Use of the hormone-biosynthesis inhibitors fluridone and paclobutrazol to determine the effects of altered abscisic acid and gibberellin levels on pre-maturity α-amylase formation in wheat grains

• For solvent-only treatment, cold-shock reduced ABA but increased GA and α-amylase.
• Under ambient conditions, FD increased α-amylase activity and GA levels in grains.
• Under cold-shock conditions, PB treatment reduced α-amylase activity and GA levels.
• FD and GA3 had an additive effect to increase α-amylase under ambient conditions.
• PB and ABA had an additive effect to reduce α-amylase under cold-shock conditions.

During germination of cereal grain, α-amylase formation is known to be inhibited by abscisic acid (ABA) and stimulated by gibberellins (GA). The role of these hormones in pre-maturity α-amylase (PMA) formation in wheat grains is less well understood. Our previous work with ABA and GA exogenously applied to grains demonstrated a clear stimulatory effect of GA, with little effect of ABA. Here, in glasshouse experiments, fluridone (ABA biosynthesis inhibitor; FD [20 μM]) or paclobutrazol (GA biosynthesis inhibitor; PB [20 μM]) were applied to intact, developing grains of the PMA-susceptible variety Rialto at 480 days after anthesis (DAA) to assess if a reduction in endogenous ABA and/or GA alters PMA formation. The experiments were conducted under non-PMA-inducing (ambient) and PMA-inducing (cold-shock) conditions. In solvent-only treated grains, a cold-shock significantly reduced the ABA content but increased GA and α-amylase activity. FD increased GA levels and α-amylase activity under ambient conditions, but decreased GA levels and α-amylase activity under cold-shock conditions, with no effect on ABA levels under either condition. PB had no effect under ambient conditions, but reduced GA levels and α-amylase under cold-shock conditions. These results indicate an association between GA levels at mid-grain development and PMA formation in wheat.