ( Phaseolus vulgaris L.) using either dehydrated attached leaves (25–40% water deficit) or cut leaves supplied with 10 –4 M abscisic acid (ABA) solution to the transpiration stream. Decreasing leaf temperature caused stomatal opening and increased net CO 2 uptake (which was close to zero at around 25° C) to a level identical to that of control leaves (without water deficit) at around 15° C. (i) The ABA effect on stomatal closure was modulated by temperature and, presumably, ABA is at least partly responsible for stomatal closure of french bean submitted to a drought stress. (ii) For leaf temperatures lower than 15° C, net CO 2 uptake was no longer limited by water deficit even on very dehydrated leaves. This shows that dehydrated leaves retain a substantial part of their photosynthetic capacity which can be revealed at normal CO 2 concentrations when stomata open at low temperature. In contrast to leaves fed with ABA, decreasing the O 2 concentration from 21% to 1% O 2 did not increase either the rate of net CO 2 uptake or the thermal optimum for photosynthesis of dehydrated leaves. The quantum yield of PSII electron flow (measured by F/F m) was lower in 1% O 2 than in 21% O 2 for each leaf pretreatment given (non-dehydrated leaves, dehydrated leaves, and leaves fed with ABA) even within a temperature range in which leaf photosynthesis at normal CO 2 concentration was the same in these two O 2 concentrations. It is concluded that this probably indicates an heterogeneity of photosynthesis, since this difference in quantum yield disappears when using high CO 2 concentrations during measurements.Abbreviations and Symbols ABA
abscisic acid
- F m
maximum chlorophyll fluorescence
- F
difference between steady-state chlorophyll fluorescence and F m
- PPFD
photosynthetic photon flux density
We would like to thank Dr. J.-M. Briantais (Laboratoire d'écologie végétale, Orsay, France) for help during fluorescence measurements and Ms. J. Liebert for technical assistance. 相似文献
17.
Transfer of N 2 and CO 2 fixation products from the bloom forming blue-green alga, Anabaena oscillarioides Bory, to attached and free swimming bacteria is common during active growth of the former. Incubation with 15N 2 and 14CO 2 followed by size fractionation filtration reveals that: i) magnitudes of fixed N and C excretion, relative to N 2 and CO 2 fixation, are dictated by dissolved inorganic carbon (DIC) availability for A. oscillarioides photosynthetic production, ii) associated bacteria exhibit preferences for recently fixed excreted N compounds, iii) bacterial utilization of excreted N is independent of ambient light conditions, and iv) lag times between N 2 fixation and detectable bacterial assimilation of excreted fixed N compounds are ca. 1–2 h. Both 14NH 4Cl dilution and Hg(NH 3) 2 Cl 2 precipitation techniques indicate that NH 3 is a major excretion product from A. oscillarioides, particularly during DIC limited growth. Active N and C excretion and transfer to associated bacteria are features of viable A. oscillarioides filaments. Hence, transfer of these metabolites reflects complex mutualistic, and possibly symbiotic associations rather than solely signaling senescence. 相似文献
18.
Changes in leaf growth, net photosynthetic rate ( P
N), incorporation pattern of photosynthetically fixed 14CO 2 in leaves 1–4 from top, roots, and rhizome, and in essential oil and curcumin contents were studied in turmeric plants grown in nutrient solution at boron (B) concentrations of 0 and 0.5 g m -3. B deficiency resulted in decrease in leaf area, fresh and dry mass, chlorophyll (Chl) content, and P
N and total 14CO 2 incorporated at all leaf positions, the maximum effect being in young growing leaves. The incorporation of 14CO 2 declined with leaf position being maximal in the youngest leaf. B deficiency resulted in reduced accumulation of sugars, amino acids, and organic acids at all leaf positions. Translocation of the metabolites towards rhizome and roots decreased. In rhizome, the amount of amino acids increased but content of organic acids did not show any change, whereas in roots there was decrease in contents of these metabolites as a result of B deficiency. Photoassimilate partitioning to essential oil in leaf and to curcumin in rhizome decreased. Although the curcumin content of rhizome increased due to B deficiency, the overall rhizome yield and curcumin yield decreased. The influence of B deficiency on leaf area, fresh and dry masses, CO 2 exchange rate, oil content, and rhizome and curcumin yields can be ascribed to reduced photosynthate formation and translocation. 相似文献
19.
为了进一步了解光照下植物呼吸作用的内在机理以及呼吸作用和光合作用的关系,该文研究了在光照下菜豆(Phaseolus vulgaris)叶片抗氰呼吸与光合作用的关系。研究发现,将黑暗下生长的菜豆幼苗叶片转到光照下10 h,总呼吸、抗氰呼吸以及抗氰呼吸在总呼吸中的比例均逐步上升;光照也导致了叶片叶绿体光合放氧和CO2固定的出现及其速率的增加,但光合放氧和CO2固定速率的增加均滞后于抗氰呼吸的增加。将黑暗下生长的叶片转到光照下之前用抗氰呼吸的抑制剂水杨基氧肟酸(SHAM)处理叶片,发现用SHAM处理并没有导致叶片在光照下光合放氧和CO2固定速率的明显变化,这也提示了黑暗下生长的叶片转至光照的过程中,抗氰呼吸和光合作用没有产生偶联。进一步研究发现,在黑暗中对叶片施加短时间的光照能够增加抗氰呼吸在总呼吸中的比例,但短时间的光照对叶片光合CO2固定速率没有影响。这些结果表明了光照对抗氰呼吸的诱导可以不依赖于光合作用,光照可能是作为一种直接的信号去诱导抗氰呼吸。 相似文献
20.
Photosystem II chlorophyll fluorescence and leaf net gas exchanges (CO 2 and H 2O) were measured simultaneously on bean leaves ( Phaseolus vulgaris L.) submitted either to different ambient CO 2 concentrations or to a drought stress. When leaves are under photorespiratory conditions, a simple fluorescence parameter F/ F m (B. Genty et al. 1989, Biochem. Biophys. Acta 990, 87–92; F = difference between maximum, F m, and steady-state fluorescence emissions) allows the calculation of the total rate of photosynthetic electron-transport and the rate of electron transport to O 2. These rates are in agreement with the measurements of leaf O 2 absorption using 18O 2 and the kinetic properties of ribulose-1,5bisphosphate carboxylase/oxygenase. The fluorescence parameter, F/F m, showed that the allocation of photosynthetic electrons to O 2 was increased during the desiccation of a leaf. Decreasing leaf net CO 2 uptake, either by decreasing the ambient CO 2 concentration or by dehydrating a leaf, had the same effect on the partitioning of photosynthetic electrons between CO 2 and O 2 reduction. It is concluded that the decline of net CO 2 uptake of a leaf under drought stress is only due, at least for a mild reversible stress (causing at most a leaf water deficit of 35%), to stomatal closure which leads to a decrease in leaf internal CO 2 concentration. Since, during the dehydration of a leaf, the calculated internal CO 2 concentration remained constant or even increased we conclude that this calculation is misleading under such conditions.Abbreviations Ca, Ci
ambient, leaf internal CO 2 concentrations
- F m, F o, F s
maximum, minimal, steady-state fluorescence emission
- F v
variable fluorescence emission
- PPFD
photosynthetic photon flux density
- q p, q N
photochemical, non-photochemical fluorescence quenching
- Rubisco
ribulose-1,5-bisphosphate carboxylase/oxygenase 相似文献
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