Abstract
The effects of <em>N</em>-1-naphthylphthalamic acid (NPA) and 2,3,5-triiodobenzoic acid (TIBA) on the swelling of the stem in intact and decapitated plants of <em>Bryophyllum calycinum</em> in relation to the interaction with auxin, indole-3-acetic acid (IAA), are described. NPA induced conspicuous local internode swelling only in the area of its application in intact plants and in the decapitated internode in the case of simultaneous application of IAA on the top of the internode. By contrast, TIBA applied to an internode of intact plants induced swelling along the entire internode above the treatment area, and similar results were obtained in the decapitated internode when TIBA was applied in the middle of the internode and IAA was applied onto the top of the internode. The differential effect of NPA and TIBA on stem swelling in <em>B. calycinum</em> is discussed in relation to their differential mode of action on auxin transport.
Highlights
One major plant hormone, auxin, plays a crucial role in controlling various physiological phenomena in plant growth and development such as cell elongation, apical dominance, and tropism
triiodobenzoic acid (TIBA) and morphactin IT 3456 completely inhibited root formation in the cuttings of Bryophyllum calycinum Salisb., B. daigremontianum Hamet & Perrier, B. tubiflora (L.f.) Ker Gawler, and Kalanchoë blossfeldiana Poelln. (Crassulaceae), but naphthylphthalamic acid (NPA) did not, when these inhibitors were applied around the stem below the leaves
When NPA was applied in Saniewski et al / Effect of NPA and TIBA on swelling of Bryophyllum calycinum shoots two places of a growing internode of intact plants, the local swelling of the stem was observed in each of the treated areas (Fig. 1c), whereas the degree of swelling was smaller than that induced by the application of NPA in one place of a growing internode
Summary
Auxin, plays a crucial role in controlling various physiological phenomena in plant growth and development such as cell elongation, apical dominance, and tropism. Auxin is mainly synthesized in the apical part of the shoot and young leaves and is transported basipetally from cell to cell through a combination of membrane diffusion and carrier-mediated transport. This polar auxin transport is well documented [1]. It is well known that polar auxin transport is almost completely inhibited by several compounds such as N-1-naphthylphthalamic acid (NPA), 2,3,5-triiodobenzoic acid (TIBA) and methyl 2-chloro-9-hydroxyfluorene-9-carboxylate (morphactin IT 3456). NPA has been shown to inhibit this transport in both dicotyledonous and monocotyledonous plants by inhibiting active auxin secretion [6].
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