Studies of hormone transport in roots of Vicia faba

Abstract

IAA 1-14C was applied in agar blocks to apical or basal ends of segments cut at various distances behind the tip, from roots of Vicia faba. Receiver blocks of plain agar were placed on the other end of segments. IAA uptake, distribution within the segments and movement out of segments was investigated. Three phases of uptake were distinguished;(1) an initial period of largely physical uptake lasting 40 minutes (2) a log period lasting 30 minutes (3) a period of linear uptake lasting several hours. The use of inhibitors indicated that this was largely metabolic uptake. Uptake increased with increasing distance behind the tip and increased proportionately with increasing IAA concentration. IAN uptake was similar to IAA uptake. There was no polarity of uptake or movement out of the segments. Movement was limited although activity in receivers increased steadily with time. It was concluded that root segments did not actively transport IAA. Radioactivity accumulated in the tip end of segments after basal uptake suggesting an inherent polarity within the segments. There was a gradient of increasing accumulation towards the tip. Alter uptake from apical donors there was a nearly linear logarithmic distribution of activity in the segment with distance from the donor. There was no evidence of loss of or IAA breakdown in the segments. Neither light, indole, sucrose or orientation of the segments with respect to gravity had any effect on uptake or distribution in the segments. Kinetin in donors stimulated IAA uptake but kinetin in receivers had no effect. The effects of pretreatment of segments in kinetin before taking up IAA were difficult to interpret owing to the complex side effects of soaking the segments. TIBA did not inhibit movement of IAA out of segments but it inhibited accumulation in the tip end of the segments.