Fig. 4

Proline dehydrogenase (PDH), △1-pyrroline-5-carboxylic acid synthetase (P5CS), ornithine aminotransferase (OAT), and diamine oxidase (DAO) in leaves of rice under two light treatments and four Zn application levels in 2019 to 2021. Zn0, Zn1, Zn2 and Zn3 mean 0 kg Zn ha^− 1, 1 kg Zn ha^− 1, 2 kg Zn ha^− 1, and 3 kg Zn ha^− 1 applied at booting stage, respectively. NL and LL mean normal light and low light, respectively. Different lowercase letters indicate statistical differences among treatments at P < 0.05