Plant Cells Peroxisomes and Glyoxysomes.pdf

7/27/2019 Plant Cells Peroxisomes and Glyoxysomes.pdf

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Plant Cells: Peroxisomes andGlyoxysomesRobert Paul Donaldson, The George Washington University, Washington DC, USA

Masoumeh Assadi,The George Washington University, Washington DC, USA

Konstantina Karyotou, The George Washington University, Washington DC, USA

Tulin Olcum, The George Washington University, Washington DC, USA

Tianqing Qiu, The George Washington University, Washington DC, USA

Peroxisomes andglyoxysomes aremembraneenclosures, both referredto as microbodies,

which contain oxidative enzymes that participate in photorespiration in leaves, nitrogen

metabolism in root nodules, and fat conversions in seeds. The enzymes found within

microbodies are brought in from the cytosol by information described as peroxisomal

targeting sequences (PTS).

Basic Structure, Basic FunctionsA peroxisome or a glyoxysome consists of a specific groupof enzymes or proteins enclosed by a single membrane.These organelles, which are in the range of 1 mm indiameter, are visible under the electron microscope and aresometimes referred to as microbodies. In higher plants, atleast four classes of peroxisomes have been identified:glyoxysomes, leaf peroxisomes, root nodule peroxisomesand unspecialized peroxisomes. All classes of peroxisomeshave the following characteristics: (1) they have a singlemembrane; (2) they have high equilibrium density of c.1.25gcm2 2 in sucrose gradient centrifugation; and (3)

their matrix (internal content) is finely granular. Althoughall classes possess the common characteristics, they havedistinct metabolic roles specified by the developmentalstage and type of cell. Catalase, which is by definitionalways found in these organelles, can be stained black suchthat the organelles are more obvious in electron micro-graphs. The proteins within this type of organelle arevisible as a granular matrixsomewhat more dense than thatof the cytosol. This type of organelle does not have anyinternal membranous structures but in some cases thematrix includes a striking proteinaceous crystal or denseaggregate, visible in electron microscopy. Peroxisomes orglyoxysomes can also be visualized in fluorescence micro-

scopy using antibodies specific to one of their proteins,such as catalase. The relatively simple structure of theinternal matrix of microbodies distinguishes them fromchloroplasts or mitochondria, which have internal mem-branes that are folded or stacked. In the photosyntheticcells of leaves the peroxisomes are often in contact withchloroplasts and mitochondria; these three organellesinteract with each other in photorespiration. Glyoxysomesare found in contact with lipid bodies in cotyledons or

endosperm where fatty acids are being converted tcarbohydrate (sugars) during germination. Images owhole plant cells indicate that there may be a few hundremicrobodies in a cell. In some instances the microbodiemay be tubular or interconnected and appear to bdividing.

All four known classes of microbodies found in plancells are organelles that, by definition, contain activitiethat produce and destroy hydrogen peroxide (H2O2which is a toxic agent.

Glyoxysomes are specialized peroxisomes that arpresent in postgerminative seedlings of oil seeds an

senescent organs. Glyoxysomes are involved in storaglipid mobilization in growing seedlings via the glyoxylatcycle. Succinate produced in glyoxysomes is ultimatelconverted to sucrose in the cytosol. It is presumed thapresence of glyoxysomes in senescent organs is in responsto the mobilization of membrane lipids.

Leaf peroxisomes are present in green and photosynthetically active tissues, such as green cotyledons and leaveThese peroxisomes contain enzymes that are required fothe light-dependent process of photorespiration.

Root nodule peroxisomes are present in the root noduleof certain legumes and involved in nitrogen metabolism. Imany tropical legumes, nitrogen is transported in the form

of ureides, allantoin and allantoic acid. Reactions of ureidbiosynthesis take place in several subcellular comparments. One of thelast steps of this pathway, the conversioof urate to allantoin, is catalysed by urate oxidase iperoxisomes.

