Influence of BA and sucrose on the competence and determination of pepper (Capsicum annuum L. var. Sweet Banana) hypocotyl cultures during shoot formation

Summary The simultaneous presence of 6-benzyladenine (BA) and sucrose in a Murashige and Skoog medium (SIM) during the initial stages of shoot initiation have been found to be obligatory for high-frequency shoot formation in the Capsicum annuum L. var. Sweet Banana upper hypocotyl explants. The explants are determined for shoot formation following a minimum of 8 days of culture on SIM. Deprivation of exogenous sucrose from day 6 to day 20 of culture had no effect on the shoot forming response of the explants. BA and sucrose appear to act independently on different aspects of the competence of explants to respond to SIM during shoot initiation.Abbreviations BA N⁶-benzyladenine - MS Murashige and Skoog medium - SIM shoot induction medium - HFM hormone free medium - SUC sucrose minus medium     

Effects of fire on abundance of Eragrostis intermedia in a semi-arid grassland in southeastern Arizona

Abstract. Eragrostis intermedia (Plains lovegrass) is a midheight perennial bunchgrass native to semi-arid grasslands of the southwestern USA, that becomes an abundant and dominant component of these grasslands in areas long protected from livestock grazing. Substantial mortality of plains lovegrass occurred on a large livestock exclosure in southeastern Arizona, after a period of declining precipitation, but only in areas that had not burned in the previous three years. Lovegrass abundance subsequently increased on both undisturbed and burned sites, but remained substantially higher on the burned area. Long-term abundance of plains lovegrass may depend on episodic fire, particularly during periods of reduced precipitation.     

Theoretical conformational analysis of the opioid δ antagonist H-Tyr-Tic-Phe-OH and the μ agonist H-Tyr-D-Tic-Phe-NH2

A molecular mechanics study (grid search and energy minimization) of the highly δ receptor-selective δ opioid antagonist H-Tyr-Tic-Phe-OH (TIP; Tic: tetrahydroisoquinoline-3-car-boxylic acid) resulted in four low energy conformers with energies within 2 kcal/mol of that of the lowest energy structure. These four conformers contain trans peptide bonds only and represent compact structures showing various patterns of aromatic ring stacking. The centrally located Tic residue imposes several conformational constraints on the N-terminal dipeptide segment; however, the results of molecular dynamics simulations indicated that this tripeptide still shows some structural flexibility, particularly at the Phe³ residue. Analogous studies performed with the structurally related μ receptor-selective μ agonist H-Tyr-D -Tic-Phe-NH₂ resulted in low energy structures that were also compact but showed patterns of ring stacking different from those obtained with TIP. Superim-position of low energy conformers of TIP and H-Tyr-D -Tic-Phe-NH₂ revealed that the Phe³ residues of the L -Tic- and the D -Tic peptide were always located on opposite sides of the plane defined by the Tic residue, thus providing an explanation for the distinct activity profiles of the two compounds in structural terms. Attempts to demonstrate spatial overlap between the pharmacophoric moieties of low energy conformers of TIP and the nonpeptide δ antagonist naltrindole were made by superimposing either the Tyr¹ and Tic² aromatic rings and the N-terminal amino group or the Tyr¹ and Phe³ aromatic rings and the N-terminal amino group of the peptide with the corresponding aromatic rings and nitrogen atom in the alkaloid structure. In each case a low energy structure of TIP was found that showed good spatial overlap of all three specified pharmacophoric groups. These two conformers may represent candidate structures for the δ receptor-bound conformation of TIP. © 1994 John Wiley & Sons, Inc.     

Polygalacturonase-inhibiting protein accumulates in Phaseolus vulgaris L. in response to wounding, elicitors and fungal infection

Polygalacturonase-inhibiting protein (PGIP) is a cell wall-associated protein that specifically binds to and inhibits the activity of fungal endopolygalacturonases. The Phaseolus vulgaris gene encoding PGIP has been cloned and characterized. Using a fragment of the cloned pgip gene as a probe in Northern blot experiments, it is demonstrated that the pgip mRNA accumulates in suspension-cultured bean cells following addition of elicitor-active oligogalacturonides or fungal glucan to the medium. Rabbit polyclonal antibodies specific for PGIP were generated against a synthetic peptide designed from the N-terminal region of PGIP; the antigenicity of the peptide was enhanced by coupling to KLH. Using the antibodies and the cloned pgip gene fragment as probes in Western and Northern blot experiments, respectively, it is shown that the levels of PGIP and its mRNA are increased in P. vulgaris hypocotyls in response to wounding or treatment with salicylic acid. Using gold-labeled goat-anti-rabbit secondary antibodies in EM studies, it has also been demonstrated that, in bean hypocotyls infected with Colletotrichum lindemuthianum, the level of PGIP preferentially increases in those cells immediately surrounding the infection site. The data support the hypothesis that synthesis of PGIP constitutes an active defense mechanism of plants that is elicited by signal molecules known to induce plant defense genes.     

Possible mechanisms of afterripening in Xanthium seeds

Breaking dormancy in some seeds requires a period of dry storage. In the seeds of Xanthium pennsylvanicum Wallr., the process of afterripening proceeds optimally at water contents between 7 and 14%: this range of dehydration can be identified with water binding region 2, in which water is bound with low enthalpy. At water contents below 7%. Seeds remained primarily dormant over 3 years. Attempts to alter the afterripening with atmospheres of elevated nitrogen showed no effect. and with oxygen there was no consistent effect. There were no changes is osmotic value of the seed sap, or in its sugar or amino acid contents. We speculate that afterripening in Xanthium may involve some nonenxymatic reactions which remove substances which inhibit germination. Candidates for these reactions include the Amadori and Maillard reactions.     

Effects of promoter,intron and enhancer elements on transient gene expression in sugar-cane and carrot protoplasts

Various chimaeric promoter regions coupled to the uidA -glucuronidase gene were evaluated for transient expression strength following electroporation into sugar-cane (monocot) and carrot (dicot) protoplasts. Multiple enhancer elements increased expression in sugar-cane, by up to 400-fold for the artificial Emu promoter relative to the CaMV 35S promoter. The relative expression strengths of promoters varied substantially between the species. Sugar-cane also differed in some respects from previously tested species in the family Poaceae. For example, in sugar-cane the nopaline synthase and CaMV 35S promoters were of equivalent strength, and insertion of Adh1 intron 1 into the 5 transcribed region decreased expression strength.     

Spin Trapping of Methyl Radicals by the Acyl Nitroso Compound PH-C (= O)NO Formed in the Photochemical Reaction Between Benzohydroxamic Acid, Dimethyl Sulfoxide and Hydrogen Peroxide. An Epr Study

By the use of EPR spectroscopy, it has been shown that acyl nitroso compounds can act as spin traps for short-lived radicals with the formation of acyl aminoxyl radicals. The reaction was studied for the system benzohydroxamicacid[Ph-C (= O)N(H)] - dimethyl sulfoxide - hydrogen peroxide. The acyl aminoxyl radicals appeared almost immediately when the reaction mixture was irradiated in situ in the EPR cavity with UV light. The trapping reaction involved two photochemical reactions, i.e. the oxidation of the hydroxamic acid to the acyl nitroso compound Ph-C (= O)NO, and the formation of methyl radicals from dimethyl sulfoxide. The EPR spectra are superpositions of the spectra of two species of acyl aminoxyl radicals, i.e. the radicals Ph-C (= O)N(O·)H formed by oxidation of the parent benzohydrox-amic acid, and the radical Ph-C (= O)N(O·)CH₃, formed by trapping of methyl radicals.