Calcium Antagonist TMB-8 Inhibits Cell Wall Formation and Growth in Pea |
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Authors: | BRUMMELL, DAVID A MACLACHLAN, GORDON A. |
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Abstract: | The effects on auxin-stimulated growth and cell wall formationof 8-(N, N-diethylamino)-octyl-3, 4, 5-trimethoxybenzoate.HCI(TMB-8), an intracellular Ca2+ antagonist, were investigatedin abraded stem segments from aetiolated seedlings of Pisumsativum L. cv. Alaska. Incubation of segments at pH 6.0 with200 mmol m3 TMB-8 resulted in a 50% inhibition of auxin-stimulatedgrowth. Added Ca2+ did not restore normal auxin-stimulated growth,presumably because of its well-known stiffening effect on thecell wall. In segments incubated at a pH (72) which preventedelongation, auxin promoted the incorporation of [3H]glucoseinto the cell wall relative to total uptake of label. TMB-8abolished about 60% of the total incorporation of label intocell walls in the presence of auxin, but was not effective inthe absence of auxin. Exogenous CaCl2 reversed the inhibitoryeffect of TMB-8 on relative cell wall incorporation in a parabolicmanner, with a 50% reversal at about 100 mmol m3 andcomplete reversal at 1.0 mol m3 Ca2+. Other ions tested(Mg2+, Mn2+, Cu2+, Zn2+) were without substantial effect atconcentrations of 0.5 mol m3. Both apparent uptake ofCa2+ and consequent reversal of TMB-8 inhibition of cell wallincorporation were blocked by the Ca2+ channel blockers verapamiland La3+. The data provide further evidence that auxin-stimulatedgrowth is dependent upon continued cell wall incorporation,and suggest that a Ca2+ messenger system may be involved inthe promotory actions of auxin on cell wall synthesis and long-termgrowth. Key words: Auxin, calcium, cell wall synthesis |
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