Salicylic Acid Modulates Grain Growth and the Activity of Carbohydrate-Metabolism Enzymes Differentially in Bold and Small Wheat (Triticum aestivum L.) Grains

Abstract

Wheat grain weight is co-limited by assimilate supply and by the grain’s capacity to convert sucrose into storage starch, a capacity that is far lower in slow-filling small (inferior) grains than in bold (superior) grains and that depresses both yield and uniformity. Whether salicylic acid (SA) can strengthen this capacity in the disadvantaged grain class is unclear. Ears of pot-grown wheat (cv. PBW 343) were treated with SA (10 ppm, applied to ears via cotton plugs at anthesis) or left untreated; bold and small grains were sampled from 7 to 28 days after anthesis and at maturity. We measured grain dry weight (fitted to a Gompertz function), growth rates, and the activities of aldolase, Rubisco, PEPCase, sucrose synthase (SuSy) and ADP-glucose pyrophosphorylase (AGPase). Three-way ANOVA showed highly significant effects of grain age, position and SA (P < 0.001). Critically, SA raised Gompertz-predicted maximum weight far more in small grains (+7.6%; 50.0→53.7 mg) than in bold grains (+2.7%; 61.5→63.2 mg), and sustained SuSy, the entry enzyme of the sucrose-to-starch pathway, otherwise depressed in small grains, alongside the carbon-fixation enzymes. By preferentially boosting the sink capacity of inferior grains, SA offers a simple, low-cost route to heavier, more uniform wheat.