PubMed Health⌕ Search

Biomedical subjects

H Kende

Publications and source records attributed to H Kende.

At least 73 records · Page 4Linked to original sources
PubMed1975

Ethylene-enhanced Ion and Sucrose Efflux in Morning Glory Flower Tissue.

Rib tissue segments excised from open flowers or buds of Ipomoea tricolor Cav. and floated on aqueous media responded to ethylene treatment by rolling up after 2 to 3 hours; a simple method for quantitating the rolling up is presented. The rolling up response was temperature- and oxygen-dependent and was critically affected by the pH of the medium. The ethylene concentration giving a half-maximal response was 0.1 mul/l; continuous ethylene treatment was not required for the response as a 1-hour ethylene exposure enhanced rolling up.Rib segments rolling up during ethylene treatment unrolled when transferred to 0.5 m sucrose, indicating that rolling up was due to asymmetric turgor changes in the segments. Compartmental analysis of (36)Cl(-) efflux from rib segments showed a fast and a slow phase; the slow phase, with a half-time of about 6 hours, is tentatively identified as efflux from the vacuolar compartment. During ethylene treatment, the rate of (36)Cl(-) efflux in the slow phase rose markedly as the rolling up response developed. A similar result was obtained with the efflux of (86)Rb(+). The release of (14)C-metabolites, labeled either by a period of (14)CO(2) fixation in darkness or by exposure to (14)C-(U)-glucose, also increased during ethylene-induced rolling up.These results suggest that ethylene causes an increase in membrane permeability in certain cells of the rib tissue.

Journal Article↗
PubMed1975

Ribonuclease in senescing morning glory: purification and demonstration of de novo synthesis.

Isolated flower buds and flowers of Ipomoea tricolor went through the same stages of development as those attached to the plant. Ribonuclease activity increased sharply in both cases during the time of flower fading and aging. Affinity chromatography using guanosine diphosphate-Sepharose was employed for fast and efficient purification of ribonuclease. Flowers which were kept on D(2)O during the senescence phase incorporated deuterium into ribonuclease as shown by isopycnic density gradient centrifugation in CsCl, suggesting that ribonuclease was de novo synthesized during aging of the flower.

Journal Article↗
PubMed1974

Comparative Studies on Nitrate Reductase in Agrostemma githago Induced by Nitrate and Benzyladenine.

NADH-nitrate reductase activity in excised embryos of Agrostemma githago develops in response to nitrate as well as benzyladenine. Induction of nitrate reductase by benzyladenine was much more susceptible to inhibition by a mixture of amino acid analogues and by cordycepin than induction by nitrate. In contrast, only induction of nitrate-nitrate reductase was decreased by chloramphenicol.NADH-cytochrome c reductase and reduced flavin mono-nucleotide-nitrate reductase activities were found to be associated with NADH-nitrate reductase and were induced by both nitrate and benzyladenine. When a partially purified enzyme sample was centrifuged in a linear 5 to 20% sucrose density gradient, a minor and a major band of NADH-cytochrome c reductase activity were observed. NADH-nitrate reductase cosedimented with the major band.The characteristics of nitrate-nitrate reductase and benzyl-adenine-nitrate reductase were compared by four methods but no differences could be detected: (a) Both enzymes sedimented with the same velocity during sucrose density gradient centrifugation. (b) Their distribution among fractions obtained by differential precipitation with (NH(4))(2)SO(4) was identical. (c) The elution profile of nitrate-nitrate reductase and benzyl-adenine-nitrate reductase after chromatography on diethyl-aminoethyl Sephadex A-25 columns showed no significant difference. (d) On polyacrylamide gel, the electrophoretic migration of the two enzymes was also identical.

Journal Article↗
PubMed1974

Control of Nitrite Reductase Activity in Excised Embryos of Agrostemma githago.

When excised embryos of Agrostemma githago were incubated with nitrate, the activities of both nitrate reductase and nitrite reductase were enhanced. By contrast, benzyladenine induced nitrate reductase only. Our data suggest that nitrate affected nitrite reductase activity directly, without first being reduced to nitrite. When the endogenous nitrite production was increased by raising the level of nitrate reductase through simultaneous treatment with nitrate and benzyladenine, the activity of nitrite reductase was not higher than in embryos treated with nitrate alone. On the other hand, tungstate given together with nitrate drastically inhibited the development of nitrate reductase activity without reducing the enhancement of nitrite reductase activity. Nitrite enhanced nitrite reductase activity, though less efficiently than nitrate.

