Polymeric derivatives of plant growth regulators: synthesis and properties

The polymeric formulations of plant growth regulators (PGRs) are high molecular weight systems in which the PGR unit is attached to the polymeric chain by a hydrolysable chemical bond. These polymeric derivatives (esters, ethers, or else) of PGRs are characterised by the ability to release the active compound (PGR) from their solutions (mainly aqueous) in certain conditions. The release of the PGR can be controlled by external factors (pH, temperature, enzymes, solution concentration), and inherent properties of the whole macrosystem chemical structure, such as the type of the hydrolysable bond between PGR unit and the main polymeric chain, the structure of the polymer chain (e.g. molecular weight, level of hydrophilicity, and the content of hydrophobic groups, macromolecular conformation in solution etc.). These controlled (slow) release PGRs display certain advantages over conventional PGR formulations due to their prolonged action, improved efficiency (e.g. wide range of effective concentrations) greater safety to non-target organisms and the applicators. In addition the ability of altering the solubility level and modifying the aplication form is of considerable interest. The biological activity efficiency of polymeric PGRs has been documented and the relation of this efficiency to the PGR unit hydrolytic release ability has been mentioned. Slow release polymeric PGRs are considered to solve certain problems in agriculture.Abbreviations PGR plant growth regulator - C(S)RF controlled (slow) release form - PD polymeric derivative - ACC 1-amino-cyclopropane-1-carboxylic acid - NAA 1-naphthylacetic acid - 2,4-D 2,4-dichlorophenoxyacetic acid - IAA indole-3-acetic acid - BAP N⁶-benzylaminopurine - ABA abscisic acid - GA gibberellin - LMW low molecular weight - HMW high molecular weight     

Recent advances in the study of gibberellin mutants

Recent advances in the study of GA mutants are reviewed. Endogenous GAs in the vast majority of GA synthesis and response mutants have now been quantified by physicochemical means, and the implications of the results are discussed. In recent papers the effects of synthesis mutations on processes other than stem elongation have received increased attention, as has the advent of mutants with reportedly elevated GA levels. The feedback theory has been formulated, explaining paradoxical observations on endogenous GA levels in certain response mutants. In a significant breakthrough, a GA biosynthesis gene has been cloned, paving the way for a combined approach to future GA research, involving GA mutants, physicochemical analyses, and molecular techniques.     

Temperature and chemical shocks induce chilling tolerance in germinating Cucumis sativus (cv. Poinsett 76) seeds

Roots of 24-h-old germinated cucumber ( Cucumis sativus cv. Poinsett 76) seeds were subjected to thermal and chemical stresses, equilibrated at 25°C for 2 h and chilled at 2.5°C for 96 h. The germinated seeds were then held at 25°C for 72 h after they were chilled and the elongation of the primary root was used as a measure of chilling tolerance. Control roots elongated from an initial length of 0.2 cm to a final length of 6.3 cm at the end of 72 h. while chilled roots elongated to a final length of only 0.4 to 0.6 cm. Exposure to 0.4 M ethanol for 4 h or to 40°C for 1 h induced substantial chilling tolerance and the roots had a final length of 4.1 and 3.1 cm. respectively. Exposure to 7.5°C for 3 h conferred less chilling tolerance (elongation to 1.4 cm). while exposure to other chemicals (i.e. aqueous solutions of Ca(NO₃)₂, mannitol. methanol and NaCl) produced less, though still significant increases in chilling tolerance. A more severe chilling treatment of 144 h at 2.5°C was required to consistently induce elevated rates of ion leakage. Only the heat and the ethanol shock treatments significantly reduced chilling-induced ion leakage. Inclusion of the protein synthesis inhibitor cycloheximide negated the protective effects of these shock treatments. It appears that de novo protein synthesis is required for induction of chilling tolerance by a variety of chemical and thermal shock treatments.     

Involvement of putrescine in the inductive rooting phase of poplar shoots raised in vitro

Micropropagated poplar shoots rooted 100% on a rooting medium (A) containing NAA, but they did not root in the absence of auxin (NA). Putrescine, but not spermidine and spermine, promoted rooting up to 42% when added to the NA medium. Cyclohexylamine (CHA), an inhibitor of spermine synthase, also promoted (up to 36%) rooting in the absence of auxin. The inhibitors of polyamine biosynthesis DFMA (α-difluoromethylarginine) and DFMO (α-difluoromethylomithine), aminoguanidine (AG) and methylglyoxal-bis-guanylhydrazone (MGBG), inhibited rooting when applied in the presence of auxin and had no effect in its absence.
The rooting inductive phase (in the presence of auxin) was determined by periodical transfer of shoots from A to NA medium, and by changes in peroxidase activity, to be 7 h. Putrescine (not spermidine and spermine) accumulated to a maximum during the inductive phase. Both putrescine and CHA promoted rooting on NA medium when applied during the first 7 h. In contrast DFMA and AG inhibited rooting during this period. The results point to the involvement of putrescine and its Δ¹-pyrroline pathway, in the inductive phase of rooting in poplar shoots.     

