Soluble auxin-oxidases were extracted from Zea mays L. cv LGlI apical root segments and partially separated from peroxidases (EC 1.11.1.7) by size-exclusion chromatography. Auxinoxidases were resolved into one main peak corresponding to a molecular mass of 32.5 kilodaltons and a minor peak at 54.5 kilodaltons. Peroxidases were separated into at least four peaks, with molecular masses from 32.5 to 78 kilodaltons. In vitro activity of indoleacetic acid-oxidases was dependent on the presence of MnCI2 and p-coumaric acid. Compound(s) present in the crude extract and several synthetic auxin transport inhibitors (including 2,3,5-triiodobenzoic acid and N-1-naphthylphthalamic acid) inhibited auxin-oxidase activity, but had no effect on peroxidases. The products resulting from the in vitro enzymatic oxidation of [3H] indoleacetic acid were separated by HPLC and the major metabolite was found to cochromatograph with indol-3yl-methanol.Two pathways for the oxidative degradation of IAA have been established. The first involves oxidation of the indole nucleus (32) by a specific enzyme which catalyzes the formation of oxindole-3-acetic acid (OxIAA2; 23), whereas the second pathway consists of the oxidative decarboxylation of the side chain. Peroxidases (EC 1.11.1.7) from numerous plant species have been shown to catalyze this oxidative decarboxylation (27), leading to the formation of either indol3yl-methanol (17) or 3-methyleneoxindole (6). The ratio of the production of these last two compounds is influenced by several factors including the nature of the cofactors added to study the reaction in vitro, the pH, and the enzyme/substrate ratio (4, 26).The breakdown of IAA catalyzed by peroxidases has been studied in a number of systems, and the requirement for added cofactors and for H202 differs between species. The degradation of auxin by HRP may occur without added cofactors, and in the presence or absence of H202 (6). However, tomato peroxidases are dependent on the presence of H202 for the oxidation of IAA (9) and fail to catalyze the reaction in the presence of compounds such as 2,4-dichloro-'Present address:

E. 1994. Cell wall-bound trans-and cis-ferulic acids in growing maize roots -Physiol. Plant. 90; 734-738.The levels of ceil wall-bound trans-and ci's-ferulic acids in roots of dark grown Zea mays cv.LGl 1 plants were measured. They were quantified after alkaline hydrolysis of purified cell walls by reversed phase HPLC using fran.!-cinnamic acid as internal standard. The total amount of ferulic acid (trans-and cH-feruilc acid) in the root ba.se was 3-4 times higher than in the root tip. Cu-ferulic acid represented between 2% (tip) and 18% (base) of the total ferulic acid content. The total content of trans-and f is-femlic acids was approximately the same in the stele and the cortex, but the level of CK-ferulic acid in the stele was 5-6 times higher than in the cortex. Trans-and cK-ferulic acid levels as well as the percentage of cis-ferulic acid in the elongation zone were steady between 48 and 96 h after the beginning of germination. Slowly growing roots contained more wall-hound ferulic acids, particularly m-femlic acid, than fast growing roots. This relationship was found in the differentiation zone but not in the elongation zone. The importance of cell wall-bound trans-and ci.s-ferulic acids is discussed in the context of root growth and differentiation.

The quantities of endogenous indol-3y1-acetic acid (IAA) in endosperms and scutella of 6-day-old maize seedlings (Zea mays L. cv Giant White Horsetooth) were determined by a fluorimetric method. Endosperms were found to contain 33A nanograms IAA per plant, and scutella 7.5 nanograms IAA per plant. [5-3HIIAA applied to endosperms of 6-day-old seedlings moved into the roots and radioactivity accumulated at the apex of the primary root within 8 hours. Two to 7-day-old seedlings were treated simultaneously with IS3HIIAA in the endosperm and 12-'4C1 IAA on the shoot apex. The patterns of transport into the root were found to change during ontogeny: in successively older plants, transport from the shoot into the roots increased relative to transport from the endosperm into the roots. The auxin required for the growth of maize roots could, therefore, partially be contributed by the shoot and endosperm. Ontogenetic changes in the relative importance of these two supplies could be of significance for the integration of growth and development between shoot and root.It has been suggested (7,(23)(24)(25) (1,2,5,12,15,29). The caryopses therefore represent a potential supply of auxin for the roots and shoots. Radioactive IAA applied to maize endosperms has been shown to be transported into the shoot (3, 9, 11, 21) and into the root (3). In Vicia faba, IAA is transported into the root from the epicotyl and from the seed (28). It has recently been shown (4) that the maize endosperm and coleoptile both influence the growth and gravireaction of primary roots, although the way in which control is achieved is not yet clear.The purposes of the present investigation were first to determine the distribution of free IAA in caryopses of 6-d-old maize seedlings, second to determine whether IAA is transported from the caryopsis into the roots, and third to investigate the relative contributions of IAA supplied by the shoot and caryopsis to the roots of plants of different ages. The last of these questions was to be resolved using a double-label technique whereby shoot-toroot transport and endosperm-to-root transport could be measured simultaneously in the same plants. ' Extraction and Assay of IAA. Five g of lyophilized plant material were finely ground and homogenized for 3 min in 37.5 ml of freshly redistilled methanol using an M.S.E. homogenizer (Measuring and Scientific Equipment, London, U.K.) fitted with an ice bath. The slurry was filtered through a glass-fiber pad on a sintered glass funnel, with suction, and the residue resuspended in 25 ml of methanol, homogenized for 3 min, and filtered. The extraction was repeated and the free extracts pooled. [2-'4C]IAA (2.1 ng; 1500 dpm) (55 Ci mol'; Radiochemical Centre, Amersham, U.K.) were added to permit the estimation oflosses during purification. The same method was used for endosperms and scutella; the quantities of solvents, etc., given above are those used when 5 g dry weight of endosperm were extracted; when scutella (which weigh less per unit) were used, the volumes of ...

