Effect of elevated nitrogen levels on endogenous gibberellin and jasmonic acid contents of three rice (Oryza sativa L.) cultivars

Three rice (Oryza sativa L.) cultivars (cv. Daesanbyeo, cv. Dongjinbyeo, cv. Junambyeo) were analyzed for endogenous gibberellin (GA) and jasmonic acid (JA) contents and their changes in response to elevated nitrogen (N) levels. The N fertilizer was applied in the form of urea [(NH₂)₂CO] at three rates (0, 36.8, 73.6 kg N ha^-1). Plant growth (height and dry weight) was enhanced by the first N rate but not further enhanced by the highest rate. The endogenous GA contents were analyzed through high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry-selected ion monitoring (GC-MS-SIM) while that of JA with GC-MS-SIM. They were analyzed one week after N application and were significantly increased with elevated N levels in all rice cultivars. The bioactive GA₁ markedly increased, but its concentration differed in different rice cultivars. Similar fluctuations were observed for endogenous GA₈, GA₁₂, GA₁₉, GA₂₀, and GA₅₃ in response to elevated N levels, showing that the rates of biosynthesis of GAs were differently affected by elevated N levels within different rice cultivars. The level of GA₂₀, a precursor of GA₁ biosynthesis, was not significantly increased, though GA₁₉, a precursor of GA₂₀, was found to be the most abundant GA type in all rice cultivars. Jasmonic acid content in the plants increased with the basic urea application (36.8 kg N ha^-1), but significantly decreased with the double urea level (73.6 kg N ha^-1). The results demonstrate that GA and JA are differentially affected in response to elevated N application in rice.