Carotenoid composition and its relationship to chlorophyll and D1 protein during leaf development in a normally senescing cultivar and a stay-green mutant of Festuca pratensis

Abstract

Chlorophyll and carotenoid were measured with reference to the developmental gradient along the expanding fourth leaf of Rossa, a normally yellowing cultivar of Festuca pratensis, and of a mutant genotype Bf993 which is unable to degrade pigments and associated thylakoid proteins during foliar senescence. Although pigment levels were highest in the central, mature portion of the leaf, there were nevertheless readily detectable amounts of chlorophyll and carotenoid even in basal tissues enclosed in the sheaths of older leaves. Carotenoid compositions were the same in all the tissues except the senescent tissue at the leaf tip. Here chlorophyll to carotenoid ratio decreased in Rossa but along the young leaf tissue of this genotype and throughout the leaf of Bf993 this ratio was constant. Amounts of D1 protein, associated with the Photosystem II reaction centre, were correspondingly retained to a somewhat greater extent in senescing tissue of Bf993 but surprisingly, given the expression of the genetic lesion in a delayed senescence, amounts of the protein were lower in young tissue from the stay-green mutant than in the normal genotype. When the leaf of Rossa was allowed to senesce until the entire blade was yellow there were marked changes in carotenoid composition, and chlorophyll degradation products accumulated. Any increase in zeaxanthin was slight and there was no evidence to suggest operation of a xanthophyll cycle.