The Appearance of Neoxanthin during the Regreening of Dark-grown Euglena (1964)

Euglena gracilis has been shown to contain large amounts of the epoxide carotenoids, antheraxanthin and neoxanthin, when cultured heterotrophically in the light (13). This green flagellate can be changed by a variety of agents and conditions into yellow or colorless forms which can no longer carry out photosynthetic reactions. This change is apparently due to the inability of these modified strains either to synthesize chlorophyll or replicate chloroplasts. There have been several reports of altered patterns in the carotenoid pigments in these yellow and colorless forms. Pringsheim and Pringsheim (16) demonstrated that high temperature treatment (34-35o) would convert E. gracilis to an irreversibly bleached form, and Goodwin and Gross (8) have studied the carotenoid pigments of such a heat-bleached substrain. They found that, as with the parent strain, xanthophylls were present to a much larger extent than the hydrocarbon polyenes. The differences noted were that the heat-bleached strain contained phvtofluene and a t-carotene-like pigment in the hydrocarbon fraction, unlike the green cells. In addition, the xanthophyll fraction was altered; neoxanthin was absent, and they reported only echinenone, zeaxanthin, and lutein in this fraction. In view of the fact that Krinsky and Goldsmith (13) identified the major xanthophyll of E. gracilis as antheraxanthin, and that this had been mistakenly identified as lutein in an earlier publication of Goodwin and Jamikorn (9), we have assumed that there is some antheraxanthin in heatbleached substrains of E. gracilis, but this remains to be proven. It would therefore seem as if heatbleached E. gracilis lacks at least one of its 2 epoxide carotenoids, neoxanthin, and may or may not retain some antheraxanthin. The drug-bleached substrains have been investigated more thoroughly. Certain antibiotics, such as streptomycin (17) and erythromycin (5) and various antihistamines (10) are capable of bleaching E. gracilis. Seven bleached substrains were studied by Goodwin and Gross (8) and they concluded that the synthesis of the typical chloroplast carotenoids, ,carotene, lutein (antheraxanthin?), and neoxanthin was upset. Indeed, they were unable to detect neoxanthin in any of these strains, and only traces of lutein (antheraxanthin?). Darkness will also induce chlorotic, or etiolated forms of E. gracilis, but unlike heat or drugs, this procedure is reversible. Goodwin and Jamikorn (9) concluded that the pigments in -dark-grown E. gracilis were the same as those found in the light-grown cells and in the same relative amounts, although at a lower concentration. This was modified by a later study, in which Goodwin (7) reported that he found only lutein (antheraxanthin?) with ,8-carotene, neoxanthin and violaxanthin being absent or present in only minute traces. All of these studies would indicate that there is an alteration in the carotenoid pigments in E. gracilis when they are made chlorotic. With the recent demonstration of the kinetics of regreening of darkgrown E. gracilis and the measurement of the rate of appearance of photosynthetic capacity during this process (21) we have investigated what changes, if any, occur in the carotenoid pigments during this process. A preliminary report of this work has appeared (14).