The Diterpene Isopimaric Acid Modulates the Phytohormone Pathway to Promote Oryza sativa L. Rice Seedling Growth

Abstract

Many plant secondary metabolites are active and important in the regulation of plant growth. Certain plant-derived diterpenes are known to promote plant growth, but the pathways by which this promotion occurs are still unknown. Activity screening revealed that the plant-derived diterpene isopimaric acid exhibits growth-promoting activity in rice (Oryza sativa L.) seedlings. Furthermore, 25 μg/mL of isopimaric acid promoted the growth of 15 self-incompatible associated populations from different rice lineages to different extents. Quantitative analyses revealed a significant decrease in the concentration of the defense-related phytohormone abscisic acid (ABA) following treatment with isopimaric acid. Correlation analysis of the phytohormone concentrations with growth characteristics revealed that the length of seedling shoots was significantly negatively correlated with concentrations of 3-indole-butyric acid (IBA). Moreover, the total root weight was not only negatively correlated with ABA concentrations but also negatively correlated with concentrations of isopentenyl adenine (iP). These data suggest that isopimaric acid is able to influence the phytohormone pathway to balance energy allocation between growth and defense in rice seedlings and also alter the correlation between the concentrations of phytohormones and traits such as shoot and root length and weight. We provide a theoretical basis for the development and utilization of isopimaric acid as a plant growth regulator for rice.