Chloroplast protection in greening leaves

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Abstract
Changes in photosynthetic activity, leaf pigments and the activities of enzymes that scavenge damaging oxygen species in chloroplasts were followed during the greening of 8‐day‐old etiolated pea (Pisum sativum L. cv. Meteor) seedlings. Accumulation of chlorophyll and carotenoids was accompanied by development of photosynthetic activity. Carotenoids present in etiolated leaves, and the high ratio of carotenoid to chlorophyll detected during the early hours of greening are suggested to provide important protection against singlet oxygen. Superoxide dismutase, ascor‐bate peroxidase and glutathione reductase, which scavenge superoxide and hydrogen peroxide in chloroplasts, are present at high activities in etiolated leaves and throughout greening. The mechanisms by which developing chloroplasts may generate damaging oxygen species, and the role of these scavengers during greening is discussed.