Some factors influencing exogenous auxin transport in intact plants

Eliezer, Jebakumar (1978) Some factors influencing exogenous auxin transport in intact plants. University of Southampton, Doctoral Thesis.

Abstract

Following the application of indol-3yl-acetic acid-l-14C (IM-1-14C)to the apical buds of intact Pisum sattivum, Phaseolus vulpnrin and Lupinus albun plants, transport profiles of 14C in the stain were constructed. Semi-logarithmic transport profiles were curvilinear aid closely fitted by error function diffusion analogue curves, from which estimates of transport velocity, transport flux and transport coefficient were obtained. These parameters of transport wore unaffected by call length in the transporting tissues of the stem. It was concluded that the speed of transport was independent of the number of calls per unit length of the, transport pathway and, therefore, was not limited by the inter-cellular ,component of the transport. The uptake of IM by the apical tissues, and the speed of movement of the transport front through the stem, were greater in light than in darkness. Tn P.sativum the velocity of movement of the transport front was directly proportional to temperature in the range 1°C to 35°C, and then decreased abruptly with further increases in temperature. The Q10 for velocity varied between 1'2 and 1.4, suggesting the major involvement of a physical process in the transport mechanism. The amount of 14C exported into the stem from the apical bud was optimal at about 25°C, and exhibited a Q10 of 2.2 in the range 10°C to 20°C. These results suggested that export, and therefore transport flux, were determined by metabolism-dependent mechanisms. The effects of temperature on transport were shown to operate directly on the transport system itself, and the speed and flux ofi transport wore not influenced Indirectly by affects of temperature on the activity of sinks for transported IM in the root system,Log velocity and Ing export wore found to be Inversely proportional to temperature and thin relationship was consistent with the involvement in IM transport of a mechanism, the rite of which in determined by the viscosity of the medium through which transport occurs. In both canon the slope of the relationship changed Abruptly at approximately 5°C, suggesting An abrupt increase in viscosity at this temperature. In view of the known Involvement of membrane-bound carriers in auxin transport it in suggested that this roprononts the temperature at which the call membrane underwent a phase change from a fluid to a crystalline form. On the basic of these results a now hypothesis to explain the mechanism of polar auxin transport is discussed. A study was also made of the kinetics of uptake, metabolism and export of IAA-l-14C by apical bud tissues of P.nativum, IAA-l-14C taken up entered a labile pool, which was not in diffusion contact with the tree space. This pool was depleted by conjugation of IM (to form IMspartate), binding (possibly to proteins), decarboxylation, and export of IM-1-14C to the transport system. A tentative scheme describing the compartmentalization of exogenous IAA in the apicali tissues is presented and discussed.

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