A comparison of the effects of IAA and 4-Cl-IAA on growth, proton secretion and membrane potential in maize coleoptile segments.
The physiological activity of exogenous 4-Cl-IAA, as compared to IAA, was examined in maize coleoptile segments. It was found that in this model system 4-Cl-IAA is much more active in the stimulation of elongation than IAA. Simultaneous measurements of growth and external pH indicated that administration of either IAA or 4-Cl-IAA resulted in medium acidification. The kinetics of the pH changes, however, were faster after the addition of 4-Cl-IAA. In contrast to IAA, the coleoptile segments treated with chlorinated auxin were not able to increase medium pH after its initial drop. The re-addition of IAA after 5 h further enhanced growth over the next 2 h by 31%. By contrast, the re-addition of 4-Cl-IAA at the same time protocol as IAA did not cause an additional effect. The administration of 10 microM IAA induced in maize coleoptile cells a transient depolarization followed by a slow hyperpolarization of their membrane potential. In contrast to IAA, 4-Cl-IAA at 1 microM caused an immediate hyperpolarization of the membrane potential which, on average, was 2-fold greater than for IAA. The results reported here provide further evidence that 4-Cl-IAA is much more active, as compared to IAA, in stimulating the growth of maize coleoptile segments. Although it has not been directly demonstrated here, a plausible interpretation for the high 4-Cl-IAA activity is that, at least in part, it might be caused via a reduced metabolism of 4-Cl-IAA. Furthermore, for the first time, the data show that membrane potential responds to 4-Cl-IAA in a qualitatively different fashion than to IAA. These findings may, in turn, suggest a specific signal transduction pathway to 4-Cl-IAA in maize coleoptile cells.
Karcz
Waldemar
W
University of Silesia, Faculty of Biology, Department of Plant Physiology, ul. Jagiellonska 28, PL-40032 Katowice, Poland. karcz@us.edu.pl
Burdach
Zbigniew
Z
D018548:Cotyledon / Q000187:drug effects* / Q000254:growth & development; D006863:Hydrogen-Ion Concentration; D007210:Indoleacetic Acids / Q000494:pharmacology*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects*; D015398:Signal Transduction; D003313:Zea mays / Q000187:drug effects* / Q000254:growth & development
D007210:Indoleacetic Acids; C096198:4-chloroindole-3-acetic acid; C030737:indoleacetic acid