Unspecialized peroxisomes are present in plant tissuethat are not photosynthetically active and that lack storaglipids, such as the roots of most plants. Unspecializeperoxisomes can be distinguished from other forms operoxisomes by their small size, low frequency and densit

Article Contents

Secondary article

. Basic Structure, Basic Functions

. Photorespiration: Leaf Peroxisomes

. Fixed Nitrogen Conversion into Ureides: Root Nodule

Peroxisomes

. Breakdown of Fatty Acids during Germination:

Glyoxysomes

. Peroxisome Formation: GlyoxysomePeroxisome

Conversions

. Conclusion

ENCYCLOPEDIA OF LIFE SCIENCES / & 2001 Nature Publishing Group / www.els.net


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compared to glyoxysomes and leaf-type peroxisomes.Their specific role in the cellular metabolism is not known.

The metabolic processes that take place in peroxisomesoften bypass energy conservation steps. The prototypicalenzyme of these organelles is an oxidase that generatesH2O2, such as the glycolate oxidase (GO) of leafperoxisomes or the fatty acylCoA oxidase (AO) of

glyoxysomes. These oxidases contain flavin (as FAD),which accepts two hydrogens from a substrate (e.g.glycolate or acylCoA) and transfers them to oxygen,resulting in H2O2. In the mitochondria this process wouldbe coupled to energy conservation, where the hydrogensrecovered from the substrate serve as a source of electronsto power mitochondrialATP generation. The advantage ofdirectly transferring the hydrogens to oxygen in peroxi-somes is that the metabolic processes can take place evenwhen the cell is not consuming ATP and when additionalATP does not need to be generated.

Photorespiration: Leaf Peroxisomes

Photorespiration and photosynthesis are opposing pro-cesses that occur in the cells of leaves or other green tissues.Both processes are initiated in chloroplasts, but photo-respiration involves a diversion into leaf peroxisomes andmitochondria. As a cell of a young leaf expands, its vacuolefills with water and spreads the cytoplasm around theperiphery of the cell. In the cytoplasm the chloroplasts,peroxisomes and mitochondria become loaded with theenzymes needed to absorb light and carbon dioxide tocreate new organic molecules for the rest of the plant. The

carbon dioxide is taken in by the chloroplast enzyme,ribulose-1,5-bisphosphate carboxylase (Rubisco), themost abundant enzyme in the cell, and is normallyassimilated into the three-carbon molecule phosphoglyce-ric acid (PGA), which is usedto synthesize sugars andotherorganic molecules.

Photorespiration commences when oxygen replacescarbon dioxide in Rubisco. This results in the two-carbonmolecule, phosphoglycolate, instead of PGA. The phos-phoglycolate can be recycled back into PGA by acircuitous process through leaf peroxisomes, mitochondriaand chloroplasts with the use of oxygen and the loss of onecarbon in four as carbon dioxide, hence the designation

photorespiration. The glycolate, relieved of its phos-phate, is passed from a chloroplastto a peroxisome. Here itis subject to a typical peroxisomal enzyme, glycolateoxidase, which transfers two hydrogens to oxygen,resulting in hydrogen peroxide, which is broken down bycatalase. The result is glyoxylate, which accepts an aminogroup (NH2) to become the amino acid glycine. This istransported into the mitochondria. In a photosynthetic cellthe proteins of photorespiration are the most abundant inthe mitochondria. Here a complex of four proteins

combines two molecules of glycine to create a moleculof serine with the release of a carbon dioxide molecule anan amino group. The serine returns to a peroxisome wheradditional enzymes complete its conversion to glycerate btransferring its amino group to glyoxylate, followed breduction by hydroxypyruvate reductase using NADHThe glycerate re-enters a chloroplast where it is phos

phorylated, finally yielding PGA.These processes require the transport of metabolite

through the membranes of the various organelles includinthe peroxisomes. There may be selective channel proteinin the membranes that regulate the transport of metabolites. A porin protein discovered in the membranes operoxisomesmayrepresent sucha channel (Reumann etal1998).

