Ka. Berube et al., Effects of chronic salt stress on the ultrastructure of Dunaliella bioculata (Chlorophyta, Volvocales): mechanisms of response and recovery, EUR J PHYC, 34(2), 1999, pp. 117-123
The ultrastructural changes taking place in Dunalielia bioculata after chro
nic exposure to a sodium chloride-induced stress were examined. Hyperosmoti
c shock was induced by raising the sodium chloride concentration of the cul
ture medium from 0.3 to 1.3 M, which affected a number of cellular organell
es during the initial stages of the stress period, i.e. 24, 48 and 72 h. Ch
anges in whole-cell volume were recorded, as well as alterations in the siz
e of the following components: starch grains and sheath, lipid and plastogl
obuli, chloroplast, pyrenoid, nucleus, mitochondria, cytoplasm, Golgi appar
atus and endoplasmic reticulum. Cells were examined using transmission elec
tron microscopy and changes to their fine structure quantified via image an
alysis of the electron micrographs. The image analysis program was designed
to measure various geometric parameters for all the cell components within
individual algal cells. Quantitative image analysis of cells subjected to
a chronic salt stress revealed marked increases in the cross-sectional area
s of the Golgi apparatus and the endoplasmic reticulum. The enhanced produc
tion of the Golgi apparatus within the algal cells was thought to be the di
rect result of a salt-stress-induced endoplasmic reticulum production withi
n the cells. The increase in the endoplasmic reticulum was manifested as ex
tensive networks of cortical endoplasmic reticulum. It is suggested that th
e endoplasmic reticulum serves both physiological and structural roles duri
ng chronic salt stress by providing the driving force behind increased synt
hetic/Golgi apparatus activities of the cells, and by providing a type of '
cellular scaffolding' to limit the degree of cell contraction in the face o
f long-term salt stress.