Cytological And Physiological Studies On Laminaria Japonica During Green Rot Disease

In this thesis, the process that the green rot disease took place on Laminaria japonica sporelings was simulated. Several experiments were carried out on sporelings through biochemical means and electron microscopy under the experimental ecology: the responses of sporelings on the green rot disease, the ultrastructural changes in cells and changes of Ca²⁺ localization were studied.All these works will provide theoretical basis for understanding the mechanism of green rot disease on sporelings and establishing effective measures to avoid and control it.Light symptoms of rot disease was observed on several sporelings at the 3rd day. The disease became more and more serious with the proceeding of culture. Till the 12th day, a lot of sporelings had dropped from the strings.At the beginning (0 day) sporelings was sampled as healthy materials, and then sampled every 3 days, 3 repeats for each sampling. The physiological changes of sporelings during the green rot disease were tested. The results showed that when healthy young sporelings became rotten gradually, the contents of soluble sugar and soluble protein decreased; total antioxidative ability , SOD activity and PPO activity had the similar trends: increased at first, and then decreased. However, the change of PPO activity was later than that of SOD ability; the change of PAL activity had a tendency of decrease; the content of polyphenol decreased, too. Analysis of correlation showed that PPO activity was negatively correlated to the content of polyphenol (r=-0.619, p=0.014). This indicated that PPO played an important role inhelping Laminaria japonica sporelings resisted the invasion of pathogens through oxidizing phenolic components. So the combination of PPO and SOD activity could be used as an effective biochemical index indicating thegreen rot disease.During the disease, changes of ultrastructure in cells of Laminaria japonica sporelings were observed. The earliest changes of organelles took lace in pigment body, followed by nucleus, and mitochondria was relatively stable. So the pigment body was the most sensitive organelle subjected to the green rot disease. This sensitivity might be one of the causes which led to the death of tissues. At the same time, the decomposing of cell wall and the break of cell membrane provided the chances for pathogens to invade the tissues.Ca²⁺ is a kind of important mineral nutrition element. It is the only substance that is proved to be the second messenger which couples the signals outside cells and the physiological and biochemical responses inside cells. It has been known that changes of cellular Ca²⁺ concentration is a key link in sensoring and transducting the signals from outside environmental stimuli. In order to disclose the mechanism of green rot disease, the changes of Ca²⁺ localization in- and out- cell membrane of Laminaria japonica sporelings were investigated with calcium antimonite precipitate-electromicroscopic-cytochemical methods and the roles of signal transduction played by Ca²⁺ was discussed preliminarily. The test indicated that, under normal circumstances, the level of Ca²⁺ in cytoplasm was low indeed and the deposits of calcium antimonite mainly concentrated within the cell wall. The tendency of Ca²⁺ inflow was shown during green rot disease. With the decomposing of cell wall, the concentration of Ca²⁺ decreased gradually and the granules became small. The Ca²⁺ became more in cell membrane and few in nucleus.In the other two experiments, during the culture of Laminaria japonicasporelings inhibitor LaCl₃ and chelator EGTA were added to the seawater respectively, and responses of cells and changes of intra- and extra- cellular Ca²⁺ distribution were then observed. After La³⁺ was added, the quantity of Ca²⁺ distributed on cell wall decreased gradually. The most obvious symptom was a large quantity of Ca²⁺ accumulated on the cell membrane or on the surface of outermembrane. The inflow of Ca²⁺ was blocked and the effect of Ca...