Wheat Leaf Extracts Research Articles

Identification and Categorization of Yellow Rust Infection in Wheat through Deep Learning Techniques

The global wheat industry faces significant challenges due to yellow rust disease, This is induced by fungus Puccinia striiformis, as it leads to substantial crop losses and economic impacts. Timely detection and classification of the disease are essential for its effective management and control. In this study, we investigate the potential of DL and ML techniques for detecting and classifying yellow rust disease in wheat. We utilize three state-of-the-art CNN models, namely ResNet50, DenseNet121, and VGG19, to analyze wheat leaf images and extract relevant features. These models were developed and refined using a large dataset of annotated wheat photos. Encompassing both healthy plants and those affected by yellow rust disease. Furthermore, we examine the effectiveness of data augmentation and transfer learning in enhancing classification performance. Our findings reveal that the DL-based CNN models surpass traditional machine learning techniques in detecting and classifying yellow rust disease in wheat. Among the tested CNN models, EfficientNetB3 demonstrates the best performance, emphasizing its suitability for large-scale and real-time monitoring of wheat crops. This research contributes to the development of precision agriculture tools, laying the groundwork for prompt intervention and management of yellow rust disease, ultimately minimizing yield loss and economic impact on wheat production.

Influence of Schumann Range Electromagnetic Fields on Components of Plant Redox Metabolism in Wheat and Peas.

The Schumann Resonances (ScR) are Extremely Low Frequency (ELF) electromagnetic resonances in the Earth-ionosphere cavity excited by global lightning discharges. ScR are the part of electromagnetic field (EMF) of Earth. The influence of ScR on biological systems is still insufficiently understood. The purpose of the study is to characterize the possible role of the plant cell redox metabolism regulating system in the Schumann Resonances EMF perception. Activity of catalase and superoxide dismutase, their isoenzyme structure, content of malondialdehyde, composition of polar lipids in leaf extracts of wheat and pea plants treated with short-time (30 min) and long-time (18 days) ELF EMF with a frequency of 7.8 Hz, 14.3 Hz, 20.8 Hz have been investigated. Short-time exposure ELF EMF caused more pronounced bio effects than long-time exposure. Wheat catalase turned out to be the most sensitive parameter to magnetic fields. It is assumed that the change in the activity of wheat catalase after a short-term ELF EMF may be associated with the ability of this enzyme to perceive the action of a weak EMF through calcium calmodulin and/or cryptochromic signaling systems.

Exploration of the Potential Mechanism of Faba Bean-Wheat Intercropping to Control Faba Bean Fusarium Wilt Due to Allelopathic Plant Extracts.

We intensively studied faba bean (Vicia faba L.) and wheat (Triticum aestivum L.) intercropping and found that this type of intercropping can effectively control the occurrence of faba bean wilt under field conditions. We conducted hydroponic experiments to explore the role of plant extracts in the process of soil-borne diseases and the mechanism of disease control of faba bean and wheat intercropping. In this experiment, three concentration gradients of faba bean and wheat stem, leaf, and root extracts were added to study the effects of faba bean and wheat extracts on faba bean growth, the physiological resistance of roots, and the growth of Fusarium oxysporum f. sp. fabae (FOF). Faba bean extracts significantly inhibited the growth of faba bean seedlings and the activity of root defense enzymes and significantly stimulated the growth of FOF at high concentrations. Compared with the treatment with faba bean extracts, wheat extracts significantly enhanced the growth of faba bean seedlings, increased the activity of defense enzymes, and inhibited the growth of FOF. Based on these results, we believe that wheat extracts can effectively alleviate the autotoxicity of faba beans and also control the occurrence of faba bean wilt in the field. This provides a theoretical basis for practical intercropping to reduce the damage caused by faba bean wilt.

Effect of Media Composition on Vegetative and Reproductive Growth of Alternaria Brassicicola and Bipolaris Sorokiniana

Experiments were conducted to evaluate the effect of some culture media on the vegetative and reproductive growth of Alternaria brassicicola and Bipolaris sorokiniana. Twenty one (21) treatment combinations each with three replications were employed. Potato Dextrose Agar (PDA) was used as the basic growth medium in this study. Supplementation with different plant extracts with this medium produced differential growth and sporulation of the tested fungi. PDA media supplemented with mustard leaf extract showed significantly highest vegetative growth (7.8 cm) and PDA with the combination of mustard leaf, tomato fruit, carrot fruit and cabbage leaf extracts showed the highest sporulation (11×105 spores/ml) of A. brassicicola. In case of B. sorokiniana, the highest vegetative growth (7.4 cm) and highest sporulation (45×104 spores/ml) were obtained by the supplementation of mustard and wheat leaf extracts respectively. Plant extract supplementation proved better than PDA as growth medium of A. brassicicola and B. sorokiniana.

