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.

Keywords: growth and defense; isopimaric acid; phytohormone; plant growth regulator; relevance analysis.

Figure 1

The shoot lengths of 14 rice seedling varieties that received isopimaric acid. (A) Growth of Japanese Nipponbare rice seedlings treated with different concentrations of gibberellin and isopimaric acid solution treatment for 3 d. (B) Effect of different concentrations of gibberellin and isopimaric acid solution on the length of the shoots of Nipponbare rice seedlings following treatment for 3 d. (C) Effect of different concentrations of gibberellin and isopimaric acid solution on the length of the roots of Nipponbare rice seedlings following treatment for 3 d. (D) Above-ground lengths of rice seedlings treated with 25 μg/mL of isopimaric acid. (E) Effect of isopimaric acid at 25 μg/mL on the root weights of Nipponbare rice seedlings. Differences in data between treatments were compared using one-way ANOVA analysed using the LSD test, and differences between data were considered statistically significant at p < 0.05, which was indicated by a, b, c, d, and e. Mean differences between every two groups were compared using independent-samples t-tests, with p < 0.01 indicated by “**”, and p < 0.001 indicated by “***”. *** represents an extremely significant difference between the two sets of data.

Figure 2

The growth phytohormone-related of 14 rice seedling varieties received isopimaric acid. (A,C,E): IAA, IBA, and IPA concentrations in the shoots of rice seedlings treated with 25 μg/mL of isopimaric acid. (B,D,F): IAA, IBA, and IPA concentrations in the roots of rice seedlings treated with 25 μg/mL of isopimaric acid. Mean differences between the two groups were compared using independent-samples t-tests, with p < 0.05 indicated by “*”, p < 0.01 indicated by “**”, and p < 0.001 indicated by “***”. *** represents an extremely significant difference between the means of the two sets of data.

Figure 3

The cytokinin-related phytohormones in 14 rice seedling varieties that received isopimaric acid. (A,C,E): BAP, iP, and tZ concentrations in the shoots of rice seedlings treated with 25 μg/mL of isopimaric acid. (B,D,F): BAP, iP, and tZ concentrations in the roots of rice seedlings treated with 25 μg/mL of isopimaric acid. Mean differences between every two groups were compared using independent-samples t-tests, with p < 0.05 indicated by “*” and p < 0.01 indicated by “**”.

Figure 4

The gibberellin-related phytohormones of 14 rice seedling varieties that received isopimaric acid. (A,C,E,G): GA₄, GA₇, GA₁₂, and GA₂₀ concentrations in the shoots of rice seedlings treated with 25 μg/mL of isopimaric acid. (B,D,F,H): GA₄, GA₇, GA₁₂, and GA₂₀ concentrations in the roots of rice seedlings treated with 25 μg/mL of isopimaric acid. Mean differences between two groups were compared using independent-samples t-tests, with p < 0.05 indicated by “*” and p < 0.01 indicated by “**”.

Figure 5

The defense-related phytohormone of 14 rice seedling varieties that received isopimaric acid. (A,C,E): ABA, SA, and JA concentrations in the shoots of rice seedlings treated with 25 μg/mL of isopimaric acid. (B,D,F): ABA, SA, and JA concentrations in the roots of rice seedlings treated with 25 μg/mL of isopimaric acid. Mean differences between two groups were compared using independent-samples t-tests, with p < 0.05 indicated by “*” and p < 0.01 indicated by “**”.

Figure 6

Correlation analysis of growth-related phytohormone concentrations in rice seedlings treated with isopimaric acid. (A): Correlation of growth-related phytohormone concentrations in the shoots of rice seedlings in the control group. (B): Correlation of growth-related phytohormones in the aboveground parts of rice seedlings treated with 25 μg/mL of isopimaric acid. (C): Correlation of growth-related phytohormone concentrations in the roots of rice in the blank control group. (D): Correlation of growth-related phytohormone concentrations in the roots of rice seedlings treated with 25 μg/mL of isopimaric acid. Red and blue circles represent positive and negative correlations, respectively. Mean differences between two groups were compared using independent-samples t-tests, with p < 0.05 indicated by “*”, p < 0.01 indicated by “**”, and p < 0.001 indicated by “***”. *** represents an extremely significant difference between the means of the two sets of data.

Figure 7

Correlation analysis of defense-related phytohormone concentrations in rice seedlings treated with isopimaric acid. (A): Correlation of defense-related phytohormone concentrations in rice seedlings of the control group. (B): Correlation of defense-related phytohormone concentrations in rice seedlings treated with 25 μg/mL of isopimaric acid. Red and blue circles represent positive and negative correlations, respectively. Mean differences between two groups were compared using independent-samples t-tests, with p < 0.05 indicated by “*”, p < 0.01 indicated by “**”, and p < 0.001 indicated by “***”. *** represents an extremely significant difference between the means of the two sets of data.