[A method for the thin-layer chromatographic separation of 14C and 32P labelled metabolic products]

Studies on a nudibranch that contains zooxanthellae. I. Photosynthesis, respiration and the translocation of newly fixed carbon by zooxanthellae in Pteraeolidia ianthina

Zooxanthellae of the genus Symbiodinium are present in the tissues of the aeolid nudibranch Pteraeolidia ianthina . Individuals with widely differing densities of zooxanthellae are found living off the mid-central coast of eastern Australia. Nudibranchs with low densities of zooxanthellae (0.02-0.5 x 10 6 cells mg -1 protein) are common in winter populations, whereas those with comparatively higher densities (1–3 x 10 6 cells mg -1 protein) are the most common form at other times of the year. Zooxanthellae at all densities in the host exhibit the capacity for photosynthesis, and they grow while resident in the host. The mitotic indices of the zooxanthellae were found to vary as a function of the population density of the algae in the host and were highest in those animals with the lowest densities of zooxanthellae. Oxygen flux was measured as a function of irradiance. Maximum photosynthetic capacity ( P max ), light utilization efficiency ( α ) and compensation irradiance ( I c ) varied between animals, although most of the variation was attributable to differences in the density of zooxanthellae between animals. P max and α were positively correlated with density ( r 2 = 0.82 and 0.88 respectively); I c exhibited an exponential decrease with the density of zooxanthellae in the host ( r 2 > 0.81). I c for animals with 1–2 x 10 6 cells mg-1 protein had values of I c between 30 and 50 μE m -2 s -1 (1 μE = 6 x 10 17 photons), similar to values of I c measured for shade-adapted corals in other studies. Between 25 and 50% of the total photosynthetic products synthesized over 1 h were shown to move from the alga to the animal in that hour. The total respiratory rate of the association was positively correlated with the density of zooxanthellae ( r 2 = 0.94). This relation was used to estimate the respiratory rate of a zooxanthella in vivo . Estimates were, however, unreasonably high; this result suggests that zooxanthellae may directly influence the respiratory rate of the host, possibly by increasing the supply of respiratory substrates.

Uridine 5'-diphospho-D-glucose-dependent vectorial sucrose synthesis in tonoplast vesicles of the storage hypocotyl of red beet (Beta vulgaris L. ssp. conditiva)

Tonoplast vesicles were prepared from red-beet (Beta vulgaris L. ssp. conditiva) hypocotyl tubers ("beetroot") known to store sucrose. Uptake experiments, employing uridine 5'-diphospho-[(14)C]glucose (UDP-[(14)C]glucose) showed the operation of an UDP-glucose-dependent group translocator for vectorial synthesis and accumulation of sucrose, recently described for sugarcane and red-beet vacuoles and for tonoplast vesicles prepared from sugarcane suspension cells. Characterization of the kinetic properties yielded the following results. Uptake of UDP-glucose was linear for 15 min. The apparent K m was 0.75 mM for UDP-glucose (at pH 7.2, 1 mM Mg(2+)), V max was 32 nmol·(mg protein)(-1)·min(-1). The incorporation of UDP-glucose exhibited a sigmoidal substrate-saturation curve in the absence of Mg(2+), the Hill coefficient (n H) was 1.33; Michaelis-Menten kinetics were obtained, however, in the presence of 1 mM MgCl2. For the reaction sequence under the control of the group translocator a dual pH optimum was found at pH 7.2 and 7.9, respectively. All reaction intermediates and the end product sucrose could be identified by two-dimensional high-performance thin-layer chromatography and autoradiography. The distribution pattern of radioactivity showed almost uniformly high labeling of all intermediates and sucrose. The physiological relevance of the results is discussed in the light of the fact that the tonoplast of red-beet storage cells accommodates two mechanisms of sucrose uptake (i) vectorial sucrose synthesis and (ii) direct ATP-dependent sucrose assimilation.

The role of malate in ammonia assimilation in cotyledons of radish (Raphanus sativus L.)