The process of photorespiration is very significant iplants and becomes especially important when leastomata close to reduce water loss. Then the supply ocarbondioxide withinthe leaf diminishesas it is assimilateand at the same time the concentrationof oxygen increase

favouring photorespiration. The carbon dioxide releaseby photorespiration can be reassimilated by Rubisco, thuallowing use of the light energy absorbed by thchloroplast. Although photorespiration is counterproductive to photosynthesis, it may be necessary to protect thleaf cells from damage due to light absorption.

Fixed Nitrogen Conversion intoUreides: Root Nodule Peroxisomes

Root nodule peroxisomes of certain tropical legumesynthesize allantoin, which serves as the major metabolitfor nitrogen transport in these plants. The ureideallantoin and allantoic acid, are the predominant form onitrogen transported in the xylem of soya bean and cowpeplants growing symbiotically. The synthesis of allantoiacid presumably derives from the degradation of purineUrate oxidase (UO), one enzyme in the purine degradatiopathway, is normally found in peroxisomes, along witcatalase, which consumes the hydrogen peroxide produceby UO. Uric acid is oxidized by UO to allantoin withiperoxisomes. Small amounts of UO are present iglyoxysomes of germinating oil seeds and of potato tuber

while traces of UO are also present in peroxisomes fromother plant tissues. In all cases UO is easily solubilized anis not part of the crystalline core of the peroxisomAllantoinase and allantoicase, enzymes participatingin thbiogenesis of allantoin and allantoic acid, have beereported to be present in peroxisomes from amphibiaand fish livers. Approximately one-half of the allantoinasactivity in castor bean endosperm is associated witglyoxysomes; the remainder is in the proplastids (Hanket al., 1981).

Plant Cells: Peroxisomes and Glyoxysomes

2 ENCYCLOPEDIA OF LIFE SCIENCES / & 2001 Nature Publishing Group / www.els.net


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Breakdown of Fatty Acids duringGermination: Glyoxysomes

Metabolically, plant and animal cells differ in manyimportant respects. In particular, plant cells, along withsome microorganisms, can carry out the net synthesis of

carbohydrate from fat. This conversion is crucial in thedevelopment of seeds, in which a great amount of energy isstored in the form of triacylglycerols. As such seedsgerminate, triacylglycerol stored in lipid bodies is brokendown, transported to glyoxysomes and eventually con-verted to sugars, which provide energy and the rawmaterial needed for growth of the plant. In contrast,animal cells cannot carry out the net synthesis ofcarbohydrate from fat.

In plants, catabolism of triacylglycerols in the lipidbodies yields fatty acids and glycerol. Fatty acids undergob-oxidation to yield acetylCoA, which can then beincorporated into carbohydrate through the glyoxylate

cycle. The conversion of triacylglycerols into sugarsinvolves metabolism in glyoxysomes. While leaf peroxi-somes have a key role in photorespiration, glyoxysomes arethe sites ofb-oxidation of fatty acids and the glyoxylatecycle (Cooper and Beevers, 1969). These pathways areessential to the maintenance of gluconeogenesis initiatedby the degradation of reserve or structural lipids. b-Oxidation of fatty acids occurs in most plant microbodies,but has a more important function in those organelles fromfat-storing tissues of oilseeds. In these organelles, fattyacids are degraded via the b-oxidation pathway to acetylCoA, which in turn is metabolized by the glyoxylate cycleto succinate, bypassing the decarboxylating steps of the

Krebs cycle (Tolbert, 1981). Succinate is then used forgluconeogenesis or synthesis of other metabolic inter-mediates.

The glyoxysomalb-oxidation of fatty acids is a recurringsequence of four reactions shown in Figure 1: oxidation(dehydrogenation) by acylCoA oxidase (AO), hydrationby enoylCoA hydratase combined with a second oxida-tion by 3-hydroxy acylCoA dehydrogenase, both cata-lysed within a bifunctional protein (BP), and finallythiolysis by 3-ketoacylCoA thiolase (TH). The FAD-linked acylCoA oxidase transfers electrons not to therespiratory electron transport chain but directly to oxygen,without recovery of chemical energy (ATP). The oxygen is

reduced to hydrogen peroxide, which in turn is scavengedby catalase (CAT). The dehydrogenase produces NADH2and the thiolase uses CoA to remove the last two carbons ofthe 3-ketoacylCoA to yield acetylCoA.

