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THE CRYPTOMONAD NUCLEOMORPH: ITS ULTRASTRUCTURE AND EVOLUTIONARY SIGNIFICANCE 1
Author(s) -
Gillott Marcelle A.,
Gibbs Sarah P.
Publication year - 1980
Publication title -
journal of phycology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.85
H-Index - 127
eISSN - 1529-8817
pISSN - 0022-3646
DOI - 10.1111/j.1529-8817.1980.tb03074.x
Subject(s) - biology , pyrenoid , chloroplast , thylakoid , ultrastructure , botany , haptophyte , chloroplast stroma , uranyl acetate , biochemistry , ecology , phytoplankton , nutrient , gene
The Cryptophyceae are a class of phytoflagellates with affinities to both the red algae and the Chromophyta, by virtue of their possession of both phycobilns and chlorophyll c. Unlike other chromophytes, the periplastidal compartment (the space between the chloroplast envelope and chloroplast ER) is extensive, containing starch grains, ribosomes and a nucleomorph in addition to the vesicles and tubules observed in other chloroplast ER‐containing algae. We have examined the nucleomorph in six species of cryptomonads. There is one nucleomorph per cell except during division, when two are present. The position of the nucleomorph in the interphase cell is species specific: in some species it is embedded in an invagination of the pyrenoid and in others it lies along the inner surface of the chloroplast. The nucleomorph is enclosed by a double membrane; this envelope is interrupted by pores which, in tangential section, appear as elongated slits and have a central dense element. Two types of inclusions have been observed in nucleomorphs: dense globules which are occasionally joined to form ribbons, and a larger fibrillogranular body which resembles a nucleolus. Using a uranyl acetate‐ EDTA‐lead stain, we have tentatively localized nucleic acid within the nucleomorph. The nucleus‐like characteristics of this organelle support the theory that the chloroplast and associated structures bounded by the chloroplast ER represent a reduced eukaryotic endosymbiont. Based on the location of the α‐1,4‐glucan storage product and the presence of phycobilins, we postulate that the endosymbiont was probably a red alga. Other chloroplast ER‐containing algae may have evolved from a cryptomonad‐like ancestor through further reduction of the endosymbiont.