Incorporation of 14CO2 in photosynthetic pigments of Chlorella pyrenoidosa

Abstract

Tracer kinetic studies of chloroplast pigments of Chlorella pyrenoidosa were carried out in a special steady-state apparatus which allowed the simultaneous recording of oxygen evolution, CO2-fixation and (14)CO2-incorporation. A special cylindrical vessel which permits labeling experiments with larger algae suspensions (800 ml) is described.-1. After 2 h of (14)CO2-photosynthesis (fixation rate 100-160 μmol CO2/μmol chlorophyllxh) 3.3% of the total (14)C-uptake (5.66 mCi) was found in the Chlorella lipid fraction. Total and specific radioactivity were higher in total carotenoids than in the chlorophylls. Chlorophyll a gave a higher labeling degree (2.4%) than chlorophyll b (1.3%).-2. Among the carotenoids α-and β-carotene were labeled after 2 h (14)CO2 exposure with the same specific radioactivity and with a particular high labeling degree of c. 19%. The xanthophylls exhibit lower labeling degree (violaxanthin 5.1%, zeaxanthin 1.9%, lutein 1.4%, antheraxanthin 1.3%, and neoxanthin 0.7%).-3. During the 4 h (12)CO2-exposure period, which followed the 2 h (14)CO2-incorporation time, the specific and total radioactivity of the α-and β-carotene pools decrease with a concomitant increase in the α-ionone-(lutein) and β-ionone xanthophylls (violaxanthin, zeaxanthin, antheraxanthin). The possibility, that the decrease of (14)C label in the carotenes may in part be due to a photo-oxidative degradation, is discussed.-4. Calculation of biological half-life-times from the (14)C-incorporation kinetics during the first hour of the experiment, when the pigment concentration is almost unchanged, results in times from 30 to 60 min. Half lives are shorter in the precursor pools such as chlorophyll a (30 min), α-carotene (40 min) and β-carotene (50 min) and violaxanthin (60 min) respectively.

The carotenoid-labeling method: measuring specific rates of carotenoid synthesis in natural phytoplankton communities

“…Post et al 1984). Results of these and our studies are contrary to a previous report of high rates of chlorophyll and carotenoid turnover in Chlorella pyrenoidosa (Grumbach et al 1978). We have discussed this study previously (Goericke & Welschmeyer 1992a, b) and concluded that these differences may be due to the physiological state of the algal culture that was used.…”

Light-Harvesting Chlorophyll a/b Complexes: Interdependent Pigment Synthesis and Protein Assembly.

“…Total isotope uptake and the incorporation of label into acetone-soluble fractions were equivalent among the two mutant and wild-type strains (data not shown). Although very brief labeling periods are preferred for analyses of pigment synthesis because the half-lives of some subpopulations can be quite short (Grumbach et al, 1978;Britton, 1986), the duration of pigment pulse labeling is constrained by the degree to which sufficient amounts of carbon-14 are incorporated to enable subsequent detection. To determine whether pigment synthesis is impaired or whether pigment degradation is accelerated in GE2.27 and PA2.1, pulselabeling periods were varied from 5 to 60 min and chases with unlabeled acetate ranged from 5 min to 70 hr.…”

Continuous Turnover of Carotenes and Chlorophyll a in Mature Leaves of Arabidopsis Revealed by 14CO2 Pulse-Chase Labeling

“…Carotenoid turnover has been studied in algae in the past by applying [ 14 C]bicarbonate (Blass et al, 1959;Grumbach et al, 1978); for example, no more than 1% to 2% of the photosynthetically incorporated 14 C was allocated to the lipophilic fraction containing Chl and carotenoid in Chlorella pyrenoidosa after a 2-h pulse application (Grumbach et al, 1978). Even lower labeling efficiency is expected for photosynthetic pigments in nongrowing green leaves, in which pigment turnover takes place almost exclusively as part of the maintenance and acclimation of photosynthetic membranes.…”