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1.
Effects of growth temperature on the photosynthetic gas-exchange rates and their underlying biochemical properties were examined in young, fully expanded leaves of rice (Oryza sativa L.). The plants were grown hydroponically under day/night temperature regimes of 18/15[deg]C, 23/18[deg]C, and 30/23[deg]C and all photosynthetic measurements were made at a leaf temperature of 25[deg]C and an irradiance of 1800 [mu]mol quanta m-2 s-1. Growth temperature affected the photosynthetic CO2 response curve. The relative ratio of the initial slope to the CO2-saturated photosynthesis increased with rising growth temperature. This was caused mainly by an increase in CO2-limited photosynthesis for a given leaf nitrogen content with rising growth temperature. However, there was no difference in ribulose-1,5-bisphosphate carboxylase (Rubisco) content at any given leaf nitrogen content among temperature treatments. In addition, the activation state and catalytic turnover rate of Rubisco were not affected by growth temperature. The increase in CO2-limited photosynthesis with rising growth temperature was the result of an increase in the CO2 transfer conductance between the intercellular airspaces and the carboxylation sites. The amounts of total chlorophyll and light-harvesting chlorophyll a/b protein II increased for the same leaf nitrogen content with rising growth temperature, but the amounts of cytochrome f and coupling factor 1 and the activities of cytosolic fructose-1,6-bisphosphatase and sucrose-phosphate synthase were the same between plants grown at 23/18[deg]C and those grown at 30/23[deg]C. Similarly, CO2-saturated photosynthesis was not different for the same leaf nitrogen content between these treatments. For the 18/15[deg]C-grown plants, a slight decrease in the amounts of cytochrome f and coupling factor 1 and an increase in the activities of cytosolic fructose-1,6-bisphosphatase and sucrose-phosphate synthase were found, but these were not reflected in CO2-saturated photosynthesis. 相似文献
2.
Changes in photosynthesis and the ribulose 1,5-bisphosphate (RuBP) carboxylase level were examined in the 12th leaf blades of rice ( Oryza sativa L.) grown under different N levels. Photosynthesis was determined using an open infrared gas analysis system. The level of RuBP carboxylase was measured by rocket immunoelectrophoresis. These changes were followed with respect to changes in the activities of RuBP carboxylase, ribulose 5-phosphate kinase, NADP-glyceraldehyde 3-phosphate dehydrogenase, and 3-phosphoglyceric acid kinase. RuBP carboxylase activity was highly correlated with the net rate of photosynthesis (r = 0.968). Although high correlations between the activities of other enzymes and photosynthesis were also found, the activity per leaf of RuBP carboxylase was much lower than those of other enzymes throughout the leaf life. The specific activity of RuBP carboxylase on a milligram of the enzyme protein basis remained fairly constant (1.16 ± 0.07 micromoles of CO2 per minute per milligram at 25°C) throughout the experimental period. Kinetic parameters related to CO2 fixation were examined using the purified carboxylase. The Km(CO2) and Vmax values were 12 micromolar and 1.45 micromoles of CO2 per minute per milligram, respectively (pH 8.2 and 25°C). The in vitro specific activity calculated at the atomospheric CO2 level from the parameters was comparable to the in situ true photosynthetic rate per milligram of the carboxylase throughout the leaf life. The results indicated that the level of RuBP carboxylase protein can be a limiting factor in photosynthesis throughout the life span of the leaf. 相似文献
3.
CO 2 gas exchange, ribulose-1,5-bisphosphate, and electron transport have been measured in leaves of a yellow-green mutant of wheat ( Triticum durum var Cappelli) and its wild type strain grown in the field. All these parameters, expressed on leaf area basis, were similar in both genotypes except electron transport which was more than double in the wild type. These results, treated according to a recent photosynthesis model for C 3 plants, seem to indicate that the electron transport rate of mutant leaves is not sufficient to support the carboxylation derived through both the assimilation rate and the in vitro ribulose-1,5-bisphosphate carboxylase activity. It is suggested that under our experimental conditions photosynthetic electron transport is not the sole energy-dependent determinant of ribulose-1,5-bisphosphate regeneration in the mutant. 相似文献
4.