Two lines of evidence have been cited to support the assertion that the root cap is the sole site of graviperception in the root. The first evidence is based on surgical removal of the cap, which abolishes the response to gravity. This is sufficient to conclude that the cap is involved in gravitropism, but not to conclude that the cap is the site of graviperception. The second is based on the results of centrifugation experiments, in which different parts of the plant are subjected to different centrifugal forces. The data from such experiments have been cited to support the conclusion that the perception of gravity is limited to the rootcap. However, these data actually support the conclusion that gravity is perceived throughout the root tip, and not only in the root cap. We believe that the data support the conclusion that the root cap is involved in root gravitropism, but that there is inadequate evidence to conclude that the cap is the sole site of graviperception.

The uptake of 5-[3Hlindol-3yl-acetic acid (IAA*) by segments of Zea mays L. roots was measured in the presence of nonradioactive indol-3yl-acetic acid (IAA°) at different concentrations. IAA uptake was found to have a nonsaturable component and a saturable part with (at pH 5.0) an apparent K, of 0.285 micromolar and apparent V,,,, 55.0 picomoles per gram fresh mass per minute. These results are consistent with those which might be expected for a saturable carrier capable of regulating IAA levels. High performance liquid chromatography analyses showed that very little metabolism of IAA* took place during 4 minute uptake experiments. Whereas nonsaturable uptake was similar for all 2 millimeter long segments prepared within the 2 to 10 millimeter region, saturable uptake was greatest for the 2 to 4 millimeter region. High levels of uptake by stelar (as compared with cortical) segments are partly attributable to the saturable carrier, and also to a high level of uptake by nonsaturable processes. The carrier may play an essential role in controlling IAA levels in maize roots, especially the accumulation of IAA in the apical region. The increase in saturable uptake toward the root tip may also contribute to the acropetal polarity of auxin transport.The natural occurrence of IAA in maize roots was unequivocally established by 5,26). There is evidence that IAA plays a part in the regulation of root growth and gravireaction, though it is not clear how this control is exercised. The growth rate of maize roots was found to be inversely correlated with the level of endogenous IAA in the elongating zone (24). Applied IAA has been shown to inhibit root growth (2) but stimulates the growth of auxin-depleted roots (23).When roots are treated with inhibitors of auxin transport, gravireaction is strongly retarded and growth is inhibited (6, 12). When triodobenzoic acid was applied only to the caps of pea roots (11) gravireaction was inhibited but growth appeared to be unaffected. The effect of auxin on growth and gravireaction may therefore depend on the level of IAA in the elongating zone or, more specifically, on the action of the carrier for IAA efflux.Transport between tissues and subcellular compartments is one of the factors influencing the levels of IAA in different tissues and in various parts of the cell. The transport of auxin in the root tip is acropetally polarized (20,21,30,31) and involves movement from cell to cell. The transfer of IAA across cell membranes comprises uptake and efflux, both of which may be partly by diffusion and partly via carriers.According to the chemiosmotic polar diffusion theory (25, 28) energy is expended creating a gradient of pH and of electrical potential across the plasmalemma and IAA, which is a weak acid (pK 4.7), accumulates as the anion inside the cytoplasm. Polarity of auxin transport is conferred by a carrier for the efflux of IAA across the plasmalemma, located preferentially at the apical end of the cell (basal end in the case of shoots). This carrier has been shown to be...