Effect on Root Growth of Endogenous and Applied IAA and ABA

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The growth of intact maize (Zea mays L.) roots and the abscisic acid (ABA) content (measured by gas chromatography-mass spectrometry of the root tip were analyzed after a white-light treatment. The decrease of the elongation rate due to the illumination corresponded to a concomitant increase in the ABA found in the root. When selecting roots, on the basis of their growth rate, it was possible to show that the relation between growth and ABA content, previously reported in darkness was conserved after light treatments. Therefore, light decreased the root growth rate while it simultaneously increased the ABA content in the roots. This increase was higher than expected, demonstrating the complexity of the involvement of ABA on root growth.

Section: Light Effect On Roots From Different Growth Classescontrasting

confidence: 36%

Section: Light Effect On Roots From Different Growth Classesmentioning

confidence: 99%

Section: Growth Measurementsmentioning

confidence: 99%

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Endogenous ABA in Growing Maize Roots: Light Effects

Saugy

Mayor²,

Pilet³

1989

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“…Pilet and Saugy (27) have reported that slow growing roots were all inhibited by exogenous IAA (at any concentration), whereas the elongation of fast growing roots was promoted by IAA at low concentrations. It has also been reported that the uptake of IAA (and therefore its cytosolic concentration) may be pH dependent (20).…”

Section: Current Generation and Root Growthmentioning

confidence: 99%

Correlation between Root-Generated Ionic Currents, pH, Fusicoccin, Indoleacetic Acid, and Growth of the Primary Root of Zea mays

Miller¹,

Gow²

1989

Correlations between root-generated ionic currents, extracellular pH, indoleacetic acid, fusicoccin, and growth were investigated. Current consistently entered the meristematic and elongating tissues of intact growing roots of Zea mays cv Golden Bantam. Mature root regions generated the outward limb of the current loop. Ion-substitution and pH-profile experiments suggested that the bulk of the ionic current was carried by H. Calcium ions did not carry current, but calcium may regulate the proton circulation since the proton current density was slightly larger in calcium-depleted media. Increased root elongation at low pH was associated with increased current density and an extended zone of inward current. Conversely decreased elongation at high pH was associated with a reduced current density and a more restricted zone of inward current. The effect of the fungal toxin fusicoccin was to increase the current density of the inward limb of the ion current and to increase root extension. Concentrations of indoleacetic acid that reduced root growth, also reduced the density of the inward current and shortened the inward current zone. The results emphasize the point that roots are electrically contiguous over many millimeters and that the electrophysiology of root growth is best studied in intact root systems.

“…Three mechanisms of galactose action have been proposed: (a) The inhibition of sugar metabolism for cell wall synthesis, (b) the inhibition of auxin synthesis (1), and (c) the promotion of ethylene production. It seems unlikely that inhibition of auxin production causes the inhibition of elongation in the root system since auxin levels are known to be supraoptimal for root elongation under some conditions, and the elongation rate increases by lowering the auxin level (20). Although ethylene is also known to suppress root elongation, the enhancement of ethylene production may not be the cause of the inhibition of acid-enhanced elongation by galactose, since galactose-enhanced ethylene production appears to take a long time and, for instance, was detected only after a 10 h lag in mung bean hypocotyls (5).…”

Section: Discussionmentioning

confidence: 99%

Inhibition of Acid-Enhanced Elongation of Zea mays Root Segments by Galactose

Tanimoto¹,

Scott²

1989

The effect of sugars and metabolic inhibitors on the elongation of Zea mays root segments was analyzed by a rhizometer which records the elongation of each of 32 root segments at the same time. Galactose suppressed the acid-enhanced rapid elongation after a lag period of 1.5 hours, but it did not inhibit the slow elongation at pH 7. Mannose was less inhibitory than galactose.Arabinose, xylose, glucose, sucrose, mannitol, and sorbitol caused no inhibition. When galactose was removed after a 1-hour treatment, the elongation was partially recovered. Cycloheximide and 2-deoxyglucose suppressed acid-enhanced elongation when these were applied at the same time as acid treatments, whereas cordycepin (3'-deoxyadenosine) inhibited elongation only if it was applied prior to acid treatment. Over the 9-hour period of elongation studied, the inhibition by galactose was comparable to that of cycloheximide. Since galactose has been reported to suppress the sugar metabolism necessary for the cell wall synthesis, the later phase of acid-enhanced elongation of root segments may at least partially depend on the synthesis or metabolism of cell wall components. The inhibition of root growth by galactose may be partially ascribed to a direct effect on the elongation process in roots, an effect that is enhanced by the acidification of the cell walls.Galactose is known to inhibit root growth in many plant species, such as wheat (3, 16), maize (1 1, 12), pea (16), and tomato (14). Galactose also inhibits the elongation of excised segments ofoat coleoptiles (15,19,30,31 The purpose ofthis study was to ascertain whether the acidinduced elongation process per se is sensitive to galactose and, if so, whether the senstivity bears a causal relationship to the inhibition of root growth by galactose. In each experiment, the elongation kinetics of large samples of root segments was measured simultaneously using the rhizometer (26-29). MATERIALS AND METHODS Plant MaterialCaryopses of Zea mays cv Sweetom 102 were surfacesterilized in 0.1% sodium hypochlorite solution and imbibed in running tap water at 20°C for 20 h. Swollen caryopses were then placed on the frames of acrylic plates sided by wet filter paper as described previously (25,26), and these frames were kept in a humid box in the dark for 42 h at 23°C.For long-term elongation (20 h), 5 mm segments were excised from selected straight roots (22 ± 2 mm) at 1 mm behind the tip, preincubated in distilled water for 1.5 h, and then treated with or without sugars at pH 4 or at pH 7. Citrate-sodium phosphate (1-2 mM) buffer was used at pH 4 and pH 7. Lots of 30 root segments were gently shaken with 20 mL buffer solution in a Petri dish (12 cm) at 23°C in room light, and the length of the segments was measured with a low power microscope after treatment.For the time course experiments (10 h), 7 mm segments were excised from 22 ± 2-mm long roots 1 mm behind the tip and mounted on the root holders with the apical end down as indicated in Figure 1. The basal end of the holder was filled with 0