Effects of (±)-phaseic acid on developing embryos of barley (Hordeum vulgare, L. cv. Bonanza) culturedin vitro

Abstract

The effects of exogenous phaseic acid (PA) on germination and protein accumulation of cultured immature barley embryos were examined. Chemically synthesized PA was racemic, 87% pure and stable over the course of the experiment. Germination was observable in >90% of the untreated embryos after 3 days of incubation, whereas embryos treated with 10μm abscisic acid (ABA) or PA showed no evidence of germination. Buffer extracts from embryos treated with ABA or PA had similar protein profiles when examined by single and two-dimensional electrophoresis. The profiles differed significantly from those of embryos incubated in the absence of the two compounds. Concentrations of α-amylase inhibitor and barley-germ agglutinin (BGA) increased upon treatment of immature embryos with ABA or PA. This was due to de novo synthesis as there was increased incorporation of radioactivity from 35S-labelled amino acids into the proteins in treated embryos. Endogenous ABA content in PA-treated embryos was not significantly different from that in untreated embryos. An analogue of ABA, 2′, 3′-dihydroabscisic acid, which cannot be metabolized to phaseic acid, inhibited germination and caused increased synthesis of α-amylase inhibitor and germ agglutinin. ABA and PA may both be active in promoting responses associated with ABA in barley embryos, but the embryos are more sensitive to ABA.

Action of Natural Abscisic Acid Precursors and Catabolites on Abscisic Acid Receptor Complexes

“…In such assays, freshly prepared 8#-OH ABA exhibited ABA-like activity in inducing lipid or storage proteinrelated gene expression (Zou et al, 1995;Jadhav et al, 2008). PA generally displays very little ABA-like activity (Balsevich et al, 1994;Hill et al, 1995;Zou et al, 1995), but in barley (Hordeum vulgare), PA shows substantial activity in the induction of ABA-responsive genes encoding barley germ agglutinin, inhibition of a-amylase activity in aleurone layers, and embryo germination inhibition (Dashek et al, 1979;Hill et al, 1992Hill et al, , 1995Todoroki et al, 1995). It is postulated that the biological activity associated with PA is actually derived from 8#-OH ABA, with which it is in equilibrium (Milborrow et al, 1988).…”

Abscisic Acid Structure-Activity Relationships in Barley Aleurone Layers and Protoplasts (Biological Activity of Optically Active, Oxygenated Abscisic Acid Analogs)

“…We have shown that 2',3'-dihydroABA inhibits GA,-induced a-amylase activity in barley aleurone layers (Hill et al, 1992). The compound was as effective as ABA at activating the Em promoter in the transformed protoplast assay (data not shown).…”

“…The isolation of aleurone layers was essentially as described earlier (Hill et al, 1992). Fourteen layers were incubated in a flask with 2 mL of treatment solutions.…”

“…The biological activity of (+I-7'-hydroxyABA has not been reported, whereas the biological activity of 8'-hydroxyABA is not known because the compound spontaneously cyclizes to PA in solution. The ABA analog racemic 2',3'-dihydroABA has potent biological activity in the induction of freezing tolerance (Robertson et al, 1994) and in the reversal of GA,-induced a-amylase activity (Hill et al, 1992). Furthermore, the (+)-optical isomer was a germination inhibitor in wheat embryos (Walker-Simmons et al, 1992).…”

Abscisic Acid Catabolism Generates Phaseic Acid, a Molecule Able to Activate a Subset of ABA Receptors

“…Thus, Walker-Simmons et al, (1997) concluded that PA lacked inhibitory effect on wheat germination at concentrations 50-fold higher than ABA but induced an ABA-responsive LEA gene. Hill et al, (1992) found that PA was about 10% as effective as ABA as a germination inhibitor of barley immature embryo. Sharkey and Raschke (1980) found that PA can cause stomatal closure in some species but it is barely effective in barley and maize.…”