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1.
Zach Adam 《Photosynthesis research》1995,43(2):143-147
A mutant of the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), in which Arg53 is replaced by Glu, was synthesized and imported into isolated chloroplasts. The mutant protein was efficiently imported into the chloroplast and correctly processed to the mature size. Like the wild type protein, it was stable over a period of at least 2 h. Unlike the wilk-type protein however, most of the mutant protein was not assembled with holo-Rubisco at the end of a 10-min import reaction. It migrated instead as a diffused band on a non-denaturing gel, slower than the precursor protein, but faster than the holoenzyme. The level of the unassembled mutant protein in the stroma decreased with time, while its level in the assembled fraction has increased, indicating that this protein is a slowly-assembled, rather than a non-assembled, mutant of the small suubunit of Rubisco. Accumulation of the mutant protein in the holoenzyme fraction was dependent on ATP and light. The transient species, migrating faster than the holoenzyme but slower than the precursor protein, may represent an intermediate in the assembly process of the small subunit of RubiscoAbbreviations LSU
large subunit of Rubisco
- Rubisco
ribulose-1,5-bisphosphate carboxylase/oxygenase
- SSU
small subunit of Rubisco 相似文献
2.
Gian Franco Soldatini Giacomo Lorenzini Ferruccio Filippi Cristina Nali Lucia Guidi 《Physiologia plantarum》1998,104(4):707-712
The photosynthetic response was studied in two clones ( Populus deltoides × maximowiczii Eridano and Populus × euramericana I‐214), known for their differential response to ozone (O3 ) in terms of visible symptoms, when exposed to O3 (60 nl l−1 5 h day−1 , 7 and 15 days). The photosynthetic ability was tested using gas exchange and chlorophyll fluorescence analysis. O3 caused a decrease in the CO2 assimilation rate at light saturation level in mature leaves of both clones. Alterations of Chl fluorescence parameters, in particular the Fv /Fm ratio and non‐photochemical quenching were also observed. The effects were similar for both clones and it could not be concluded that differential effects on electron transport capacity were responsible for the observed reduction in photosynthesis. The reduction of photosynthetic rate in Eridano was due mainly to a reduced mesophyll activity, as evidenced by the increase in intercellular CO2 concentration and the minimal changes in stomatal conductance. In contrast, in I‐214, stomatal effects were primarily responsible, although effects on the mesophyll cannot be excluded. Data obtained indicate that the effects observed at the mesophyll level may be attributed to indirect effects caused by membrane disorders. 相似文献
3.
Hiroshi Fukayama Naotsugu Uchida Tetsushi Azuma Takeshi Yasuda 《Physiologia plantarum》1998,104(4):541-548
The effects of the ratio of Rubisco activase to Rubisco (activase/Rubisco ratio) on light dependent activation of CO2 assimilation were investigated during leaf aging of rice. Changes of photosynthetic CO2 gas exchange rates in relation to step increases of light intensity from two photon flux densities of 60 µmol m−2 s−1 (low initial PFD) and 500 µmol m−2 s−1 (high initial PFD) to saturated PFD of 1 800 µmol m−2 s−1 were measured. These photosynthetic activation processes were considered to be limited by the Rubisco activation rate when analyzed by the relaxation method. The relaxation time of low initial PFD gradually declined from 3 to 33 days after leaf emergence and showed high and negative correlation to the activase/Rubisco ratio. The initial rate of Rubisco activation under low initial PFD linearly correlated to the amounts of Rubisco activase, whereas these were almost constant from 3 to 23 days after leaf emergence. But these correlations could not be recognized in the case of high initial PFD. Moreover, the relaxation times were more sensitive to intercellular CO2 concentration (Ci ) under high initial PFD than under low initial PFD, especially, at Ci below 300 µl l−1 . These results suggest the involvement of the activase/Rubisco ratio in the photosynthetic activation under relatively low initial PFD, and the limitation of photosynthetic activation under relatively high initial PFD by Rubisco carbamylation during leaf aging of rice. 相似文献
4.
5.
