I. Intrazellulärer Transport von Zwischenprodukten der Photosynthese im Photosynthese-Gleichgewicht und im Dunkel-Licht-Dunkel-Wechsel

Abstract

1. The distribution -before, during and after photosynthesis -of different phosphate esters in chloroplasts and cytoplasm of leaf cells of spinach and Elodea has been investigated. In steady state experiments intact leaves were fed, during illumination, with 14 C02 . The kinetics of the distribution of labelled phosphate esters between chloroplasts and cytoplasm were determined. In further experiments with intact leaves fluctuations in the pool sizes of phosphate esters in chloroplasts and in the cytoplasm were recorded in the dark/light and the light/dark transient. Independent fluctuations served as an indication that little or no exchange between chloroplasts and cytoplasm takes place. Concomitant fluctuations suggest rapid exchange.2. Although labelling takes place in the chloroplasts, a number of labelled phosphorylated intermediates appear rapidly in the cytoplasm during steady state photosynthesis of intact leaves in the presence of 14 C02 . This is particularly true for phosphoglyceric acid, glucose-6-phosphate, fructose-6-phosphate and fructose-l,6-diphosphate. On the other hand, labelled ribulosediphosphate, sedoheptulosediphosphate and sedoheptulosemonophosphate remain largely in the chloroplasts. This agrees with earlier work on the behaviour of phosphorylated intermediates during the induction period of photosynthesis.3. In the dark the level of the bulk of the sugar diphosphates is lower in the chloroplasts than in the cytoplasm of intact leaves. On illumination, a large accumulation occurs only in the chloroplasts. This behaviour suggests impermeability of the chloroplast membrane towards at least some of the sugar diphosphates. In contrast, concomitant large fluctuations in the levels of dihydroxyacetonephosphate and fructose-l,6-diphosphate have been observed during the transients from dark to light and vice versa in chloroplasts and cytoplasm alike indicating that at least one of these compounds functions as a transport metabolite. Changes in the concentrations of glucose-6-phosphate and fructose-6-phosphate were much smaller under the influence of light than those of other sugar phosphates.4. The results demonstrate the role of phosphorylated transport metabolites in carbon metabolism in chloroplasts and cytoplasm. Implications of these findings in relation to photosynthesis, respiration and the regulation of metabolism are discussed. In vorangegangenen Arbeiten haben wir mit Hilfe von 14 C02 und 32 P04 39 die intrazelluläre Lokalisation und die Wanderung von Zwischenprodukten der Photosynthese im Verlauf der Induktionsphase näher untersucht 2 . Dabei ergab sich, daß bei 14 C02-Gabe im Dunkeln und anschließender Belichtung einige Intermediärprodukte der Photosynthese wie RuDP**, SuDP und SuMP auch über längere Versuchszeiten (4 Min.) 14 C-markiert ausschließlich oder fast ausschließlich in den Chloroplasten vorkommen, während andere Verbindungen wie PGS, * Gegenwärtige Adresse: University of Bristol, Dept. Agr.-and Horticulture, Res. St., Long Ashton, Bristol. ** Benutzte Abkürzungen: ADP, ATP ...

Role of Orthophosphate and Other Factors in the Regulation of Starch Formation in Leaves and Isolated Chloroplasts

“…In leaves, the concentration of triosephosphate remains very low in the chloroplasts even in the light. About 75% of the total PGA pool of the cells is located in the chloroplasts, but only about 35%o of the triosephosphate pool (12 59,1977 in situ was observed to be between about 0.005 and 0.02 in the light (recalculated from refs. 12 and 38), which is similar to the ratios found in isolated chloroplasts photosynthesizing in a medium at pH 7.6 (Table IV).…”

Determination of Compartmented Metabolite Pools by a Combination of Rapid Fractionation of Oat Mesophyll Protoplasts and Enzymic Cycling

“…Information on in vivo pool sizes of metabolites in various compartments is limited and mainly has been derived from nonaqueous fractionations of leaf tissue into chloroplast and extrachloroplast material (e.g. Heber and coworkers [11][12][13]29]). A better insight into mechanisms regulating mitochondrial respiration is only possible, however, when pool sizes of a wider range of metabolites within different cellular compartments are known.…”

“…Information on in vivo pool sizes of metabolites in various compartments is limited and mainly has been derived from nonaqueous fractionations of leaf tissue into chloroplast and extrachloroplast material (e.g. Heber and coworkers [11][12][13]29] Isolation of Protoplasts. Enzymic isolation and purification of protoplasts from 0.5-to 1-mm-wide leaf segments was carried out as reported earlier (6,9).…”

Effects of the Relative Extrachloroplastic Concentrations of Inorganic Phosphate, 3-Phosphoglycerate, and Dihydroxyacetone Phosphate on the Rate of Starch Synthesis in Isolated Spinach Chloroplasts

“…Since millimolar concentrations of Pi, PGA, and DAP have been estimated to be present in the cytoplasm (5,(14)(15)(16), I have investigated the effects of variations in both the absolute and relative concentrations of these metabolites on the rate of starch synthesis with isolated chloroplasts. I find that while CO2 fixation is unaffected by the relative concentrations of Pi, PGA, and DAP over a relatively broad range, starch synthesis is very sensitive to the relative concentrations of these metabolites.…”