Phosphorylation and Dephosphorylation of the Presequence of Precursor MULTIPLE ORGANELLAR RNA EDITING FACTOR3 during Import into Mitochondria from Arabidopsis.

The nucleus-encoded mitochondria-targeted proteins, multiple organellar RNA editing factors (MORF3, MORF5, and MORF6), interact with Arabidopsis (Arabidopsis thaliana) PURPLE ACID PHOSPHATASE2 (AtPAP2) located on the chloroplast and mitochondrial outer membranes in a presequence-dependent manner. Phosphorylation of the presequence of the precursor MORF3 (pMORF3) by endogenous kinases in wheat germ translation lysate, leaf extracts, or STY kinases, but not in rabbit reticulocyte translation lysate, resulted in the inhibition of protein import into mitochondria. This inhibition of import could be overcome by altering threonine/serine residues to alanine on the presequence, thus preventing phosphorylation. Phosphorylated pMORF3, but not the phosphorylation-deficient pMORF3, can form a complex with 14-3-3 proteins and HEAT SHOCK PROTEIN70. The phosphorylation-deficient mutant of pMORF3 also displayed faster rates of import when translated in wheat germ lysates. Mitochondria isolated from plants with altered amounts of AtPAP2 displayed altered protein import kinetics. The import rate of pMORF3 synthesized in wheat germ translation lysate into pap2 mitochondria was slower than that into wild-type mitochondria, and this rate disparity was not seen for pMORF3 synthesized in rabbit reticulocyte translation lysate, the latter translation lysate largely deficient in kinase activity. Taken together, these results support a role for the phosphorylation and dephosphorylation of pMORF3 during the import into plant mitochondria. These results suggest that kinases, possibly STY kinases, and AtPAP2 are involved in the import of protein into both mitochondria and chloroplasts and provide a mechanism by which the import of proteins into both organelles may be coordinated.

Antioxidant activity of three components of wheat leaves: ferulic acid, flavonoids and ascorbic acid

Recent studies have shown that wheat leaves are sources of natural antioxidant substances. In this study, the content of three antioxidants (ascorbic acid, total flavonoids and ferulic acid) and antioxidant activities of wheat leaf extracts were evaluated using 2,2-diphenyl-β-picrylhydrazyl and 2,2-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid (ABTS) assays. The interaction activities among different antioxidants were analyzed by factorial and path analyses. Wheat leaves were extracted with solvents of different polarities. The ABTS test showed that the ethanol extract had the highest antioxidant activity. There were highly significant linear correlations between antioxidant capacities of the investigated wheat leaves and their ascorbic acid, ferulic acid and flavonoid contents. Total flavonoids and ascorbic acid were major contributors to total antioxidant capacity in wheat leaves.

Formation and Germination ofSeptoria triticiSecondary Conidia as Affected by Environmental Factors

The effects of medium, isolate, temperature, light and pH on the formation and germination of Septoria tritici secondary conidia were tested. Of the six media tested, the malt-yeast extract agar was the best and generated 1.82 x 109 conidia/plate. The ten isolates tested showed different ability of conidia production. Darkness significantly reduced conidial formation and enhanced the transition of intermediates. The conidial germination and germ tube growth was strongly inhibited at 30°C. The suitable pH for conidial budding in malt-yeast broth (MYB) was between 5 and 9. At pH 2, 10 and 11, almost no new conidia were formed. The number of conidia reached 1.27 x 10 8 conidia/ml after 7 days in MYB, significantly more than that in potato dextrose broth, wheat leaf extract and H 2 O.

Development of an ID-ELISA for the detection of Riceblack-streakeddwarfvirus in plants

The Rice black-streaked dwarf virus (RBSDV) virion is composed of two layers of capsid proteins and 10 segments of double-stranded genomic RNA (S1–S10). Due to the fragility of the RBSDV outer capsid, it is very difficult to obtain intact virus particles for preparation of antiserum needed in virus detection. In this work, the major outer capsid protein (P10) encoded by S10 of RBSDV was expressed in Escherichia coli cells as a glutathione- S-transferase (GST) fusion protein. After purification of GST-P10 through affinity chromatography, P10 was released from the fusion protein by thrombin digestion and the purified P10 protein was used to immunize rabbits. The resulting polyclonal antiserum specifically recognized RBSDV from infected plant tissue and a planthopper vector in Western blotting assays. To facilitate screening of large numbers of samples, an indirect enzyme-linked immunosorbent assay (ID-ELISA) protocol capable of detecting RBSDV in very dilute wheat leaf extracts was developed. Based on the results, we conclude that efficient and economic detection of RBSDV can be performed routinely using polyclonal antiserum against P10 expressed in prokaryotic cells.