The relationships between the metabolism of malate, nitrogen assimilation and biosynthesis of amino acids in response to different nitrogen sources (nitrate and ammonium) have been examined in cotyledons of radish (Raphanus sativus L.). Measurements of the activities of some key enzymes and pulse-chase experiments with [(14)C]malate indicate the operation of an anaplerotic pathway for malate, which is involved in the synthesis of glutamine during increased ammonia assimilation. It is most likely that the tricarboxylicacid cycle is supplied with carbon through entry of malate, formed via the phosphoenolpyruvate (PEP)-carboxylation pathway, when 2-oxoglutarate leaves the cycle to serve as precursor for an increased synthesis of glutamine via glutamate. This might occur predominantly in the cytosol via the activity of the glutamine synthetase/glutamate synthase (GS/GOGAT) cycle, the NADH-dependent GOGAT being the rate-limiting activity.

Characterization of the glutamate/aspartate-transport system in a symbiotic Nostoc sp

The permeability properties of the cell membrane of a symbiotic Nostoc sp. for glutamate and aspartate were investigated. These compounds were translocated across the plasmalemma by a transport system which showed a very high affinity for glutamate and a lower one for aspartate. Since a concomitant release of glutamate was observed during the uptake of these two amino acids it is concluded that the transport proceeds via a counterexchange mechanism. In addition to this counterexchange a net release of glutamate occurred in the dark. Some aspects concerning the possible function of this transport system in the symbiotic association Geosiphon pyriforme are discussed.

Tissue-distribution of secondary phenolic biosynthesis in developing primary leaves of Avena sativa L

Primary leaves of oats (Avena sativa L.) have been used to study the integration of secondary phenolic metabolism into organ differentiation and development. In particular, the tissue-specific distribution of products and enzymes involved in their biosynthesis has been investigated. C-Glucosylflavones along with minor amounts of hydroxycinnamic-acid esters constitute the soluble phenolic compounds in these leaves. In addition, considerable amounts of insoluble products such as lignin and wall-bound ferulic-acid esters are formed. The tissue-specific activities of seven enzymes were determined in different stages of leaf growth. The rate-limiting enzyme of flavonoid biosynthesis in this system, chalcone synthase, together with chalcone isomerase (EC 5.5.1.6) and the terminal enzymes of the vitexin and isovitexin branches of the pathway (a flavonoid O-methyltransferase and an isovitexin arabinosyltransferase) are located in the leaf mesophyll. Since the flavonoids accumulate predominantly (up to 70%) in both epidermal layers, an intercellular transport of products is postulated. In contrast to the flavonoid enzymes, L-phenylalanine ammonia-lyase (EC 4.3.1.5), 4-coumarate: CoA ligase (EC 6.2.1.12), and S-adenosyl-L-methionine: caffeate 3-O-methyltransferase (EC 2.1.1.-), all involved in general phenylpropanoid metabolism, showed highest activities in the basal leaf region as well as in the epidermis and the vascular bundles. We suggest that these latter enzymes participate mainly in the biosynthesis of non-flavonoid phenolic products, such as lignin in the xylem tissue and wall-bound hydroxycinnamic acid-esters in epidermal, phloem, and sclerenchyma tissues.

Plastid ultrastructure and photosynthesis in greening petaloid hypsophylls

The ultrastructural and biochemicalphysiological aspects of postfloral greening have been studied in hypsophylls of Heliconia aurantiaca Ghiesbr., Guzmania cf. x magnifica Richter and Spathiphyllum wallisii Regel. In all three species the greening of the hypsophylls is due to plastid transformation, chloroplast formation proceeding from the initially different types of plastids. The degradation process of the original plastid structures and the mode of thylakoid formation are distinct in each case. In none of the species do the transformed plastids look identical to the chloroplasts of the corresponding foliage leaves. On a chlorophyll basis, the rate of photosynthesis of the greened hypsophylls surpasses the rate of the leaves considerably in Spathiphyllum, but is much lower in Heliconia (no data for Guzmania). In all species, anatomy, plastid structure, pigments, 77° K-fluorescence emission, ribulose-1,5-bis-phosphate carboxylase activities and short-term photosynthesis (14)CO2-assimilation patterns prove the greened hypsophylls to be capable of providing additional carbon to the developing fruits, thus supplementing the import of organic matter from the foliage leaves.

