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Application of indoleacetic acid (IAA) and other auxins causes cultured radish (Raphanus sativus L. 'Scarlet Globe') seedling root segments to produce an increased frequency (FR, no. cm ') of lateral roots (LR); in the absence of auxin, segments spontaneously form about 6 LR cm-'. A dose-response study has revealed that the increase in FR follows a biphasic Michaelis-Menten relationship with the medium concentration of the undissociated form of IAA ([IAAH] MATERIALS AND METHODSRadish (Raphanus sativus L. 'Scarlet Globe') seeds were germinated in the dark at 24°C. After 3 d, root segments were excised between 0.5 and 3 cm behind the tip. Four segments were inoculated into 25 ml of medium contained in 125 ml Erlenmeyer flasks. Three or more replicate flasks were used for each treatment. The culture medium consisted of MurashigeSkoog salts (14), 88 mm sucrose, and 10 mm Mes and/or 10 mM succinic acid. Mes was used to buffer pH in the range 5.5 to 6.5, while succinic acid was used for the range 4 to 5.5; both were added to the medium when the pH was varied across the two ranges. Autoclaving caused pHm to change by as much as 0.

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ABSTRACI Segments (2.5 cm) cut from 3day-old seedling roots of radish (Raphanus sativus L. 'Scarlet Globe') were cultured in medium with or without indoleacetic acid (IAA). Lateral root primordia frequency, determined for the central centimeter of segments, was dependent on IAA concentration and on conditions affecting IAA uptake. Dimethyl sulfoxide treatment, or a relatively low medium pH, greatly enhanced the response to exogenous IAA. It was concluded that a permeation barrier exists between the external medium and the hormone responsive sites within the radish seedling root.A characteristic action of IAA is to stimulate the formation of LR.3 This IAA effect has been studied using simple experimental systems employing excised or intact seedling roots (1, 10-1 3, and references cited therein). Using our system (1) based on the radish (Raphanus sativus L. 'Scarlet Globe') seedling root, we find that the response to exogenous auxin can be substantially modulated by chemical or physical factors known or presumed to influence diffusional IAA uptake by plant cells. The observations reported here indicate that there is an IAA permeation barrier between the external medium and the auxin-responsive sites involved with LR formation within the radish seedling root. MATERIALS AND METHODSThese studies were performed with roots of seedlings germinated and grown in the dark at 24C for 3 d, during which time the roots grew to an average length of 6 cm. Excised 2.5 cm segments, cut starting 0.5 to 1.5 cm behind the seedling root tip, were cultured 4 d in medium containing Murashige-Skoog salts (7), 88 mol m-3 sucrose, and 10 mol m-3 each of the buffers Mes and succinic acid. IAA RESULTS AND DISCUSSION Exogenous IAA greatly increased the frequency (i.e. the number/cm) of LRP formation, which varied from 5 cm-' in the absence of IAA to about 60 cm-' under optimal conditions. Excess IAA inhibited LRP formation. Figure 1 illustrates the effect of 30 mmol m-3 IAA, and the modulation ofthe response by pH and DMSO. Typical treatment mean frequencies of LRP formation in medium containing IAA were: 49.7 ± 3.6 SE LRP cmn' at pH 4.5 and 19.0 ± 1.9 SE LRP cm ' at pH 6. Treatment with DMSO increased the response to IAA at pH 6; a typical treatment mean frequency was 48.1 ± 3.8 SE LRP cm-'.DMSO is known to increase plasmalemma permeability to small molecules (3). In our experience, it was found most effective when given as a pulse treatment at a medium concentration of 5% (v/v) during the first 1 to 4 h of culture. Longer exposure to DMSO, or higher concentrations of DMSO, were inhibitory. DMSO by itself (i.e. with no exogenous auxin) had no promotive effects on the frequency of LRP formation. Administration of a 5% DMSO 4 h pulse treatment when medium containing 30 mmol m-3 IAA was buffered at pH 4.5, rather than 6, inhibited LRP formation.The effect of pH on IAA uptake by plant cells has been well characterized (4, 9). Since the membrane permeability coefficient to the lipophilic IAAH is on the order of 103 times that of IAA-(9), lowe...

Broad Breasted Bronze male turkeys, 20 weeks of age, were fed all mash finishing diets with and without whole rape seed as an energy source. Whole rape seed, at a level of 22.8 per cent, was substituted for all of the soybean oil meal and part of the ground wheat in the ration. Each treatment was replicated six times with 12 male turkeys per replicate. At the end of the 4-week feeding period the following results were evident: 1) no statistically significant differences in feed conversion (P > 0.05), and 2) highly significant improvements in carcass finish and live weight gains (P < 0.01) for those birds receiving the diet containing whole rape seed.