Journal Article↗
PubMed1974

Some effects of applied gibberellic Acid on the synthesis and degradation of lipids in isolated barley aleurone layers.

An analysis of the lipids in isolated barley (Hordeum vulgare L.) aleurone layers after 12 hours incubation in the presence or absence of gibberellic acid showed no quantitative or qualitative changes. Longer incubation periods resulted in some lipid degradation which was greater in the presence of 1 mum gibberellic acid.Glycerolipid synthesis was measured in isolated barley aleurone layers during the first 12 hours of incubation in the presence or absence of gibberellic acid by following the incorporation of (3)H-glycerol. No significant effect of the hormone was found on either the incorporation of glycerol into lipids or on the types of lipid being synthesized.

Journal Article↗
PubMed1971

The cytokinins.

Explore the source record for details and available documents.

Animals↗
PubMed1971

Hormonal Control of Lecithin Synthesis in Barley Aleurone Cells: Regulation of the CDP-Choline Pathway by Gibberellin.

The enzymes of the cytidine diphosphate-choline pathway, which is involved in lecithin biosynthesis, are present in imbibed barley aleurone cells. The first enzyme, choline kinase (EC 2.7.1.32), is found in the soluble protein fraction. Its activity is not affected by prior treatment of aleurone layers with gibberellin. The second and third enzymes of the pathway, phosphorylcholine-cytidyl (EC 2.7.7.15) and phosphorylcholine-glyceride (EC 2.7.8.2) transferases, are associated with the particulate fractions. Their activities are greatly increased by gibberellin treatment during the lag phase (0-8 hr) of gibberellin-effected alpha-amylase synthesis. The hormonal effects are evident two hours after gibberellin treatment. Inhibitors that block gibberellin-effected alpha-amylase formation also inhibit the stimulation of these membrane-bound enzymes by the hormone.

Journal Article↗
PubMed1971

Enhancement of Nitrate Reductase Activity by Benzyladenine in Agrostemma githago.

Nitrate reductase activity in excised embryos of Agrostemma githago increases in response to both NO(3) (-) and cytokinins. We asked the question whether cytokinins affected nitrate reductase activity directly or through NO(3) (-), either by amplifying the effect of low endogenous NO(3) (-) levels, or by making NO(3) (-) available for induction from a metabolically inactive compartment. Nitrate reductase activity was enhanced on the average by 50% after 1 hour of benzyladenine treatment. In some experiments, the cytokinin response was detectable as early as 30 minutes after addition of benzyladenine. Nitrate reductase activity increased linearly for 4 hours and began to decay 13 hours after start of the hormone treatment. When embryos were incubated in solutions containing mixtures of NO(3) (-) and benzyladenine, additive responses were obtained. The effects of NO(3) (-) and benzyladenine were counteracted by abscisic acid. The increase in nitrate reductase activity was inhibited at lower abscisic acid concentrations in embryos which were induced with NO(3) (-), as compared to embryos treated with benzyladenine. Casein hydrolysate inhibited the development of nitrate reductase activity. The response to NO(3) (-) was more susceptible to inhibition by casein hydrolysate than the response to the hormone. When NO(3) (-) and benzyladenine were withdrawn from the medium after maximal enhancement of nitrate reductase activity, the level of the enzyme decreased rapidly. Nitrate reductase activity increasd again as a result of a second treatment with benzyladenine but not with NO(3) (-). At the time of the second exposure to benzyladenine, no NO(3) (-) was detectable in extracts of Agrostemma embryos. This is taken as evidence that cytokinins enhance nitrate reductase activity directly and not through induction by NO(3) (-).

Journal Article↗
PubMed1970

Radioactive gibberellin a(5) and its metabolism in dwarf peas.

Radioactive gibberellin A(5) ((3)H-GA(5)) was synthesized from gibberellic acid. When it was applied to dwarf peas grown in the dark, an average of 3% was converted to another acid gibberellin within 48 hours. The biological activity of the metabolite did not account for the response to applied GA(5). GA(5) is therefore assumed to be biologically active per se.(3)H-GA(5) did not appear to form a stable complex with a macromolecule in pea shoots. When injected into dwarf pea pods, (3)H-GA(5) was readily metabolized by maturing seed to more water-soluble substances and to two other acidic compounds. This metabolism continued even throughout germination of the seed without reconversion of the metabolites to GA(5). It is concluded that "bound" GA(5) plays no part in the germination of dwarf pea seeds.

