Studies on the biochemistry and fine structure of silica shell formation in diatoms. IV. Fine structure of the apochlorotic diatom Nitzschia alba Lewin and Lewin.

Abstract

The fine structure and pigmentation of an apochlorotic diatom isolated from decaying Macrocystis pyrifera is described. The morphology of acid cleaned shells suggests that the isolate is Nitzschia alba Lewin and Lewin. Light microscope observations indicated a centrally located nucleus and numerous highly refractile bodies which stained differentially with Nile blue and Sudan black B. The stained globules could be correlated in thin-sectioned profiles with either electron dense or lucent areas depending on the fixation technique. In the electron microscope the nucleus, Golgi complex, and mitochondria were similar in appearance to those described for other diatoms. Proplastid-like organelles, delimited by a double membrane, and containing small vesicles were also observed. Neither carotenoids nor chlorophylls could be detected by spectroscopic or spectrofluorometric analysis in vivo or in organic solvent extracts. Deposition of new walls was initiated by formation of silicon deposition-vesicles in the central region of dividing cells. The acentric raphes were deposited last. The genesis and interrelationship of the old plasmalemma, silicalemma, and newly formed plasmalemma are discussed.