Inhibition of Low pH-induced Elongation in Avena Coleoptiles by Abscisic Acid

Abstract

An angular position-sensing transducer was used to make continuous measurements of acid-induced elongation of Avena sativa coleoptile segments. Elongation rates at pH 4.5 (5 mM succinate buffer) were about 5-fold greater than those at pH 6.0. Buffered 0.1 mM abscisic acid produced a partial decrease of the growth rate. Pretreatments with abscisic acid buffered at pH 6.0 usualy caused a further reduction of the elongation response when the coleoptile segments were subsequently placed in buffer at pH 4.5 containing abscisic acid. Abscisic acid did not completely prevent the pH effect in any of these experiments, and the brief latent period of the pH response was not affected by abscisic acid treatments. At pH 4.5, where the inhibitory effect of ABA was maximum, low pH-induced elongation was also inhibited by KCN these segments were strung on a wire and inserted in a measuring chamber in which they were completely immersed in an aerated buffer. The segments were allowed to equilibrate in a succinate buffer, pH 6.0, for 1 hr or longer, after which time a low growth rate was established. The chamber was then quickly drained and refilled with the buffer to be tested. An angular position-sensing transducer was used to produce continuous elongation curves which were analyzed by computer and replotted by an IBM 1130 line plotter as previously described (5). A 5 mm succinate buffer was selected for use in these experiments, since it consistently maintained the pH required for the various trials. Citrate buffer was also tested but proved less satisfactory, since the citrate at pH 6.0 caused a large initial stimulation of growth during the hour equilibration period before switching to a low pH. An inorganic MOPS3 buffer gave pH responses comparable to succinate but was somewhat more variable, and the pH-induced elongation rates did not remain constant as long. RESULTSAfter 1-hr equilibration in succinate buffer at a pH of 6.0, a low, steady growth rate was established which was not altered by a fresh addition of the pH 6.0 buffer. However, as the pH of the new bathing solution was lowered below 6.0, the elongation rate of the coleoptiles increased (Fig. 1). About a 10-fold increase in elongation rate was observed after a change in pH from 6.0 to 3.2, but the increase persisted for only about 20 min, after which time elongation ceased, and, in some cases, slight shrinkage occurred.The effects of pH 4.5 were investigated most thoroughly, since this treatment produced about a 5-fold increase in elongation rate which persisted for longer than 1 hr. When 0.1 mM ABA was present in the pH 4.5 buffer, the stimulating effect of the low pH was reduced (Fig. 2). Pretreatment with 0.1 mM ABA at pH 6.0 usually caused further inhibition of the elongation rate, when the coleoptiles were subsequently placed in pH 4.5 buffered ABA. The magnitude of the pH responses and their inhibition by ABA were somewhat variable, but when an entire set of experiments was performed on 1 day with seedlings from the same planting, inhibitory effec...

Cyanide Inhibition of Acid-induced Growth in Avena Coleoptile Segments

“…Thus, there is little direct evidence in the literature in support of the notion that acid-induced growth in A vena is independent of metabolism, although the data of Rehm and Cline (19) and the data presented in this paper provide evidence to the contrary.…”

“…In a previous study (19) The data presented here indicate that the metabolic poisons KCN and NaF suppress acid-induced growth in A vena. Anaerobic conditions also appear to inhibit acid growth.…”

Stomatal behaviour and water movement through roots of wheat plants treated with abscisic acid

“…extension rates on the second day after ABA application, despite the existence of quite high water potentials when the stomata were closed. Rehm & Kline (1973) have suggested that the reduction in coleoptile growth caused by ABA is mediated through a cell wall stiffening effect. This effect of ABA on guard cells may be considered to be indirect when compared to the more direct effect of the compound on guard cell potassium content (MacRobbie, 1981).…”

Droopy: a wilty mutant of potato deficient in abscisic acid

“…However, this conclusion conflicts with the reported effects of ABA on cell elongation. In coleoptiles, ABA treatment is thought to result in a physical stiffening of cell walls (Rehm & Cline, 1973). A study of the response to plasmolytic solutions of stomata of droopy plants treated with ABA throughout leaf development may help to resolve the problem.…”