Exogenous GA3 Enhances Nitrogen Uptake and Metabolism under Low Nitrate Conditions in ‘Duli’ (Pyrus betulifolia Bunge) Seedlings

Abstract

‘Duli’ (Pyrus betulifolia 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 (NO3−) uptake and metabolism in plants remain unclear. In this study, we investigated the effects of exogenous GA3 on the N metabolism of ‘Duli’ seedlings under NO3− deficiency. The results showed that exogenous GA3 significantly improves ‘Duli’ growth under NO3− deficiency. On the one hand, GA3 altered the root architecture, increased the content of endogenous hormones (GA3, 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 (PbNRT2) and the metabolism genes (PbNR, PbGILE, PbGS, and PbGOGAT). However, GA3 did not delay the degradation of chlorophyll. Paclobutrazol had the opposite effect on growth. Overall, GA3 can increase NO3− uptake and metabolism and relieve the growth inhibition of ‘Duli’ seedlings under NO3− deficiency.