The amounts of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), total chlorophyll (Chl), and total leaf nitrogen were measured in fully expanded, young leaves of wheat ( Triticum aestivum L.), rice ( Oryza sativa L.), spinach ( Spinacia oleracea L.), bean ( Phaseolus vulgaris L.), and pea ( Pisum sativum L.). In addition, the activities of whole-chain electron transport and carbonic anhydrase were measured. All plants were grown hydroponically at different nitrogen concentrations. Although a greater than proportional increase in Rubisco content relative to leaf nitrogen content and Chl was found with increasing nitrogen supply for rice, spinach, bean, and pea, the ratio of Rubisco to total leaf nitrogen or Chl in wheat was essentially independent of nitrogen treatment. In addition, the ratio of Rubisco to electron transport activities remained constant only in wheat. Nevertheless, gas-exchange analysis showed that the in vivo balance between the capacities of Rubisco and electron transport in wheat, rice, and spinach remained almost constant, irrespective of nitrogen treatment. The in vitro carbonic anhydrase activity in wheat was very low and strongly responsive to increasing nitrogen content. Such a response was not found for the other C 3 plants examined, which had 10- to 30-fold higher carbonic anhydrase activity than wheat at any leaf-nitrogen content. These distinctive responses of carbonic anhydrase activity in wheat were discussed in relation to CO 2-transfer resistance and the in vivo balance between the capacities of Rubisco and electron transport. 相似文献
5.
水稻生育过程中,RuBP羧化酶活性与光合速率、RuBP加氧酶活性与光呼吸速率、RuBP羧化酶活性与加氢酶活性以及光合速率与光呼吸速率之间是相关的。籼型品种与粳型品种间酶活性的高低及光合、光呼吸速率的高低基本一致,籼型三系杂交稻(F1)无明显的光合优势。酶的羧化活性的高低只在一定范围内与光合速率的高低平行。在正常生育条件下,酶蛋白的数量不是水稻光合速率的限制因子。 相似文献
6.
Salinity (100 millimolar NaCl) was found to reduce photosynthetic capacity independent of stomatal closure in Phaseolus vulgaris. This reduction was shown to be a consequence of a reduction in the efficiency of ribulose-1,5-bisphosphate (RuBP) carboxylase (RuBPCase) rather than a reduction in the leaf content of photosynthetic machinery. In control plants, photosynthesis became RuBP-limited at approximately 1.75 moles RuBP per mole 2-carboxyarabinitol bisphosphate binding sites. Salinization caused the RuBP pool size to reach this limiting value for CO 2 fixation at much lower values of intercellular CO 2. Plants grown at low nitrogen and ± NaCl became RuBP limited at similar RuBP pool sizes as the high nitrogen-grown plants. At limiting RuBP pool sizes and equal values of intercellular CO 2 photosynthetic capacity of salt-stressed plants was less than control plants. This effect of salinity on RuBPCase activity could not be explained by deactivation of the enzyme or inhibitor synthesis. Thus, salinity reduced photosynthetic capacity by reducing both the RuBP pool size by an effect on RuBP regeneration capacity and RuBPCase activity by an unknown mechanism when RuBP was limiting. 相似文献
7.
The relation between N content and ribulose-l,5-bisphosphate(RuBP) carboxylase protein was examined in the 12th leaf bladeof rice. Plants were grown under different amounts of N afterthe emergence of the 12th leaf blade. RuBP carboxylase proteinincreased with leaf N during leaf expansion. The synthesis ofRuBP carboxylase predominated during this period, and changesin the amounts of carboxylase synthesized until leaf death paralleledchanges in the N influx to the leaves. When the carboxylasereached its maximum content, the proportion of RuBP carboxylaseto leaf N was 27 to 28% irrespective of N treatment. As theleaf senesced, however, this proportion differed significantlywith the treatment. It was higher in the N-deficient leaf thanin the N-sufficient leaf. This was due to different patternsof RuBP carboxylase degradation for the treatments during senescence.RuBP carboxylase was degraded actively during the early stageof senescence in the N-sufficient leaf, whereas its degradationproceeded almost constantly in the N-deficient leaf during senescence. (Received October 17, 1983; Accepted January 27, 1984) 相似文献
8.