Analysis of DNA polymerase activity in Petunia protoplasts treated with clastogenic agents

Clastogenic agents, i.e. agents that can induce chromosome or DNA breakage, have been shown to enhance the rale of direct gene transfer to protoplasts. The effect was analysed at the enzymatic level using protoplast homogenates as well as intact protoplasts. For that purpose existing procedures were modified to enable measurement of DNA polymerase in vivo. In the system used, external DNA was able to enter the cells without the addition of membrane-permeabilizing compounds. When comparing total DNA polymerase activity of protoplasts irradiated with X-rays or UV-light with that of untreated cells we did not observe significant differences. Incubation of protoplasts with high doses of bleomycin affected total DNA polymerase activity negatively. but dideoxythymidine triphosphate-sensitive activity was not influenced. We conclude that the DNA strand-breaks induced by low doses of X-rays. UV-light or bleomycin do not increase the total or the repair-DNA polymerase activity and. therefore. that the increase in the transformation rates after DNA strand-breaking is not preceded by enhanced DNA polymerase activity.     

Interaction between fatty-acid and starch synthesis in isolated amyloplasts from cauliflower floral buds

The interaction of fatty-acid synthesis with starch synthesis has been studied in intact amyloplasts isolated from floral buds of cauliflower (Brassica oleracea L.). These amyloplasts perform acetate-dependent fatty acid synthesis at maximum rates only at high external ATP concentrations. Neither pyruvate nor malate inhibit acetate-dependent fatty-acid synthesis. In contrast, acetate is inhibitory to the low pyruvate-dependent fatty acid synthesis. These observations indicate that neither pyruvate nor malate are used as natural precursors of fatty-acid synthesis. In contrast to fatty-acid synthesis, the rate of glucose-6-phosphate-dependent starch synthesis is already saturated in the presence of much lower ATP concentrations. Rising rates of starch synthesis influence negatively the process of acetate-dependent fatty acid synthesis. This inhibition appears to occur under both limiting and saturating concentrations of external ATP, indicating that the rate of ATP uptake is limiting when both biochemical pathways are active. The rate of starch synthesis is modulated specifically by the concentration of 3-phosphoglycerate in the incubation medium. This observation leads to the conclusion that the activity of ADP-glucose pyrophosphorylase is of primary importance for the control of both, starch and fatty-acid synthesis. Using the modified approach of Kacser and Burns (1973; Symp. Soc. Exp. Biol.27, 65–104) we have quantified the contribution of the rate of starch synthesis to the control of the metabolic flux through fatty-acid synthesis.Abbreviations ADPGlc-PPase ADPglucose pyrophosphorylase - Glc6P glucose-6-phosphate - PGA 3-phosphoglyceric acid     

Side reactions in the synthesis of phosphotyrosine-containing peptides

Summary A series of phosphopeptides Tyr(PO₃H₂)-Val-Pro-Xxx-Leu (Xxx=Met, Met(O), Nle, Dab or Cys), derived from the native platelet-derived growth factor- receptor (PDGF-) sequence, has been prepared to study their interaction with the src-homology 2 (SH2) domains of the p85 subunit of PI3 kinase. The phosphopeptides were synthesized using Fmoc methodology incorporating N-Boc dibenzyl-protected phosphotyrosine (Boc-Tyr[PO₃(Bzl)₂]) as the N-terminal amino acid, since the benzyl groups can be removed during resin cleavage with TFA. Only peptides containing methionine were found to exist partially as S-benzyl sulfonium salts after TFA cleavage from the resin. The desired peptide could be obtained from the S-benzyl sulfonium salt by hydrogenolysis.     

A facile method to prepare C-terminal fluorescently labelled peptides by an Fmoc strategy

Summary Spectrophotometric peptide probes, derivatized at the C-terminus, are conveniently prepared by means of an Fmoc solid-phase strategy. Using a resin such as Sasrin, the fully protected peptide can be cleaved from the resin with hydrazine, yielding the protected peptide-hydrazide which is subsequently oxidized to the azide. An amino-containing chromophore or fluorophore such as 5-[(2-aminoethyl)-amino]-naphthalene sulfonic acid (EDANS) can be coupled directly to this activated carboxyl group. This allows for specific placement of the fluorophore at the C-terminal carboxyl group in the presence of trifunctional amino acids.     

Prerequisite for His4 in deltorphin A for highδ opioid receptor selectivity

Summary Analysis of deltorphin A position 4 analogues included: backbone constrained N MeHis, spinacine (Spi), N MePhe and the tetrahydroisoquinoline-3-carboxylic acid (Tic); spatially confined side-chain (Phg); and imidazole alkylation ofl- andd-His⁴ enantiomers. High selectivity was lost with the following replacements: N MeHis⁴, N MePhe⁴ and Phg⁴ reduced binding and the constrained residues also increasedµ binding; ring closure between the side-chain and amino group to yield Spi⁴ or Tic⁴ increasedµ affinity. Imidazole methylation of His⁴ marginally affected opioid binding and doubled selectivity; alkylatedd-His⁴-derivatives generally maintained selectivity in spite of decreased affinities. Thus, His⁴ imidazole preserves selectivity by facilitating high binding and by repulsion at theµ receptor. Several low energy conformers of deltorphin A indicated that the His⁴ imidazole preferred a spatial orientation parallel to the phenolic side-chain of Tyr¹ suggestive that this conformation might contribute to high affinity and selectivity.