R. Goericke et Na. Welschmeyer, THE CAROTENOID-LABELING METHOD - MEASURING SPECIFIC RATES OF CAROTENOID SYNTHESIS IN NATURAL PHYTOPLANKTON COMMUNITIES, Marine ecology. Progress series, 98(1-2), 1993, pp. 157-171
The physiological basis of the carotenoid-C-14-labeling method for the
determination of growth rates (mu, d-1) of specific groups of microal
gae was established in the laboratory and the method was tested in the
subarctic Pacific and in Chesapeake Bay (USA). C-14-labeling patterns
of carotenoids in a variety of algal species grown in batch cultures
were described successfully with a simple precursor-pigment model whos
e free parameters, the specific rate of carotenoid synthesis (mu(caro)
, d-1) and the precursor and the pigment turnover rates (d-1), were de
termined by least squares analysis. All xanthophylls except peridinin
had turnover rates that did not differ significantly from zero; the tu
rnover rate of peridinin was 0.7 mu. Precursor turnover rates varied f
rom about 5 mu for fucoxanthin to 36 mu for lutein. We propose to use
the precursor-pigment model to calculate mu(caro) from the amount of C
-14 incorporated into carotenoids and values of carotenoid precursor t
urnover rates, which are assumed to be known a priori. A well-constrai
ned estimate of the fucoxanthin precursor turnover rate is presented h
ere. It was shown for laboratory cultures that the carotenoid-labeling
method is capable of measuring specific rates of carotenoid synthesis
and that these rates equal rates of cell growth only when growth is b
alanced. We demonstrated that pigment synthesis and carbon fixation ca
n be unbalanced in natural phytoplankton populations due to the effect
s of light perturbations and growth under a natural photocycle. We rec
ommend that labeling experiments last 24 h to average rates of synthes
is over the diel photoperiod since rates of carotenoid synthesis and c
ell growth can be unbalanced at any time during the photoperiod. The f
ield experiments also demonstrated that the carotenoid-labeling method
is a powerful tool to study the physiological ecology of natural popu
lations of phytoplankton.