The effects of abscisic acid,kinetin and 5-fluorouracil on ribonucleic acid and protein synthesis in senescing radish leaf disks

Summary The effects of abscisic acid and kinetin on RNA synthesis in senescing radish leaf disks were investigated using the improved resolution afforded by polyacrylamide gel electrophoresis. Kinetin stimulated and abscisic acid inhibited incorporation of radioactivity into cytoplasmic ribosomal RNA and soluble RNA. Chloroplast ribosomal RNA synthesis appeared to be confined to the period of leaf expansion and was not detected in fully mature leaves. The effects of kinetin in retarding and of abscisic acid in accelerating leaf senescence were not altered by the inhibition of cytoplasmic ribosomal RNA synthesis with 5-fluorouracil. Following inhibition of cytoplasmic ribosomal RNA synthesis with 5-fluorouracil, kinetin stimulated and abscisic acid inhibited incorporation of radioactivity into polydisperse RNA. These results are discussed in relation to the possible mode of action of kinetin and abscisic acid in senescing leaf tissue.     

Abscission-promoting activities of abscisic acid and five abscisic acid analogs in cotton seedlings and explants

The abscission-promoting activities of abscisic acid (ABA) and 5 ABA analogs were examined in cotton (Gossypium hirsutum L. cv LG102) seedlings and cotyledonary node explants. The analogs tested included a series of acetylenic derivatives that differ in the oxidation state of the C-1 atom, a 2,3 dihydro-derivative of ABA and a 2,3 dihydro-derivative of an acetylenic analog with a C-1 carboxyl moiety. ABA and all five analogs were active in stimulating petiole abscission in explants. Following treatment with 100,µM ABA or analog, 50% abscission of explants was observed after 29 h and complete abscission occurred within 40 h. With one exception, none of the treatments resulted in an increase in explant ethylene production. Pretreatment of the explants with the ethylene antagonist silver thiosulfate completely abolished the abscission-promoting activities of ABA and all of the analogs. Daily application of ABA or any of the analogs had no effect on cotyledon abscission in intact seedlings. The implications of the results with respect to the development of a commercial ABA-like regulator as well as to ABA structure-activity studies are discussed.Mention of trademark or proprietary product does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable.     

Jasmonic acid and abscisic acid in shoots,coleoptiles, and roots of wheat seedlings

The endogenous levels of abscisic acid (ABA) and jasmonic acid (JA) were analyzed in wheat seedlings grown in water, a system which in the past has been used to test the effects of these plant growth inhibitors. The levels in different plant parts and in the medium were measured by gas chromatography-mass spectrometry-selected ion monitoring, using [²H₃]ABA and [²H₆]JA as internal standards. In every plant part, JA levels were about 2 orders of magnitude greater than those of ABA. The exudation of JA from roots per seedling was about 14,000-fold greater than that of ABA, although the roots contained only about 170 times more JA than ABA. It is suggested that JA is a possible allelopathic compound.     

Synthesis and biological activity of Boc [Nle28, Nle31]CCK27-33, a highly potent CCK8 analogue

A new CCK8 related peptide, Boc[Nle28,Nle31]CCK27-33 (Boc[diNle]CCK7) was synthesized and tested for cholecystokinic activity, at both the peripheral and the central level. This analogue, protected against both chemical oxidation and enzymatic degradation by aminopeptidases, was shown to be equipotent to CCK8 in releasing amylase from rat pancreas fragments. In addition, the EC50 values of Boc[diNle]CCK7 in the guinea pig gallbladder and ileum contraction assays (3.2 nM and 3.0 nM respectively) were similar to those of CCK8 (6.0 nM and 2.0 nM). Moreover both Boc[diNle]CCK7 and CCK8 elicited similar effects on the open field test over the same concentrations range. These results demonstrate the ability of Boc[diNle]CCK7 to be a suitable tool for investigating the physiological role of native CCK8.     

