Purification and properties of a polyamine oxidase from Zea mays

Polyamine oxidase, purified 260-fold from maize shoots, was light yellow in colour. Maximum light-absorption was at 450 nm and was decreased by the addition of either sodium dithionite or spermidine, but not by putrescine. Under aerobic conditions, the enzyme could use p-benzoquinone as an electron acceptor. Cu²⁺ inhibited the enzyme activity, while SO₃⁻ was stimulatory. Several metal-binding agents and thiol reagents were without effect.     

C-Glycosylflavones from Zea mays that inhibit insect development

A new C-glycosylflavone isolated from corn silk inhibits the growth and development of the corn earworm, Heliothis zea. This new compound was shown to be a 2″-O-α-l-rhamnosyl-6-C-(6-deoxy-xylo-hexos-4-ulosyl)luteolin. Also found co-occurring in corn silk were minor amounts of the corresponding 6-C-glycosylated analogs of chrysoeriol and apigenin.     

Polyamine oxidase from Zea mays shoots

Polyamine oxidase of maize shoots purified 10-fold had a pH optimum of 6·3 with spermidine as substrate, and K_m of 6 × 10^?4 M. The enzyme was inhibited by the acridine compounds quinacrine, 6,9-diamino-2-ethoxyacridine and acriflavin, but carbonyl reagents, typical thiol inhibitors and copper-binding agents were without effect. Inhibition by quinacrine was reversed by FMN and FAD. Furthermore, about 50 % of the activity of the apoenzyme was restored by the addition of FAD, but not by FMN or riboflavin, indicating that the maize polyamine oxidase is an FAD-dependent flavoprotein.     

Galactolipid biosynthesis in Zea mays shoots

Illumination of dark-grown maize seedlings produced an increase in their mono- and di-galactosyl contents with the two galactose moieties being donated by UDP-galactose. Diolein was an effective exogenous acceptor of the first galactosylation and endogenous maize mono-galactosyl diglyceride of the second.     

Urease from leaves of Glycine max and Zea mays

Extracts of Glycine max and Zea mays leaves catalysed the release of ¹⁴CO₂ from [¹⁴C] urea with multiple pH maxima (5.5 and 9.0 for G. max; 5.5, 7.5 and 8.8 for Z. mays). Evidence was obtained that the principal activities, at pH 5.5 and 8.8–9.0 catalysed the same reaction stoichiometry as did urease purified from jackbean seeds (EC 3.5.1.5). The urease activities with these pH optima were not resolved by ammonium sulphate fractionation, DEAE-cellulose chromatography, or gel filtration chromatography. Many structural analogues of urea inhibited leaf urease, the most effective being amino acid hydroxamates, hydroxyurea and selenourea. Allantoic acid and ureidoglycolate are probably not alternative substrates because they showed at most only weak competitive inhibition with respect to radioactive urea.     

La desoxycytidine aminohydrolase des feuilles de Zea mays

Deoxycytidine aminohydrolase was extracted from Zea Mays leaves and purified 22-fold. The extract deaminates deoxycytidine, cytidine, 5-methyldeoxycytidine, 5-bromodeoxycytidine and arabinosylcytosine. Its molecular weight was estimated to be 77 000-78 000 based on the elution pattern from Sephadex G100 and G200. Kinetic studies indicated that the hydrolysis of the substrates proceeds at rates which can formally be described by Michaelis-Menten kinetics. p-Chloromercuribenzoate inhibits deoxycytidine aminohydrolase activity, as do mercaptoethanol and dithiothreitol. The activity is also inhibited by deoxyuridine (mixed type), uridine (non competitive), 5-bromodeoxyuridine (competitive).     

Activation of particulate starch synthetase from Zea mays embryo

The effect of spermine on particulate ADP-glucose: starch synthetase from the developing embryo of sweet corn has been studied. Spermine induces a considerable increase of glucose incorporation from ADP-glucose into the starch granules. The change in kinetic constants, the distribution of incorporated glucose between amylose and amylopectin and the pattern of incorporation into starch granules or malto-oligosaccharides has been studied. The data were compared with those obtained with citrate ions.     