Isolated heterocysts of Anabaena variabilis synthesize envelope polysaccharide

Isolated heterocysts, incubated for 1 h at 30 degrees C [14C]mannose, synthesize [14C]arabinose and [14C]glucose, and incorporate the three 14C-labeled sugars into their envelopes with glycosidic linkages characteristic of their envelope polysaccharide. In extracts of metabolic intermediates with hot 80% methanol, [14C]mannose is associated with the nucleotide GDP and [14C]glucose and [14C]arabinose with UDP. Chloroform/methanolic extracts of the heterocysts contain phosphoglycolipids in which 14C-labeled mannose, arabinose, and glucose are present. The lipids have the same as dolichol phosphate mannose under varying chromatographic conditions, RF and like polyisoprenol monophosphate glycolipids are stable to treatment with mild alkali but labile to mild acid hydrolysis. If bacitracin is added to the incubation mixture, 14C-labeled nucleotide sugars accumulate, but incorporation of 14C into envelope polysaccharide is greatly diminished. This observation supports the interpretation that polyisoprenol phosphoglycolipids are intermediates in the biosynthesis of this polysaccharide.

Nitrogenase activity and dark CO2 fixation in the lichen Peltigera aphthosa Willd

The lichen Peltigera aphthosa consists of a fungus and green alga (Coccomyxa) in the main thallus and of a Nostoc located in superficial packets, intermixed with fungus, called cephalodia. Dark nitrogenase activity (acetylene reduction) of lichen discs (of alga, fungus and Nostoc) and of excised cephalodia was sustained at higher rates and for longer than was the dark nitrogenase activity of the isolated Nostoc growing exponentially. Dark nitrogenase activity of the symbiotic Nostoc was supported by the catabolism of polyglucose accumulated in the ligh and which in darkness served to supply ATP and reductant. The decrease in glucose content of the cephalodia paralleled the decline in dark nitrogenase activity in the presence of CO2; in the absence of CO2 dark nitrogenase activity declined faster although the rate of glucose loss was similar in the presence and absence of CO2. Dark CO2 fixation, which after 30 min in darkness represented 17 and 20% of the light rates of discs and cephalodia, respectively, also facilitated dark nitrogenase activity. The isolated Nostoc, the Coccomyxa and the excised fungus all fixed CO2 in the dark; in the lichen most dark CO2 fixation was probably due to the fungus. Kinetic studies using discs or cephalodia showed highest initial incorporation of (14)CO2 in the dark in to oxaloacetate, aspartate, malate and fumarate; incorporation in to alanine and citrulline was low; incorporation in to sugar phosphates, phosphoglyceric acid and sugar alcohols was not significant. Substantial activities of the enzymes phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31) and carbamoyl-phosphate synthase (EC 2.7.2.5 and 2.7.2.9) were detected but the activities of PEP carboxykinase (EC 4.1.1.49) and PEP carboxyphosphotransferase (EC 4.1.1.38) were negligible. In the dark nitrogenase activity by the cephalodia, but not by the free-living Nostoc, declined more rapidly in the absence than in the presence of CO2 in the gas phase. Exogenous NH 4 (+) inhibited nitrogenase activity by cephalodia in the dark especially in the absence of CO2 but had no effect in the light. The overall data suggest that in the lichen dark CO2 fixation by the fungus may provide carbon skeletons which accept NH 4 (+) released by the cyanobacterium and that in the absence of CO2, NH 4 (+) directly, or indirectly via a mechanism which involves glutamine synthetase, inhibits nitrogenase activity.

