Ml. Dionisiosese et al., UV-ABSORBING SUBSTANCES IN THE TUNIC OF A COLONIAL ASCIDIAN PROTECT ITS SYMBIONT, PROCHLORON SP, FROM DAMAGE BY UV-B RADIATION, Marine Biology, 128(3), 1997, pp. 455-461
Photosynthesis by cells of Prochloron sp. freshly isolated from the as
cidian host, Lissoclinum patella, collected from shallow waters in Pal
au, was severely inhibited by ultraviolet (UV) irradiation. No photoin
hibition, however, was observed in Prochloron cells isolated from inta
ct colonies after UV irradiation, suggesting some protection by the as
cidian host. It was shown that UV protection was brought about by the
thick gelatinous tunic covering the whole ascidian colony. Analysis re
vealed that the surface tunic of L. patella, although transparent to v
isible light, contains several UV-absorbing substances, identified by
highperformance liquid chromatography as mycosporine-like amino acids
(MAAs). The predominant MAA identified was shinorine (lambda(max) = 33
4 nm), followed by mycosporine-glycine (lambda(max) = 310 nm) and a sm
all amount of palythine (lambda(max) = 320 nm). Although isolated Proc
hloron cells also contained shinorine, on a protein-weight basis it wa
s less than half of that observed in the host tunic. These results sug
gest that the surface tunic of a L. patella colony, which is transpare
nt to visible light for photosynthesis, also contains UV-absorbing com
pounds that protect its photoautotrophic symbiont, Prochloron sp., fro
m damage by the intense UV-irradiation that they receive daily in shal
low, tropical marine waters.