LAUSR

Abstract Seed yield and nutritional quality are dependent on seed development in oil crops. In a previous study, we showed that light shading improved seed yield and quality in oilseed peony, but the underlying mechanisms driving light shading impacts on seed yield and nutritional quality as mediated through seed development remain unclear. To develop an understanding of these mechanisms, oilseed peony trees were shaded by different density polyethylene nets starting at 28 days after pollination (DAP) and continuing until harvest. The seed volume, weight, and nutritional quality parameters, as well as the expression of genes related to the synthesis of unsaturated fatty acids (UFAs), were examined at 14-day intervals. Results showed that hundred-seed volume (Vh), fresh weight (Wf), and dry weight (Wd) increased by 8.2, 15.2, and 33.0 times, respectively, from 14 to 70 DAP. During the same period, the contents of starch, soluble protein, crude oil, and UFAs increased by 2.8, 3.7, 20.4, and 21.1 times, respectively. From 71 to 98 DAP, Vh, Wf, and Wd increased by 4.1, 5.4, and 20.8%, respectively. During this period, the contents of soluble protein, crude oil, and UFAs increased by 36.8, 51.4, and 49.5%, respectively. From 99 to 112 DAP, Vh, Wf, and Wd slightly increased, and the content of soluble protein increased by 25.2%. In contrast, the contents of soluble sugar, starch, and crude oil decreased by 28.3, 15.1, and 6.3%, respectively. Thus, seed development of oilseed peony can be divided into three periods of rapid growth (before 70 DAP), slow growth (71–98 DAP), and maturation (99–112 DAP). At 98 DAP, light shading increased the content of soluble sugar by 8.3%. At 112 DAP, light shading increased Vh, Wf, Wd, the content of crude oil, and UFAs by 6.9, 8.3, 8.3, 6.6, and 9.6%, respectively. The expression level of FAD2 in peony seed was up-regulated by 87.1 and 219.3% at 98 and 112 DAP, respectively. The expression level of FAD8 was up-regulated by 10.8, 71.7, 162.1, and 371.3% at 70, 84, 98, and 112 DAP, respectively. The expression level of SAD was up-regulated by 53.5 and 150.3% at 98 and 112 DAP, respectively. It is thus concluded that light shading significantly improved seed yield and nutritional quality parameters via increased seed growth and the expression of fatty acid desaturase genes during the slow growth and the maturation periods of seed development.