Interactions Between Exogenous Cytokinin and Nitrogen Application Regulate Tiller Bud Growth via Sucrose and Nitrogen Allocation in Winter Wheat

Abstract

In this study, we assessed the effects of exogenous cytokinin and nitrogen levels on sucrose and nitrogen allocation and tiller bud growth. Results showed that low nitrogen (1.25 mmol L−1, LN) inhibited tiller bud growth and decreased tiller occurrence rate, compared with high nitrogen (7.5 mmol L−1, HN). SPAD readings and leaf photosynthesis rate was decreased by LN, which resulted in the decrease of sucrose content in the tiller bud. Furthermore, LN promoted the primary and lateral root growth, which may compete with the tiller bud for sucrose and nitrogen. Application of 6-BA (30 mg L−1) increased tiller bud length and the occurrence rate. Compared with LN, leaf photosynthesis and root activity was improved by application of 6-BA under LN condition (LN + 6-BA), which caused the increase of sucrose and nitrogen accumulation in tiller bud. Moreover, LN + 6-BA significantly increased endogenous zeatin (Zt) contents and decreased abscisic acid (ABA) levels in the tiller node. Correlation analysis indicated that tiller bud growth was positively correlated with sucrose and nitrogen accumulation. The latter two were positively correlated with endogenous Zt but negatively correlated with ABA and auxin (IAA):Zt, gibberellin (GA3):Zt, and ABA:Zt. Application of 6-BA with reduced nitrogen fertilizer (240 kg N ha−1, N1 + 6-BA) increased both grain yield and the partial factor productivity of applied N. Therefore, an appropriate combination of exogenous cytokinin with reduced N application could regulate tiller growth to enhance yield by endogenous hormones balance and sucrose and nitrogen allocation in the plant.