Allelopathy in two durum wheat ( Triticum durum L.) varieties

Two varieties of durum wheat ( Triticum durum L.), ‘Karim’ and ‘Om rabii’ commonly used in northern Tunisia were grown to maturity. Their allelopathic effects were measured in terms of germination rate and radicel length of a barley variety ‘Manel’ ( Hordeum vulgare L.) and a bread wheat variety ‘Ariana’ ( Triticum aestivum L.). Diluted extracts of roots, leaves and stems of durum wheat were applied to seeds of the test varieties. Leaf extracts of durum wheat depressed the germination rate, radicels also being susceptible to durum wheat extracts. The allelopathy of durum wheat varied with the source of extracts, leaf extracts being the most active. Results suggest that durum wheat allelopathy takes the form of heterotoxicity, depressive to crops in a sequence.

Physical features of grass leaves influence the placement of eggs within the plant by the Hessian fly

AbstractHessian fly eggs are more likely to be found on adaxial rather than abaxial surfaces of wheat leaves. These leaf surfaces differ in their physical features: the adaxial side of the leaf has parallel grooves and ridges while the abaxial side is relatively smooth. We used leaf models to investigate the relationship between Hessian fly egglaying and these physical features. When both sides of a green paper leaf model were treated with a wheat leaf extract, but only one side of the model was scored with parallel grooves, the grooved side received more eggs than the smooth side. As the number of grooves per surface increased from 0 to 10, eggs per model increased. When grooves and the wheat leaf extract were tested together and separately, the grooves significantly increased egg numbers in the presence, but not the absence, of wheat extract. In contrast, wheat extract increased egg numbers both in the absence and presence of grooves. Molding techniques were used to recreate the physical features of the adaxial and abaxial leaf surfaces of five grasses. For four of the grass genotypes (a triticale, two common wheats, and a durum wheat), patterns of egglaying on real leaves and molded models were similar, i.e., adaxial leaf surfaces and adaxial molded models were preferred over abaxial leaf surfaces and abaxial models. On the fifth grass, oat, preferences for the adaxial side of real leaves and for adaxial models were not as obvious. We conclude that the adult female Hessian fly obtains information about the leaf surface through her tactile and/or kinesthetic senses and uses this information when making egglaying decisions.

Capillary gel electrophoretic separation of superoxide dismutases in leaf extracts of Triticum aestivum L.

Capillary gel electrophoretic (CGE) separation of metal superoxide dismutase (SOD; EC 1.15.1.1) types is described. A mixture of standard SOD types was fully denatured into SDS–SOD complexes in the presence of excess sodium dodecylsulphate (SDS). The SDS–SOD complexes were separated using an uncoated fused silica capillary filled with a polymer running buffer and detected spectrophotometrically at 200 nm. Three types of SOD were separated, namely, Cu/ZnSOD (32 kDa), FeSOD (38 kDa) and MnSOD (40 kDa). Calibration curves were linear in the concentration range of 0.1–5.0 mg/mL with a detection limit in the order of 0.05 mg/mL. The reproducibility of the migration time was high with a relative standard deviation of less than 1.50%. The proposed method was demonstrated to be applicable to the separation of SOD types in leaf extracts of wheat. Copyright © 2000 John Wiley & Sons, Ltd.

The major β-amylase isoforms of wheat leaves correspond to one of two ubiquitously expressed β-amylase genes

