RIASSUNTO
ABSTRACT:
It was previously mentioned that the mechanical stimulus (touch) caused the active movements of the tunic in Halocynthia roretzi, a solitary ascidian. However, how the direction of the mechanical stimulus is important, and what helps the tunic to have mechanical senses, have not been clear. In this study, whether or not rubbing the tunic outermost surface caused the active deformation, and the structural difference between the outermost surface and other regions, were examined. The rubbing caused the tunic deformation as the touching did. The outermost surface was different from the other regions structurally, and varied by the portion.
INTRODUCTION
The tunic of Halocynthia roretzi, a solitary ascidian, contains cellulose Iβ (Belton, Tannerr, Cartier and Chanzy, 1988; Larsson, Westermark and Iversen, 1995) and a chitin sulfate-like polysaccharide (Anno, Otsuka and Seno, 1974). While chitin exists in various kinds of species, cellulose Iβ is mainly in higher plants. Moreover, cellulose Iβin the tunic is highly pure and crystalline. On the other hand, it is well known that the tunic of ascidians is not a shelter, but an active tissue because it has blood vessels, cells and microorganisms (Das, 1936; Goodbody, 1974; Burighel and Cloney, 1997; MartÍnez-GracÍa, DÍaz-Valdes, Wanner, Ramos-Esplá and Anton, 2007; Hirose, 2009). Because both of chitin and cellulose Iβ are abundant in the world, the development of a novel technique based on them is important in the effective usage of the limited resources. They have the remarkable characteristics. For example, cellulose Iβshows the high elastic modulus in whisker crystalline (143 GPa) (Štrucova, Davies, and Eichhorm, 2005), and low density (1.599 g/cm3) (Sugiyama, Vuong and Chanzy, 1991). Also, sulfated chitin and chitosan are useful as biomaterials (Jayakumar, Nwe, Tokura and Tamura, 2007). The tunic of H. roretzi is actively moved by acetylcholine, and mechanical stimulus (touch) (Kato, 2010).