Soluble auxin-binding proteins (ABPs) were purified to constant specific activity from bean and pea leaves by a procedure involving (NH 4) 2SO 4 fractionation, anion exchange chromatography and gel filtration. Pea and bean ABPs exactly co-purify with ribulose-1,5-bisphosphate carboxylase (RuBPCase) in a variety of chromatographic separation procedures. The subunit compositions, electrophoretic purities and indole-3-acetic acid (IAA)-binding stoichiometries of the purified ABPs provide further evidence for the identity of RuBPCase and ABP. Pea ABP and bean ABP have dissociation constants for IAA of 0.8 and 1.3 micromolar, respectively, as determined by an (NH 4) 2SO 4 precipitation assay for IAA-binding to insolubilized ABP. IAA can bind to soluble bean and pea ABP (RuBPCase) as determined by equilibrium dialysis with affinities and stoichiometries similar to those determined for insolubilized ABP. 相似文献
9.
报道了在光照和暗处培养下,不同的浓度的蔗水稻幼苗叶片GS及其同工酶、1,5-二磷酸核酮糖羧化酶/加氧酶(Rubisco)的影响。无论是在光照或在暗处,蔗糖对GS活性均有抑制作用,尤其是在较高蔗糖下作用更为明显;虽然Rubisco及可溶性蛋白的水平在光照和暗处有显著的差别,但蔗糖对其未见明显影响。NativePAGE与活性染色表明,在光照下或在暗处,蔗糖对GS2的抑制蔗糖浓度升同而加强,但对GS1未有明显影响。这些结果提示,在水稻幼苗生长中,蔗糖不能象不光一样诱导叶水GS活性及其同工酶表达。 相似文献
10.
The content of
ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco)
( Et; EC 4.1.1.39) measured in different-aged
leaves of sunflower ( Helianthus annuus) and other plants
grown under different light intensities, varied from 2 to 75 μmol
active sites m −2. Mesophyll conductance (μ) was measured
under 1.5% O 2, as well as postillumination CO 2
uptake (assimilatory charge, a gas-exchange measure of the
ribulose-1,5-bisphosphate pool). The dependence of μ on
Et saturated at
Et = 30 μmol active sites m −2
and μ = 11 mm s −1 in high-light-grown leaves. In
low-light-grown leaves the dependence tended toward saturation at
similar Et but reached a μ of only 6 to 8
mm s −1. μ was proportional to the assimilatory charge,
with the proportionality constant (specific carboxylation efficiency)
between 0.04 and 0.075 μ m−1
s −1. Our data show that the saturation of the relationship
between Et and μ is caused by three
limiting components: (a) the physical diffusion resistance (a minor
limitation), (b) less than full activation of Rubisco (related to
Rubisco activase and the slower diffusibility of Rubisco at high
protein concentrations in the stroma), and (c) chloroplast metabolites,
especially 3-phosphoglyceric acid and free inorganic phosphate, which
control the reaction kinetics of ribulose-1,5-bisphosphate
carboxylation by competitive binding to active sites.Rubisco (EC 4.1.1.39) catalyzes the irreversible carboxylation of
RuBP to form two PGA molecules (in this work the oxygenase reaction was
not active since a low O 2 concentration was
used). RuBP carboxylation is the major rate-determining reaction in
photosynthetic CO 2 assimilation. All factors that
influence the photosynthetic rate do so by influencing the activity of
Rubisco and the concentration of its substrates,
CO 2 and RuBP. Et in
leaves may be as high as 75 μmol m −2, and for
the extracted enzyme
Km(CO 2) = 9.4
μ m ( Makino et al., 1985a) and
Km(RuBP) = 30 to 40 μ m ( Yeoh
et al., 1981). In leaves photosynthesizing under atmospheric
conditions, the concentration of RuBP may increase to 10 to 15
m m ( Badger et al., 1984; Sharkey et al., 1986), but the
concentration of CO 2 is usually about 4 to 8
μ m in leaf intercellular spaces, depending on stomatal
conductance. This CO 2 concentration is well below
the Km(CO 2) of the
enzyme, and it is the initial slope of the kinetic curve
VM/ Km(CO 2),
termed carboxylation conductance, that becomes important. rc limits the
CO 2-fixation rate in series with the other
resistances, rg and
rmd. The carboxylation rates are usually
expressed in relation to Ci or
Cw. Cc is
usually about 20% to 30% lower than Cw
because of concentration decrease generated by the carboxylation flux
on rmd. Considering the above, the
carboxylation conductance in intact leaves in vivo may be found as the
initial slope of the A versus Cc
graph at low Cc values. If
Cc cannot be calculated because
rmd is unknown, the closest approximation
is a plot of A versus Cw or
A versus Ci. The true parameters
of the carboxylase can be found only from experiments carried out in
nonphotorespiratory conditions (1%–2% O 2);
otherwise the competing oxygenase reaction consumes a part of RuBP and
partially inhibits carboxylase activity.Because of technical problems with the measurement of A
versus Cw relationships, in many studies
only the net photosynthetic rate under atmospheric conditions (21%
O 2) was related to Rubisco activity or content.