Photosynthetic CO2 fixation is the ultimate source of organic carbon on earth and thus is essential for crop production and carbon sequestration. Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) catalyzes the first step of photosynthetic CO2 fixation. However, the extreme low carboxylation efficiency of Rubisco makes it the most attractive target for improving photosynthetic efficiency. Extensive studies have focused on re-engineering a more efficient enzyme, but the effort has been impeded by the limited understanding of its structure-function relationships and the lack of an efficient selection system towards its activity. To address the unsuccessful molecular engineering of Rubisco, we developed an Escherichia coli-based activity-directed selection system which links the growth of host cell solely to the Rubisco activity therein. A Synechococcus sp. PCC7002 Rubisco mutant with E49V and D82G substitutions in the small subunit was selected from a total of 15,000 mutants by one round of evolution. This mutant showed an 85% increase in specific carboxylation activity and a 45% improvement in catalytic efficiency towards CO2. The small-subunit E49V mutation was speculated to influence holoenzyme catalysis through interaction with the large-subunit Q225. This interaction is conserved among various Rubisco from higher plants and Chlamydomonas reinhardtii. Knowledge of these might provide clues for engineering Rubisco from higher plants, with the potential of increasing the crop yield. 相似文献
6.
In wheat (Triticum aestivum L.), leaf senescence can be initiated by different factors. Depending on the plant system (intact plants or detached leaves)
or the environmental conditions (light, nutrient availability), the symptoms of senescence differ. The aim of this work was
to elucidate the catabolism of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco, EC. 4.1.1.39) under various senescence-inducing
conditions. Leaf senescence was initiated in intact plants by darkness or by N-deprivation and in leaf segments by exposure
to light or darkness. Depending on the treatment, a 50 kDa fragment of Rubisco was observed. The formation of this fragment
was enhanced by leaf detachment and low light. In segments exposed to high light and in intact plants induced to senesce by
N-deprivation, the fragment was essentially absent. Since an antibody against the N-terminus of a large subunit of Rubisco
(LSU) did not cross-react with the fragment, it appears likely that a smaller fragment was removed from the N-terminus of
LSU. Inhibitor studies suggest that a cysteine endopeptidase was involved in the formation of the 50 kDa fragment. Non-denaturing-PAGE
followed by SDS-PAGE revealed that the fragment was produced while LSU was integrated in the holoenzyme complex, and that
it remained there after being produced. It remains open how the putative endopeptidase reaches the stromal protein Rubisco.
The results indicate that depending on the senescence-inducing conditions, different proteolytic enzymes may be involved.
The involvement of vacuolar proteases must be considered as occurring during LSU degradation, which takes place in darkness,
low light or under carbon limitation. 相似文献
7.
Oxidative stress in plants and green algae has multiple damaging effects, and leads to the degradation of Ribulose-1,5-biphosphate
carboxylase/oxygenase (Rubisco). We recently showed for the green algae Chlamydomonas reinhardtii that in response to a photo-oxidative stress, nascent synthesis of its chloroplast encoded large subunit (LSU) stops. In
parallel, newly synthesized small subunits (SSU) that are encoded by the nucleus are rapidly degraded, thus assembly of new
holoenzyme particles is inhibited. Here we show that under extreme oxidizing conditions, the steady-state level of the SSU
is also reduced. Cleavage of the LSU under oxidizing conditions is well established, and we show, using sucrose gradients,
that the resulting fragments of the LSU co-exist as parts of the holoenzyme. In parallel, we demonstrate the selective in-vivo
formation of high-density aggregates of Rubisco particles, in response to oxidative stress. Given the known tendency of unassembled
LSUs to aggregate, we propose that the rapid elimination of the SSU during oxidative stress along with the fragmentation of
the LSU and formation of intra-protein disulfide bridges, leads to the observed aggregation of Rubisco particles. Indeed,
we note here a substantially decreased ratio of SSU in the aggregated Rubisco particles. We also observed that this aggregation
marks the viability threshold of C. reinhardtii cells exposed to oxidative stress. 相似文献
8.
9.
