Exogenous Jasmonic and Abscisic Acids Act Differentially in Elongating Tissues from Oat Stem Segments

Abstract

Segments can be cut from the peducular-1 internode of oat (Avena sativa L.) shoots so as to contain the graviresponsive, auxin-sensitive leaf sheath pulvinus, and the gibberellin-sensitive internodal tissue. These two growth-capable tissues were used to study the effects and interactions of jasmonic acid (JA) and abscisic acid (ABA) in regulating cell elongation. When supplied alone at physiologic concentrations (10 −5 , 10 −4 M), JA promoted growth and cell wall synthesis in the internodal tissue, whereas by itself, ABA inhibited internodal elongation and even inhibited JA-promoted growth. When gibberellic acid (GA 3 ) was used to stimulate internodal elongation, JA and ABA caused similar levels of inhibition and, at certain concentrations, were synergistic. Inhibition by ABA was initiated several hours earlier than inhibition by JA, and only the ABA effect could be partially overcome by 10 −3 M aminoethoxyvinylglycine. Both JA and ABA inhibited elongation of pulvinar tissue that was induced to grow by gravistimulus or auxin, although here JA was more potent than ABA at equimolar concentrations. When 10 −5 M fusicoccin was used as a general nonphysiologic growth stimulus, JA had no effect on the internode but inhibited the pulvinus, whereas ABA had no effect on the pulvinus but inhibited the internode. These results provide strong physiologic evidence that JA and ABA act by different mechanisms in the regulation of elongation, at least in this representative grass.

Effects of Exogenously Applied Jasmonates on Growth and Intracellular pH in Maize Coleoptile Segments

“…However, more recent work suggests that JA alone does not inhibit growth (Montague 1997, Ueda et al 1994Ueda et al , 1995 and may in some instances even promote growth as in oat internode tissue (Montague 1997). Our results indicate that JA at physiological concentrations of 10 −9 -10 −5 M can inhibit elongation growth in etiolated maize coleoptiles (Fig.…”

“…that JA antagonizes elongation-promoting signals such as IAA and GA. For example, elongation growth promoted by auxin in oat coleoptiles and pulvini was inhibited by JA (Montague 1997, Ueda et al 1994, 1995 as was GA-promoted elongation in oat internodes (Montague 1997). In this work, we have found that JA or JA-Me at concentrations from 10 −8 , 10 −7 , and 10 −5 M inhibited the IAA-induced growth of excised maize coleoptiles (Figs.…”

“…However, we observed that sucrose had no effect on the response to JA in maize coleoptiles, indicating differences between maize and oat coleoptiles. ABA and JA act with different kinetics to synergistically inhibit growth in the GA-responsive oat internode region (Montague 1997). The elongation growth of maize coleoptiles is also inhibited by ABA (Kutschera and Schopfer 1986) and procaine (Brummer et al 1985).…”

“…Furthermore, different regions of the oat appear to have distinct responses to JA. The internode contains a GA-responsive region, where JA acts synergistically with ABA to inhibit GA-induced growth and a graviresponsive (or auxin responsive) region where JA inhibits growth more potently than ABA (Montague 1997). The effects of JA in this tissue were independent of glucose (Montague 1997), suggesting that mechanisms underlying growth inhibition differ in different tissues of the same species.…”

“…For example, some early reports (see Sembdner and Parthier 1993) suggest that JA inhibits seedling growth. More recently Montague (1997) found that JA alone induces elongation growth in the GA-responsive oat internodal tissue. However, when GA was present, elongation growth was reduced by JA in a synergistic fashion with ABA (Montague 1997), suggesting that these two plant hormones act independently of each other.…”