Nevertheless, good correlation has been found ( Makino et al., 1983;
Hudson et al., 1992; Jacob and Lawlor, 1992; Jiang and Rodermel, 1995;
Nakano et al., 1997). These results indicated that the level of Rubisco
protein could be a limiting factor in photosynthesis throughout the
life span of the leaf under natural environmental conditions. On the
other hand, when Rubisco levels in leaves exceeded 4 g
m −2 (60 μmol m −2), the
in vivo Rubisco activity (measured as photosynthesis under
pC i = 20 to 30 Pa and 21%
O 2) became curvilinearly correlated with
Et ( Makino et al., 1994, 1997). When
measurements were made over the whole life span of wheat leaves, the
measured rates of photosynthesis were lower in young leaves, which had
high protein content, than would have been expected from the amount and
activity of Rubisco ( Lawlor et al., 1989).During senescence the decrease in Rubisco activity was initially
greater than the decrease in net photosynthesis ( Hall et al., 1978). In
a willow canopy, Rubisco-specific activity was higher when the apparent
Et (N content in leaves) was smaller
( Vapaavuori and Vuorinen, 1989). A similar nonlinearity was found in
our previous experiments ( Eichelmann and Laisk, 1990), in which we
obtained a saturating relationship when Et
exceeded 30 μmol m −2. In the latter work the
initial slope of the A versus Cw
curves under nonphotorespiratory conditions (1.5% O 2)
was assumed to represent the Rubisco activity in vivo and was compared
with the Et. We discovered that growth
light had the strongest influence on the saturation of the relationship
between μ and Et. In the present work we
present insight into this relationship, using not only plants grown
under different light intensities but also leaves adapted to different
light intensities. 相似文献
11.
Characterisation of proteases degrading ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO, EC: 4.1.1.39) was studied in the cowpea leaf during monocarpic senescence 3 and 9 d after flowering (DAF), representing early and mid pod fill. The stage at 3 DAF coincided with decrease in the metabolic parameters characterising senescence, i.e., contents of total soluble proteins, RuBPCO, and leaf nitrogen. At 9 DAF, there was a decline in total soluble proteins and an appearance of a 48 kDa cysteine protease. Characterisation of the proteases was done using specific inhibitors. Subcellular localisation at 3 DAF was studied by following the degradation of RuBPCO large subunit (LSU) in the vacuole lysates using immunoblot analyses. Cysteine proteases played a predominant role in the degradation of RuBPCO LSU at the crude extract level. At 9 DAF, expression of cysteine protease isoforms was monitored using polyclonal antibodies against papain and two polypeptides of molecular masses 48 and 35 kDa were observed in the vacuole lysates. We confirmed thus the predominance of cysteine proteases in the vacuoles during different stages of pod development in cowpea leaf. 相似文献
12.
