Photosynthetic pigments in developing seeds of Acer platanoides and Acer pseudoplatanus

Photosynthetic pigments were investigated in developing and dried seeds of desiccation-tolerant (orthodox) Acer platanoides and desiccation-sensitive (recalcitrant) Acer pseudoplatanus. The seeds of both Acer species contained higher levels of chlorophyll a (Chl a), particularly in cotyledons, than chlorophyll b (Chl b). Chl a and Chl b peaked during seed morphogenesis, then declined. The decrease was greater in A. platanoides (eight-fold) than in A. pseudoplatanus (three-fold) seeds. The total chlorophyll content was greater in the A. pseudoplatanus seeds only for three weeks, before morphogenesis began in the A. platanoides seeds. Photosystem II activity suggested that photosynthesis might be more active in A. pseudoplatanus at the initial and final stages of seed development. The carotenoid (Car) content increased during the initial stages of A. pseudoplatanus embryo development. The Car/Chl ratio indicated a significant contribution of Car to the pigment pool during the initial stages of development and drying in Acer seeds. The chlorophyll autofluorescence signal was irregular and diffuse in the embryonic axes of mature Acer seeds; however, a spherical and compact autofluorescence signal was reported in A. platanoides cotyledons. Differences in photosynthetic pigments are discussed in relation to seed orthodoxy and recalcitrance, as potentially influencing the longevity variations associated with seed categories.