Lodging Resistance of japonica Rice (Oryza sativa L.): Lignin Accumulation and Its Related Synthesis Due to the Application of Gibberellins Acid or Uniconazole.

Lodging resistance of japonica rice (Oryza sativa L.): Lignin accumulation and its related synthesis due to the application of gibberellins acid or Uniconazole Longmei Wu1, Wujun Zhang2, Yanfeng Ding1, Elidio David Cambula1, Shaohua Wang1, Ganghua Li* 1 Jiangsu Collaborative Innovation Center for Modern Crop Production/National Engineering and Technology Center for Information Agriculture/ Key Laboratory of Crop Physiology and Ecology In Southern China, Nanjing Agricultural University, Nanjing 210095, China 2 Chongqing Academy of Agricultural Sciences/Chongqing Rationing Rice Research Center, Chongqing 402160, China *Corresponding author: Mailing address: Agronomy College, NAU; #1 Weigang Street, Nanjing, China, 210095 Ganghua Li, Tel: +86-25-84396475; Fax: +86 25 84396475; E-mail: lgh@njau.edu.cn Abstract: It is well known that the application of exogenous plant growth regulators, such as uniconazole (Uni) and gibberellins (GA3), affect lodging resistance in crops. However, the information is limited about the effects of exogenous plant growth regulators on stem strength of japonica rice, especially how the lignin biosynthesis in culms are affected by the Uni and GA3. In this study, field experiments on two rice cultivars, Wuyunjing 23 (lodging-resistance cultivar) and W3668 (lodging-susceptible cultivar) were used. The lodging rate, stem strength, lignin accumulation, genes expression involved in lignin biosynthesis were measured. Results showed that no lodging happened in Uni, but GA3 lodged highly. Compared with CK, the Uni significantly decreased lodging index, but GA3 decreased it, which could be explained by followings: 1) the Uni significantly reduced plant height, gravity center height and the length of the basal second internodes, but it was increased in GA3; 2) the Uni significantly increased stem strength which attributed to stronger morphological traits and higher lignin content, while GA3 had the opposite effect. With histochemical straining, Uni largely increased lignin deposition in the sclerenchyma cells and vascular bundle cells compared with CK, but GA3 decreased it. Compared with CK, expression levels of gene involved in lignin biosynthesis were down-regulated under Uni condition; but the expression levels of genes, including OsPAL, Os4CL3, OsCCoAOMT and OsCAD2 were first up-regulated and then down-regulated, the OsCOMT, OsCCR exhibited up-regulation with GA3. These findings could be explained by the feedback regulation mechanism between lignin accumulation and gene expression involved in lignin biosynthesis. These results suggested that lignin content is closely related to stem strength and lodging resistance. Uni or GA3 significantly alter the lodging resistance by affecting morphological traits but also altering the stem mechanical strength, especially changing the lignin content and its related genes expression in culms. Keywords: Japonica rice (Oryza sativa L.); Gibberellins; Uniconazole; Lodging resistance; Lignin