ABSTRACT
Allene oxide synthase (AOS; hydroperoxide dehydratase; EC 4.2.1.92) catalyzes the first step in the biosynthesis of jasmonic acid from lipoxygenase-derived hydroperoxides of free fatty acids. Using the AOS cDNA from tomato (Lycopersicon esculentum), in which the role of jasmonic acid in wound-induced defense gene activation has been best described, we examined the kinetics of AOS induction in response to wounding and elicitors, in parallel with that of the wound-inducible PIN II (proteinase inhibitor II) gene. AOS was induced in leaves by wounding, systemin, 12-oxophytodienoic acid, and methyl jasmonate. The levels of AOS mRNA started declining by 4 h after induction, whereas the levels of PIN II mRNA continued to increase up to 20 h after induction. Salicylic acid inhibited AOS and PIN II expression, and the addition of 12-oxophytodienoic acid or methyl jasmonate did not prevent the inhibition of PIN II expression in the presence of salicylic acid. Ethylene induced the expression of AOS, but the presence of ethylene alone did not produce an optimal induction of PIN II. The addition of silver thiosulfate, an ethylene action inhibitor, prevented the wound-induced expression of both AOS and PIN II. Products of hydroperoxide lyase affected neither AOS nor PIN II, but induced expression of prosystemin. Based on these results, we propose an updated model for defense gene activation in tomato.
Subject(s)
Gene Expression Regulation, Enzymologic , Gene Expression Regulation, Plant , Intramolecular Oxidoreductases/genetics , Solanum lycopersicum/genetics , Amino Acid Sequence , Base Sequence , DNA, Complementary , Enzyme Induction , Ethylenes/pharmacology , Gene Expression Regulation, Enzymologic/drug effects , Gene Expression Regulation, Plant/drug effects , Intramolecular Oxidoreductases/biosynthesis , Solanum lycopersicum/enzymology , Molecular Sequence Data , Salicylic Acid/pharmacology , Sequence Homology, Amino Acid , Transcriptional ActivationABSTRACT
The three-dimensional structures of the 2-, 3-, 4- and 6-monosulphates of methyl alpha-D-galactopyranoside have been determined by X-ray crystallography; the first two as the sodium salt, the third as both the sodium and potassium salts, and the fourth as a potassium salt. These represent the principal sulphated monomers of the carrageenan polysaccharides. The results extend our knowledge of the stereochemical features, such as ring conformation, sulphate geometry, hydrogen bonding and cation co-ordination, which characterize sulphated monosaccharides. The stereochemical data have been used to derive a mean geometry of the O-sulphate group and a set of force constants for use in molecular mechanics calculations on sulphated monosaccharides. These may be used in an extrapolation of the populations of stable conformers of related oligo- and polysaccharides.
Subject(s)
Carrageenan/chemistry , Galactose/analogs & derivatives , Carbohydrate Conformation , Crystallography, X-Ray/methods , Galactose/chemistry , Hydrogen Bonding , Models, MolecularABSTRACT
The crystal structure of neocarrabiose monohydrate, 3-O-(3,6-anhydro-alpha-D-galactopyranosyl)-beta-D-galactopyranose (C12H20O10.H2O) belongs to the monoclinic space group P2(1), and has a unit cell of dimensions a = 6.351(1), b = 7.675(2), c = 15.096(8) A, and beta = 91.11(1) degree. The reducing unit is in the 4C1 conformation, the non-reducing residue is 1C4, with the 3,6-anhydro bridge in an E conformation, and HO-6 is in a gauche-trans conformation. The orientation about the (1----3) linkage is defined by phi = 94.5 degrees and psi = 141.9 degrees. There is an intramolecular hydrogen bond (O-5'...O-2 = 2.777A). The conformation of the pyranose rings in solution, derived from 3JH.H values, were not significantly different from those in the crystal, but the 3,6-anhydro bridge assumed a half-chair conformation. All these features have been rationalised through molecular modelling and computation of potential energy surfaces.
