Hyoscyamine 6beta-hydroxylase, a 2-oxoglutarate-dependent dioxygenase, in alkaloid-producing root cultures

Root cultures of various solanaceous plants grow well in vitro and produce large amounts of tropane alkaloids. Enzyme activity that converts hyoscyamine to 6β-hydroxyhyoscyamine is present in cell-free extracts from cultured roots of Hyoscyamus niger L. The enzyme hyoscyamine 6β-hydroxylase was purified 3.3-fold and characterized. The hydroxylation reaction has absolute requirements for hyoscyamine, 2-oxoglutarate, Fe²⁺ ions and molecular oxygen, and ascorbate stimulates this reaction. Only the l-isomer of hyoscyamine serves as a substrate; d-hyoscyamine is nearly inactive. Comparisons were made with a number of root, shoot, and callus cultures of the Atropa, Datura, Duboisia, Hyoscyamus, and Nicotiana species for the presence of the hydroxylase activity. Decarboxylation of 2-oxoglutarate during the conversion reaction was studied using [1-¹⁴C]-2-oxoglutarate. A 1:1 stoichiometry was shown between the hyoscyamine-dependent formation of CO₂ from 2-oxoglutarate and the hydroxylation of hyoscyamine. Therefore, the enzyme can be classified as a 2-oxoglutarate-dependent dioxygenase (EC 1.14.11.-). Both the supply of hyoscyamine and the hydroxylase activity determine the amounts of 6β-hydroxyhyoscyamine and scopolamine produced in alkaloid-producing cultures.     

Sucrose synthase activity in developing wheat endosperms differing in maximum weight

Past research on kernel growth in wheat (Triticum aestivum) has shown that the kernel itself largely regulates the influx of sucrose for consequent starch synthesis in the endosperm of the grain. The first step in the conversion of sucrose to starch is catalyzed by sucrose synthase (EC 2.4.13). Sucrose synthase activity was assayed in developing endosperms from kernels differing in growth rate and in maximum dry weight accumulation. From 10 to 22 days after anthesis, sucrose synthase activity per wheat endosperm remained constant with respect to time in all grains. However, kernels which had higher rates of kernel growth and which achieved greatest maximum weight had consistently and significantly higher sucrose synthase activities at any point in time than did kernels with slower rates of dry matter accumulation and lower maximum weight. In addition, larger kernels had a significantly greater amount of water in which this activity could be expressed. Although the results do not implicate sucrose synthase as the “rate limiting” enzyme in wheat kernel growth, they do emphasize the importance of sucrose synthase activity in larger or more rapidly growing kernels, as compared to smaller slower growing kernels.     

Phycomyces: fine structure analysis of the growing zone

Fine structure analysis of the stage IVb Phycomyces sporangiophore growing zone (GZ) was performed during steady-state growth using a computer-video digitizer and recorder. By simultaneously measuring the trajectory of two independent particles above and within the GZ, we have confirmed the previous findings of R. Cohen and M. Delbrück (1958 J Cell Comp Physiol 52: 361-388) that the GZ is not uniform. We have been unable to confirm their findings that counterclockwise rotation exists in a mature sporangiophore. The rates of rotation and elongation change independently as a function of position in the GZ. This change is not linear as would be expected if the GZ were uniform. The importance of this finding is discussed in terms of the fibril reorientation model.     

Polyamine Uptake, Kinetics, and Competition among Polyamines and between Polyamines and Inorganic Cations

Polyamine uptake, the kinetics of this uptake, and the competition among polyamines and between polyamines and inorganic cations were studied in petals of Saintpaulia ionantha Wendl. Uptake experiments using ¹⁴C-labeled polyamines were carried out on single petals, at room temperaure (20°C) and in the light. The results show that putrescine, spermidine, and spermine uptake was dependent on the external pH and occurred up to high external polyamine concentrations with K_m values of 8.6, 1.2, and 2.1 millimolar, respectively, with spermidine being the most absorbed at low concentration (17 micromolar). Putrescine and spermidine did not seem to compete for the same site of absorption. Furthermore, putrescine and spermidine uptake was not inhibited by Ca²⁺, Mg²⁺, and K⁺ at the same concentrations (17 micromolar), whereas 1.7 millimolar Ca²⁺ inhibited and K⁺ enhanced spermidine uptake. The intracellular localization of the absorbed putrescine was determined using two different methods. Very little label was found in the apoplast, while most of it was localized in the 98,500g supernatant. According to our data the vacuole, which represents a substantial part of Saintpaulia parenchyma cells, could be a site of putrescine accumulation. 2,4-Dinitrophenol and diethylstilbestrol did not inhibit uptake; however, at 0°C there was a 35% inhibition of spermidine uptake, compared with the controls kept at 20°C as well as a 68% inhibition with 20 millimolar NaSCN.     

Reciprocal Antagonism between the Herbicides, Diclofop-Methyl and 2,4-D, in Corn and Soybean Tissue Culture

The antagonistic interaction between the grass herbicide, diclofopmethyl (methyl 2-[4(2′,4′-dichlorophenoxy)phenoxy]propanoate) (DM), and 2,4-dichlorophenoxyacetic acid (2,4-D), was demonstrated in DM-resistant soybean (Glycine max [L.] Merr.) and DM-susceptible corn (Zea mays L.). 2,4-D caused root shortening and thickening, and induced callus growth in soybean and corn root tissue cultures at 1 and 10 micromolar. Normal soybean root growth was unaffected by 10 micromolar DM whereas corn root growth was inhibited completely by 1 to 10 micromolar DM. DM at 10 micromolar reversed completely the induction of callus growth by 1 micromolar 2,4-D in soybean roots. In corn, 10 micromolar 2,4-D reversed the growth inhibiting activity of 1 micromolar DM and induced callus growth. The antagonistic interaction between DM and 2,4-D was reciprocal and the activity of either compound depended upon the relative concentration of the other. 2,4-D did not antagonize or decrease the activity of DM by decreasing its uptake by root tissues or increasing the rate of its detoxication. The antagonistic interaction between DM and 2,4-D probably involves involves cellular activity associated with actively growing and proliferating cells and requires the presence of both compounds at the sensitive site.     