In Vivo Photomodification of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase Holoenzyme by Ultraviolet-B Radiation (Formation of a 66-Kilodalton Variant of the Large Subunit) 总被引:3,自引:1,他引:2
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Wilson MI Ghosh S Gerhardt KE Holland N Babu TS Edelman M Dumbroff EB Greenberg BM 《Plant physiology》1995,109(1):221-229
Increased levels of solar ultraviolet (290-320 nm) (UV-B) radiation could have profound effects on plant proteins because the aromatic amino acids in proteins absorb strongly in this spectral region. We have investigated the effects of UV-B radiation on plant proteins and have observed a novel 66-kD protein. This product was formed in vivo when Brassica napus L. plants grown for 21 d in 65 [mu]mol m-2 s-1 photosynthetically active radiation were subsequently exposed to 65 [mu]mol m-2 s-1 photosynthetically active radiation plus UV-B radiation (1.5 [mu]mol m-2 s-1). The protein appeared after 4 h of UV-B irradiation and accumulated during the next 16 h in UV-B. The 66-kD protein cross-reacted with an antiserum against the ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) holoenzyme. Analysis of soluble leaf proteins revealed that the 66-kD product had a number of isoforms corresponding closely to those of the large subunit of Rubisco (LSU). Partial proteolytic digests of the LSU and the 66-kD protein resulted in an equivalent pattern of protein fragments, leading to the conclusion that the 66-kD protein was a photomodified form of the LSU. A similar high molecular mass variant of Rubisco was observed in soluble protein extracts from leaves of tomato (Lycopersicon esculentum), tobacco (Nicotiana tabacum), and pea (Pisum sativum L.) plants treated in vivo with UV-B, suggesting that it might be a common product, at least among C3 plants. It is interesting that the 66-kD product appears to be generated after incorporation of the LSU into holoenzyme complexes. This conclusion was drawn from two lines of evidence. First, the LSU variant co-purified with holoenzyme complexes isolated by nondenaturing polyacrylamide gel electrophoresis. Second, a UV-B-specific 66-kD protein did not accumulate in a tobacco mutant that synthesizes the Rubisco subunits but does not assemble them into normal holoenzyme complexes. 相似文献
10.
Yosef I Irihimovitch V Knopf JA Cohen I Orr-Dahan I Nahum E Keasar C Shapira M 《The Journal of biological chemistry》2004,279(11):10148-10156
Transfer of the green algae Chlamydomonas reinhardtii from low light to high light generated an oxidative stress that led to a dramatic arrest in the synthesis of the large subunit (LSU) of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). The translational arrest correlated with transient changes in the intracellular levels of reactive oxygen species and with shifting the glutathione pool toward its oxidized form (Irihimovitch, V., and Shapira, M. (2000) J. Biol. Chem. 275, 16289-16295). Here we examined how the redox potential of glutathione affected the RNA-protein interactions with the 5'-untranslated region of rbcL. This RNA region specifically binds a group of proteins with molecular masses of 81, 62, 51, and 47 kDa in UV-cross-linking experiments under reducing conditions. Binding of these proteins was interrupted by exposure to oxidizing conditions (GSSG), and a new protein of 55 kDa was shown to interact with the RNA. The 55-kDa protein comigrated with Rubisco LSU in one- and two-dimensional gels, and its RNA binding activity was further verified by using the purified protein in UV-cross-linking experiments under oxidizing conditions. However, the LSU of purified and oxidized Rubisco bound to RNA in a sequence-independent manner. A remarkable structural similarity was found between the amino-terminal domain of Rubisco LSU in C. reinhardtii and the RNA binding domain, a highly prevailing motif among RNA-binding proteins. It appears from the crystal structure of Rubisco that the amino terminus of LSU is buried within the holoenzyme. We propose that under oxidizing conditions it is exposed to the surface and can, therefore, bind RNA. Accordingly, a recombinant form of the polypeptide domain that corresponds to the amino terminus of LSU was found to bind RNA in vitro with or without GSSG. 相似文献
11.
Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) from fir ( Abies alba Mill.) and spruce ( Picea abies [L.] Karst.) needles was purified to homogeneity. The enzyme was isolated from crude extracts through quantitative precipitation in 40-55% and 40-60% (NH4 )2 SO4 for fir and spruce. respectively, followed by linear sucrose gradient centrifugation. Using two dimensional gel electrophoresis, the isoelectric points were determined. For the large subunit (LSU) it was 6.7 for both species, and for the small subunit (SSU) it was 7.1 and 7.7 for fir and spruce, respectively. Very few differences in tryptic peptides and amino acid composition of Rubisco LSU were observed between fir and spruce. By contrast, marked differences characterized the same analyses for the Rubisco SSU of the two species. Moreover, substitution of residues was observed in the sequenced N-terminal region when comparing fir and spruce SSU. The Ouchterlony technique showed no immu-nochemical difference between Rubisco of fir and spruce when a rabbit antiserum to spinach Rubisco was used. The Eadie-Hofstee plots of carboxylase activity indicated that the apparent Km (CO2 ) were 31 and 36 μ M for the fir and spruce enzymes, respectively. 相似文献
12.
