Fruit initiation in Helleborus niger L. triggers chloroplast formation and photosynthesis in the perianth

• Published in: Journal of plant physiology 2000-10, Vol.157 (4), p.357-364
• Main Authors: Salopek-Sondi, Branka, Kovač, Maja, Ljubešić, Nikola, Magnus, Volker
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; carotenoid; chlorophyll; Economic plant physiology; Fructification and ripening; Fructification, ripening. Postharvest physiology; fruit-induced morphogenesis; Fundamental and applied biological sciences. Psychology; Growth and development; Helleborus niger L; perianth; photosynthesis; Plant physiology and development; plastid metamorphosis; Vegetative and sexual reproduction, floral biology, fructification
• ISSN: 0176-1617; 1618-1328
• DOI: 10.1016/S0176-1617(00)80020-6

The sepals of the Christmas rose ( Helleborus niger L.), which are white or rose at anthesis, persist until the seeds are ripe and become intensely green (in shaded plants), or dark red (in sun-exposed plants), during that period. An essential element in this color change is the fact that after pollination the leucoplasts which are present at anthesis start turning into chloroplasts. These show ultrastructural features indicating photosynthetic activity, contain high levels of a complete set of chlorophylls and carotenoids, photooxidize 3,3'-diaminobenzidine as an indicator for the presence of photosystem I, and synthesize light-harvesting complex proteins (LHC II) attributed to photosystem II. The photosynthetic capacity ultimately attained by the sepals, expressed in μmol O 2/hour/g fresh weight (or dry weight), is about half that of the leaves present at the same time, while the respective values per mg of total chlorophylls are identical within the limits of experimental error. Leaves in this species emerge during the final stages of fruit ripening, fully expand after seed aturity, and will survive until next spring, to die back at anthesis of the next generation of flowers or shortly thereafter. During fruit development, the chloroplasts in the sepals are thus a major source of assimilates. The metamorphosis of the sepals into photosynthetically active organs only occurs in fruit-bearing flowers and is arrested at a very early stage in controls in which the pistils are removed before pollination.