Physiological characteristics of seed reserve utilization during the early seedling growth in rice

Seed reserve utilization is an important characteristic of seed quality. In this study, the rice varieties Jiucaiqing (Oryza sativa ssp. japonica) and IR26 (Oryza sativa ssp. indica) and their recombinant inbred lines were used to determine the physiological and genetic control of seed reserve utilization during the early seedling growth. Seedling dry weight and weight of mobilized seed reserve increased with seed germination, while seed reserve utilization efficiency decreased after the first rise. The early seedling growth is firstly determined by the mobilization of storage reserve followed by the conversion efficiency of utilized seed reserve into seedling tissues. The major soluble sugars in grains were fructose and glucose, while fructose in shoots and roots. Glucose content in grains and fructose in shoots and roots slightly decreased after the first rise with seed germination, while fructose content in grains increased and sucrose content in grains, shoots, and roots changed slightly. Seed reserve utilization was significantly and positively correlated with sugar contents. Amylase activity significantly associated with seed reserve utilization increased with seed germination, while there was a slight change in sucrose synthase activity. Each of the three α-amylase (OsAmy3B, OsAmy3C, and OsAmy3E) and sucrose synthase (OsSus2, OsSus3, and OsSus4) genes might be involved in seed reserve utilization. Two and seven quantitative trait loci (QTL) were identified for amylase and sucrose synthase activity, respectively, in which four were novel QTLs. The identified amylase and sucrose synthase genes/QTLs might be applicable to improve seed reserve utilization during the early seedling growth in rice by the transgenic and marker-assisted selection approaches.