Effects of Exogenous GA3 and DPC Treatments on Levels of Endogenous Hormone and Expression of Key Gibberellin Biosynthesis Pathway Genes During Stem Elongation in Sugarcane

Abstract

Internode elongation determines plant height, which in turn affects the cane yield in sugarcane. This study aimed to explore the mechanisms of sugarcane internode elongation regulation by plant growth regulators, gibberellic acid (GA3) and its inhibitor 1, 1-dimethylpiperidinium chloride (DPC, also called mepiquat chloride). We sprayed GA3 or DPC on the leaves at the early shoot elongation stage with water as the control. The contents of endogenous hormones and the expression of GA20 ox1, GID1, and GAI in sugarcane leaves were measured at days 3, 6, 12, and 24 after treatment. It was found that the height of sugarcane plants treated with GA3 showed a significant increase compared to the control, whereas an opposite trend was observed in the DPC-treated plants. Compared to the control, the content of gibberellins (GAs) in leaves was increased significantly, while the indole acetic acid (IAA) content showed an initial increase, then a decline, and eventually remained stable in the GA3-treated plants. The contents of cytokinins (CTK), abscisic acid (ABA), and ethylene (ETH) in leaves exhibited a significant downward trend in the GA3-treated plants compared to the control. In the DCP-treated plants, however, the levels of ABA and ETH in leaves were significantly increased, IAA and GAs significantly decreased, and CTK showed a trend of an initial decline followed by an increase. After GA3 treatment, the gene expression levels of GA20 ox1 and GID1 in sugarcane increased first then decreased, whereas the gene expression level of GAI first decreased and then stabilized. After DPC treatment, the expression of GA20 ox1 in sugarcane showed an initial decrease followed by an increase, while the expression of GID1 decreased gradually and then stabilized, and the expression of GAI showed a trend of an initial increase followed by stabilization. The results of the present study indicate that exogenous GA3 treatment stimulated the internode elongation in sugarcane mainly by increasing the endogenous levels of GAs, decreasing the levels of ABA and ETH, and regulating the expression of GA20 ox1, GID1 and GAI genes; the DPC treatment mainly increased the contents of ABA and ETH and reduced the contents of GAs and IAA, thereby inhibiting the expression of GID1, promoting the expression of GAI, and ultimately inhibiting the internode elongation in sugarcane.