Vol. 57, 2018 (update: 2018.06.04; 06.22) Cytoplasmic UV-R Absorption in an Integumentary Matrix (tunic) of Photosymbiotic Ascidian ColoniesNoburu
Sensui1 and Euichi Hirose2,* doi:10.6620/ZS.2018.57-33
1Department
of Human Biology and Anatomy, Graduate School of Medicine, University
of the Ryukyus, Nishihara, Okinawa 903-0215, Japan. E-mail:
sensuiso@med.u-ryukyu.ac.jp (Received 15 January 2018; Accepted 28 May
2018; Communicated by Yoko Nozawa) Noburu
Sensui and Euichi Hirose (2018)
In didemnid ascidians with cyanobacterial symbionts, the tunic has a
specific peak absorbing ultraviolet radiation (UV-R) due to the
presence of ultraviolet (UV)-absorbing compounds, which probably
include mycosporine-like amino acids (MAAs). The UV-R absorbing tunic
is supposed to protect the symbionts in the common cloacal cavity of
the host colony. The histological distribution of UV-R absorption in
the tunic was examined using a UV light microscope equipped with a
digital camera, from which the low-pass filter of the UV-sensitive
image sensor was removed. The cell peripheries of tunic bladder cells
and cell-like objects were visualized with the trans-illumination of UV
light, indicating UV-R absorption at that site. In contrast, tunic
matrix and vacuolar content of tunic bladder cells appeared to lack of
UV-R absorption, allowing damaging wavelengths to penetrate.
Accordingly, UV-absorbing compounds are expected to be contained in the
cytoplasmic matrix of tunic bladder cells and possibly other types of
tunic cells. Key words: Colonial ascidian, Cyanobacterial
symbiosis, Prochloron, Tunic,
UV microscopy. *Correspondence: E-mail: euichi@sci.u-ryukyu.ac.jp |