The homozygous and heterozygous effects of an aurea mutation on plastid development in spruce (Picea abies (L.) Karst.)

A11 electron niicroscopical investigation has been made of plastid developnienti n spruce plants which are homozygous or heterozygous for a semi-dominant aurea mutation. The cotyledons of normal spruce seedlings synthesise chlorophyll and develop chloroplasts both in the dark and in the light. The chloroplasts in dark-grown seedlings have grana and severa1 prolamellar bodies. No chlorophyll was detected in acetone extracts of light-grown or dark-grown seedlings which were homozygous for the aurea factor. In these yellow lethal seedlings,plastid morphogenesis is blocked prior to the formation of prolamellar bodies. In the yellon-green heterozygous aurea seedlings, clorophyll synthesis is reduced; when grown in the dark they have a clorophyll content that is only 50 per cent of that in corresponding wild type individuals. The chloroplasts of these dark-grown aurea seedlings possess several prolamellar bodies and a poorly differentiated lamellar system, in which the grana usually contain only two or three discs. Aurea plants develop in the light an abnormal lamellar system with grana which appear sickle-shaped in cross-section. The yellon-green needles possess the ability of spontaneous greening. The chloroplasts in older green needles of the mutant are normalised and indistinguishable from wild type chloroplasts