As stored lipids are metabolized during seed germina-tion, the acetylCoA produced by b-oxidation in glyoxy-somes is transferred to the glyoxylate cycle, which can beconsidered as an anabolic variant of the citric acid cycle.The glyoxylate cycle converts two molecules of acetylCoA into one molecule of succinate, as shown in Figure 1.

This involves two glyoxylate cycle-specific enzymenamely isocitrate lyase (IL) and malate synthase (MSand three enzyme activities similar to those from the citriacid cycle, namely citrate synthase (CS), aconitase (ACand malate dehydrogenase (MD). Since the glyoxylatpathway bypasses the two reactions of the Krebs cyclwhere carbon is lost, each turn of the cycle involve

incorporation of two two-carbon molecules and results ithe net synthesis of the four-carbon molecule, succinateThis is transported from the glyoxysome to the mitochondria where it is converted through the Krebs cycle toxalacetate, which is readily utilized by gluconeogenesifor carbohydrate synthesis.

The reduced cofactors that are produced during both boxidation and glyoxylate cycle, namely NADH2 anFADH2, do not have direct access to the mitochondriaelectron transport system. They must therefore be reoxidized in order for both pathways to remain functionaThe acylCoA oxidase of glyoxysomal b-oxidation avoidthat by transferring electrons from the FADH2 directly t

oxygen, resulting in hydrogen peroxide. Hydrogen peroxide is produced in abundance within glyoxysomeduring this process or from the disproportionation osuperoxide radicals by superoxide dismutase. Superoxidradicals can be produced by the transfer of electrons fromNADH2 to oxygen via a protein in the membrane (Del Riet al., 1992). The hydrogen peroxide is decomposed eitheby catalase (CAT) inside the glyoxysome or by aascorbate-specific peroxidase (AP) present at the glyoxysomal membrane. NADH2 produced by the 3-hydroxacylCoA dehydrogenase and by malate dehydrogenase ithe glyoxylate cycle also accumulates within glyoxysomeand is oxidized by the electron transport proteins in th

glyoxysomal membrane. These proteins include ascorbatperoxidase (AP), ascorbate free radical reductase (ARand, possibly, cytochrome b5 and glutathione reductaseAscorbate peroxidase utilizes hydrogen peroxide tcatalyse a one-electron oxidation of ascorbate, resultinin the formationof ascorbate freeradicals.Regenerationoascorbate is achieved by ascorbate free radical reductas(AR), using NADH2 as an electron donor. Overalglyoxysomal metabolism results in the production of variety of reactive species, such as O2

2., H2O2 anascorbate free radicals. At the same time the glyoxysomeinclude the appropriate detoxifying enzymes, such acatalase and the enzymes located in the membrane A

and AR, which can protect against cell damage (Bunkemann and Trelease, 1996; Ishikawa et al., 1998).

Peroxisome Formation: GlyoxysomePeroxisome Conversions

In the oil-storing cotyledons of seeds such as cottoncucumber or legumes, a population of glyoxysomes




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converted into a population of leaf peroxisomes followingexposure to light, resulting in greening of the tissue. Thefunctions of the microbodies are thus converted from lipidmetabolism to photorespiratory metabolism. Two ideas,the one-population and the two-population hypotheses,have been proposed for the interconversions and origins ofspecialized peroxisomes. According to the first hypothesis,leaf peroxisomes are formed from existing glyoxysomes byinsertion of newly synthesized leaf peroxisome-specificenzymes and depletion of glyoxysomal-specific enzymes.In contrast, the second hypothesis suggests de novoformation of glyoxysomes and leaf peroxisomes. Accord-ing to the one-population hypothesis, glyoxysomal-specific