We compared responses of maize, tomato, and bean plants to water stress. Maize reached a severe water deficit (leaf water potential –1.90 MPa) in a longer period of time as compared with tomato and bean plants. Maize stomatal conductance ( g
s) decreased at mild water deficit. g
s of tomato and bean decreased gradually and did not reach values as low as in maize. The protein content was maintained in maize and decreased at low water potential ( w); in tomato it fluctuated and also decreased at low w; in bean it gradually decreased. Ribulose-1,5-bisphosphate carboxylase/oxygenase activity remained high at mild and moderate stress in maize and tomato plants; in bean it remained high only at mild stress. 相似文献
13.
Increasing the leaf temperature of intact cotton ( Gossypium hirsutum L.) and wheat ( Triticum aestivum L.) plants caused a progressive decline in the light-saturated CO 2-exchange rate (CER). CER was more sensitive to increased leaf temperature in wheat than in cotton, and both species demonstrated photosynthetic acclimation when leaf temperature was increased gradually. Inhibition of CER was not a consequence of stomatal closure, as indicated by a positive relationship between leaf temperature and transpiration. The activation state of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), which is regulated by Rubisco activase, was closely correlated with temperature-induced changes in CER. Nonphotochemical chlorophyll fluorescence quenching increased with leaf temperature in a manner consistent with inhibited CER and Rubisco activation. Both nonphotochemical fluorescence quenching and Rubisco activation were more sensitive to heat stress than the maximum quantum yield of photochemistry of photosystem II. Heat stress led to decreased 3-phosphoglyceric acid content and increased ribulose-1,5-bisphosphate content, which is indicative of inhibited metabolite flow through Rubisco. We conclude that heat stress inhibited CER primarily by decreasing the activation state of Rubisco via inhibition of Rubisco activase. Although Rubisco activation was more closely correlated with CER than the maximum quantum yield of photochemistry of photosystem II, both processes could be acclimated to heat stress by gradually increasing the leaf temperature. 相似文献
14.
The requirements for activation of ribulose 1,5-bisphosphate carboxylase/oxygenase (rubisco) were investigated in leaves of Arabidopsis wild-type and a mutant incapable of light activating rubisco in vivo. Upon illumination with saturating light intensities, the activation state of rubisco increased 2-fold in the wild-type and decreased in the mutant. Activation of fructose 1,6-bisphosphate phosphatase was unaffected by the mutation. Under low light, rubisco deactivated in both the wild-type and the mutant. Deactivation of rubisco in the mutant under high and low light led to the accumulation of high concentrations of ribulose 1,5-bisphosphate. Inhibiting photosynthesis with methyl viologen prevented ribulose 1,5-bisphosphate accumulation but was ineffective in restoring rubisco activation to the mutant. Net photosynthesis and the rubisco activation level were closely correlated and saturated at a lower light intensity in the mutant than in wild-type. At CO 2 concentrations between 100 and 2000 microliters per liter, the activation state was a function of the CO 2 concentration in the dark but was independent of CO 2 concentration in the light. High CO 2 concentration (1%) suppressed activation in the wild-type and deactivation in the mutant. These results support the concept that rubisco activation in vivo is not a spontaneous process but is catalyzed by a specific protein. The absence of this protein, rubisco activase, is responsible for the altered characteristics of rubisco activation in the mutant. 相似文献
15.
The enzymic properties of ribulose 1,5-bisphosphate (RuBP) carboxylase/oxygenase purified from rice ( Oryza sativa L.) leaves were studied. Rice RuBPcarboxylase, activated by preincubation with CO 2 and Mg 2+ like other higher plant carboxylases, had an activation equilibrium constant ( KcKMg) of 1.90 × 10 5 to 2.41 × 10 5 micromolar 2 (pH 8.2 and 25°C). Kinetic parameters of carboxylation and oxygenation catalyzed by the completely activated enzyme were examined at 25°C and the respective optimal pHs. The Km(CO 2), Km(RuBP), and Vmax values for carboxylation were 8 micromolar, 31 micromolar, and 1.79 units milligram −1, respectively. The Km(O 2), Km(RuBP), and Vmax values for oxygenation were 370 micromolar, 29 micromolar, and 0.60 units milligram −1, respectively. Comparison of rice leaf RuBP carboxylase with other C3 plant carboxylases showed that it had a relatively high affinity for CO2 but the lowest catalytic turnover number (Vmax) among the species examined. 相似文献
16.
