Alanine Synthesis by Bundle Sheath Cells of Maize

Valle, Estela M.; Heldt, Hans W.

doi:10.1104/pp.95.3.839

Cited by 16 publications

(14 citation statements)

References 14 publications

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“…Recently, the permeability of isolated bundle-sheath cells from maize has been utilized to differentiate between possible pathways for alanine biosynthesis (Valle and Heldt 1991). In animal systems, channeling of glycolytic intermediates has been demonstrated using mouse L-929 cells permeabilized with dextran sulfate (Clegg and Jackson 1989).…”

Section: Discussionmentioning

confidence: 99%

Morphology and monoterpene biosynthetic capabilities of secretory cell clusters isolated from glandular trichomes of peppermint (Mentha piperita L.)

McCaskill

Gershenzon

Croteau

1992

Planta

157

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Secretory cells were isolated from the monoterpene-producing glandular trichomes (peltate form) of peppermint as clusters of eight cells each. These isolated structures were shown to be non-specifically permeable to low-molecular-weight, water-soluble cofactors and substrates. Short incubation periods with the polar dye Lucifer yellow iodoacetamide (Mr=660) resulted in a uniform staining of the cytoplasm, with exclusion of the dye from the vacuole. The molecular-weight exclusion limit for this permeability was shown to be less than approx. 1800, based on exclusion of fluorescein-conjugated dextran (Mr ∼ 1800). Intact secretory cell clusters very efficiently incorporated [(3)H]geranyl pyrophosphate into monoterpenes. The addition of exogenous cofactors and redox substrates affected the distribution of monoterpenes synthesized from [(3)H]geranyl pyrophosphate, demonstrating that the cell clusters were permeable to these compounds and that the levels of endogenous cofactors and redox substrates were depleted in the isolated cells. When provided with the appropriate cofactors, such as NADPH, NAD(+), ATP, ADP and coenzyme A, the isolated secretory cell clusters incorporated [(14)C]sucrose into monoterpenes, indicating that these structures are capable of the de-novo biosynthesis of monoterpenes from a primary carbon source, and that they maintain a high degree of metabolic competence in spite of their permeable nature.

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Section: Discussionmentioning

confidence: 99%

Morphology and monoterpene biosynthetic capabilities of secretory cell clusters isolated from glandular trichomes of peppermint (Mentha piperita L.)

McCaskill

Gershenzon

Croteau

1992

Planta

157

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“…Bundle-sheath strands consisting of a segment of vascular bundle surrounded by BSC of high functional integrity and metabolic competence can be obtained easily by blending leaf segments in an appropriate medium with a polytron (Valle and Heldt, 1991). The intact plasmodesmata that originally connected the bundle-sheath cytosol with MC are permeable to molecules up to a molecular mass of about 900 D (Valle et al, 1989).…”

Section: Discussionmentioning

confidence: 99%

“…Two grams of 1-mm leaf segments was blended in 16 mL of medium according to the method of Valle and Heldt (1991) in a polytron with 1-s (20,000 rpm) and 20-s (15,000 rpm) bursts. The bundle-sheath strands were collected on a 280-m nylon net, washed thoroughly, and resuspended at a level of approximately 50 g chlorophyll mL Ϫ1 resuspending medium (0.3 m sorbitol, 20 mm Tricine-KOH (pH 7.5), 4 mm MgCl 2 , 10 mm KCl, 2 mm KH 2 PO 4 , 1 mm ADP, 10 mm glycerate 3-phosphate, 5 mm glutamate, 5 mm malate, 2 mm O-acetyl-l-Ser, and 0.2 mm K 2 SO 4 ).…”

Section: S Labeling Of Isolated Bundle-sheath Strandsmentioning

confidence: 99%

Cyst(e)ine Is the Transport Metabolite of Assimilated Sulfur from Bundle-Sheath to Mesophyll Cells in Maize Leaves1

Burgener¹,

Suter²,

Jones³

et al. 1998

Plant Physiology

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The intercellular distribution of the enzymes and metabolites of assimilatory sulfate reduction and glutathione synthesis was analyzed in maize (Zea mays L. cv LG 9) leaves. Mesophyll cells and strands of bundle-sheath cells from second leaves of 11-d-old maize seedlings were obtained by two different mechanical-isolation methods. Cross-contamination of cell preparations was determined using ribulose bisphosphate carboxylase (EC 4.1.1.39) and nitrate reductase (EC 1.6.6.1) as marker enzymes for bundle-sheath and mesophyll cells, respectively. ATP sulfurylase (EC 2.7.7.4) and adenosine 5-phosphosulfate sulfotransferase activities were detected almost exclusively in the bundle-sheath cells, whereas GSH synthetase (EC 6.3.2.3) and cyst(e)ine, ␥-glutamylcysteine, and glutathione were located predominantly in the mesophyll cells. Feeding experiments using [35 S]sulfate with intact leaves indicated that cyst(e)ine was the transport metabolite of reduced sulfur from bundle-sheath to mesophyll cells. This result was corroborated by tracer experiments, which showed that isolated bundle-sheath strands fed with [ 35 S]sulfate secreted radioactive cyst(e)ine as the sole thiol into the resuspending medium. The results presented in this paper show that assimilatory sulfate reduction is restricted to the bundle-sheath cells, whereas the formation of glutathione takes place predominantly in the mesophyll cells, with cyst(e)ine functioning as a transport metabolite between the two cell types.

