[en] The assimilatory reduction of nitrate and nitrite in the white and green leaves of chlorophyll mutants of rice (Oryza sativa L.) were investigated by feeding the leaf sections with ¹⁵N-labeled substrates in vivo in darkness. Small nitrate reduction and considerable nitrite assimilation into amino acids were observed in the white leaves, while both activities were active in the green leaves. This work confirmed the occurrence of dark nitrate and nitrite reduction in the leaves even if they lacked in the development of the chloroplasts (author)

[en] Isolated nuclei from etiolated sunflower hypocotyls were prepared by centrifugation through a layer of a 45% sucrose solution. The final pellet contained many nuclei in a good state but also small starch grains. The lipids of the nuclei contained 58% phospholipids (mainly phosphatidylcholine and phosphatidylethanolamine), 29% neutral lipids and 13% glycolipids. The major fatty acids were palmitic, stearic, oleic and linoleic acids. When [¹⁴C] acetate was given to hypocotyl slices, the lipids of microsomes and mitochondria were heavily labelled whilst the labelling of the nuclear lipids was very low. No lipid biosynthesis could be observed in isolated nuclei from any assayed ¹⁴C-precursor. The possibility of lipid transfers to the nuclei, in vivo, was illustrated by organizing in vitro lipid transfers from labelled liposomes to non-labelled nuclei

[en] A mutagenic procedure of carrot cell suspension by means of UV-light has been established. The application of this procedure to the selection of cell lines resistant to 5-methyltryptophan (5MT) increased 11 times the spontaneous mutation rate. Eighteen colonies selected in the course of one experiment have been analyzed for quantitative resistance to the analogue. Four of the most 5MT-resistant lines selected (one spontaneous and three induced) were also tested for their resistance to azetidine-2-carboxylic acid (A2C) to which all of them proved to be resistant even though this was an unselected trait. The four lines were tested for the intracellular content of some free amino acids. Results of such determination showed that the content of tryptophan and proline was roughly proportional to the degree of resistance of the lines to the two analogues. The fact that all the lines resistant to 5MT over-produced proline suggests that the latter feature may be a direct consequence of the increased pool of free tryptophan. The four cell lines tested showed a rate of tryptophan uptake similar to that of the parental line. On the contrary the rate of proline and A2C by the 5MT-11 cell line was reduced to 23% and 10% of that of the parental line, respectively. (author)

[en] The transfer of (¹⁴C) sucrose and D-(¹⁴C) mannitol from the bundles to the bundle-free parenchyma regions in sugar beet roots was studied after feeding 10 mM solutions to the storage organ via xylem. Both solutes entered the bundle free parenchyma region with comparable velocities, but mannitol mainly remained in the free space during the transfer period whereas sucrose was quickly taken up by the cells near the bundles. The apoplastic transfer of mannitol indicated the absence of a barrier between the xylem vessels and the free space of storage parenchyma. Consequently, the sugar concentration cannot be much higher in the free space than in xylem exudate. Considering low extracellular sugar concentrations in situ and the finding of symplastic transport in the xylem feeding experiment it is assumed that also in natural parenchymal transport of sucrose after unloading of phloem the symplastic pathway is involved (author)

[en] When [2-¹⁴C]mevalonic acid was fed to the retarded young leaf cell-free system of iris (Iris hollandica cv. Professor Blaauw), squalene was one of the major biosynthesized products. Squalene has been characterized by TLC, GLC and MS

[en] [1-¹⁴C]Glycolate metabolism was examined in leafy shoots of soybean plants (Glycine max (L.) Merr., var. Adepta). Only small amounts of ¹⁴C were incorporated into evolved carbon dioxide and glucidic compounds. Free and protein glycine was labelled but higher levels of radioactivity were found in free serine. Changes in the distribution of ¹⁴C with time showed that metabolic conversion glycollate → glycine → serine occurred very early and serine biosynthesis was more important in the shoot than in the leaves. Carbon dioxide labelling was always slight compared to serine labelling. These data suggest strong relations between glycollate and nitrogen metabolism

[en] σ-Aminolevulinate dehydratase has been found to be activated in vitro by dithiotreitol and factors isolated from radish cotyledons grown under continuous far-red light. Cross experiments, between fructose 1-6 bisphosphatase system, and σ-aminolevulinate dehydratase, show that these factors are functionally identical to thioredoxin f (author)

[en] Chlorophyll fluorescence in vivo was progressively lost in pea leaves irradiated with either short or long-wave light. The changes were consistent with the development in the intact leaves of an inhibitory site on the photooxidizing side of photosystem II. In contrast, leaves of two species of Agave, plants regarded as more resistant to UV radiation, showed only minor changes in chlorophyll fluorescence. Agave americana was affected less than A. attenuata. The application of measurements of chlorophyll fluorescence in vivo to screening for tolerance to UV radiation is discussed. (author)

[en] The rate of uptake of [³H]leucine by tobacco mesophyll protoplasts increased several-fold during the first 8 h in culture at 22 deg C, remained at this higher level for about 12 h, and then declined slowly until after 45 h in culture it was at or below the original rate. The increase in rate was observed not only with protoplasts in various physiological conditions but also with isolated cells, and was due neither to recovery from the trauma of centrifugation nor to depletion of a nutrient or accumulation of a product in the medium. It was prevented by cycloheximide or puromycin but not by chloramphenicol. Although the actual rates of uptake were different, similar changes occurred with [³H]uracil, [³H]UTP, [¹⁴C]glucose and [³²P]phosphate

[en] Stable embryogenic, organogenic and undifferentiated cell lines of the maize (Zea mays L.) inbred B73 were used to assess the value of using isozyme analyses and the composition of secreted polysaccharides to identify embryogenic cells. Esterase, glutamate dehydrogenase, alcohol dehydrogenase and β-glucosidase all possessed developmentally regulated isozymes but only esterase and glutamate dehydrogenase could be used to distinguish between embryogenic and shoot-forming cultures. Embryogenic callus and suspension cultures secreted a mucilagenous polysaccharide whose production was stimulated by 2, 4-dichlorophenozyacetic acid (2, 4-D). The polysaccharide was different from root slime and corn hull gum and may be related to the 'cementing layer' in maize kernels (author)