Rna polymerase from opaque-2 and normal Zea mays endosperm

RNA polymerase from Opaque-2 and normal maize showed qualitative differences during endosperm development. DEAE-Sephadex column chromatography indicated the presence of one and three RNA polymerases respectively at 15 and 25 days post-pollination. The polymerases from Opaque-2 and normal endosperms at 15 days post-pollination showed considerable differences in Mn²⁺ optimum. The optimum Mn²⁺ for normal polymerase was ten times higher than for Opaque-2 polymerase. The polymerase activity from endosperms at 15 days post-pollination was due to nucleoplasmic RNA polymerase II.     

Flavonol glucosyltransferase activity in Bronze embryos of Zea mays

The major UDPG: flavonol glucosyltransferase (UFGT) in maize is an enzyme of strict positional specificity known to be coded by the Bz locus. In bz mature endosperms, no UFGT can be detected. However, bz embryos possess a residual flavonol glucosyltransferase activity which is independent of Bz locus control. The products of this activity have been identified as the 3′-, 7- and 3-glucosides.     

The effect of salts on malate dehydrogenase from leaves of Zea mays

The effect of sodium and potassium chlorides and of sodium sulphate on malic dehydrogenase (EC 1.1.1.37) from Zea mays chloroplasts and cytosol has     

Hormones of young tassels of Zea mays

The ethyl acetate-soluble acids from an aqueous methanolic extract of young tassels from Zea mays plants were fractionated by treatment with PVP, then by chromatography on a column of celite-charcoal. Methylated and trimethylsilylated fractions were analysed by GC/MS and the following compounds were identified by comparison with reference spectra: GA₁₇, GA₁₉, GA₂₀, GA₄₄, GA₅₃, ABA, phaseic acid and dihydrophaseic acid. Evidence is also presented for the presence of metabolise C of ABA and of a 16,17-dihydro-17-hydroxy-derivative of GA₅₃. In addition, the presence of small amounts of GA₁, GA₈ and GA₂₉, was indicated from a derivatized fraction analysed by capillary GC/SICM.     

Lipid biosynthesis by chloroplasts isolated from developing Zea mays

Fatty acid biosynthesis by isolated plastids has been examined in relation to chloroplast development and differentiation in leaves of maize plants grown in light for 7 days. Biosynthesis of fatty acids from acetate by proplastids prepared from the basal regions of the leaf was low and mainly palmitate was synthesized. The greatly increased utilization of acetate for fatty acid biosynthesis as the plastids increased in size was due to an increased synthesis of oleate. The maximum synthesis of total fatty acids and monoenoic fatty acids was obtained in chloroplasts prepared from leaf tissue 6–8 cm from the base of the plant where granal formation was most active. Fully-developed chloroplasts prepared from distal regions of the leaf were less active in fatty acid biosynthesis. Maize chloroplasts failed to synthesize fatty acids when isolated by methods commonly used to prepare active spinach chloroplasts. The method of isolation which included a density gradient gave a high proportion of Class I chloroplasts from maize leaves and incorporated up to about 10% of the acetate used. Biosynthesis of unsaturated fatty acids, especially with chloroplasts prepared from the most mature tissue, was increased by the addition of both mitochondrial and microsomal fractions. Increases in polyunsaturated fatty acids were also obtained but the proportions in the newly-synthesized fatty acids were well below the endogenous levels. Monoenoic synthesis was greatly stimulated by increasing the pH in the range 7·0–8·0 and also the highest proportions of unsaturated fatty acids were obtained at short incubation times.     

Indol-3yl-acetic acid in roots of Zea mays

Indol-3yl-acetic acid was identified in extracts of sterile roots of Zeamays seedlings by means of TLC, chromogenic reactions, GLC and GC-MS.     

1,4-Benzoxazine glucosides from Zea mays

One new benzoxazine glucoside has been found in corn and identified as 2-(2-hydroxy-7,8-dimethoxy-2H-1,4-benzoxazin-3[4H]-one)-β-D-glucopyranosid     

Enzymes of starch and sucrose metabolism in Zea mays leaves

Mesophyll and bundle sheath cells of maize leaves were separated and enzymes of starch and sucrose metabolism assayed. The starch content and activities of ADPglucose (ADPG) starch synthetase and phosphorylase expressed both on a chlorophyll and a protein basis were much lower in mesophyll cells compared to bundle sheath preparations. Exposure of the leaves to continuous illumination for 2·5 days caused the starch content of mesophyll cells to rise greatly and led to considerable increases in ADPG starch synthetase and phosphorylase activity. In glasshouse grown leaves the bulk of invertase, sucrose phosphate synthetase, sucrose phosphatase, UDPglucose pyrophosphorylase and amylase was situated in the mesophyll layer. Sucrose synthetase, ADPG starch synthetase and phosphorylase were largely confined to the bundle sheath. No enzyme could be completely assigned to one particular cell layer. Upon continuous illumination both ADPG starch synthetase and phosphorylase increased in the mesophyll bythe same relative amount. The mesophyll is likely to be a major site for sucrose synthesis in maize leaves.     

