NEW PYRENOID FORMATION IN THE BROWN ALGA,SCYTOSIPHON LOMENTARIA(SCYTOSIPHONALES, PHAEOPHYCEAE)¹

Abstract

The Scytosiphon lomentaria (Lyngbye) Link cell characteristically has only one chloroplast with a prominent protruding pyrenoid. We observed the appearance of a new pyrenoid in each chloroplast during first mitosis in zygotes of S. lomentaria, using the freeze substitution technique. At first, a pyrenoid matrix appeared within the outermost stroma, in which thylakoid triplets and ribosomes were absent. At this time, the surface of this part remained smooth. The old pyrenoid was covered with a pyrenoid cap on the cytoplasmic side, whereas there was no pyrenoid cap on the new pyrenoid before protrusion. Irregularly shaped membranous sacs containing fine granular materials associated with the cytoplasmic side of the new pyrenoid. The sacs fused with each other and changed conformation and finally transformed into the pyrenoid cap. The new pyrenoid gradually protruded toward the cytoplasm, and the new pyrenoid cap became curved along the surface of pyrenoid. Cytokinesis occurred, and each chloroplast had two prominent protruding pyrenoids in two‐celled zygotes. We examined immunolocalization of β‐1,3‐glucans within the pyrenoid cap with a monoclonal antibody, using EM. Gold particles indicating localization of β‐1,3‐glucans were detected in vacuoles but never in the pyrenoid cap. This observation suggests that the pyrenoid cap in brown algae contains no photosynthetic products such as polysaccharide.

The glucans extracted with warm water from diatoms are mainly derived from intracellular chrysolaminaran and not extracellular polysaccharides

“…This result was consistent with the localization of chrysolaminaran in Pinnularia cells reported by Waterkeyn & Beinfait (1987), who used aniline blue staining to localize 1,3-b-D-glucans. The same anti-1,3-b-D-glucan antibody was recently used to demonstrate that laminaran was localized in the vacuoles in zygotes of a phaeophycean alga, Scytosiphon lomentaria (Nagasato & Motomura, 2002), and not in the pyrenoids as previously thought. Interestingly, although several vacuoles were often seen inside T. pseudonana cells in the present study, occasionally one was not labelled by the antibody (Fig.…”

PYRENOID FORMATION ASSOCIATED WITH THE CELL CYCLE IN THE BROWN ALGA,SCYTOSIPHON LOMENTARIA(SCYTOSIPHONALES, PHAEOPHYCEAE)1

“…One is that a new pyrenoid is budded off from the root of the old pyrenoid in Ectocarpus confervoides (Evans 1966). Another is that a new pyrenoid is formed away from the old one (Nagasato and Motomura 2002). The present study, using anti‐RUBISCO antibody, confirms our previous study (Nagasato and Motomura 2002).…”

“…Another is that a new pyrenoid is formed away from the old one (Nagasato and Motomura 2002). The present study, using anti‐RUBISCO antibody, confirms our previous study (Nagasato and Motomura 2002). Several spots that reacted positively with anti‐RUBISCO antibody first appeared away from the original old pyrenoid in the chloroplast.…”

“…During new pyrenoid formation, the pyrenoid matrix is not covered with the pyrenoid cap before protruding. An irregularly shaped membrane structure transforms into the characteristic dumbbell shape and becomes the pyrenoid cap covering the cytoplasmic site of the matrix of the new pyrenoid just before the protrusion of the pyrenoid matrix (Nagasato and Motomura 2002). In this electron microscopic study, when Scytosiphon zygotes were treated with chloramphenicol, a prepyrenoid cap was observed near a small electron‐dense projection.…”

“…Recently, Nagasato and Motomura (2002) reported ultrastructural observations on new pyrenoid formation in the brown alga Scytosiphon lomentaria . The cells characteristically have only one chloroplast with a protruding pyrenoid (Clayton and Beakes 1983).…”