Exogenous GA Enhances Nitrogen Uptake and Metabolism under Low Nitrate Conditions in 'Duli' ( Bunge) Seedlings.

'Duli' ( Bunge) is one of the main rootstocks of pear trees in China. Gibberellin (GA) is a key plant hormone and the roles of GA in nitrate (NO) uptake and metabolism in plants remain unclear. In this study, we investigated the effects of exogenous GA on the N metabolism of 'Duli' seedlings under NO deficiency. The results showed that exogenous GA significantly improves 'Duli' growth under NO deficiency. On the one hand, GA altered the root architecture, increased the content of endogenous hormones (GA, IAA, and ZR), and enhanced photosynthesis; on the other hand, it enhanced the activities of N-metabolizing enzymes and the accumulation of N, and increased the expression levels of N absorption () and the metabolism genes (, , , and ). However, GA did not delay the degradation of chlorophyll. Paclobutrazol had the opposite effect on growth. Overall, GA can increase NO uptake and metabolism and relieve the growth inhibition of 'Duli' seedlings under NO deficiency.