Interaction of coumarin, gibberellic acid and abscisic acid in the translocation of auxin in bean seedlings

The effects of coumarin on the translocation of 2,4,5-trichlorophenoxyaceticacid (2,4,5-T) in bean (Phaseolus vulgaris L. cv. StringlessGreenpod) seedlings was determined. ¹⁴C-labeled 2,4,5-T wasinjected in the stem tissue at the cotyledonary node along withthe coumarin or the coumarin was added to the nutrient solutionprior to, or at the time of, 2,4,5-T treatment. The amount oftranslocation of radioactive 2,4,5-T to plant parts was thendetermined at various times after treatment. An immediate effectof coumarin was to enhance acropetal 2,4,5-T translocation tothe young shoots. This effect occurred at low 2,4,5-T treatmentlevels and appeared to be specific for 2,4,5-T since sucrosetranslocation was not affected. Prolonged treatment with coumarininhibited acropetal and basipetal 2,4,5-T translocation in amanner similar to prolonged treatment with abscisic acid (ABA).Gibberellin A₃ (GA) reversed the inhibitory effects of coumarinand ABA on 2,4,5-T acropetal translocation. ¹ Journal article 3244 of the Agricultural Experiment Station,Oklahoma State University. (Received December 6, 1976; )     

Effect of paclobutrazol on abscisic acid levels in wheat seedlings

Contradictory results have been reported for the effects of triazoles on abscisic acid (ABA) levels in plants. Paclobutrazol reduced the height, fresh weight, and ABA levels of wheat seedlings. The magnitude of the inhibitory effect of paclobutrazol on ABA levels was dependent on the length of time after application. ABA levels in plants as determined by gas chromatography-selected ion monitoring-mass spectrometry (GC-SIM-MS) were reduced by 50–60% 2 days after soil application. A further 15% reduction occurred by the seventh day after treatment. ABA level analyses began at the time of treatment with 4-day-old seedlings and continued until 21 days after treatment when only a 20% reduction was detected. These determinations using GC-SIM-MS should increase the understanding of triazole effects on ABA levels.     

26,26,26,27,27,27-hexafluoro-1,25-dihydroxyvitamin D3: a highly potent, long-lasting analog of 1,25-dihydroxyvitamin D3

A new fluoro analog of 1,25-dihydroxyvitamin D3, i.e., 26,26,26,27,27,27-hexafluoro-1,25-dihydroxyvitamin D3, has been compared with the native hormone, 1,25-dihydroxyvitamin D3, in its biological potency, duration of action, and binding to the vitamin D transport protein and intestinal receptor protein. The fluoro analog is about 5 times more active than the native hormone in healing rickets and elevating serum inorganic phosphorus levels of rachitic rats. It is about 10 times more active than 1,25-dihydroxyvitamin D3 in increasing intestinal calcium transport and bone calcium mobilization of vitamin D-deficient rats fed a low-calcium diet. Furthermore, the higher biopotency is manifested in animals after oral dosing. Of great importance is that the action of the fluoro analog is longer lasting than that of 1,25-dihydroxyvitamin D3. This is especially apparent in the elevation of serum phosphorus and bone mineralization responses. The fluoro analog is only slightly less competent than 1,25-dihydroxyvitamin D3 in binding to the vitamin D transport protein in rat blood, and is one-third as competent as 1,25-dihydroxyvitamin D3 in binding to the chick intestinal cytosol receptor for 1,25-dihydroxyvitamin D3. These results suggest that the basis for increased potency of this analog is likely the result of less rapid metabolism.     

Metabolism of a proline analogue, l-thiazolidine-4-carboxylic acid, by Escherichia coli

Unger, Leon (University of Illinois, Urbana), and R. D. DeMoss. Metabolism of a proline analogue, l-thiazolidine-4-carboxylic acid, by Escherichia coli. J. Bacteriol. 91:1564-1569. 1966.-Resting cells of Escherichia coli K-12, pregrown in a proline- and thioproline-free medium, oxidize the proline analogue, l-thiazolidine-4-carboxylic acid (l-thioproline), without a lag with the consumption of 1 atom of oxygen per mole of thioproline. The organism also oxidizes cysteine and formaldehyde, the chemical precursors of thioproline. The total oxygen consumed is the same whether the substrate is thioproline, cysteine, formaldehyde, or an equimolar mixture of cysteine and formaldehyde. The results suggest that neither cysteine nor formaldehyde are free intermediates in the oxidative pathway. Thioproline is available as a metabolic carbon source for the synthesis of the ribonucleic acid bases, guanine and uracil.     