Photosynthetic parameters were measured in triticale and its parents wheat and rye. Soluble protein content in leaves, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) content per fresh mass, total chlorophyll content, biomass yield, leaf area, leaf mass and specific leaf mass were higher but Rubisco content expressed as percentage of soluble protein, carboxylase activity, photosynthetic rate and stomatal conductance were significantly lower in rye than in wheat. Native-PAGE of Rubisco revealed that rye carboxylase was different from that of wheat. The difference was not related to either the small or large subunit of Rubisco but, may be, to the ionic and/or other properties of the Rubisco protein moiety. Triticale Rubisco was similar to wheat. For most of the studied physiological parameters, triticale showed much more similarity with wheat than with rye. 相似文献
17.
Three clones of tobacco transformed with the T-DNA of Agrobacterium rhizogenes Ri plasmid A4b cultivated in vitro on a solid agar medium neither showed pronounced morphological diversity nor significantly differed in chlorophyll (Chl) contents from control plants. However, the transformation caused a 27 to 83 % decay in leaf oxygen evolution and in both ribulose-1,5-bisphosphate carboxylase (RuBPC) and phospho enolpyruvate carboxylase (PEPC) activities. Therefore, the transformation brought about a reduction of active PEPC as well as activable RuBPC amounts in plant tissues. Individual clones did not mutually differ. In tobacco transformed with A. rhizogenes strain TR101 and grown in soil only the mean leaf area tended to reduce. Chl contents, Chl a/b ratio, oxygen evolution, and activities of both RuBPC and PEPC were insignificantly affected by the transformation. 相似文献
18.
Wheat (Triticum aestivum cv Chinese Spring) supplied with 0.45 mM SO42- for 14 d with relative growth rates (RGR) of 0.22 to 0.24 d-1 was deprived of S for 7 to 8 d. There was no significant effect on RGR or leaf development (leaf 2 length was constant; leaf 3 expanded for 2-4 d; leaf 4 emerged and elongated throughout the experiment) during the S deprivation. In controls the net assimilation rate (A) closely reflected leaf ontogeny. S deprivation affected A in all leaves, particularly leaf 4, in which A remained at 8 to 10 [mu]mol CO2 m-2 s-1, whereas in controls A rose steadily to >20 [mu]mol CO2 m-2 s-1. In leaf 2, with a fully assembled photosynthetic system, A decreased in S-deprived plants relative to controls only at the end of the experiment. Effects on A were not due to altered stomatal conductance or leaf internal [CO2] ([C]i); decreases in the initial slope of A/[C]i curves indicated an effect of S deprivation on the carboxylase efficiency. Measurement of Rubisco activity and large subunit protein abundance paralleled effects on A and A/[C]i in S-deprived leaves. Negative effects on photosynthesis in S-deprived plants are discussed in relation to mobilization of S reserves, including Rubisco, emphasizing the need for continuous S supply during vegetative growth. 相似文献
20.
Ribulose-1,5-bisphosphate carboxylase/oxygenase, catalase, glycolate oxidase, and hydroxypyruvate reductase activities on a protein and fresh weight basis were measured over seven stages of tomato fruit development and ripening. Ribulose-1,5-bisphosphate carboxylase decreased steadily during fruit development from 23 ± 8 nmoles per minute per milligram protein at the mature green stage to 13.4 ± 2 at the table ripe stage. There was no change in partially purified preparations of the enzyme in the ratio of carboxylase to oxygenase activity, which was about 10. Catalase activity reached a maximum during the climacteric, simultaneously with increased ethylene and CO 2 formation. Glycolate oxidase activity decreased during early stages of development and was barely detectable at the climacteric. Hydroxypyruvate reductase, associated with serine formation by the glycerate pathway, increased in specific activity during early stages of tomato fruit ripening. In the fruit of the rin tomato mutant, which does not ripen normally, none of these changes in enzyme activity occurred. 相似文献
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