Regreening of involucral leaves of female Leucadendron (Proteaceae) after flowering

Abstract

Involucral leaves of Leucadendron have the remarkable ability to turn yellow upon flowering and regreen naturally as the florets of the inflorescence wilt. This colour change results from degradation of chlorophyll and to a lesser degree carotenoids, resulting in the unmasking of yellow colour. Chlorophyll levels were restored upon regreening. Degreening coincided with the complete dismantling of the thylakoid system, while keeping the outer plastid envelope intact. Regreening resulted from the complete redifferentiation of these gerontoplast-like plastids into functional chloroplasts. The colour change was directly linked to the development of the inflorescence. Complete removal of the inflorescence before flowering prevented the colour change while removal at full bloom, when involucral leaves were yellow, resulted in significantly faster regreening. This designates the inflorescence or florets as the possible origin of the colour change trigger and suggests that the colour change is involved with attraction of pollinators. Degreening and regreening also took place in a growth chamber under continuous high light intensity. Therefore neither pollination nor the presence of roots is required for regreening. It appears that colour change in Leucadendron results from a well-regulated degradation and subsequent synthesis of photosynthetic pigments.