The effect of coumarin on the root growth was studied on roots from intact plants, isolated roots and isolated elongating zones. All material was cultivated aseptically. A new method was developed for sterile culture of intact plants in flowing nutrient medium.The effects on cell division and cell elongation were studied separately. An effect on both these processes can be established at all concentrations that affect the root growth. The concentration-growth curve has an "all-or-none" appearance.Coumarin inhibits the transverse divisions in all cell layers; the perivascular layers seem to be more sensitive. Also the mitotic activity that is involved in the initiation of laterals is inhibited. The longitudinal divisions within the stele are enhanced.Coumarin decreases the cell length in all cell layers, most likely with greater relative sensitivity in the perivascular layers. Studies on the time course of cell elongation in both attached corn roots and isolated elongating zones reveal that the decrease in cell length is caused exclusively by a decrease in the maximal rate of elongation, whereas the duration of the elongation is unchanged.With each decrease of the cell length, the cell diameter is increased. The two changes are intimately connected within the greater part of the active region of concentration. Studies on the time course of the radial expansion in isolated elongating zones show a strict connection in time between cell elongation and radial expansion.The radial expansion leads to unchanged or increased cell volume at most concentrations and for most cell types.Coumarin causes an inhibition of the longitudinally directed processes and a stimulation of the radially directed ones. This is interpreted as indicating that the formative system is disengaged or reorientated, i.e., the polarity of the cells is changed.Through experiments partly with isolated elongating zones and partly by disruption of the linear phase by means of mannitol, the inhibitory effect of coumarin could be localized to the first non-linear phase of the elongation.The results were compared with earlier findings in the literature. The microtubuli are proposed as a conceivable main component in the formative system common to both cell division and cell elongation. These are assumed to be affected by changes in the SH/SS balance produced by coumarin. Abbreviations: tubules. IAA = indol-3-acetic acid; MT = micro-10 1520 3040uM COUMARIN Figure 4. The effect of coumarin on the growth of wheat roots. -= growth in length during 2 days of roots of intact sterile plants. -= growth in length during 7 days of isolated roots. The concentration on a logarithmic scale.SVEN-BDRJE SVENSSON Physiol. Plant., 24, 19 '1

AbstraetThe effect of coumarin, IAA, ethylene, kinetin and gibberellic acid on roots of maize and wheat was investigated. Sterile attached and detached roots and isolated elongation zones were used. In some experiments a semi-sterile procedure was followed. The effects of the different regulators separately or in various combinations together with coumarin were studied on the root growth with regard to division, elongation and swelling of the cells. The ethylene production in isolated elongation zones was measured after treatment with coumarin, IAA, PCIB, kinetin, colchicine and dinitrophenol.The results show the following: 1) Each substance produces a specific morphologic pattern, 2) Changes in polarity were demonstrated for auxin-induced swelling in cell divisions and cell expansion and for coumarin-induced swelling in cell divisions. Other cell expansion in swollen parts was due to cylindric cells increasing in width while retaining their cylindric form, 3) Coumarin-induced inhibition could not be counteracted by IAA, PCIB, carbon dioxide, kinetin, gibberellic acid or Cycocel, 4) The ethylene production in isolated elongation zones increases noticeably after kinetin treatment, less strongly after auxin treatment and least after coumarin treatment. The production of ethylene does not seem to be correlated with the morphogenetic effect of the different substances, 5) The isolated elongation zones reacted to a) IAA and kinetin -with an increase in length in some cases and b) gibberellic acid with a reduction of their width, 6) The inhibitory effect of coumarin on the growth in length of the elongation zones was diminished by kinetin. The swelling produced by coumarin in these zones was reduced by gibberellic acid. The effects just mentioned of kinetin and gibberellic acid were considered as indirect ones, -From the present findings it was concluded that concomitant effects of auxin, ethylene, cytokinins and gibberellins are not obligatory for coumarin to exert its morphogenetic effects on root growth. In discussing the results some pitfalls in studies of growth reactions after application of hormones to roots containing meristem were emphasized.• , ,., . - -BaRJE SVENSSON Physiol. Plant., 26, 1972 SVEN

Short‐term effects of ABA, ABA + kinetin and kinetin on ion (86Rb‐potassium and phosphate) and water uptake in sunflower plants (Helianthus annuus var. californicus) were examined with a continuous‐recording technique. Ion uptake in the roots and transport to the shoots were also investigated by conventional tracer uptake experiments and by sap bleeding experiments with excised roots. After addition of 5 × 10−6‐4 × 10−5M ABA to the root medium there was an immediate decrease (30–70%) in the rate of ion uptake which lasted 30–70 min. The rate of water uptake was not significantly affected as measured with this method. Ion transport to the shoots and to the bleeding sap of excised roots was decreased by ABA. ABA‐induced inhibition of ion uptake was abolished by the presence of kinetin, and uptake was slightly stimulated by 2 × 10−5M kinetin alone. We suggest that concentration gradients of ABA or rapid changes in the ABA‐kinetin balance in the roots affect ion uptake and transport.

Coumarin induced root formation and stimulated fresh weight production in hypocotyl explants of Glycine max L. cultured in vitro. All stimulatory effects caused by coumarin were induced within a relatively narrow range of concentrations between 1–500 μM, yielding optimum dose response curves. When coumarin was combined with kinetin fresh weight increased considerably, at optimum concentrations to a level almost as high as that obtained with NAA (10 μM) and kinetin (10 μM). Root formation was almost completely inhibited when kinetin was added in combination with coumarin. NAA + coumarin had small stimulatory effects on fresh weight. but were inhibitory in root formation. The frequency of rooting per explant, texture and pigmentation were also affected by different treatments.

By means of the resonance frequency method Young's, modulus has been determined after coumarin treatment of growing segments of etiolated sunflower hypocotyl segments and in maize roots. Coumarin caused a decrease in Young's modulus in both shoot and root tissue. The response was very rapid; in sunflower hypocotyls the decrease in elastic modulus appeared 3 min after application of coumarin. The effects produced by coumarin were similar to those found by auxin. Coumarin increased the rate of water efflux out of potato parenchyma by about 20%. The increase in water permeability was evident within 3 min.