scholarly journals Starch degradation in chloroplasts isolated from C3 or CAM (crassulacean acid metabolism)-induced Mesembryanthemum crystallinum L

1996 ◽  
Vol 318 (3) ◽  
pp. 945-953 ◽  
Author(s):  
H. Ekkehard NEUHAUS ◽  
Norbert SCHULTE
Keyword(s):  
Crassulacean Acid Metabolism ◽  
Metabolic Flux ◽  
Acid Metabolism ◽  
Starch Content ◽  
Pentose Phosphate ◽  
Mesembryanthemum Crystallinum ◽  
Starch Degradation ◽  
Dihydroxyacetone Phosphate ◽  
Phosphoglyceric Acid ◽  
Isolated Chloroplasts

C3 or crassulacean acid metabolism (CAM)-induced Mesembryanthemum crystallinum plants perform nocturnal starch degradation which is linear with time. To analyse the composition of metabolites released by isolated leaf chloroplasts during starch degradation we developed a protocol for the purification of starch-containing plastids. Isolated chloroplasts from C3 or CAM-induced M. crystallinum plants are also able to degrade starch. With respect to the endogenous starch content of isolated plastids the rate of starch degradation in these organelles is close to the observed rates of starch degradation in intact leaves. The combined presence of Pi, ATP, and oxaloacetate is identified to be the most positive effector combination to induce starch mobilization. The metabolic flux through the oxidative pentose-phosphate pathway in chloroplasts isolated from CAM-induced M. crystallinum is less than 3.5% compared with other metabolic routes of starch degradation. Here we report that starch-degrading chloroplasts isolated from CAM-induced M. crystallinum plants use exogenously supplied oxaloacetate for the synthesis of malate. The main products of starch degradation exported into the incubation medium by these chloroplasts are glucose 6-phosphate, 3-phosphoglyceric acid, dihydroxyacetone phosphate and glucose. The identification of glucose 6-phosphate as an important metabolite released during starch degradation is in contrast to the observations made on all other types of plastids analysed so far, including chloroplasts isolated from M. crystallinum in the C3 state. Therefore, we analysed the transport properties of isolated chloroplasts from M. crystallinum. Surprisingly, both types of chloroplasts, isolated from either C3 or CAM-induced plants, are able to transport glucose 6-phosphate in counter exchange with endogenous Pi, indicating the presence of a glucose 6-phosphate translocator as recently demonstrated to occur in other types of plastids. The composition of metabolites released and the stimulatory effect of oxaloacetate on the rate of starch degradation are discussed with respect to the acidification observed for CAM leaves during the night.

Verteilung und Wanderung von Phosphoglycerat zwischen den Chloroplasten und dem Cytoplasma während der Photosynthese

1965 ◽  
Vol 20 (9) ◽  
pp. 890-898 ◽  
Author(s):  
W. Urbach ◽  
M. A. Hudson ◽  
W. Ullrich ◽  
K. A. Santarius ◽  
U. Heber
Keyword(s):  
Turnover Rate ◽  
Rapid Decrease ◽  
Permeability Barrier ◽  
Dihydroxyacetone Phosphate ◽  
Cyanide Poisoning ◽  
Similar Extent ◽  
Slow Increase ◽  
Phosphoglyceric Acid ◽  
Inhibition Of Metabolism ◽  
Isolated Chloroplasts