A homozygous, dominant, C2 H4 -resistant line of Arabidopsis thaliana (L.) Heynh (cv. Columbia; er ) was selected from ethylmethylsulfonate-mutagenized seed, and used to test the role of C2 H4 and other growth regulators in senescence of mature leaves. Chlorophyll (Chl) loss from disks excised from leaves of er was much slower than that from wild-type (WT) disks, whether they were held in the light or in the dark. C2 H4 accelerated Che loss from WT disks but had no effect on the yellowing of mutant disks. C2 H4 biosynthesis was higher in disks from the mutant plants, particularly in the light. In the dark, treatment with the cytokinin, 6-benzyladenine (BA), reduced Chl loss from wild-type disks, but had no effect on mutant disks. In the light, BA treatment stimulated chlorophyll breakdown in both wild type and mutant disks. Treatment with abscisic acid (ABA) stimulated chlorophyll loss in wild-type and mutant disks, whether they were held in the light or the dark. C2 H4 production was stimulated in ABA-treated disks, but they still yellowed even when C2 H4 production was inhibited by application of aminooxyacetic acid (AOA). These data indicate that C2 H4 is only one of the factors involved in leaf senescence, and that the promotion of senescence by ABA is not mediated through its stimulation of C2 H4 production. 相似文献
13.
The influence of the plastid genome (plastome) on the temperature dependence of chlorophyll fluorescence parameters was studied in four Oenothera species from climatically different habitats. Equipped with their natural plastome, the species could be arranged with respect to their low-temperature tolerance in the order Oe'villosa' (plastome I) = Oe argillicola (V) > Oe. grandiflora (III) > Oe elata ssp. hookeri (J). Exchanging the naturally occurring plastome with those from other species did not result in changes of the photosynthetic performance of the genotypes, except for decreasing pigment contents and photosynthesis rates (on area basis) in Oe. elata ssp. hookeri with plastome III. Furthermore, plastome exchange in Oe. elata ssp. hookeri and in Oe. grandiflora did not affect kinetic properties of purified ribulose-l,5-bis-phosphate carboxylase/oxygenase (EC 4,1.1.39), indicating that the gene for the large subunit of this enzyme has remained conserved during plastome evolution in Oenothera . It is concluded that the evolution of the plastome in North American Oenothera spp. did not influence the temperature adaptation of the photosynthetic apparatus, but that the latter is governed by effects residing in the nuclear genome. 相似文献
14.
The Nostoc-Gunnera symbiosis: carbon fixation and translocation 总被引:2,自引:0,他引:2
The in vitro specific activity of ribulose-1,5-bisphosphate carboxylase (Rubisco; EC 4. 1. 1. 39) and the dark and light in vivo CO2 fixation activities were determined in the cyanobiont of Gunnera . Compared to the free-living isolate Nostoc PCC 9231, the in vitro Rubisco activity was high, while the in vivo CO2 fixation was very low. Light did not significantly influence CO2 fixation if the cyanobiont was left in the sliced Gunnera tissues, while a small light stimulation was found for CO2 fixation of the freshly-isolated cyanobiont. The adjacent non-infected Gunnera tissue showed a very low CO2 fixation. A rapid translocation of fixed 14 CO2 from leaves towards apical parts of the plant was apparent, in particular to the symbiotic tissue. The 14 C label appeared mainly in soluble form in this tissue and was rapidly catabolised as shown by 14 C chase experiments. Also, short-term experiments revealed that maximum 14 C accumulation occurred in the symbiotic tissue showing the highest rates of nitrogen fixation (Söderbäck et al. 1990), about 10–15 mm from the plant apex. The data were taken to indicate that there is a modification in the photosynthetic light reaction of the cyanobiont and that the cyanobiont lives heterotrophically in the dark on photo-synthate rapidly delivered from nearby leaves of the host plant. 相似文献
15.
