Abstract
Halocynthia roretzi, belonging to class Ascidiacea, has highly pure and crystalline cellulose Iβ, and sulfated chitin in its tunic. Cells, including hemocytes in the open circulatory system, are scattered in the tunic. The tunic, which maintains its thickness by continuous proliferation and removal, can be classified into active tissues. Recently, it has been reported that various stimuli, such as mechanical stimuli and changes in the mechanical environment, could cause active deformations of the tunic without changes in the characteristics of the tissue structure, which would be associated with influx and efflux of water. In this chapter, the system associated with active deformation, tissue structure and flux of water in the tunic is shown, with reference to the previous reports.
Keywords
- cellulose
- sulfated chitin
- active deformation
- water
- stimuli
- adaptation
- tissue structure
1. Introduction
As Figure 1 shows, the tunic tissue can be categorized by characteristics in shape: siphon, tubular parts where seawater is passing through; M1, tunic with spines; M2, tunic without a spine; and bottom, thickest part. While the mechanical stimuli caused a decrease in mass in every category, the tunic in the seawater at 5°C indicated an increase in the mass of the tunic, which became smaller as the position was closer to bottom [21]. While the outer layer and collapse of blood vessels could cause the difference in change of mass [21], the cells extracted from the tunic by centrifugation, kept in the seawater at 5°C for 10 days, showed motility [28] so that these cells would also influence change in mass. While the absorbance at 220 nm and 250–350 nm in the seawater used for keeping the tunic at 5°C was decreased after the removal of the tunic samples [28], the influence of the tunic category has been barely examined. Also, whether or not the cells in the tunic are obtained from all the tunic categories by centrifugation at the same degree has not been clear. If the effect of centrifugation on separating the cells from the tunic tissue is dependent on the tunic category, the characteristics of the tunic structure would be diverse and influence mass transfer.
In this chapter, why the tunic category, composed of siphon, M1, M2 and bottom, could influence the active deformation was examined. The absorbance of the seawater, which kept the tunic sample in each category separately, was evaluated by spectroscopic analysis in order to examine the change in the components of the seawater. The seawater after removing the tunic sample was also evaluated in the same way. In the meantime, the hemocytes in each category of the tunic, which would secrete halocyamines (antimicrobial substance) [5] and hemagglutinin [10], were obtained by centrifugation to examine the influence of the tissue category on separating the cells from the tunic.
2. The following materials and methods have been followed to find out the findings
2.1 Change in mass and components from the tunic
The samples of
2.2 Hemocytes
While there are several types of hemocytes in
3. Outcomes of the present study
3.1 Change in the mass of the tunic and components from the tunic
An example of a change in mass of the tunic sample is shown in Figure 2. The tunic bottom underwent smaller changes than those in other categories. The tendency, which was observed in all the samples, agreed with that in the previous report [21].
An example of the absorbance at 190–1100 nm is shown in Figure 3. The shape of the absorbance curve is almost the same in all the samples. The absorbance at the characteristic wavelength and related parameter, shape index, and their changes, caused by the adjacent process, in each seawater sample are shown in Figure 4. Considering the influences of the tunic sample categories (siphon, M1, M2 and bottom) on the absorbance, the absorbance and related parameter are indicated in each sample category. The mean value and change between the adjacent processes and their ranges through all the processes are indicated in Figures 5 and 6, respectively. As Figures 4–6 show, the absorbance values at the characteristic wavelength and related parameters were changed by the tunic category as well as the presence and removal of the tunic samples. While the change in shape index between the adjacent processes was zero or less, other absorbance values and parameters increased before the removal of the tunic samples, and decreased after the removal, in all the tunic categories, as Figure 5B shows. Because the presence and absence of the tunic samples in the seawater directly influenced these parameters, and change in the component ratio of the seawater was kept through the processes, the substances released from the tunic sample would be partially degradable with progress in the change of the component ratio in the seawater. But the influences of the tunic category and process in other results were so complicated that they could be hardly explained in such a simple way. These results indicated that each category might have different systems to control its active deformation.
3.2 Cells
Figure 7 shows the cells from M1 by centrifugation (1000 G, 7 min). The cells were also obtained from the tunic samples of siphon and M2, but barely from bottom. Considering blood vessels in bottom and open circulation in the entire body, few cells in bottom would be hardly expected. Hence, there might be the characteristics of the tissue structure in bottom, which would cause cells to be hardly separated by an external force, but not in other categories of the tunic, siphon, M1 and M2.
4. Discussion of the findings as compared to earlier studies
In this chapter, the difference in the tunic categories, which are siphon, M1, M2 and bottom, was investigated to examine the system for active deformation in the tunic. Considering that influx and efflux from the tunic, which are associated with the active deformation of the tunic, would bring some components to the seawater, change in the components of the seawater was evaluated by the absorbance at the characteristic wavelength and related parameters. In all the tunic categories, these parameters, except shape index, which continuously decreased, were increased by keeping the tunic in the seawater and decreased by removing them. These results indicated that the substances, released from the tunic, would disappear without continuous supply and keep the change in the component ratio of the seawater. The released substances would be degradable partially as well as reactive, associated with the change of the component ratio of the seawater. In the meantime, the influence of each tunic category on these parameters was complicated. Hence, the active deformation would be controlled by two types of substances, which would be in every category of the tunic sample, and specific in each category. The details of the substances will be investigated in the future.
In the meantime, the cells were obtained from siphon, M1 and M2 by centrifugation, but not from bottom. Considering the open circulation system and blood vessels in bottom, bottom would have cells, which would be hardly separated from the surrounding by centrifugation because of the characteristics in the tissue structure of bottom, different from those in other tunic categories. The result that change in mass of the tunic was smallest at bottom would agree with this unique feature of bottom. Why the cells in bottom are hardly obtained by centrifugation and how the cells in bottom can be obtained will be investigated in the future.
5. Conclusion
In this chapter, the active deformation of the tunic in
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