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Lateral diffusion of polarly transported indoleacetic acid and its role in the growth of Lupinus albus L. hypocotyls (1991)

Sánchez-Bravo, J. ; Ortuno, A. ; Botia, J. M. ; [et al.]

Springer

Planta 185 (1991), S. 391-396

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ISSN: 1432-2048

Keywords: Auxin metabolism, transport ; Elongation growth ; Cortex-stele auxin distribution ; Lupinus (auxin transport) ; Polar auxin transport

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract The transport and metabolism of indole-3-acetic acid (IAA) was studied in etiolated lupin (Lupinus albus L, cv. Multolupa) hypocotyls, following application of dual-isotope-labelled indole-3-acetic acid, [5-3H]IAA plus [1-14C]IAA, to decapitated plants. To study the radial distribution of the transported and metabolized IAA, experiments were carried out with plants in which the stele was separated from the cortex by a glass capillary. After local application of labelled IAA to the cortex, radioactivity remained immobilized in the cortex, near the application point, showing that polar transport cannot occur in the outer tissues. However, following application of IAA to the stele, radioactivity appeared in the cortex in those hypocotyl sections below the first 1 cm (in which the capillary was inserted), and the basipetal IAA movement was similar to that observed after application of IAA to the complete cut surface. In both assays, longitudinal distribution of 14C and 3H in the stele outside the first 1 cm was positively correlated with that of cortex, indicating that there was a lateral migration of IAA from the transport pathway (in the stele) to the outer tissues and that this migration depended on the amount of IAA in the stele. Both tissues (stele and cortex) exhibited intensive IAA metabolism, decarboxylation being higher in the stele than in the cortex while IAA conjugation was the opposite. Decapitation of the seedlings caused a drastic reduction of hypocotyl growth in the 24 h following decapitation, unless the hypocotyls were treated apically with IAA. Thus, exogenous IAA, polarly transported, was able to substitute the endogenous source of auxin (cotyledons plus meristem) to permit hypocotyl growth. It is proposed that IAA escapes from the transporting cells (in the stele) to the outer tissues in order to reach the growth-responsive cells. The IAA metabolism in the outer tissues could generate the IAA gradient necessary for the maintenance of its lateral flow, and consequently the auxin-induced cell elongation.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00201062

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A CI pseudopotential-based description of the low-lying states of Ag O2 (1990)

Bravo, G. ; Flores-Riveros, A. ; Novaro, O.

New York, NY : Wiley-Blackwell

International Journal of Quantum Chemistry 37 (1990), S. 785-796

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ISSN: 0020-7608

Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology

Notes: Extensive SCF-LCAO-MO variational and perturbative configuration interaction (CI) calculations framed within an effective core potential approximation have been performed to determine the two experimentally observed geometrical isomers of Ag O2 and the interconversion route between them. These structural forms, associated to the ground-state local minima, yield virtually the same energy, and their spontaneous interconversion is strongly indicated, which agrees fairly well with the experimental measurements. The reaction Ag + O2 → Ag O2 was theoretically analyzed along a CI fully optimized energy pathway for the ground and various excited states, within C2v and Cs symmetry. Although a tight-ion pair (Ag+ O2-) character is predicted for the ground state at the equilibrium geometries, its dissociation leads to neutral rather than to ionic fragments. The study of the reaction path within Cs symmetry shows an avoided crossing between the ground state and another 2A″ potential curve where the former correlates adiabatically with the reactants Ag(2S) + O2(1Δg). This indicates that the formation of the complex proceeds via a reactive state of molecular oxygen. The higher 2A″ electronic curves correlate with the metal 2P excited state, and the oxygen binding is found to be less favorable. The present results are shown to have an important bearing on the experimentally known catalytic properties of oxygen adsorbed on silver surfaces.

Additional Material: 4 Ill.