Uptake, translocation and metabolism of "%C-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 "%C-formaldehyde (500 µg m −$ ) in gas exposure chambers. The amount of "%C-incorporation into the soluble (waterextractable) and insoluble fractions of leaves, stem sections and roots was determined. The soluble "%C-activity was fractionated by ion exchange chromatography followed by thin-layer chromatography\autoradiography. Approximately 60-70% of the applied "%C-formaldehyde was recovered from the plants. In the light about five times more "%C-formaldehyde was assimilated than in the dark. The amount of "%C-label derived from "%C-formaldehyde, which was incorporated into acid-stable metabolites, was enhanced to an even larger extent in the light. The "%C-activity pattern closely resembled the general labelling spectrum of photosynthates, obtained after a "%CO # exposure. A substantial amount of labelled material, mostly sucrose, was translocated into the stems and roots. Our results suggest that in the light "%C enters the Calvin cycle after an enzymatic two-step oxidation process of "%C-formaldehyde to "%CO # . 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.

The patterns of seasonal variation of enzyme levels in the brown alga Laminaria hyperborea (Gunn.) Fosl. have been investigated for the following enzymes: Ribulosebisphosphate-carboxylase (EC 4.1.1.39), phosphoenolpyruvate-carboxykinase (EC 4.1.1.32), glyceraldehyde-3-phosphate-dehydrogenase (NADP dep., EC 1.2.1.12), malate-dehydrogenase (NAD dep., EC 1.1.1.37), L-aspartate-2-oxoglutarate aminotransferase (EC 2.6.1.1), and mannitol-l-phosphate-dehydrogenase (EC 1.1.1.17). The first four enzymes exhibit a circannual periodicity, characterized by a pronounced 'spring-maximum' of enzyme activity in April and May. As a consequence, the phylloid can maintain high metabolic rates from early spring on, although water temperature has then only slightly risen above the annual minimum. This findings is discussed in relationship to the growth- and developmental cycle of L. hyperborea and to the seasonal variation of photosynthesis and light-independent CO2-fixation. The seasonal pattern, outlined above, correlates well with the circannual fluctuations of the nitrogen content of the sea and with the variation of the internal nitrogen- and nitrate-content of the alga. This coincidence may indicate that nitrogen levels play an important role in the regulation of enzyme activities and, hence, the metabolic capacities of L. hyperborea.

The growth rate of Laminaria saccharina (L.) Lamour. is dependent on inorganic nitrogen in culture. Growth rates were saturated between 5 and 10 μmol · L−1 nitrate. The activities of ribulose‐1,5 bisphosphate carboxylase, phosphoenolpyruvate carboxykinase, mannitol‐1‐phosphate dehydrogenase, nitrate reductase and glutamine synthetase also varied with the concentration of inorganic nitrogen in the medium. All enzyme activities were lowest at 2.5 μmol · L−1 nitrate (the lowest concentration used) increasing to a maximum activity between 10 and 30 μmol · L−1 nitrate. Most enzyme activities followed a hyperbolic curve resembling those described by the Michaelis‐Menten equation, with different half‐saturation constants.

The optimum temperature of protein synthesis in wheat seedlings (Triticum aestivum L.), measured as (14)C-leucine incorporation, depends on the growing temperature. Plants grown at reduced temperature (4 C) reach their optimum at 27.5 C, whereas plants kept at 36 C have the highest rate of protein synthesis at 35 C. The transition is gradual. The activation energy of protein synthesis for seedlings grown at medium or reduced temperature is lower (about 11 kcal/mole), than for plants grown at higher temperatures (15 keal/mole). The decline of the rate of protein synthesis beyond the temperature optimum is also affected by the growth temperature; only plants kept at 30 or 36 C show a sharp decrease with increasing slope; plants kept at 4, 10, and 20 C exhibit a linear and comparatively moderate decline.

The translational efficiency of wheat ribosomes was studied as a function of an in vivo temperature pretreatment of wheat seedlings (Triticum aestivum L.). Ribosomes were isolated from heat-pretreated (36°C) and reference (4°C, 20°C) wheat seedlings. The efficiency of the ribosomes in translating polyuridylic acid was assayed. Ribosomes from heat-pretreated seedlings exhibit a threefold enhanced incorporation rate of phenylalanine as compared to ribosomes from wheat seedlings adapted to 20 or 4°C. This difference develops within 24 hours after onset of the heat treatment of seedlings following a 3 hour lag phase. The temperature induced changes can be traced back to the cytoplasmic ribosomes, since cycloheximide inhibits translation almost completely. Thermal inactivation of ribosomes occurs at 45°C, irrespective of the temperature pretreatment of the wheat seedlings. Specific differences in the yield of ribosomes, in the polyribosomal profiles, and in the apparent Arrhenius' activation energy of protein synthesis were observed depending on the age and the temperature pretreatments. The results presented here are considered an important molecular correlation to phenotypical temperature adaptation of in vivo protein synthesis in wheat (M Weidner, C Mathee, FK Schmitz 1982 Plant Physiol 69: 1281-1288 FEHLING AND WEIDNERFor fractionation of polyribosomes 7 d old wheat seedlings were temperature-treated at 4, 20, or 36°C for 24 h. Extraction was performed as described previously, except that the time for ultracentrifugation was set at 75 min. The ribosomal pellet was rinsed once and suspended in 0.5 ml of 40 mM Tris-HCl (pH 8.5), containing 20 mm KCl and 10mM MgCl2. Seven A260-units of ribosomal material were layered on a 100 to 500 mg-ml-' sucrose gradient (in Tris-buffer) and centrifuged at 188,000gavfor 65 min in a Beckman rotor SW 41 Ti. Gradients were withdrawn with a density gradient removing apparatus (Auto Densi Flow, Haake-Buchler, Saddle Brook NJ) and scanned at 254 nm with a Serva-Chromatocord absorbance monitor (Serva, Heidelberg, FRG). The peak areas of the polysome profiles were calculated planimetrically using a Kontron MOP-AMO2 image analyzer (Kontron, Eching, FRG). RESULTSIn Vitro Translation Rates in Dependence on Incubation Time and Ribosomal Concentration. The translational efficiency of ribosomes, obtained from wheat plants adapted to medium (20°C) and high (36°C) temperature, was tested, employing a wheat germ postribosomal supematant. The translation of endogenous mRNA was excluded, because no other amino acids besides phenylalanine were present in the assay cocktail. All data, presented here, result from subtraction of the 'minus poly(U)'-values (background) from the poly(U)-stimulated phenylalanine incorporation rates. The use of poly(U) offers certain advantages as compared to natural mRNA when, as in our case, interest is focused on translation rates rather than on translation products. Saturating conditions with respect to messenger concentration can be more easily (and economic...