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“…3). Valle and Heldt (1991) measured similar activities of pyruvate kinase in BS strands of maize and concluded that these activities were not high enough to fully account for the formation of Ala from PEP. In addition, activities of pyruvate kinase in PEPCK-type species either are lower than rates of photosynthesis (Smith and Woolhouse, 1983) or are not detectable (Rathnam and Edwards, 1977).…”

Section: Photosynthetic Metabolism In Maizementioning

confidence: 99%

Phosphoenolpyruvate Carboxykinase Is Involved in the Decarboxylation of Aspartate in the Bundle Sheath of Maize1

et al. 1999

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We recently showed that maize (Zea mays L.) leaves contain appreciable amounts of phosphoenolpyruvate carboxykinase (PEPCK; R.P. Walker, R.M. Acheson, L.I. Técsi, R.C. Leegood [1997] Aust J Plant Physiol 24: 459-468). In the present study, we investigated the role of PEPCK in C 4 photosynthesis in maize. PEPCK activity and protein were enriched in extracts from bundle-sheath (BS) strands compared with whole-leaf extracts. Decarboxylation of [4-14 C]aspartate (Asp) by BS strands was dependent on the presence of 2-oxoglutarate and Mn 2؉ , was stimulated by ATP, was inhibited by the PEPCK-specific inhibitor 3-mercaptopicolinic acid, and was independent of illumination. The principal product of Asp metabolism was phosphoenolpyruvate, whereas pyruvate was a minor product. Decarboxylation of [4-14 C]malate was stimulated severalfold by Asp and 3-phosphoglycerate, was only slightly reduced in the absence of Mn 2؉ or in the presence of 3-mercaptopicolinic acid, and was light dependent. Our data show that decarboxylation of Asp and malate in BS cells of maize occurs via two different pathways: Whereas malate is mainly decarboxylated by NADPmalic enzyme, decarboxylation of Asp is dependent on the activity of PEPCK. C 4 plants have been classified as NADP-ME, NAD-ME, and PEPCK types, according to the major decarboxylase involved in the decarboxylation of C 4 acids in the BS cells Hatch et al., 1975). Maize (Zea mays) belongs to the NADP-ME subgroup of C 4 plants and possesses negligible activity of PEPCK, although suggested that some other NADP-ME species utilize PEPCK as an auxiliary decarboxylase. However, we showed previously that maize leaves contain large amounts of PEPCK (Walker et al., 1997), andFurumoto et al. (1999) identified a PEPCK gene from maize that is specifically expressed in BS cells. Other NADP-ME species such as Echinochloa colona, Echinochloa crus-galli, Digitaria sanguinalis, and Paspalum notatum also contain PEPCK, whereas PEPCK protein was not detectable in Sorghum bicolor, Saccharum officinarum, or Flaveria bidentis (Walker et al., 1997). The reason that the occurrence of PEPCK in these plants has been overlooked may be due to difficulties in measuring PEPCK activity (Walker et al., 1997) or to the lack of an antibody.PEPCK-type C 4 species mainly use Asp as the CO 2 donor and decarboxylate the oxaloacetate formed via the following reaction:In NADP-ME species such as maize, 14 CO 2 is initially incorporated into the C-4 position of malate and Asp (about 75% and 25%, respectively), and the C-4 of both is subsequently incorporated into other metabolites (Hatch, 1971; Morot-Gaudry and Farineau, 1978). Using isolated BS strands, Chapman and Hatch (1981) showed that BS cells of maize have a significant capacity to decarboxylate Asp, and they assumed that NADP-ME was responsible. In view of the occurrence of PEPCK in maize, the involvement of PEPCK in the decarboxylation of Asp appears more likely, because PEPCK can directly catalyze the decarboxylation of oxaloacetate formed from Asp without previous...

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Alanine Synthesis by Bundle Sheath Cells of Maize

Cited by 16 publications

References 14 publications

Morphology and monoterpene biosynthetic capabilities of secretory cell clusters isolated from glandular trichomes of peppermint (Mentha piperita L.)

Morphology and monoterpene biosynthetic capabilities of secretory cell clusters isolated from glandular trichomes of peppermint (Mentha piperita L.)

Cyst(e)ine Is the Transport Metabolite of Assimilated Sulfur from Bundle-Sheath to Mesophyll Cells in Maize Leaves1

Phosphoenolpyruvate Carboxykinase Is Involved in the Decarboxylation of Aspartate in the Bundle Sheath of Maize1

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