The effects of abscisic acid on senescence in leaf discs of radish,Raphanus sativus L.

Summary After a 6 day incubation period, abscisic acid (ABA) at 10^-4 M retarded the decline in pigment levels and promoted the decline in protein levels of radish leaf discs. ABA treatment also retarded the rise in the specific activity of the RNA fraction (calculated by counts per minute incorporated of ¹⁴C-8-adenine as a fraction of optical density at 260 nm) observed in water-treated control discs. The results indicated that ABA was primarily effective in enhancing senescence in the early stages following leaf excision. Thus the increase in RNA specific activity during an initial 24 h incubation period was especially pronounced with ABA treatment although there was no effect of the hormone on RNA level. Moreover, in contrast to control discs, the pigment levels declined markedly in ABA-treated discs in this period. When the discs had been incubated in water (preaged) for 3 or 5 days prior to ABA treatment, however, the hormone then had little effect on RNA metabolism and protein and pigment levels relative to the water control.Data are collated from different experiments to show the changes in RNA, pigment and protein with ABA treatment during a 6 day senescence period.It is considered that ABA is speeding up the natural changes in RNA metabolism possibly by affecting both RNA synthesis and degradation.     

Phloem transport of abscisic acid in Ricinus communis L. seedlings

Sieve tube sap exuded from the cut hypocotyl of castor bean seedlings (Ricinus communis L.) was found to contain 0.2–0.5 mmol m^?3abscisic acid (ABA). The ABA concentration in the sieve tube sap always exceeded that in root pressure exudate under a wide range of water supply. Exudation of sieve tube sap from the cut hypocotyls caused water loss, and this induced ‘water shortage’ in the cotyledons which resulted in the ABA concentration in the cotyledons increasing by 3-fold and that in the sieve tube sap increasing by up to 50-fold within 7h. The wounded surface of the cut hypocotyl was not responsible for the ABA increase. Incubation of the cotyledons of endosperm-free seedlings in various ABA concentrations (up to 100 mmol m^?3) increased the ABA concentration in sieve tube sap. The concomitant increase in ABA, both in cotyledons and in sieve tube sap, had no effect on the phloem loading of sucrose, K⁺ and Mg²⁺ within the experimental period, i.e. up to 10h. It can be concluded that (i) the phloem is an important transport path for ABA, (ii) water stress at the phloem loading sites elevates phloem-mobile ABA, which may then serve as a water stress signal for sinks, for example stem and roots (not only for stomata), and (iii) the ABA concentration of cells next to or in the phloem is more important than the average ABA content in the whole cotyledon for determining the ABA concentration in sieve tube sap.     

Synthesis and opioid receptor binding properties of a highly potent 4-hydroxy analogue of naltrexone

Very high affinity for opioid receptors (e.g., K(i)=0.052nM for mu) has been observed in the rationally designed naltrexone analogue 5. SAR and physical data supports the hypothesis that the 4-OH group of 5 stabilizes the 3-carboxamido group in the putative bioactive conformation.     

Inhibitory effect of gabaculine on 5-aminolevulinate dehydratase activity in radish seedlings

We have compared the activity of 5-aminolevulinate dehydratase (5-ALAD) with the amount of protein detected by specific antibodies in rocket immunoelectrophoresis. Parallel kinetic evolutions of enzymic activity and amount of antigen were observed in radish (Raphanus sativus L.) cotyledons, both in complete darkness or under standard far red light involving phytochrome. However, the treatment of seedlings with gabaculine leads to an important decrease in enzymic activity, while the specific protein content is maintained. This inhibition is not overcome by the addition of glutamic acid, but by 5-aminolevulinic acid which points to a specific control of 5-ALAD activity by its substrate. As there is no discrepancy between the enzymic activity and the amount of antigen during the time course development of seedlings, this could confirm a coordinate cellular control between 5-aminolevulinic acid formation and 5-ALAD protein synthesis, both being amplified by the action of phytochrome.     

