| Phytosulfokine (PSK), a new plant peptide hormone found in a few of higher plants, was isolated firstly from conditioned medium (CM) and identified to be a sulfated pentapeptide. There are two members or PSK, one is sulfated pentapeptide [H-Tyr(SO3H)-Ile-Tyr(SO3H)-Thr-Gln-OH] (PSK-α) and another sulfated tetrapeptide [H-Tyr(SO3H)-Ile-Tyr(SO3H)-Thr-OH] (PSK-β). In 1996, Matsubyashi et al originally found PSK in asparagus mesophyll cell cultures. PSK-α very strongly stimulated the proliferation of plant cells. However, all studies on PSK-α were from Matsubayashi's laboratory until now. The deeper and broader works are needed to verify its functions and existence in plant kingdom. This paper involves in PSK-α chemical synthesis, physiological effects, bioassay and so on. The main results were as follows:1. Synthetical pentapeptide (Tyr-Ile-Tyr-Thr-Gln) was sulfated by co-incubating it with DMF/SO3. Sephadax G-15 column could efficiently isolate the sulfated pentapeptide from non-reactants and isolated matter was further purified by TLC. The result of MS identification showed that PSK-α was synthesized successfully.2. Under lower cell density (3.6×04 cell·ml-1) condition, BY-2 tobacco suspension cells could not proliferate even with the proper hormone concentration (0.6 mg L-1 2,4-D) in the medium. However, at low initial cell density culture, the cells could divide and grow normally when various concentrations of conditioned medium (CM) was added in the medium. The result indicates that there are definitely signal molecules of mitogenic activity in CM.3. Chemical synthetic PSK-α, instead of CM, was used in mitogenic activity test system mentioned above. The results showed that chemical synthetic PSK-α could completely replace CM and stimulate proliferation of suspension BY-2 cells under low initial cell density culture condition. The significant linear relationship between ability...
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