. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 80 T. S. WAKEFIELD ET Figure 11. Svmbioilininin bermiulfiixi' within heist .4/i/.w'</ Standard glutaraldehyde-osmium tissue fixation. Note scrolled membrane in region where thecal vesicles should be (arrowheads), ch = chloroplast; cw = cell wall: ml = multiple layers of symbiosome membrane; arrow- heads identify area where thecal vesicles should be located. Scale bar = 200 nm. Inset (a) is a higher magnification of an additional symbiont showing layered membranes internal to the cell wall. Scale bar = 100 nm. each en
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 80 T. S. WAKEFIELD ET Figure 11. Svmbioilininin bermiulfiixi' within heist .4/i/.w'</ Standard glutaraldehyde-osmium tissue fixation. Note scrolled membrane in region where thecal vesicles should be (arrowheads), ch = chloroplast; cw = cell wall: ml = multiple layers of symbiosome membrane; arrow- heads identify area where thecal vesicles should be located. Scale bar = 200 nm. Inset (a) is a higher magnification of an additional symbiont showing layered membranes internal to the cell wall. Scale bar = 100 nm. each end, with a distinct cytoplasmic separation between adjacent vesicles. Internal thecal plates were apparent within some vesicles of S. benmulense (Fig. 1. arrow). The enclosed thecal plate lies separate from the vesicle mem- brane. The overall thickness of the vesicles for each species is reported in Table 1 . Since serial sections of an entire cell were not cut, we could not determine whether the differing widths of the vesicles reflect differences among species, large and small vesicles, or different vesicle profiles. In several micrographs, a linear array of microtubules was present underlying the vesicles (Fig. 10). Standard aldehyde-osmium fixed tissues of all three spe- cies of symbiont failed to show many of the fine structures seen in the freeze-substituted tissue. The multiple-layered symbiosome membrane was apparent; but only the OL and the IL of the cell wall were seen in S. benmulense. and all three species failed to show any thecal vesicles or plates. Instead, there appeared to be several layers of membrane beneath the vegetative cell wall ( Fig. 11, 1 la). Discussion A multiple-layered cell wall in Symbiodiniwn dcnse has been previously described by Palincsar et al. ( 1988; they identified the symbiont of Aiptcixin pulliilii as S. inifrodtlriiiticiim at 'hat time; however, the species has subsequently been rcdescribed as S. bermudense [see Trench. 1993]). The d
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