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Applications of indole-3yl-acetic acid (IAA) and abscisic acid (ABA) were done on two-day-old intact maize (cv LG 11) roots. The effect of the treatment on the root growth depends on their initial elongation rate. The slow growing roots were all inhibited by exogenous IAA and ABA at any concentrations used whereas for the fast growing roots their elongation was promoted by these two hormones at low concentrations. Quantitative analyses of endogenous IAA and ABA were performed using the gas chromatography-mass spectrometry technique. Detection and quantification of endogenous IAA and ABA were done on the zone of the root implicated in elongation. These techniques were achieved by electron impact on the IAA-Me-heptafluorobutyryl derivative and by negative ion chemical ionization with NH3 on the ABA-Me ester derivative. A negative correlation between the growth and the endogenous content of these two hormones was obtained. ABA presented a larger range of endogenous level than IAA on the whole population of roots tested. When using applied IAA and ABA at different concentrations the same differentiating effect on the growth was observed. This allowed us to conclude that for identical concentrations, IAA has a more powerful effect on root elongation than ABA. Present results are discussed in relation to previous data related to the role of IAA and ABA in the growth and gravireaction of maize roots.Root elongation is controlled by several endogenous regulators (2,3,24) whose interaction appears essential (19). Many published results indicate that, at least in the elongating part of the root, some growth inhibitors produced in the cap move from the tip to the base (8,15,16). The preferential movement of ABA is basipetal (6,10,17) while that of IAA is acropetal (2, 9, 14). Exogenous IAA usually inhibits root growth (19, 22,30) as does applied ABA (18,20). But in some cases IAA (13, 22) gravitropism (4, 29). The same technique has also indicated similar relations with ABA content in roots (21,28).The aim of the present work was to analyze the level of endogenous IAA and ABA in maize roots to understand better some controversial data obtained on the growth effect of these hormones when applied. It was necessary to correlate for identical material which means growth in the same conditions, information about the endogenous hormone content and the concentration effect of applied hormone on root growth. The reason that we insisted on identical material was that, unfortunately, many reports have used different material for testing both elongation and for analyzing hormone content. Furthermore, in the roots which we have used, it is the zone 2.5 to 5.00 mm behind the tip which is most relevant to total axial growth. It is in this zone that the hormone status of the root has been analyzed. which humid atmosphere (90 ± 5%) was maintained. After 4 h, the elongation that had occurred in that period was measured and two groups of roots were selected: roots having a low (about 0.37 mm-h-') or a high (about 0.81 mm-h-') gro...

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:

The distribution of elongation and surface pH patterns along the primary roots of maize (cv. LG 11), maintained vertically in humid air (darkness, 22°C), have been analysed quantitatively. A new technique employing Sephadex G 25 beads containing a pH indicator dye (bromocresol purple), was used for measuring both the growth gradient of the roots (Sephadex beads as markers) and at the same time, the surface pH changes (referring to a standard scale). The optimal axial growth was located between 2 and 4 mm from the tip. This coincides with the optimal decrease in surface pH.

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The level of endogenous Indol-3-yl-acetic acid (IAA) measured by gas chromatography-mass spectrometry in the elongating zone of intact primary roots of Zea mays showed a good linear correlation with the growth rate of these roots. When they were treated with IAA, their relative elongation decreased; this indicates a supraoptimal content of endogenous IAA. However, the growth of some of the relatively rapidly extending roots was enhanced by such treatment. Interactions between endogenous and applied IAA in the control of root growth are discussed.

Abstract. Water-stress conditions were applied to the apical 12 mm of intact or excised roots of Zea mays L. (cv.LG 11) using mannitol solutions (0 to 0.66 M) and changes in weight, water content, growth and IAA level of these roots were investigated. With increasing stress a decrease in growth, correlated with an increased IAA level, was observed. The largest increase in IAA (about 2.7-fold) was found in the apical 5 mm of the root and was obtained under a stress corresponding to an osmotic potential of -1.39 MPa in the solution. This stress led to an isotonic state in the cells after 1 h. When the duration of water stress (-1.09 MPa) was increased to 2 or 3 h, no further increase in the IAA content was observed in the root segments. This indicated that there was no correlation between a hypothetical passive penetration of mannitol in the cells and IAA content. Indol-3yl-acetic acid rose to the same level in excised as in intact roots. In both cases, IAA accumulation was apparently independent of the hydrolysis of the conjugated form. The caryopsis and shoot seem not to be necessary to induce the increase of the IAA level in the roots during water stress (-1.09 MPa). Therefore, there seems to be a high rate of IAA biosynthesis in excised maize roots under waterstress conditions. Exodiffusion of IAA was observed during an immersion in either buffer or stress (-1.09 MPa) solution. In both cases, this IAA efflux into the medium represented about 50% of the endogenous level. Considering the present results, IAA appears to play an important part in the regulation of maize root metabolism and growth under water deficiency.Key words: Auxin -Mannitol -Root -Water stress -Zea bolic changes (Morgan 1990). Such results, and those related to the effects of applied hormones, suggest the involvement of plant growth substances in the metabolic responses of plants during and after dehydration. Hormones control stomatal opening, and regulate growth and water uptake (Pilet and Barlow 1987). By far the most-studied hormone under water-stress conditions is cis-abscisic acid (ABA), and review articles (Bradford and Hsiao 1982;Davies et al. 1986) point out the paucity of information concerning the synthesis of other growth regulators under these conditions.Results concerning the effect of water stress on IAA level are scarce and often conflicting. It has been reported (Hartung and Witt 1968) that the diffusable IAA content in both Helianthus annuus (stem segments) and Anastatica hierochuntica (leaves) decreases with decreasing availability of water in the soil. On the other hand the IAA level in Viciafaba leaves strongly increases during a drying cycle (Hall et al. 1977). In cotton, water stress reduces the concentration of free and conjugated IAA in flower buds during the first irrigation cycle, but increases them during the second one. In flowers, dehydration slightly increases the content of conjugated IAA but has no effect on the level of free 1AA (Guinn et al. 1990). To our knowledge, IAA has never been quantified under water-st...

Quantitative analyses of abscisic acid (ABA) in different parts of maize root tips (Zea mays L. cv. Kelvedon 33) were performed by mass fragmentography using the hexadeuterated analog of ABA as internal standard. It was found that the cap and the apex contained 36.1 μg and 66.5 μg ABA kg(-1) fresh weight, respectively. The possibility that the growth regulator formed in the cap and inhibiting the elongation of the extending zone of the root is ABA is discussed.