Abstract: 【Objective】The aim of this paper was to investigate the effect of plant growth regulators on carbohydrate content, sucrose metabolizing enzyme activities and yield of soybean in the source-sink theory aiming to provide scientific basis for PGRs on agricultural production.【Method】Foliar spray field experiments were conducted successively in 2013 and 2014 in the main soybean producing zone, Heilongjiang Bayi Agricultural University. The experiment was in the early flowering by foliar spray one time. Taking Hefeng50 and Kefeng16 soybean varieties as the main research materials. Two chemical regulators, 2-N,N-diethylamino ethylcaproate (DTA-6, 60 mg·L^-1) and uniconazole (S3307, 50 mg·L^-1) were tested with water as the control. The first sampling was carried out after sprayed 30 d, and then leaf samples were collected once every five days. The contents of sucrose, starch or fructose in leaves and seeds, and invertase activity，SPS or SS activity in leaves were measured. The grain yield of soybean were investigated.【Result】At the early seed filling stage（30-35 days since spraying of DTA-6 and S3307）, the sucrose，fructose and starch contents of leaves showed the downtrends, and that of seeds showed increasing trends, which showed that more carbohydrates were applied to seeds growth and development. At the middle seed filling stage（35-45 days since spraying of DTA-6 and S3307）, the sucrose, fructose and starch contents of leaves always showed increasing trends by S3307 .The sucrose and fructose contents were all higher than the control, which was based to provide sufficient materials for the grain filling. At the late seed filling stage（after the 50th day since the spraying by DTA-6 and S3307）, the sucrose contents of leaves reached the maximum by DTA-6 and S3307, and reached significant levels to CK. The starch content of leaves sprayed with S3307 were higher than CK, and the fructose contents of leaves sprayed with DTA-6 were higher than CK. The sucrose contents of seeds were significantly increased by both S3307 and DTA-6 treatments. The fructose contents of two varieties seeds were increased by S3307, but that of Hefeng50 seed was decreased by DTA-6. The starch content of Hefeng50 seed but that were of Kefeng16 seed were increased by both S3307 and DTA-6 treatments, which showed that PGRs were different effect for soybean varieties. With sucrose contents were increased, SPS and SS activities were improved by S3307 and DTA-6. In most times, foliar spray of S3307 and DTA-6 could significantly decrease invertase activity of leaves to regulate carbohydrate metabolism in different varieties. Thereby, sucrose was neutral for carbohydrate metabolism. Balance of carbohydrate metabolism in source and sink by S3307 and DTA-6 to significantly increase yield. To controls（H-CK and K-CK），the yield of PGRs (H-S, H-D and K-S, K-D) treatments were significantly increased by 20.07%, 14.57% and 10.54%, 10.95%. By the correlation analysis, The sucrose contents of the leaves were positively correlated with SPS, SS activities and starch contents of leaves and the sucrose, fructose and starch contents of seeds (0.893**, 0.888** and 0.981** or 0.918**, 0.832 and 0.810), or were negatively correlated with activities and invertase activities and fructose contents of leaves (-0.872 and -0.862).【Conclusion】The activity of SS and SPS which are of great importance in sucrose synthesis were increased and the activity of invertase was decreased by PGRs, the source-sink physiological metabolism of carbohydrates was regulated to increase yield by S3307 were higher than DTA-6.

Key words: PGRs, soybean, source and sink, carbohydrate, physiological metabolism, yield