Gibberellins synthesis is involved in the reduction of cell flux and elemental growth rate in maize leaf under low nitrogen supply

One strategy for plants to adapt to low nitrogen is to reduce shoot growth and allocate more nitrogen and carbon for root growth. The mechanism underlying the response of leaf growth to low-nitrogen remains unknown. In this study, we investigated cell division and elongation in maize leaf growth in response to low-nitrogen by using an integrated approach. Kinematic analysis revealed that low-nitrogen inhibited leaf elongation mainly by shortening length of division zone, reducing cell flux and elemental growth rate. Hormone analysis revealed that changes of gibberellins caused by low-nitrogen correlate with the observed changes in division zone size and elemental growth rate in response to low-nitrogen, suggesting role of gibberellin in low-nitrogen induced inhibition of leaf elongation. RNA-Seq identified that GA20ox4 (GRMZM2G060940), a key enzyme for synthesis of gibberellins, was down-regulated in both division and elongation zone of leaf under low-nitrogen supply. Furthermore, exogenous GA3 application on low-nitrogen plants restored leaf growth. However, application of gibberellin biosynthesis inhibitor reduced leaf growth. It is concluded that low-nitrogen reduces cell flux and elemental growth rate in maize leaf via reducing gibberellin synthesis. As a result, leaf elongation rate was slower and leaf area was smaller, freeing nitrogen for export to roots.