enzymes and leaf peroxisome-specific enzymes are presentin single microbody species throughout seedling growth,even after illumination. The second hypothesis suggeststhat glyoxysomes and peroxisomes contain completelydifferent enzymes. However, several lines of evidencesupport the first hypothesis. For example, microbodieswith both glyoxysomal-specific and leaf peroxisomal-specific enzymes have been identified during the transi-tional stage, using immunocytochemical analysis. Thisindicates that glyoxysomes are directly transformed to leaf

peroxisomes during greening. Additional support for thiidea comes fromthe same kind of findingduring senescencof cotyledons or leaves, a stage in which leaf peroxisomeare converted to glyoxysomes and the stores of carbon annitrogen are transferred to newly developing tissueImmunocytochemical analysis revealed that enzymespecific to glyoxysomes and to leaf peroxisomes are botpresent in microbodies of senescing cotyledons (Titus anBecker, 1985).

Although the morphological appearance of microbodiein cotyledons is the same during transitions from glyoxysomes to peroxisomes, their enzymatic contents archanged drastically. As discussed above, each specialize

microbody contains different enzymes. Activities oglyoxysomal-specific enzymes, such as malate synthasand citrate synthase, increase with germination andecrease gradually after lipid stores are depleted. At thistage, activities of leaf peroxisome-specific enzymes are athe lowest level. Rapid increase in activities of leaperoxisome-specific enzymes and decrease in activities oglyoxysomal-specific enzymes occurs when seedlings artransferred to the light. The transition of glyoxysomes tleaf peroxisomes and the accumulations of new proteins i

Glycerol

Fatty acid

Glyoxysome

Succinate

AcylCoA

AcetylCoA

EnoylCoA 3-OH-acylCoA

Asc Asc

Asc

-Oxidation

Glyoxylate cycle

Asc

AscFAD

AO BP

O2 H2O2H2O

BP

3-ketoacylCoACoA-SH

NADH2

NAD+

TH

Cytosol

GlyoxylateIL

MS

Malate

MD

NAD+

NADH2

Oxaloacetate

CS

AcetylCoA

Citrate

AC

Isocitrate

Succinate

Mitochondrion

Fatty acids

Triacyl glycerols

H2OCAT

AP

AR

AR

AR

Lipid body

Figure 1 b-Oxidation and glyoxylate cycle enzymes in glyoxysomes. The b-oxidation enzymes are acylCoA oxidase (AO), enoylCoA hydratase

combined with 3-hydroxy acylCoA dehydrogenase in the bifunctional protein (BP) and 3-ketoacylCoA thiolase (TH). Glyoxylate-cycle enzymes areisocitrate lyase (IL) and malate synthase (MS), citrate synthase (CS), aconitase (AC) and malate dehydrogenase (MD). Membrane enzymes include

ascorbate peroxidase (AP) and ascorbate free radical reductase (AR). Both catalase (CAT) and AP consume hydrogen peroxide. Asc, ascorbate; Asc .;ascorbate free radical.




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microbodies can be regulated in several ways: throughgeneexpression, protein transport, mRNA splicing and proteindegradation. These are discussed below.

Regulation of gene expression

The mRNA levels for glyoxysomal-specific enzymes malate synthase and citrate synthase increase rapidlyduring germination in the dark and decline markedly afterexposure of the cotyledons to the light. Expression of themalate synthase gene is inhibited by sucrose, the endproduct of the metabolism of stored lipid. On the otherhand mRNA levels of leaf peroxisome enzymes such asglycolate oxidase are low during germination in the darkand increase rapidly during greening. Regulation of leafperoxisome enzymes is light dependent and it has beenreported that phytochrome plays a role in signal transduc-tion. Accordingly, it is suggested that light and levels ofmetabolites are regulatory factors for microbody transi-tion events.

