5-Aminolevulinic acid regulates the grain morphology, carbohydrate and hormone contents, increasing grain yield of maize in field land

5-aminolaevulinic acid (ALA), being a plant growth promoter, effectively improves plant growth and development. However, relevant reports are deficient on how ALA regulates the maize grain yield. In this study, the leaves of maize were sprayed with ALA solution (40 mg L) at the 12th leave stage. We measured the grain morphology, carbohydrate and hormone contents after silking stage, while the yield and components were measured at maturity. The ALA improved the grain morphology (fresh weight, dry weight, volume and length) of two varieties, and also increased the content of starch, soluble sugar, sucrose and fructose in two varieties. Furthermore, its application increased the auxins (IAA), gibberellin (GA), abscisic acid (ABA) and zeatin riboside (ZR) content of two varieties. These improvements had a positive correlation with the yield, as being illustrated by its induced-increases in the 1000-grain weight and grain yield in maturity. Thus, our findings highlight that the ALA applications can improve the maize yield via enhancing grain morphology and increasing carbohydrate and hormone contents.