Violaxanthin,the major carotenoid pigment in Zea mays root cap during seed germination

Violaxanthin (5,6,5′,6′-diepoxy-5,6,5′,6′-tetrahydro-β,β-carotene-3,3′-diol) was shown to be the major carotenoid in maize root cap during seed germination according to chromatographic and spectroscopic studies. The biosynthesis of this pigment is not influenced by light and the biological significance of this carotenoid in maize root tip is briefly discussed.     

Observations on the biosynthesis of 24-methylcholesterol and 24-ethylcholesterol by Zea mays

Examination of the sterols of Zea mays shoots has established that the 24-ethylcholesterol is predominately the 24α-epimer, sitosterol, but the 24-methylcholesterol is a mixture of the 24α- and 24β-epimers. After incubation of Z. mays shoots with [2-¹⁴C, (4R)4-³H₁]mevalonic acid the sitosterol had a ³H: ¹⁴C atomic ratio of 2.09:5 which is consistent with previous results indicating that a Δ²⁴⁽²⁵⁾ -sterol is implicated in its biosynthesis. By contrast, the 24α- and 24β-methylcholesterol mixture had a higher ³H: ¹⁴C atomic ratio of 2.82:5. This can be explained by the operation of two routes for the elaboration of the 24-methylcholesterol side chain. One may proceed via Δ²⁴⁽²⁵⁾- and Δ²⁴⁽²⁵⁾-sterols to produce the 24α-methylcholesterol with a ³H: ¹⁴C atomic ratio of 2:5. The other route may involve reduction of either a Δ²⁴⁽²⁸⁾-, a Δ²³- or a Δ²⁵-sterol intermediate to give the 24β1-methylcholesterol with a ³H: ¹⁴C atomic ratio of 3:5. The proportion of these two labelled compounds in the mixture then determines the observed ³H: ¹⁴C atomic ratio (2.82:5). Some evidence for the formation of a Δ²⁵-compound, cyclolaudenol, by Z. mays shoots was provided by incorporation studies employing either [2-¹⁴C]mevalonic acid or [Me-¹⁴C]methionine as the sterol precursor.     

Abscisic acid levels in the root tips of seven Zea mays varieties

Seven varieties of Zea mays were analysed for cis-abscisic acid (ABA) and trans-ABA levels in the primary root tips by a stable isotope dilution technique. Differences in ABA levels were observed between the first 1 mm apical segments of the different varieties. No trans-ABA could be detected. In the next 2 mm ofthe root segments, the amount of ABA did not vary very much from one variety to another. The levels of ABA might very well reflect the growth reactivity of the root tips towards geotropism and light.     

Changes in isoenzymes in embryo and endosperm of normal and opaque-2 Zea mays during imbibition

Electrophoretic patterns of soluble proteins, peroxidase, esterase, alcohol dehydrogenase (ADH) and glutamic dehydrogenase (GDR) from embryos and endosperm of normal and opaque-2 maize were studied after different periods of imbibition. The soluble protein pattern from endosperm of normal and opaque-2 differed both qualitatively as well as quantitatively. The embryo protein patterns were identical. Multiple forms (isoenzymes) were found for all the enzymes studied. The enzyme patterns changed during imbibition. Peroxidase and GDH patterns from embryos of normal and opaque-2 showed considerable differences during imbibition. Esterase and ADH pattern from embryo and endosperm of normal and opaque-2 showed few differences.     

Changes in soluble protein and isoenzymes in normal and opaque-2 Zea mays endosperm during grain development

Electrophoretic patterns of soluble proteins, pH 5 enzyme fraction, peroxidase, glutamic dehydrogenase, leucine aminopeptidase in developing endosperm of normal and opaque-2 were studied. Multiple forms were found for all the enzymes studied. The GDH pattern showed considerable differences in normal and opaque-2 maize; the soluble protein pattern also differed, both qualitatively and quantitatively. The leucine-amino-peptidase pattern was identical and the peroxidase pattern showed slight differences.