Leaves of wheat (Triticum aestivum L.), cv. Star) exhibit five distinguishable isoforms of a β-amylase (EC 3.2.1.2) considered to represent the tissue-‘ubiquitous’ type of exohydrolase common to all cereals. The object of this study was to determine whether the multiple leaf isoforms originate from different genes or reflect post-translational processing of an isoform first expressed in juvenile leaf tissue. Two different cDNAs encoding for β-amylase were isolated from leaves and each produced an active β-amylase protein upon heterologous expression in Escherichia coli. Transcripts of these two genes were detected in tissues of wheat leaves, roots, flowers and seeds. However, only one of the two heterologously expressed β-amylases appeared to correspond to the β-amylase isoforms detectable in non-endosperm wheat tissues. It exhibited specific sequence identities with, and electrophoretic mobility under non-denaturing conditions similar to, the initially expressed leaf β-amylase isoforms. As does the initially in vivo expressed leaf isoform, the heterologously expressed β-amylase was converted by a β-amylase-free wheat leaf extract into secondary isoforms which closely resemble β-amylase isoforms appearing in vivo upon the maturation of leaf tissue. The molecular masses and the N-terminal amino acid sequences of the heterologously expressed β-amylase, its secondary conversion products and the extractable leaf β-amylases indicate that at least the major components of wheat leaf β-amylase polymorphism reflect C-terminal proteolytic processing of a single β-amylase translation product.

Ribonucleases in Leaves and Roots of Triticum durum and x Haynaldoticum sardoum Submitted to Low non Freezing Temperatures

In wheat leaf and root crude extracts several RNases can be distinguished by pH optima analysis, and SDS-PAGE and activity staining. One acidic RNase (approximately 20 kD in size) and a group of neutral RNases have been identified by electrophoretic separation. Neutral RNases can be divided into salt-stimu- lated (about 24 and 26 kD) and salt-inhibited (about 27kD). Following low temperature treatment, acidic and neutral salt-inhibited RNases remain unchanged, while the neutral salt-stimulated RNases with higher mobility generally increase with respect to the control.

Influence of the activation status and of ATP on phosphoribulokinase degradation

The light-regulated choroplast enzyme phosphoribulokinase (EC 2.7.1. 19) exists in two forms. In darkness this enzyme is present in an oxidized form, which is inactive. It is activated in the light by a thioredoxin-mediated reduction. In extracts from young wheat leaves (Triticum aestivum L.) phosphoribulokinase as well as some other thioredoxin-modulated enzymes can be activated by the artificial reductant dithiothreitol (DTT). The influence of the activation status and of the substrate ATP on phosphoribulokinase stability was investigated in the presence of endogenous endopeptidases from senescing wheat leaves. Similar experiments were performed with purified phosphoribulokinase from spinach in the presence of exogenous, purified endopeptidases (chymotrypsin and trypsin). Phosphoribulokinase stability was analysed by immunoblotting and activity measurements. Both systems led to similar conclusions. DTT (reductant) and ATP (substrate) stabilized phosphoribulokinase in wheat leaf extracts as well as partially purified phosphoribulokinase from spinach. The combination of both effectors was far more protective than either effector alone. DTT had hardly any effect on the degradation of thioredoxin-independent chloroplast enzymes such as glutamate synthase and glutamine synthetase. These results suggest that the activation status and substrate concentrations are not only important for the activity of phosphoribulokinase, but are also relevant for the susceptibility of this enzyme to proteolysis.

Comparison and differentiation of Wheat Yellow Mosaic Virus(WYMV), Wheat Spindle Streak Mosaic Virus (WSSMV) and Barley Yellow Mosaic Virus (BaYMV) isolates using WYMV monoclonal antibodies

Twelve monoclonal antibodies (MAbs) were obtained by immunizing mice with a French isolate (F1) of wheat yellow mosaic virus (WYMV). Three of these (3D12, 2C1, 6C3) belong to the IgM class and the nine others to the IgG class (3D8, 3H1, 2B8, 1F2, 3C10, 4F12, 3H9, 1G5, 54). In antigen-coated plate (ACP) ELISA and indirect double antibody sandwich (IDAS) ELISA, all MAbs recognize the WYMV (F1) both in the form of purified particles and in wheat leaf extract. The analysis of numerous French isolates of WYMV shows a variable reactivity with MAbs 3D8, 3H1, 2B8, 3C10, 3H9 and 1G5 in IDAS — and ACP-ELISA. The Japanese isolate of WYMV and United States isolates of wheat spindle streak mosaic virus (WSSMV) were detected in IDAS- and ACP-ELISA by ten of the MAbs tested showing that the wheat bymoviruses originating from the three locations share a high epitopic homology. French isolates of barley yellow mosaic virus (BaYMV; pathotypes 1 and 2) were only detected in ACP-ELISA with MAbs 6C3, 3D8, 3H1 and 2B8 whereas the two Japanese strains (I-1, II-1) of MaYMV were recognized with these and also with that of 3C10. In IDAS-ELISA, the two Japanese strains were clearly detected by MAbs, 6C3, 3D8, 3H1, 1F2, 3C10 and 1G5 and the British and Belgian (pathotype 2) isolates only by that of 6C3. Only the Japanese strain of BaYMV, 1-1 could be detected with MAb 3H9 in this ELISA system.