The distribution of phosphoglyceric acid (PGA) * between chloroplasts and cytoplasm of leaf cells during transients from dark to light and vice versa has been investigated. The data indicate that pools of PGA in the chloroplasts and cytoplasm are interchangeable and that PGA may function as a transport metabolite in actively metabolising leaf cells. These views are supported by the following results:1. In the presence of 14CO2 and light, labelled PGA rapidly appears in the cytoplasm, even though the carboxydismutase reaction, in which 14C enters into PGA, proceeds in the chloroplasts.2. After less than 1 min. illumination in the presence of 14CO2, the distribution of labelled PGA between chloroplasts and cytoplasm reaches an equilibrium, which is then maintained. The same distribution is to be found by enzymatic analyses of the total pools of PGA in chloroplasts and cytoplasm. When equilibrium is reached, the percentages of both 14C labelled and of total PGA to be found in the chloroplasts of Spinach and Elodea are approximately 75% and 35 —40% respectively.3. In both the chloroplasts and the cytoplasm, the levels of PGA first decrease after illumination to a fraction of the original dark levels and then show a concomitant slow increase. On darkening a further very rapid increase in PGA occurs in chloroplasts and cytoplasm.4. In photosynthetically active leaf material the rate of decrease in the level of cytoplasmic PGA, as observed after 12 —15 secs. illumination, is higher than the turnover rate of PGA in respiration.5. Upon illumination, aqueously isolated chloroplasts, suspended in isotonic sucrose buffer, reduce added PGA to dihydroxyacetone phosphate and other products far faster than they reduce added NADP. Whereas PGA reduction is not increased by ultrasonic disintegration of the chloroplasts, the reduction of NADP is stimulated. This indicates that whereas the movement of NADP is prevented by a permeability barrier, the transferance of PGA across the chloroplast membrane occurs easily.6. In illuminated Elodea shoots the inhibition of metabolism by cyanide after 15 secs. photosynthesis in the presence of Η14CO3⊖ leads to a rapid decrease in PGA. This applies to both the 14C labelled PGA and the total PGA to a similar extent. The decrease in PGA amounts from 70 — 85% of the original dark levels. Since the chloroplasts of Elodea contain only 35—40% of the total PGA of the cell, a fall in the level of PGA as a result of the cyanide poisoning obviously occurs not only in the chloroplasts, but also in the cytoplasm. Since cyanide effectively inhibits cytochrome oxidase, while PGA reduction in the chloroplasts is relatively resistant, the large decrease in PGA suggests that part of the cytoplasmic PGA is transferred into the chloroplasts and reduced there.

scholarly journals Transcriptional profiles of organellar metabolite transporters during induction of crassulacean acid metabolism in Mesembryanthemum crystallinum

2005 ◽  
Vol 32 (5) ◽  
pp. 451 ◽  
Author(s):  
Shin Kore-eda ◽  
Chiyuki Noake ◽  
Masahisa Ohishi ◽  
Jun-ichi Ohnishi ◽  
John C. Cushman
Keyword(s):  
Crassulacean Acid Metabolism ◽  
Acid Metabolism ◽  
Expression Patterns ◽  
Transcript Abundance ◽  
Transport Processes ◽  
Mesembryanthemum Crystallinum ◽  
Water Deficit Stress ◽  
Diurnal Changes ◽  
Metabolite Transport ◽  
Leaf Tissues

Metabolite transport across multiple organellar compartments is essential for the operation of crassulacean acid metabolism (CAM). To investigate potential circadian regulation of inter-organellar metabolite transport processes, we have identified eight full-length cDNAs encoding an organellar triose phosphate / Pi translocator (McTPT1), a phosphoenolpyruvate / Pi translocator (McPPT1), two glucose-6-phosphate / Pi translocators (McGPT1, 2), two plastidic Pi translocator-like proteins (McPTL1, 2), two adenylate transporters (McANT1, 2), a dicarboxylate transporter (McDCT2), and a partial cDNA encoding a second dicarboxylate transporter (McDCT1) in the model CAM plant, Mesembryanthemum crystallinum L. We next investigated day / night changes in steady-state transcript abundance of each of these transporters in plants performing either C3 photosynthesis or CAM induced by salinity or water-deficit stress. We observed that the expression of both isogenes of the glucose-6-phosphate / Pi translocator (McGPT1, 2) was enhanced by CAM induction, with McGPT2 transcripts exhibiting much more pronounced diurnal changes in transcript abundance than McGPT1. Transcripts for McTPT1, McPPT1, and McDCT1 also exhibited more pronounced diurnal changes in abundance in the CAM mode relative to the C3 mode. McGPT2 and McDCT1 transcripts exhibited sustained oscillations for at least 3 d under constant light and temperature conditions suggesting their expression is under circadian clock control. McTPT1 and McGPT2 transcripts were preferentially expressed in leaf tissues in either C3 or CAM modes. The leaf-specific and / or circadian controlled gene expression patterns are consistent with McTPT1, McGPT2 and McDCT1 playing CAM-specific metabolite transport roles.

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