Page 133 - Algae Anatomy, Biochemistry, and Biotechnology

116 Algae: Anatomy, Biochemistry, and Biotechnology

FIGURE 2.79 Transmission electron microscopy image of Nannochloropsis sp. in transverse section,
showing the chloroplast (a) (Bar: 0.50 mm); chloroplast at higher magnification (b) (Bar: 0.10 mm).

inner face of the chloroplast, pear-shaped in the Phaeophyceae, or stalked in the Eustigmatophy-
ceae. They can be one or many (Bacillariophyceae and Phaeophyceae). No storage material or
capping vesicles have been found to be associated with pyrenoids, but lipid or oil droplets normally
distributed randomly in the chloroplast matrix are often concentrated at the periphery of the
pyrenoid.

Haptophyta
Cells of Haptophyceae species normally possess one or two chloroplasts containing thylakoids
stacked in three to form lamellae. There is no girdle lamella. Spindle-shaped pyrenoids are com-
monly immersed within the chloroplast, penetrated by one or a few pairs of thylakoids, but in
some genera they bulge from the inner face of the organelle. Both the chloroplast and the pyrenoid
are surrounded by endoplasmic reticulum confluent with the nuclear envelope, the nucleus itself
lying close to the chloroplast. Chlorophylls a, c 1 , and c 2 and in some genera also c 3 are found in
the thylakoidal membranes together with carotenes, such as b-carotene, and xanthophylls, the
most commonly occurring being fucoxanthin. DNA is organized into numerous nucleoids scattered
throughout the chloroplast.

Cryptophyta
The chloroplasts of these algae, one or two per cell, are unusual in both their pigment composition
and ultrastructure. Four membranes enclose these organelles: the inner pair forms the plastid envel-
ope and the outer pair forms the plastid endoplasmic reticulum. This four-membrane configuration
is common in chlorophyll c-containing algae. An expanded space is present between the plastid
endoplasmic reticulum and the plastid envelope on its inward face. This compartment contains
80S ribosomes, starch grains, and the nucleomorph. Thylakoids inside the chloroplast are typically
in pairs, although single thylakoids as well as large stacks have been also observed, with no girdle
lamella. A pyrenoid is present, projecting from the inner side of the chloroplast. Cryptomonads
are characterized by the presence of chlorophylls a and c 2 ; phycoerythrin, phycocyanin, and
allophycocyanin; carotenes, and several xanthophylls.