CO2 and malate metabolism in starch-containing and starch-lacking guard-cell protoplasts

Isolated, purified mesophyll and guard-cell protoplasts of Vicia faba L. and Allium cepa L. were exposed to (14)CO2 in the light and in the dark. The guard-cell protoplasts of Vicia and Allium did not show any labeling in phosphorylated products of the Calvin cycle, thus appearing to lack the ability to reduce CO2 photosynthetically. In Vicia, high amounts of radioactivity (35%) appeared in starch after 60-s pulses of (14)CO2 both in the light and in the dark. Presumably, the (14)CO2 is fixed into the malate via PEP carboxylase and then metabolized into starch as the final product of gluconeogenesis. This is supported by the fact that guard-cell protoplasts exposed to malic acid uniformly labeled with (14)CO2 showed high amounts of labeled starch after the incubation, whereas cells labeled with [4-(14)C]malate had minimal amounts of labeled starch (1/120).In contrast, the starch-deficient Allium, guard-cell protoplasts did not show any significant (14)CO2 fixation. However, adding PEP to an homogenate stimulated (14)CO2 uptake, thus supporting the interpretation that the presence of starch as a source of PEP is necessary for incorporating CO2 and delivering malate. With starch-containing Vicia guard-cell protoplasts, the correlation between changes in volume and the interconversion of malate and starch was demonstrated. It was shown that the rapid gluconeogenic conversion of malate into starch prevents an increase of the volume of the protoplasts, whereas the degradation of starch to malate is accompanied by a swelling of the protoplasts.

Accumulation of sucrose in vacuoles isolated from red beet tissue

Vacuoles were isolated from red beets (Beta vulgaris L.) by slicing the tissue and separated using a discontinuous dextran gradient centrifugation. The uptake of sucrose against a concentration gradient into the dextran-impermeable [(3)H]-H2O space of these organelles was studied using silicone layer filtering centrifugation on both fluorometric and (14)C-measurement of sucrose. The rate is 24 nmol sucrose (unit betacyanin)(-1) h(-1) and appears to be stimulated by ATP to an uptake rate of 34 nmol. Control experiments with slices cut from red beet tissue and incubated with [(14)C]sucrose gave comparable results. An ATPase activity dependent on both Mg(2+) and K(+) seems to be localized at the inner surface of the tonoplast. This activity is strongly inhibited by EDAC and tartrate and there is no effect of oligomycin, whereas a slight stimulation was caused by DCCD.

Carbon assimilation by different developmental stages of Laminaria saccharina

Various stages of the life cycle of the marine brown alga Laminaria saccharina (L.) Lamour. (Laminariales, Phaeophyta) including male and female gametophytes, female gametes, zygotes and young sporophytes of different age were investigated for their potentials of carbon dioxide ((14)CO2) fixation. Rates of photosynthesis attain the same order of magnitude in all stages. Photosynthetic (14)CO2-fixation is accompanied by a substantial light independent carbon assimilation. This is confirmed by rate determinations of the equivalent carboxylating enzymes present in the plants, ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39) and phosphoenolpyruvate carboxokinase (EC 4.1.1.32) as well as by chromatographic analyses of the appropriate [(14)C]-assimilate patterns.

Sulfite: Preferential sulfur source and modifier of CO2 fixation in Chlorella vulgaris

Sulfite was added at the time of inoculation to a standard and to a sulfate deficient medium of Chlorella vulgaris. It was not only used as a sulfur source, but besides this, at concentrations <1.0 mmol l(-1), the growth yield was enhanced up to 30% compared to sulfate saturated conditions. Higher sulfite concentrations increasingly inhibited cell growth. Growth rate determinations indicated that the enhancement, and the inhibition respectively, were confined to the very beginning of culture growth; the time period during which the sulfite was not yet oxidized (5-10 h). In contrast, an increased CO2 fixation rate/unit of protein, occurring up to 5.0 mmol l(-1) sulfite and a shift towards the β-carboxylation pathway, are persisting at least during the growth period of 4 days. The preferential uptake of sulfite, also indicated by a marked increase in methionine content of algal protein, presumably causes an increase in thylakoidal sulfolipids, and is such modifying the CO2 fixation.