Contents of abscisic acid and cytokinins in shoots during dehydration of wheat seedlings

Accumulation of ABA in shoots during 30-min dehydration of wheat seedlings was accompanied by the decline in the content of zeatin nucleotide and the accumulation of zeatin 9-N-glucoside. The total content of zeatin derivatives as well as the content of free base of zeatin remained almost constant. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of chlorocholine chloride and gibberellic acid on the anthocyanin synthesis in radish seedlings

Anthocyanin synthesis in radish ( Raphanus sativus L. cv. Scarlet Globe) seedlings after treatment with chlorocholine chloride (CCC) and gibberellic acid (GA) has been investigated. CCC promotes and GA₃ inhibits the synthesis. When both substances are given together, CCC reverses the inhibition caused by GA₃. Simultaneous external feeding of anthocyanin precursors (sucrose and phenylalanine) reverses the GA₃ inhibition. A higher amount of total free amino acids, in particular phenylalanine, was present in CCC-treated seedlings compared to controls grown on distilled water. The amount of phenylalanine was lower in seedlings treated with both CCC and GA₃ as compared to seedlings treated with CCC alone, and total free sugars (reducing plus non-reducing) was lower in CCC treated seedlings than in controls grown on distilled water. We conclude that CCC and GA3 control the anthocyanin synthesis at the level of precursors.     

Some growth responses of apple seedlings to abscisic acid and growth stimulators

Antonovka seedlings were obtained from the embryos soaked in abscisic acid (ABA) alone, gibberellin A₄₊₇, benzyladenine or the mixtures of these regulators. The inhibitory effect of ABA on the growth of the seedlings was of temporary duration. The height of the 12 week-old seedlings was dependent only on the degree of seed after-ripening and not on the ABA treatment. The growth stimulators studied were unable to overcome the inhibitory effect of ABA observed in the early stages of seedling growth. The growth stimulators did not substitute, for cold treatment of apple seeds which is the only treatment so far known to overcome the dwarf conditions of the seedlings obtained from non-after-ripened embryos. ABA greatly suppressed the early stages of apple seedling growth (up to 6 weeks) during which they resembled physiological dwarfs. The highest concentrations of ABA (2·0 μg ml^?1) greatly modified the root system of the seedlings, and produced a larger percentage of seedlings with unbranched roots.     

Discovery,synthesis and in combo studies of a tetrazole analogue of clofibric acid as a potent hypoglycemic agent

A tetrazole isosteric analogue of clofibric acid (1) was prepared using a short synthetic route and was characterized by elemental analysis, NMR (¹H, ¹³C) spectroscopy, and single-crystal X-ray diffraction. The in vitro inhibitory activity of 1 against 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) was evaluated, showing a moderate inhibitory enzyme activity (51.17% of inhibition at 10 μM), being more active than clofibrate and clofibric acid. The antidiabetic activity of compound 1 was determined at 50 mg/Kg single dose using a non insulin dependent diabetes mellitus rat model. The results indicated a significant decrease of plasma glucose levels, during the 7 h post-administration. Additionally, we performed a molecular docking of 1 into the ligand binding pocket of one subunit of human 11β-HSD1. In this model, compound 1 binds into the catalytic site of 11β-HSD1 in two different orientations. Both of them, show important short contacts with the catalytic residues Ser 170, Tyr 183, Asp 259 and also with the nicotinamide ring of NADP⁺.     

Low concentration of exogenous abscisic acid increases lead tolerance in rice seedlings

The effects of exogenous abscisic acid (ABA) on lead tolerance in rice (Oryza sativa L.) seedlings were investigated. Pre-treatment with 0.1 g m³ ABA for 2 d restricted amount of Pb translocated from roots to shoots, decreased malondialdehyde and H₂O₂ contents in leaves, and alleviated Pb-induced decrease in plant growth and leaf chlorophyll content. Further, ABA pre-treatment adjusted leaf antioxidative enzyme activities (increased ascorbate peroxidase and catalase activities while decreased superoxide dismutase activity) and so alleviated oxidative stress.