Regulation of protein transport intomicrobodies

All microbody enzymes are synthesized in the cytoplasmand transported into microbodies posttranslationally. Theenzymes include certain sequences of amino acids thatserve as targeting information. Only two major types ofmicrobody targeting signals are known in plants as well asin mammals, insects, fungi and protists. The peroxisomaltargeting signal-1, PTS-1, is a C-terminal tripeptide such asSer-Lys-Leu (SKL) that is present in mature proteins in

microbodies. Conservative variations in the amino acids ofthe PTS-1 sequence can be tolerated without loss oftargeting activity. For example, the targeting sequences areSRL for malate synthase from castor bean, PRL forglycolate oxidase, and ARM or SRM for isocitrate lyases.However, the removal of the ARM from castor beanisocitrate lyase does not stop import of the protein,suggesting that there is additional targeting informationin the protein (Gao et al., 1996). Experimental alterationsof the PTS-1 suggest that other amino acids may befunctionalin the tripeptide and that additional amino acidsnearby may also contribute to recognition (Mullen et al.,1997a; Wolins and Donaldson, 1997). The C-terminal

sequence of cotton seed glyoxysomal catalase is -NVKPSIand the experimental evidence indicates that some of theamino acids in addition to the PSI are necessary for import(Mullen et al., 1997b). Many other proteins from a varietyof plant species (see Table 1) fit the rather relaxed PTS-1consensus, but in the absence of experimental evidence itcannot be assumed that each of these sequences functionsas a PTS-1. Comparisons of the amino acid sequences fromseveral enzymes indicate that each enzyme has a particularversion of the PTS-1 that is found in several species. A

cytosolic PTS-1 receptor that interacts with a peroxisomamembrane docking protein has been described for humaand yeast peroxisomes. Some in vitro studies indicate thatsimilar receptor exists in plants (Wolins and Donaldson1994; Brickner et al., 1997; Kragler et al., 1998).

Most of the microbody proteins have the C-terminaPTS-1, but a few have a second type of targeting signal nea

their N-terminal, PTS-2. This consists of a sequence sucas RLXXXXXHL, where X can be any amino acid (Gietet al., 1994). These proteins include glyoxysomal 3ketoacylCoA thiolase, malate dehydrogenase and citratsynthase, which are synthesized with larger molecular masin the cytosol. Their N-terminal PTS-2 peptides are thecleaved upon the targeting of the enzymes into microbodies. Experiments showed that a fusion protein composed of the N-terminal region of glyoxysomal citratsynthase was transported to glyoxysomes, leaf peroxsomes and unspecialized microbodies and was subsequently processed. This suggests that microbodies use thsame transport mechanism and that differentiation o

microbodies is not regulated at the level of recognition othe targeting information.

It has been observed that proteins that have had theitargeting information removed experimentally are imported into glyoxysomes if accompanied by proteins thado have the targeting information (Lee et al., 1997). Thimplication is that the protein lacking a PTS can piggyback or associate with the protein having the PTS, anthat the two proteins can enter together. How such aassemblage would traverse the membrane of the glyoxysome is not understood.

Regulation of mRNA splicingHydroxypyruvate reductase (HPR) is one of the leaperoxisome-specific enzymes that is induced and accumulates in microbodies during greening. cDNA analysis opumpkin cotyledons showed that two very similar cDNAencode for this enzyme. The only difference between thtwo encoded proteins is that HPR-1 contains PTS-1 anHPR-2 does not. Genomic DNA analysis suggested thathe HPR-1 and HPR-2 are encoded from the same gene balternative splicing. Accumulation during greening oHPR-1 and HPR-2, in leaf peroxisomes and the cytosorespectively, suggests that alternative mRNA splicing ma

play a regulatory role in microbody transition (Hayashet al., 1996).

Regulation at the level of protein degradatio

During transition of glyoxysomes to leaf peroxisomes, dnovo synthesis of glyoxysomal-specific enzymes is prevented by depletion and degradation of mRNA for thesenzymes. Furthermore, preexisting glyoxysomal-specifienzymes are degraded by proteolytic enzymes present i




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the matrix of glyoxysomes during the transitional stage. Avariety of proteases have been discovered in leaf peroxi-

somes but nothing is known about how these mightcontribute to the selective degradation of enzymes inmicrobodies (Distefano et al., 1997).

