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 [3H]-H2O space of these organelles was studied using silicone layer filtering centrifugation on both fluorometric and 14C-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 [14C]sucrose gave comparable results. An ATPase activity dependent on both Mg2+ 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.

Accumulation of sucrose in vacuoles isolated from red beet tissue

Photosynthesis and translocation of photosynthetic products from symbiotic zooxanthellae in four species of temperate-latitude invertebrates were investigated in vivo and in vitro. In vivo, zooxanthellae fixed 14C and translocated a substantial proportion of fixed products to host tissues. In vitro, the effect of host tissue extracts on isolated zooxanthellae varied. Extracts of the soft coral Capnella gaboensis, lysed zooxanthellae after a relatively short exposure. Those of the zoanthid Zoanthus robustus and the nudibranch Pteraeolidia ianthina had little effect on translocation of organic carbon from zooxanthellae. In contrast, host extract of the scleractinian coral Plesiastrea versipora stimulated the release of up to 42% of the total 14C fixed, and the magnitude of release was positively correlated with the protein concentration of the extract. Host extracts had no effect on photosynthetic rates in algal symbionts. The effect of P. versipora extract on isolated zooxanthellae was studied. This extrac...

Host-Zooxanthella Interactions in Four Temperate Marine Invertebrate Symbioses: Assessment of Effect of Host Extracts on Symbionts.

In the plastids of Cuscuta reflexa the number of thylakoids is strongly reduced compared with true chloroplasts and no typical grana are visible. The plastids of Cuscuta europaea lack thylakoids and the stroma is filled with either starch grains or lipid droplets. In Cuscuta reflexa both chlorophylls are present in low concentrations, while in C. europaea chlorophylls are totally absent. Light slightly stimulates the incorporation of 14CO2 in C. reflexa. This is in accordance with a low activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) which was measured in extracts of this parasite. No stimulation of 14CO2 incorporation by light was observed in C. europaea. Instead, a relatively strong incorporation was measured in darkness. Malate and aspartate were the main products of this incorporation. In agreement with these results, no Rubisco activity was detected in C. europaea but there was a moderate activity of phosphoenolpyruvate-carboxylase. The presence of the genes for both subunits of Rubisco (rbcL, rbcS) and of the gene which codes for the 32-kDa protein of photosystem II (psbA) was established for C. europaea by hybridization experiments. In both species only very small amounts of transcripts of these genes were detected.

A structural, functional and molecular analysis of plastids of the holoparasites Cuscuta reflexa and Cuscuta europaea.

Uptake, translocation and metabolism of 14C-labelled formaldehyde in the leaves of Epipremnum aureum (Golden Potho) and Ficus benjamina (Weeping Fig) were investigated. Plants were exposed in light and dark to 14C-formaldehyde (500 μg m−3) in gas exposure chambers. The amount of 14C-incorporation into the soluble (water-extractable) and insoluble fractions of leaves, stem sections and roots was determined. The soluble 14C-activity was fractionated by ion exchange chromatography followed by thin-layer chromatography/autoradiography. Approximately 60–70% of the applied 14C-formaldehyde was recovered from the plants. In the light about five times more 14C-formaldehyde was assimilated than in the dark. The amount of 14C-label derived from 14C-formaldehyde, which was incorporated into acid-stable metabolites, was enhanced to an even larger extent in the light. The 14C-activity pattern closely resembled the general labelling spectrum of photosynthates, obtained after a 14CO2 exposure. A substantial amount of labelled material, mostly sucrose, was translocated into the stems and roots. Our results suggest that in the light 14C enters the Calvin cycle after an enzymatic two-step oxidation process of 14C-formaldehyde to 14CO2. The activities of the respective enzymes, formaldehyde dehydrogenase and formate dehydrogenase, were determined. Among 27 ‘leafy’ indoor decorative plants, a screening experiment revealed no outstanding species with regard to its capacity for metabolism of formaldehyde, and rate of uptake through stomata was too low to justify claims that plants contribute usefully to indoor air purification.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1046/j.1469-8137.2000.00701.x

Assimilation and metabolism of formaldehyde by leaves appear unlikely to be of value for indoor air purification

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.

B. Feige

Papers

Eine Methode zur Dünnschichtchromatographischen Auftrennung von 14C- und 32P-markierten Stoffwechselprodukten