The degradation of Ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39) in wheat (Triticum aestivum L. cv. Yangmai 158) leaves during dark-induced senescence was studied. An in vivo degradation product of Rubisco large subunit (LSU) with molecular weight of 50 kD was detected by SDS-PAGE and immunoblotting with antibody against tobacco Rubisco. This fragment could also be detected in natural senescence. The result also suggested that the Rubisco holoenzyme had not dissociated when LSU hydrolyzed from 53 kD to 50 kD. And LSU could be fragmented to 50 kD at 30-35 ℃ and at pH 7.5 in crude enzyme extracts of wheat leaves dark-induced for 48 h, which suggested that maybe LSU was degraded to 50 kD by an unknown protease in chloroplast. 相似文献
16.
Nicholas J. Bate John C. M. Riley John E. Thompson Steven J. Rothstein 《Physiologia plantarum》1998,104(1):97-104
Six‐carbon (C6 ) volatile products are released from the enzymatic action of hydroperoxide lyase (HPL), a component of the lipoxygenase (LOX) pathway and form the basis of the "green‐note" flavour characteristic of many consumed plant products. Arabidopsis leaf tissue contains the C6 ‐aldehydes hexanal, and trans ‐2‐hexenal as well as the C6 ‐alcohols: hexanol, and 3‐hexenol. Interconversion between C6 ‐aldehydes and alcohols is thought to proceed through the action of alcohol dehydrogenase (ADH). Using an ADH mutant of Arabidopsis , we have shown that there are large quantitative and qualitative differences in the accumulation of C6 ‐volatiles in the absence of ADH activity. The total quantity of LOX‐derived volatiles is greater on a fresh weight basis in the ADH mutant. Qualitatively, hexanol and 3‐hexenol levels are approximately 62% and 51% lower in the mutant, respectively, whereas levels of hexenal are approximately 10‐fold higher. Hexanal accumulation, however, is unaffected in the mutant. The altered profile of LOX‐derived volatiles does not have an effect on the steady‐state levels of mRNA for allene oxide synthase (AOS) or LOX. HPL activity and mRNA quantity, however, are higher in the mutant relative to wild type, suggesting that altered product levels in the mutant affect HPL regulation. 相似文献
17.
V. V. Rassadina A. V. Usatov G. M. Fedorenko N. G. Averina 《Russian Journal of Plant Physiology》2005,52(5):606-615
Chlorophyll (Chl) deficiency in leaves of a plastome sunflower (Helianthus annuus L.) en:chlorina-5 mutant is due to the formation of smaller chloroplasts with a markedly reduced membrane system, as compared to the parent 3629 line. Abnormalities in the structure of the photosynthetic apparatus in the mutant can be mainly attributed to changes in the formation of photosystem I and its light-harvesting complexes. Chl deficiency in en:chlorina-5 correlated with its lower capability of synthesizing the first specific Chl precursor, 5-aminolevulinic acid (ALA) in the light. Light-independent stages of Chl biosynthesis in the mutant had the same efficiency as in leaves of the parent line. ALA formation in darkness and its conversion into protochlorophyllide did not depend on the extent of photosynthetic membrane development and photosynthetic activity. 相似文献
18.
