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Bundle Sheath Cells (bundle + sheath_cell)
Selected AbstractsImplication of the glutamine synthetase/glutamate synthase pathway in conditioning the amino acid metabolism in bundle sheath and mesophyll cells of maize leavesFEBS JOURNAL, Issue 12 2008Marie-Hélène Valadier We investigated the role of glutamine synthetases (cytosolic GS1 and chloroplast GS2) and glutamate synthases (ferredoxin-GOGAT and NADH-GOGAT) in the inorganic nitrogen assimilation and reassimilation into amino acids between bundle sheath cells and mesophyll cells for the remobilization of amino acids during the early phase of grain filling in Zea mays L. The plants responded to a light/dark cycle at the level of nitrate, ammonium and amino acids in the second leaf, upward from the primary ear, which acted as the source organ. The assimilation of ammonium issued from distinct pathways and amino acid synthesis were evaluated from the diurnal rhythms of the transcripts and the encoded enzyme activities of nitrate reductase, nitrite reductase, GS1, GS2, ferredoxin-GOGAT, NADH-GOGAT, NADH-glutamate dehydrogenase and asparagine synthetase. We discerned the specific role of the isoproteins of ferredoxin and ferredoxin:NADP+ oxidoreductase in providing ferredoxin-GOGAT with photoreduced or enzymatically reduced ferredoxin as the electron donor. The spatial distribution of ferredoxin-GOGAT supported its role in the nitrogen (re)assimilation and reallocation in bundle sheath cells and mesophyll cells of the source leaf. The diurnal nitrogen recycling within the plants took place via the specific amino acids in the phloem and xylem exudates. Taken together, we conclude that the GS1/ferredoxin-GOGAT cycle is the main pathway of inorganic nitrogen assimilation and recycling into glutamine and glutamate, and preconditions amino acid interconversion and remobilization. [source] Transgenic maize lines with cell-type specific expression of fluorescent proteins in plastidsPLANT BIOTECHNOLOGY JOURNAL, Issue 2 2010Amir Sattarzadeh Summary Plastid number and morphology vary dramatically between cell types and at different developmental stages. Furthermore, in C4 plants such as maize, chloroplast ultrastructure and biochemical functions are specialized in mesophyll and bundle sheath cells, which differentiate acropetally from the proplastid form in the leaf base. To develop visible markers for maize plastids, we have created a series of stable transgenics expressing fluorescent proteins fused to either the maize ubiquitin promoter, the mesophyll-specific phosphoenolpyruvate carboxylase (PepC) promoter, or the bundle sheath-specific Rubisco small subunit 1 (RbcS) promoter. Multiple independent events were examined and revealed that maize codon-optimized versions of YFP and GFP were particularly well expressed, and that expression was stably inherited. Plants carrying PepC promoter constructs exhibit YFP expression in mesophyll plastids and the RbcS promoter mediated expression in bundle sheath plastids. The PepC and RbcS promoter fusions also proved useful for identifying plastids in organs such as epidermis, silks, roots and trichomes. These tools will inform future plastid-related studies of wild-type and mutant maize plants and provide material from which different plastid types may be isolated. [source] Comparison of leaf structure and photosynthetic characteristics of C3 and C4Alloteropsis semialata subspeciesPLANT CELL & ENVIRONMENT, Issue 2 2006O. UENO ABSTRACT Alloteropsis semialata (R. Br.) Hitchcock includes both C3 and C4 subspecies: the C3 subspecies eckloniana and the C4 subspecies semialata. We examined the leaf structural and photosynthetic characteristics of these plants. A. semialata ssp. semialata showed high activities of photosynthetic enzymes involved in phosphoenolpyruvate carboxykinase-type C4 photosynthesis and an anomalous Kranz anatomy. Phosphoenolpyruvate carboxylase; pyruvate, Pi dikinase and glycine decarboxylase (GDC) were compartmentalized between the mesophyll (M) and inner bundle sheath cells, whereas ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) occurred in both cells. A. semialata ssp. eckloniana also showed an anomalous non-Kranz anatomy, in which the mestome sheath cells included abundant chloroplasts and mitochondria. Rubisco and GDC accumulated densely in the M and mestome sheath cells, whereas the levels of C4 enzymes were low. The activity levels of photorespiratory enzymes in both subspecies were intermediate between those in typical C3 and C4 plants. The values of CO2 compensation points in A. semialata ssp. semialata were within the C4 range, whereas those in A. semialata ssp. eckloniana were somewhat lower than the C3 range. These data suggest that the plants are C3 -like and C4 -like but not typical C3 and C4, and when integrated with previous findings, point to important variability in the expression of C4 physiology in this species complex. A. semialata is therefore an intriguing grass species with which to study the evolutionary linkage between C3 and C4 plants. [source] Utilization of O2 in the metabolic optimization of C4 photosynthesisPLANT CELL & ENVIRONMENT, Issue 1 2000J. P. Maroco ABSTRACT The combined effects of O2 on net rates of photosynthesis, photosystem II activity, steady-state pool size of key metabolites of photosynthetic metabolism in the C4 pathway, C3 pathway and C2 photorespiratory cycle and on growth were evaluated in the C4 species Amaranthus edulis and the C3 species Flaveria pringlei. Increasing O2 reduced net CO2 assimilation in F. pringlei due to an increased flux of C through the photorespiratory pathway. However, in A. edulis increasing O2 up to 5,10% stimulated photosynthesis. Analysis of the pool size of key metabolites in A. edulis suggests that while there is some O2 dependent photorespiration, O2 is required for maximizing C4 cycle activity to concentrate CO2 in bundle sheath cells. Therefore, the response of net photosynthesis to O2 in C4 plants may result from the balance of these two opposing effects. Under 21 versus 5% O2, growth of A. edulis was stimulated about 30% whereas that of F. pringlei was inhibited about 40%. 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