Conclusion

Since the 1980s considerable progress has been madetoward understanding the processes that take place in the

different types of microbodies in plant cells and how thproteins that conduct these processes are directed from th

cytosol into peroxisomes and glyoxysomes. Yet little iknown about how cells maintain and propagate microbodies, how the proteins and lipid molecules of thmembrane are assembled, and how proteins pass througthe membrane. Nothing is known about how light anlevels of metabolites regulate the expression and delivery oproteins to microbodies. Furthermore, there is littknowledge of how metabolites such as fatty acids ancarboxylic acids or cofactors such as haem, CoA or/anNAD enteror leave the organelle. Thus, there is much to b

Table 1 Peroxisomal targeting sequences (PTS-1 and PTS-2)

aIndicates there is experimental evidence for the targeting function of this sequence. The bold types indicates the targeting sequence.

Protein Species

PTS-1

C-terminal amino acid sequence

Malate synthase Cucumbera FLT LDA YNY IVI HHP REL SKL-C'

Soya beana FLT LDA YNY IVV HHP RET SKL

Rapea FLT LDA YNN IVI HYP KGS SRL

Castor beana FLT LAV YDH IVA HYP INA SRL

Glycolate oxidase Spinach ISR SHI AAD WDG PSS RAV ARL

Arabidopsisa SEI TRN HIV TEW DIP RHL PRL

Cucumber QEI TRN HIV ADW DTP RVV PRL

Rice DIT RAH IYT DAE RLA RPF PRL

Isocitrate lyase Tomato WTR TGA TNL GDG SVV IAK ARM

Soya beana WTR SGA VNI DRG SIV VAK ARM

Castor beana TRP GAM EMG SAG SEV VAK ARM

Cucurbita TRA GAG NLG EEG SVV VAK SRM

Hydroxypyruvate reductase Arabidopsis PPN ASP SIV NSK ALG LPV SKL

Pumpkin PPA ASP SIV NAK ALE LPV SKL

Catalase Tomato SYL SQA DKS CGQ KVA SRL TVK PTM

Arabidopsis SYW LKA DRS LGQ KLA SRL NVR PSI

Cottona SYW SQA DKS LGQ KIA SRL NVR PSI

Cucurbit SYW SQA DRS LGQ KIA SRL NVR PNI

PTS-2

N'- terminal amino acid sequence

AcylCoA oxidase Pumpkin N'-ASPGEPNRTAEDESQAAAR RIERLSLHL TPI

Phalaenopsis MTKEAQMTSLASEHDTQQALR RIQKLSLHL LQP

Arabidopsis MESRREKNPMTEEESDGLIAAR RIQRLSLHL SPS

Malate dehydrogenase Watermelona

MQPIPDVNQ RIARISAHL HPPSoya bean MEANSGASD RISRIAGHL RPQ

Rape MPHK RIAMISAHL QPS

Cucumber MQPIPDVNQ RIARISAHL HPP

Citrate synthase Winter squash MPTDMELSPSNVARH RLAVLAAHL SAA

Arabidopsis MVFFRSVSAFTRLS RVQGQQSSL SNS




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learned about how microbodies interact with othersubcellular molecules and processes.

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Further Reading

Nishimura M, Hayashi M, Kato A, Yamaguchi K and Mano S (199

Functional transformation of microbodies in higher plant cells. Ce

Structure and Function 21(5): 387393.

Olsen LJ andHarada JJ (1995)Peroxisomes andtheirassemblyin high

plants.Annual Review of PlantPhysiology and PlantMolecular Biolog46: 123146.

Tolbert NE and Essner E (1981) Peroxisomes and glyoxysomes.Journ

of Cell Biology 91: 271s283s.



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Plant Cells Peroxisomes and Glyoxysomes.pdf