Growth Substance Interactions during Uptake by Mesocotyl Segments of Zea mays L.

Abstract

The effects of various growth substances on the ‘metabolic’ uptake of indol-3yl-acetic acid (IAA) by Zea mesocotyl segments was investigated using methods of fluorescence spectroscopy and radioactivity assay. 2, 4-Dichlorophenoxyacetic acid (2, 4-D) and α-(I-naphthylmethylthio)propionic acid (NMSP) exerted no discernible effects on IAA uptake, whereas N-I-naphthylphthalmic acid (NPA) stimulated uptake to some degree. Low concentrations of 2,3,5-tri-iodobenzoic acid (TIBA) promoted the uptake of low IAA concentrations, while higher concentrations were decidedly inhibitory. 2,4-Dinitrophenol (DNP), ioxynil, and bromoxynil also induced marked inhibition presumably by preventing oxidative phosphorylation. The uptake interactions between these compounds were examined in relation to concentration and time. In no case was there evidence of competitive interaction. The inhibitory effects of TIBA on IAA uptake were considerably greater than those of DNP. SH-enzyme protectors such as BAL and cysteine did not relieve these inhibitions. The absorption of TIBA-¹³¹I was completely unaffected by any concentration of IAA tested. Chromatographic and radio-autographic analysis revealed no detectable products of IAA-I-¹⁴C metabolism or degradation in maize mesocotyl tissue during the 6-h experimental period and this was not altered by TIBA treatment. Respiratory decarboxylation of IAA-I-¹⁴C was found to be negligible and unaffected by TIBA.