Symplastic Transport in Ipomea tricolor Source Leaves : Demonstration of Functional Symplastic Connections from Mesophyll to Minor Veins by a Novel Dye-Tracer Method

A novel method for the delivery of the fluorescent dye Lucifer Yellow CH to the cytosol of a source leaf mesophyll cell was devised which utilized a preencapsulation of the dye in phospholipid vesicles (liposomes). The liposomes were easily injected into the vacuoles of leaf cells of Beta vulgaris or Ipomea tricolor, where fusion with the tonoplast resulted in the release of the dye into the cytosol. Subsequent cell-to-cell movement of the dye was readily followed by fluorescence microscopy. Using this liposome technique symplastic continuity from the the mesophyll to the minor veins of the source leaf of Ipomea tricolor was demonstrated. This agreed with ultrastructural studies which demonstrated the presence of plasmodesmata between all cells from the mesophyll to the minor veins. The symplastic movement of dye from the injected mesophyll cell to the minor veins was unaffected by pretreatment of the leaf tissues with 2 millimolar p-chloromercuribenzenesulfonic acid. Pretreatment of the leaf tissues at alkaline pH (3-[N-morpholino] propanesulfonic acid-KOH, pH 8.0) had no apparent effect on dye movement between adjacent mesophyll cells but inhibited the movement of dye into and along the minor veins. Thus, although there were no apparent barriers to symplastic solute movement in this leaf, symplastic barriers could be imposed by the experimental conditions used.     

Regulation of Gene Expression in Developing Zea mays Embryos: Protein Synthesis during Embryogenesis and Early Germination of Maize

Polypeptides synthesized in dissected embryos of Zea mays at different stages of embryogenesis and early germination have been characterized by their migration in two-dimensional gel electrophoresis. This analysis has been carried out with in vivo labeled polypeptides from excised embryos and with proteins synthesized in vitro in the rabbit reticulocyte system directed by poly(A⁺) RNA isolated from the different developmental stages. We have identified three main sets of expressed polypeptides: (a) embryonic set: this group of polypeptides is synthesized in young and mature embryos but not in early germination; (b) maturation set: this group of polypeptides is not present in young embryos and appears during the maturation period. Some of these polypeptides are still present in early germination while others disappear from stored mRNAs in dry embryos. One particular group from this set can be induced prematurely in young embryos by incubation with abscisic acid; and (c) germination set: this group of polypeptides is not expressed in the maturation period and appears after brief imbibition of the dry embryos.     

A Calcium-Activated Phytase from Pollen of Lilium longiflorum

A phytase was isolated and partially purified from the pollen of Lilium longiflorum Thumb. Optimum activity was at pH 8.0. The phytase was activated by Ca²⁺ and Sr²⁺ but not by the other divalent cations tested. Activity was inhibited by ethylenediaminetetraacetate. The phytase had a temperature optimum of 55 to 60°C and an activation energy of about 12,700 calories/mole. Extraction of L. longiflorum pollen with 0.1% Triton X-100 increased recovery of the phytase by nearly 4-fold. The phytase had a molecular weight of about 88,000 as determined by gel filtration chromatography and a K_m value of 7.2 micromolar for phytic acid in the presence of Ca²⁺.     

Labeling of fructans in winter wheat stems

Fructans synthesized from newly formed assimilates accumulate in wheat stems as nonstructural carbohydrates. Experiments performed tested the hypothesis that the fructose moiety from translocated sucrose is used preferentially in biosynthesis of these fructans. Results indicated: (a) a large percentage of labeled sucrose was translocated and unloaded in an unaltered state; and (b) sucrose contributed its fructose moiety to fructan synthesis in stems.     

Essentiality of Boron for Dinitrogen Fixation in Anabaena sp. PCC 7119

The relationship between the requirement for boron and the form of N supplied in nutrient media to cyanobacterium Anabaena sp. PCC 7119 was investigated. When cells were grown in a medium which contained nitrate or ammonium-N, boron deficiency in the nutrient media did not inhibit growth or change cell composition. However, when cells were dependent on N₂ fixation, the lack of boron inhibited growth (i.e. growth ceased after 96 hours under these conditions). Additionally, boron-deficient cells showed a significant decrease in their content of phycobiliproteins and chlorophyll and accumulated carbohydrates within 24 hours of removing boron from the nutrient media. Inhibition of photosynthetic O₂ evolution accompanied the decrease in photosynthetic pigments. Boron deficiency symptoms were relieved when either boron or combined N was added to boron-deficient cultures. The degree of recovery depended upon the age of the cultures. Assays of nitrogenase activity showed that, after 2 hours of growth, nitrogenase activity of boron-deficient cells was inhibited by 40%. After 24 hours a total inactivation of nitrogenase activity was observed in boron-deficient cells. These results strongly suggest an involvement of boron in N₂ fixation in cyanobacteria.