DISTRIBUTION AND GEOMETRIC ISOMERISM OF NEOXANTHIN IN OXYGENIC PHOTOTROPHS - 9'-CIS, A SOLE MOLECULAR-FORM

The distribution and geometric form (cis or trans) of neoxanthin, one of the major carotenoids of oxygenic phototrophs, were systematically examined. The 9'-cis form of neoxanthin, but not the all-trans form, w as found in chloroplasts of seed plants, ferns, mosses and green algae , all of which contain chlorophylls a and b. In contrast, neoxanthin w as not found in other algal classes, such as Heterokontophyta, Rhodoph yta and oxygenic phototrophic prokaryotes. Consequently, with regard t o phylogeny, the appearance of neoxanthin appears to be associated wit h the appearance of chlorophyll b. In non-photosynthetic organs, such as petals and fruits, the presence of neoxanthin was classified into f our types; those having only the 9'-cis form, those with only the all- trans form, those with both forms, and those without either form. Thus only 9'-cis neoxanthin is found in chloroplasts, and the all-trans ne oxanthin is found only in non-photosynthetic organs. Because the absor ption spectra of both forms are almost identical, their functions in p hotosynthesis might be similar. 9'-Cis neoxanthin is not involved in t he xanthophyll-cycle, whereas it is a suitable substrate for abscisic acid synthesis. Differences in geometric isomerism are discussed in re lation to abscisic acid synthesis.