Journal Article↗
PubMed1969

Studies on the distribution and properties of a new class of cell division--promoting substances from higher plant species.

One member of a new class of cell division-promoting substances, which are nicotinamide derivatives, has been found to be present in dividing cells of tobacco and cactus. These plants are taxonomically far removed from one another and from Vinca rosea L., the plant species from which the new substances were first isolated. Because of their apparent wide distribution among dicotyledonous plant species, the question is raised as to whether the nicotinamide derivatives rather than the purine cytokinins may not, in fact, be the naturally occurring cell division factors that are directly involved in promoting cytokinesis in higher plant species. Unequivocal evidence is presented to show that the nicotinamide derivatives do not owe their biological activity to contamination by 6-substituted purine cytokinins.

Cell Division↗
PubMed1968

Fate of radioactive gibberellin a(1) in maturing and germinating seeds of peas and Japanese morning glory.

Radioactive gibberellin A(1) ((3)H-GA(1)) was injected into excised fruits of peas and Japanese morning glory. These were then grown in sterile culture to maturity and the label was followed in the seeds during further development and subsequent germination. During development of both pea and morning-glory seeds a large part of the radioactivity became associated with the aqueous fraction, while another part of the (3)H-GA(1) was converted into 2 new, acidic, biologically active compounds, designated X(1) and X(2). A relatively small part of the neutral compounds could be converted back to (3)H-GA(1), X(1), and X(2) by means of mild acid hydrolysis. During germination of pea and morning-glory seeds, part of the bound compounds was released in the form of (3)H-GA(1), X(1) and X(2) while, particularly during rapid seedling growth, a further conversion of (3)H-GA(1), mainly to X(1), took place. In pea seedlings, growth during the first 2 to 3 days after imbibition was not affected by Amo-1618, an inhibitor of gibberellin biosynthesis. This, in conjunction with the findings on the interconversions between free and bound (3)H-GA(1) suggests that, at least in peas, early seedling growth may at least partly be regulated by gibberellins released from a bound form which was formed during seed development.

Journal Article↗
PubMed1968

Studies on cytokinin-controlled bud formation in moss protonemata.

Application of cytokinins to moss protonemata of the proper physiological age causes bud formation on specific cells (caulonema). During the early stages of their development, buds revert to protonemal filaments if the cytokinin has been removed by washing the protonemata. This indicates that the hormone is not acting as a "trigger" but has to be present during a critical period of time until differentiation is stabilized. Autoradiographs of protonemata treated with a labeled cytokinin, benzyladenine-benzyl-7-(14)C, show a striking accumulation of the radioactivity in caulonema cells which are in the stage of bud formation, and in the buds themselves. Cells which did not react to the hormone contained very little radioactivity. The accumulation of benzyladenine in the "target cells" may be due to the presence of binding sites which, in turn, may distinguish responding cells from non-responding ones.

Journal Article↗
PubMed1968

On the significance of cytokinin incorporation into RNA.

The clarification of the following 2 questions was attempted: (a) are cytokinins precursors in the formation of sRNA, (b) is the observed incorporation of cytokinins into sRNA related to the action of the hormone? Although Escherichia coli contains cytokinins in its sRNA, no cytokinin auxotroph mutants of E. coli could be found and the statistical probability for the existence of such mutants is extremely low. This suggests that cytokinins are not precursors in the synthesis of sRNA. A radioactive cytokinin, 6-benzylamino-9-methyl-purine was synthesized and it was tested whether or not it is incorporated into sRNA of soybean callus tissue. Masking the 9-position of the purine inhibited the incorporation of this cytokinin into RNA while not affecting its biological activity. This is taken as an indication that the observed incorporation of cytokinins such as benzyladenine into sRNA is not related to the action of this hormone.

Kinins↗
PubMed1967

Preparation of radioactive gibberellin a(1) and its metabolism in dwarf peas.

Gibberellin A(1)-3,4-(3)H was prepared by selective catalytic reduction of gibberellic acid with a mixture of tritium and hydrogen. (3)H-GA(1) was applied at physiological concentrations to dwarf peas and the metabolism of the hormone was investigated. (3)H-GA(1) was converted to an acidic, biologically active compound. Radioactive but biologically inactive compounds were also found in the neutral fraction and could not be converted to acidic gibberellins by hydrolysis. No attachment of gibberellin to any macromolecular fraction was evident.

Journal Article↗