Changes of cell wall composition in Laminaria japonica（901 and Rongcheng number 1） with the process of infection by alginic acid decomposing bacteria were studied.The results showed that the obvious decline of relative yield of monocells and protoplasts in Laminaria japonica Rongcheng number 1 appeared under cell wall decomposing enzymes at early stage of infection.Moreover

the relative yield decreased more remarkably with the prolonging of infection time.On the contrary

the relative yield of monocells and protoplasts did not exhibit notable change with the continuous infection by alginic acid decomposing bacteria in 3 days later.While relative yield rate of monocells and protoplasts in Laminaria japonica 901 always did not exhibit notable change during whole infection.Therefore the cell wall composition in Laminaria japonica Rongcheng number 1 changed notably under the infection by alginic acid decomposing bacteria

and it did not change in Laminaria japonica 901.Meanwhile

the results also showed that during infection by alginic acid decomposing bacteria

the changes of cell wall composition in Laminaria japonica Rongcheng number 1 were mainly expressed by alginic acid

and were not related to cellulose

semicellulose and pectin.