Effects of Shade Stress on the Synthesis of Cellulose and Lignin in Maize Nodal Roots

Low solar radiation is an important factor affecting maize root growth and development. Roots have an anchoring function, and their important components are cellulose and lignin. Here, shade experiments were conducted using shade nets with 50% light transmittance (L50). The experiment was conducted in 2021 and 2022 using the 'Xianyu 335' maize variety under two nitrogen conditions (N1 = 180 kg ha-1 and N2 = 240 kg ha-1) to investigate the effect of shading on the structural carbohydrate content of maize nodal roots. The results showed that light had a highly significant effect on cellulose and lignin contents. Compared with normal light (L100), the cellulose content significantly decreased by 10.36%-13.87% and the lignin content significantly decreased by 12.96%-18.68% under shading (L50). Shading decreased the sucrose and soluble sugar contents and the cellulose and lignin-related enzyme activities. The cellulose and lignin contents were significantly positively correlated with the sucrose content. The cellulose content at the silking (R1) stage was significantly positively correlated with the soluble sugar content and sucrose synthase (SS) and sucrose phosphate synthase activities at the 15th leaf (V15) stage; the lignin content at R1 was significantly positively correlated with the soluble sugar content and SS, acid invertase, tyrosine ammonia-lyase, cinnamyl alcohol dehydrogenase, polyphenol oxidase and peroxidase activities at V15. Genes related to cellulose synthesis, including sucrose synthase (SS), cellulose synthase (CESA), cellulose synthase-interactive protein 1 (CSI1), Chitinase-Like1 (CTL1) and STELLO2 (STL2), were downregulated under shading, as were the lignin synthesis-related phenylalanine/tyrosine ammonia-lyase (PTAL), 4-coumarate-CoA ligase (4CL) and peroxidase (POD) genes. Auxin and jasmonic acid were significantly affected by light and decreased under shading, thereby reducing cellulose and lignin synthesis. These findings provide theoretical support for the development of appropriate maize cultivation practices under reduced solar radiation.