Integration of photosynthetic carbon and nitrogen metabolism in higher plants

Concomitant assimilation of C and N in illuminated leaves requires the regulated partitioning of reductant and photosynthate to sustain the demands of amino acid and carbohydrate biosynthesis. The short-term responses of photosynthesis and photosynthate partitioning to N enrichment in wheat (Triticum aestivum, L.) and maize (Zea mays L.) leaves were studied in order to understand the regulatory strategy employed in higher plants. Transgenic tobacco plants (Tobacco plumbaginifolia) over-expressing NR or with poor NR expression were used to compare plants differing in their capacities for NO3 (-) assimilation. Similar regulatory responses to NO3 (-) were observed in leaves having C4- and C3-type photosynthesis. It was shown that the extra- C needed in the short-term to sustain amino acid synthesis was not provided by an increase in photosynthetic CO2 fixation but rather by a rapid shift in the partitioning of photosynthetic C to amino acid at the expense of sucrose biosynthesis. The modulation of three enzymes was shown to be important in this C and N interaction, namely PEPCase (EC 4.1.1.31), SPS (EC 2.4.1.14) and NADH/NR (EC 1.6.6.1). The first two enzymes were shown to share the common feature of regulatory post-transcriptional NO3 (-)-dependent phosphorylation of their proteins on a seryl-residue. While PEPCase is activated, SPS activity is decreased. In contrast the NR phosphorylation state is unchanged and all N-dependent control of NR activity is regulated at the protein level. A number of arguments support the hypothesis that Gln, the primary product of NO3 (-) assimilation, is the metabolite effector for short-term modulation of PEPCase, and SPS in response to N enrichment. Since a major effect of NO3 (-) on the PEPCase-protein kinase activity in concentrated wheat leaf extracts was demonstrated, the hypothesis is put forward that protein phosphorylation is the primary event allowing the short-term adaptation of leaf C metabolism to changes in N supply.

A 5,10-methylenetetrahydrofolate dehydrogenase: 5,10-methenyltetrahydrofolate cyclohydrolase protein from Pisum sativum

A cytosolic protein, that exhibits NADP-dependent 5,10-methylenetetrahydrofolate dehydrogenase (EC 1.5.1.5) and 5,10-methenyltetrahydrofolate cyclohydrolase (EC 3.5.4.9) activities but lacks 10-formyltetrahydrofolate synthetase (EC 6.3.4.3) activity, was isolated from extracts of pea ( Pisum sativum L.) cotyledons and leaves. Dehydrogenase: cyclohydrolase activities co-purified when protein was fractionated by (NH 4) 2SO 4 precipitation, followed by chromatography on Sephacryl S-300, Matrex Green A and heparin agarose. The resulting protein ( M r 38 500) was apparently homogeneous after SDS-polyacrylamide gel electrophoresis and silver staining. Purified enzyme preparations lacked methylenetetrahydrofolate dehydrogenase activity when NAD replaced NADP in the reaction system. Attempts to sequence this protein suggested that it may be blocked at the N-terminus. Tryptic digestion of the purified protein resulted in coordinate losses of dehydrogenase and cyclohydrolase activity. The NADP provided significant protection of both enzyme activities during short-term treatments with trypsin but additions of 5,10-methylenetetrahydrofolate appeared to accentuate the proteolytic loss of dehydrogenase activity. The apparent Michaelis constants for NADP (11 μM) and methylenetetrahydrofolate (21 μM) in the dehydrogenase reaction were not changed significantly when the folylpentaglutamate substrate was provided (8 and 25 μM, respectively). The dehydrogenase and cyclohydrolase activities were competitively inhibited by dihydrofolates. The K i values of the dehydrogenase reaction indicated that the pentaglutamate derivative was a more potent inhibitor than dihydrofolate monoglutamate. The ELISA and Western blot analyses, using rabbit polyclonal antibodies raised against the purified enzyme, revealed cross-reactivity with proteins of similar molecular size in leaf extracts of wheat, barley, corn, bean and pea. Chromatography of these leaf extracts on Matrex Green A, in the presence of protease inhibitors, showed that 10-formyltetrahydrofolate synthetase was readily separated from protein with dehydrogenase and cyclohydrolase activity.

