Water stress and indol-3yl-acetic acid content of maize roots

Abstract

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...

Effect of IAA produced by Klebsiella oxytoca Rs-5 on cotton growth under salt stress

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An Ethylene-Mediated Increase in Sensitivity to Auxin Induces Adventitious Root Formation in Flooded Rumex palustris Sm

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Effects of indole-3-acetic acid and zinc on the growth, osmotic potential and soluble carbon and nitrogen components of soybean plants growing under water deficit

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