Photosynthetic capacity in relation to nitrogen content and its partitioning in lichens with different photobionts 总被引:4,自引:0,他引:4
We tested the hypothesis that lichen species with a photosynthetic CO2 -concentrating mechanism (CCM) use nitrogen more efficiently in photosynthesis than species without this mechanism. Total ribulose bisphosphate carboxylase-oxygenase (Rubisco; EC 4.1.1.39) and chitin (the nitrogenous component of fungal cell walls), were quantified and related to photosynthetic capacity in eight lichens. The species represented three modes of CO2 acquisition and two modes of nitrogen acquisition, and included one cyanobacterial ( Nostoc ) lichen with a CCM and N2 fixation, four green algal ( Trebouxia ) lichens with a CCM but without N2 fixation and three lichens with green algal primary photobionts ( Coccomyxa or Dictyochloropsis ) lacking a CCM. The latter have N2 -fixing Nostoc in cephalodia. When related to thallus dry weight, total thallus nitrogen varied 20-fold, chitin 40-fold, Chl a 5-fold and Rubisco 4-fold among the species. Total nitrogen was lowest in three of the four Trebouxia lichens and highest in the bipartite cyanobacterial lichen. Lichens with the lowest nitrogen invested a larger proportion of this into photosynthetic components, while the species with high nitrogen made relatively more chitin. As a result, the potential photosynthetic nitrogen use efficiency was negatively correlated to total thallus nitrogen for this range of species. The cyanobacterial lichen had a higher photosynthetic capacity in relation to both Chl a and Rubisco compared with the green algal lichens. For the range of green algal lichens both Chl a and Rubisco contents were linearly related to photosynthetic capacity, so the data did not support the hypothesis of an enhanced photosynthetic nitrogen use efficiency in green-algal lichens with a CCM. 相似文献
19.
Harald Liß Christian Bockelmann Nicola Werner Hillel Fromm Elmar W. Weiler 《Physiologia plantarum》1998,102(4):561-572
Erythrosin b, a potent inhibitor of the Ca2+ ‐ATPases and the Ca2+ ‐release channel (BCC1) in mechanosensitive tissue of Bryonia dioica Jacq., effectively suppresses a tendril's reaction to touch, suggesting that Ca2+ ‐transporters are involved in signal transduction in this organ. The Ca2+ ‐ATPase located in the endoplasmic reticulum (ER) represents a multiregulated enzyme that is stimulated by calmodulin (CaM), KCl and lysophospholipids. Limited proteolysis of ER‐membranes by trypsin results in an irreversible activation of the Ca2+ ‐ATPase and loss of the CaM sensitivity, presumably through removal of an autoinhibitory domain where CaM binds. Mild trypsination mimics the effects of CaM on Vmax and the affinity for Ca2+ and ATP. Irrespective of a trypsin treatment, the enzyme can be additionally stimulated by KCl and lysolipids, indicating that the sites of interaction for these effectors are not located in the domain removed by the protease. CaM‐stimulated ATPase activity was purified from microsomal and ER fractions using a combination of CaM‐affinity and anion‐exchange chromatography. The isolated polypeptide was enzymatically active, showed a calcium‐dependent mobility‐shift in SDS‐PAGE from 109 kDa in the absence of Ca2+ to 104 kDa in the presence of 10 m M CaCl2 and could be radiolabeled with [35 S]‐CaM. The characteristics of the purified enzyme remained closely similar to those of the ER‐bound Ca2+ ‐transporting activity, including the enzymatic data, CaM stimulation, and the sensitivity towards a range of inhibitors. 相似文献
20.
FOYER CHRISTINE H.; NURMI ARJA; DULIEU HUBERT; PARRY MARTIN A. J. 《Journal of experimental botany》1993,44(9):1445-1452
The basis for the lesions in the Sp25 and H7 ribulose-l,5-bisphosphatecarboxylase/oxygenase (Rubisco) mutants of tobacco was studiedin detail because these plants may be suitable hosts for transformationwith the genes for Rubisco enzymes of various origins that havedifferent substrate specificities. We show that the Sp25 mutantlacks active holoenzyme, but contains the large and small subunitpolypeptides, Rubisco activase and the chloroplast chaperonin,Cpn 60. The large subunit polypeptides were not distributeduniformly in the stroma in the Sp25 mutant as they were in thewild-type plants, but had an anomalous distribution being presentonly in aggregated clusters notably in chloroplasts with largestarch grains. Furthermore, these clusters were not uniformlydistributed throughout the photosynthetic cells but were localizedlargely in the mesophyll cells surrounding the vascular tissue.In contrast to the Sp25 mutant, the H7 mutant contained theRubisco holoenzyme, but in this case the enzyme was inactive.It is clear that in both these mutants the Rubisco holoenzymefails to assemble correctly. In the Sp25 mutant assembly islost completely while in the H7 mutant the holoenzyme is formed,but the assembly process fails to produce an active enzyme.We suggest that the flaw in assembly in the Sp25 mutant resultsfrom a defect in chloroplast encoded proteins. Key words: Rubisco, assembly, tobacco, mutants 相似文献