Pigments in mesocotyls of corn (Zea mays) and oats (Avena sativa) in darkness, and after irradiation and treatment with 5-aminolevulinic acid

The aim of the study was to clarify the pigment content and light-induced pigment formation in the grass mesocotyl (oats, Avena sativa L. cv. Seger I, and corn, Zea mays L. cv. Seneca). This organ, localized between root and coleoptile, only develops in darkness. To date, there are no data on its pigment content in the literature. The data found indicate a close relationship with conditions in roots, particularly with respect to the importance of yellow pigments as bleaching-preventing agents and response to red and blue light. The mesocotyl contained small amounts of both Pchl_628–632 and Pchl_636–642 with a dominance of the former. Occasionally minute amounts of Pchl_650–652 were present, particularly in corn. The highest pigment concentration was found in the zone around the primordia of the pair of roots, which after several days in darkness protruded from the upper part of the mesocotyl close to the attachment to the coleoptile. Carotenoids were not detectable with absorption spectrophotometry. All pigments present in darkness were rapidly bleached in daylight and in strong red and blue light, and no more were synthesized under continuous irradiation. In continuous weak red and blue light small amounts of chlorophyll were formed at the same time as the protochlorophylls disappeared. Red light seemed to be somewhat more effective than blue, at least in corn. This chlorophyll biosynthesis stopped at very low values. The mesocotyls never became visibly green. Normal chloroplasts with grana did not develop. Mesocotyls, which had been irradiated for a short time, with no additional pigment formed, synthesized small amounts of Pchl when placed in darkness. ALA treatment of dark-grown mesocotyls yielded Pchl_628–632 to a higher degree than did irradiation.