Why are higher plants green? Evolution of the higher plant photosynthetic pigment complement
The physiological reason that higher plants are green is unknown. Other photosynthetic organisms utilize pigments that strongly absorb green light; therefore, there must have been natural forces that ‘selected’ the photosynthetic pigments found in higher plants. Based on previously published data and our recent findings about green light and photosynthesis within leaves (Sun et al.), a specific functional role is described for the primary photosynthetic pigments of higher plants, that were derived from green algal progenitors. The particular absorptive characteristics of chlorophylls a and b appear to perform two contradictory, but necessary functions in higher plants. Firstly, chlorophylls a and b absorb light for maximum utilization under non-saturating conditions, a function that is well understood. Secondly, they can act as protective pigments under over-saturating light conditions, when absorbed light is dissipated as heat. Under such conditions, a significant portion of light can also be efficiently utilized, especially in the bottom portion of the leaf, that is mainly illuminated by green light and not down-regulated. The second function may have been the selective force that gave rise to the extremely successful terrestrial plants, that evolved from green algae.
Keywords: Chl; NPQ; PAR; PET; PM; SM; Spinacia oleracea; carbon fixation; chlorophyll; evolution; green light; non-photochemical quenching; palisade mesophyll; photosynthetic electron transport; photosynthetic pigments; photosynthetically active radiation; spongy mesophyll
Document Type: Research Article
Affiliations: Department of Botany, University of Wyoming, PO Box 3165, Laramie, Wyoming 82071–3165, USA
Publication date: 01 June 2000