Abstract: 【Objective】The objective of this study is to establish a PTN（parent control-transgenic plant-nontransgenic control) system for the safety assessment of genetically modified (GM) rice, to provide technical supports for GM rice safety assessment by tracing the technical sources of unintended variations of soluble proteins in GM rice seed according to the comparative analysis of substantial equivalency.【Method】The transgenic rice lines (T), the parent variety controls (P) and other genetic background related non-transgenic controls including regeneration lines from tissue culture (NR) and segregated negative offspring lines (NS) were collected, according to the technological principle for GM rice development. Two glyphosate-resistant GM rice lines T13 and T23, which harboring 2mG2-epsps transgene, and their respective control samples (P, NR, NS) were used as experimental materials, while seed soluble protein contents and components as research subjects. The technical sources of unintended variations from GM rices were interpreted and traced on the basis of the multiple comparison analysis results of rice protein variations among PTN samples. The rice soluble proteins were prepared by sequential extraction method, the albumin, globulin, prolamin and glutelin were extracted successively with distilled water, 5% NaCl, 70% ethanol and 0.1 mol·L-1 NaOH. Bradford method was used for the seed protein content analysis. Analysis of protein components was done by SDS-PAGE method. 【Result】 The contents of seed total soluble protein of GM rice lines T13 and T23 were significantly decreased by 3.29% and 6.84%, respectively, and those variations are mainly affected by the glutelin content changes. While the top grade difference value from GM rice lines and their corresponding parents was less than that from the two natural parent rice varieties P1 and P2, indicating the variations of seed soluble protein content from GM rice are inside the scope of safety. Comparing to their respective parents, the components of albumin and prolamin proteins of GM rice lines T13 and T23 had no variation, but several components of globulin and glutelin varied significantly or extremely significantly, mainly shown as increase or decrease in content. The content of 56 kD and 24 kD globulin of T13 line increased significantly while the content of 65 kD globulin of T23 line decreased extremely significantly than their corresponding parent P1 and P2. The variation tendency of glutenin components from GM rice lines T13 and T23 was similar, mainly shown as the content of 19-23 kD and 33-38 kD glutelin components increased significantly as well as the content of 100 kD and 9 kD glutenin decreased significantly, when compared with their corresponding parent controls. The remarkable variation was that two new glutenin components of 41 kD and 56 kD presented in GM rice lines，while these new variation glutelin components also existed in the NR and NS control samples. The unintended variation characteristics of seed soluble proteins from GM rice lines T13 and T23 were basically consistent with that from their corresponding NR control samples. Additionally, there were unique unintended variations concerning seed albumin content and globulin components in NS23 line.【Conclusion】The content variations of seed total soluble protein from GM rice line are mainly affected by the glutelin content changes, with less variation range than the difference value of natural rice varieties. Components of albumin and prolamin proteins in GM rice seed did not vary notably, but several components of globulin and glutelin varied significantly. The unintended variations of soluble proteins in GM rice seed mainly derived from the somaclonal variations of tissue culture, with little compact caused by transgene insertion mutation.

Key words: genetically modified rice, seed soluble protein, PTN system, unintended variation, technical source