Effect of phosphon-D on photosynthetic light reactions and on reactions of the oxidative and reductive pentose phosphate cycle in a reconstituted spinach (Spinacia oleracea L.) chloroplast system

Phosphon-D (tributyl-2, 4-dichlorobenzylphosphonium chloride), known as an inhibitor of gibberellin biosynthesis, enhances photosynthetic electron transport by up to 200%, with Fe(CN) 6 (3-) and NADP(+) being the electron acceptors. Maximum stimulation is reached at phosphon-D concentrations around 2-5 μM. At the same time photosynthetic ATP formation is gradually inhibited. Phosphon-D concentrations over 0.1 mM inhibit electron transport. The uncoupling activity of phosphon-D is manifested by inhibition of noncyclic ATP synthesis and by stimulation of light-induced electron flow. The inhibition of ATP synthesis drastically decreases photosynthetic carbon assimilation in a reconstituted spinach chloroplast system. The two ATP-dependent kinase reactions of the reductive pentose phosphate cycle become the rate-limiting steps. On the other hand a stimulated photoelectron transport increases the NADPH/NADP(+) ratio, resulting in a drastic inhibition of chloroplast glucose-6-phosphate dehydrogenase (EC 1.1.1.49), the key enzyme of the oxidative pentose phosphate cycle. When light-induced electron flow is inhibited by high phosphon-D concentrations and the NADPH/NADP(+) ratio is low, the light-dependent inhibition of glucose-6-phosphate dehydrogenase is gradually abolished.

Isolation and identification of soluble polysaccharides in epidermal tissue of Allium cepa

Because starch is absent from Allium-guard cells, another polysaccharide was sought that, in connection with stomatal opening, could be a source of organic anions. Analysis of isolated polysaccharides revealed xylose, arabinose, glucose, galactose, and galacturonic acid (3.4:1:1.6:0.7) to be components of the water-soluble mucilage of the epidermal strips of Allium cepa. However, the experiments gave no indication that the mucilage is the malate donator during the stomatal opening. After (14)CO2 fixation the following substances were labeled: organic acids, especially malate and citrate, amino acids and the polysaccharide mentioned above; radioactive 3-phosphoglyceric acid and sugar phosphates were not found. Therefore we conclude that the Calvin cycle does not operate in the guard cells of Allium cepa.

Dark fixation of CO2 by flowers of cut roses

Complete flower heads of cut roses (cv. Baccara) were exposed to (14)CO2 for 1-4 h. The flower tissue was able to fix CO2 via PEP carboxylase (E.C. 4.1.1.31) in the dark; various TCA products were identified in petals, ovary and anthers, including malate, aspartate, citrate, serine/glycine, glutamate and asparagine. The concentrations of these labelled products were similar in the petals and anthers, but lower in the ovary. After removal of the petals the amounts of these components were reduced in the anthers to a relatively high extent (to 1/6), whereas the amounts in the ovary increased slightly. It is suggested that the petals are necessary for supplying the anthers with the described components.

[Enhancement of pyruvate kinase activity by blue light or glucose in a chlorophyll-free Chlorella-mutant]

Crude extracts of dark-kept resting cells of a chlorophyll-free, carotenoid-containing mutant of Chlorella vulgaris Beijerinck (211-11h/20) were found to convert 14.44±0.77 nmol PEP per min and mg protein into pyruvate by the action of pyruvate kinase (=PK; EC 2.7.1.40). When such cells were exposed to blue light (λ<550 nm, ∼300 μW cm(-2)) for 3 hrs the PK-activity/protein of their crude extracts rose to 21.47±1.30, i.e., it was enhanced by 43%. Poisoning with 10(-3) mol cycloheximide or with 150 μg actinomycin D/ml prevented the effect of blue light by 80-90% (Table 1). This result points to an induction of enzyme synthesis in blue light. Addition of 1% glucose in the dark resulted in an increase in PK-activity, too. Three hrs after application of glucose the PK-activity was 28.05±1.88 nmol/min and mg protein, which was 94% greater than in the control. The effect of glucose was also largely preventable by cycloheximide (10(-3) mol) or by actinomycin D (150 μg/ml) (Table 2). These results lead to the conclusion that blue light may induce the synthesis of PK by supplying free sugars at the site of enzyme synthesis. The assumption is supported by the observation that in hot water extracts of blue illuminated cells in which glucose oxidation had been poisoned by. 10(-2) mol monoiodoacetic acid there was 60% more glucose, glucose-6-phosphate, fructose-6-phosphate and sucrose detectable than in extracts of equally poisoned algae from darkness (Table 3). It is suggested that blue light activates a system for the transport of sugar out of the chloroplast, which results in the induction of respiratory enzyme synthesis and thus in enhanced respiration.