The absence of Rubisco activase activity in total wheat leaf extracts is recovered in the purified protein

When desalted extracts of soluble protein from dark-adapted wheat leaves were assayed for ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activase activity in the presence of 1 mM ATP and an ATP-regenerating system, very little ATP-dependent activation of RuBP-inactivated Rubisco was found. In extracts from light-adapted leaves a very similar pattern of Rubisco activation was observed except that the overall level of Rubisco activity was much lower than in the extracts from dark-adapted leaves. These features were apparent both at low (120 μg per ml) and high (640 μg per ml) protein concentrations. We were unable to demonstrate Rubisco activase activity in crude leaf extracts. Consequently, in order to establish that Rubisco activase was present in wheat leaf extracts the wheat leaf protein was purified to homogeneity. The identity of the protein was confirmed with antibodies to the spinach enzyme, ATPase activity and activase-mediated release of the inhibitor, carboxyarabinitol-1-phosphate (CA1P) from the tertiary Rubisco complex. The pure wheat Rubisco activase relieved the CA1P-induced inhibition of Rubisco activity. Rubisco activase had no significant effect on the affinity of wheat Rubisco for the substrate, ribulose-1,5-bisphosphate (RuBP).

In vitro production of pycnidia by Septoria tritici

The in vitro production of pycnidia bySeptoria tritici was examined on six media reported to induce the formation of fruiting bodies. Among 26 freshly isolated cultures from various parts of the world, consistent differences in growth type were found which were only partially influenced by nutritional and environmental conditions. Cultures with yeast-like growth produced hardly any pycnidia or pseudopycnidia, while cultures with intermediate or mycelial growth types produced them frequently. Incubation in continuous darkness induced intermediate to mycelial growth types rather than yeast-like growth types in some cultures, and concomitantly the production of more pycnidia. Potato-dextrose agar induced intermediate to mycelial growth types and production of (pseudo)pycnidia more often than V8 agar and wheat leaf extract agar, which had previously been reported to be especially beneficial to (pseudo) pycnidium formation byS. tritici. Isolates with a consistently yeast-like growth type, producing (virtually) no fructifications under any of the experimental conditions, were slightly stimulated to form pseudopycnidia on water agar supplemented with sterile pieces of maize, wheat or carnation leaves.

Plant protein phosphatases. Subcellular distribution, detection of protein phosphatase 2C and identification of protein phosphatase 2A as the major quinate dehydrogenase phosphatase

Protein phosphatases 1 and 2A (PP1 and PP2A) were identified in a variety of plant cells and found to be particulate or soluble depending on the species. In extracts prepared from oilseed-rape seeds these enzymes were associated with microsomes and more rapidly sedimenting fractions, whereas in wheat leaf extracts they were largely microsomal, the remainder being present in the soluble fraction. In pea leaf and carrot cell extracts PP1 and PP2A were almost entirely soluble. No PP1 or PP2A activity was associated with the membranes or stroma of chloroplasts in oilseed-rape seeds, pea leaves and wheat leaves. An Mg2(+)-dependent okadaic acid-insensitive protein phosphatase that resembles protein phosphatase 2C (PP2C) was detected in carrot cells, pea leaves and wheat leaves, but not in oilseed-rape seeds. In wheat leaf extracts PP2C was mostly present in the soluble fraction, a different location from PP1 or PP2A. The rapid inactivation of the cytosolic enzyme quinate dehydrogenase (QDH) in a fraction prepared from light-grown carrot cells was completely blocked by either okadaic acid or microcystin (two potent and specific inhibitors of PP1 and PP2A), whereas inhibitor 2 (a specific inhibitor of PP1) inhibited inactivation by only about 10%. Addition of the purified PP2A catalytic subunit from mammalian skeletal muscle increased the rate of QDH inactivation, whereas addition of mammalian PP1 did not. It is concluded that PP2A is the major enzyme responsible for dephosphorylating (inactivating) QDH in carrot cells. These observations indicate that okadaic acid and microcystin may be useful for identifying other plant processes that are controlled by phosphorylation/dephosphorylation mechanisms. Okadaic acid did not prevent the rapid inactivation of phosphoribulokinase or activation of glucose-6-phosphate dehydrogenase in a fraction prepared from light-grown pea leaves, and addition of the purified catalytic subunits of PP1 and PP2A did not accelerate either process. These observations, in conjunction with the absence of PP1 and PP2A activity in chloroplasts, suggest that these phosphatases are not involved in the regulation of chloroplast metabolism.