Bj. Butow et al., ANTIOXIDATIVE PROTECTION OF PERIDINIUM-GATUNENSE IN LAKE KINNERET - SEASONAL AND DAILY VARIATION, Journal of phycology, 33(5), 1997, pp. 780-786
A comprehensive antioxidative mechanism was found in the freshwater di
noflagellate Peridinium gatunense Lemm. during the spring bloom in Lak
e Kinneret. Ascorbate runs present throughout the bloom period and was
responsible, together with catalase, for the elimination of photosynt
hetically produced H2O2. As glutathione conc entrations and ascorbate
regenerative enzymes were negligible during mid-spring, ascorbate was
presumably biosynthesized during the photosynthetically active period.
Antioxidative activity increased overall at the end of the spring in
conjunction with elevated ambient stress conditions, for example high
light. Under such circumstaces, ascorbate was regenerated. Ascorbate l
evels doubled when cells were exposed to an increase in irradiance fr
om 60 to 600 mu mol photons.m(-2). s(-1), and on addition of H2O2, con
centrations increased a further 20-fold. Significant antioxidative act
ivity was also noted in the dark, although this was dependent on the p
resence of H2O2. Diurnal changes in antioxidants and their regenterati
ve enzymes were observed. The activities of monodehydroascorbate reduc
tase, glutathione reductase, and ascorbate concentrations showed ultra
radian periodicity and were completely in phase throughout the day/nig
ht period. Dehydroascorbate reductase activity and glutathione concent
rations were also in phase but showed aperiodic variation, as did asco
rbate peroxidase activity Superoxide dismutase and catalase activities
were generally out of phase during the 24-h period but did show ultra
radian periodicity. Lake samples entrained under constant light reveal
ed an inate 12-h rhythm for catalase activity, during at least 36 h.