Experiments on enzymatic acylation of sn-glycerol 3-phosphate with enzyme preparations from pea and spinach leaves

Optimal reaction conditions were investigated for acylation of sn-[U-(14)C]glycerol 3-phosphate in cell-free systems from leaves of Pisum sativum L. and Spinacia oleracea L. With palmitoyl-CoA as acyl donor the major product formed was monoacyl glycerol phosphate. In pea seedlings enzymatic activity was found to be dependent on the age of shoots going through a maximum 12 days after planting. In such plants the highest enzymatic activity is found in leaves and not in the shoot apex. Also in leaves activity varies according to the age of these organs. In leaves of maximal activity the highest total and specific activity was found in soluble proteins from chloroplasts. In older pea and spinach leaves higher activities were observed in membranes from chloroplasts and microsomes.

(14)C-Assimilate pattern and kinetics of photosynthetic (14)CO 2-assimilation of the marine red alga Bostrychia scorpioides

Occurrence and metabolism of dulcitol and sorbitol in the marine red alga Bostrychia scorpioides (Huds.) Mont. (Ceramiales: Rhodomelaceae) were investigated. Both hexitols are rapidly (14)C-labelled during photosynthesis in a H(14)CO3-seawater medium and are accumulated at comparable rates. The absolute quantity amounts to about 3.2% on a dry weight basis; the percentage of (14)C-labelling after 60 min is 30% for dulcitol and 40% for sorbitol. Additionally small amounts of free [(14)C] glucose were found. Pulse labelling experiments and changes in specific activity provide evidence that both hexitols are rapidly available respiratory substrates, which, however, are probably not interconvertible with polymeric compounds. Some chemotaxonomic aspects are discussed.

[Regulation of development and metabolism of the green algae Urospora by temperature]

In the life cycle of Urospora wormskioldii (Mert. in Hornem) Rosenv. and U. vancouveriana (Tilden) Setschell and Gardner unbranched monosiphonous filaments (exceeding 15 cm in length) alternate with microscopic dwarf plants and a unicellular Codiolum stage. The interrelationship between these very different forms and the regulating effect of temperature on this life cycle are shown in Fig. 1. Beyond the morphological differences between the three forms there are large differences in the composition of the cell wall (Fig. 2). While the cell wall of the Codiolum stage is mainly built up of mannans, glucose-containing polysaccharides predominate in the cell wall of the dwarf plants and xylose-containing polysaccharides are abundant in the cell wall of the filamentous plants. Differences in metabolism between dwarf plants and filamentous plants were detected by (14)CO2-incorporating experiments. On the basis of chlorophyll content dwarf plants have a higher total (14)CO2-fixation rate than filamentous plants cultured at either 2°C or 14°C (Fig. 3). Furthermore, a higher rate of synthesis for Calvin-cycle intermediates and other metabolites was generally demonstrated in dwarf plants with one important exception: Uridine diphosphate glucose was synthesized faster in filamentous plants cultured at 2° C (Fig. 4). Studies of (14)CO2-incorporation in filamentous plants cultivated at 2° C or 14° C (at the higher temperature filamentous plants survive only for a limited time) revealed that the latter show a much higher incorporation of (14)C into insoluble substances than the former. On the other hand, pools of soluble substances - especially Calvin-cycle intermediates - are much smaller in 14° C-plants than in 2° C-plants with the exception of that of sucrose, which is accumulated in 14° C-plants in high amounts (more than 70% of the total radioactivity in soluble compounds, Fig. 5). These facts may be explained by temperature-sensitive differential gene expression and/or steps in metabolism (see discussion).