Young and mature canopy leaves of tropical forest trees ( Anacardium excelsum, Castilla elastica) and cold- and non-acclimated leaves of spinach ( Spinacia oleracea) grown in temperate climate were used as systems of differing susceptibility to high light stress to assess the role of xanthophyll cycle activity and D1 protein turnover in photoinhibition of photosynthesis. Previous investigations with spinach revealed two distinct stages of photoinhibition (indicated by a decline in the ratio of variable to maximum chlorophyll fluorescence) which were reflected in different kinetics of recovery in low light. An initial fast recovery phase of unknown biochemical mechanism (about 1 h) was followed by a slow phase (several hours), which may be based upon resynthesis of the D1 protein in the photosystem II reaction center. All leaves studied exhibited these two phases. However, the kinetics and relative amplitude of the two phases varied strongly and were dependent on leaf age and light acclimation. Recovery was rapid in young canopy sun leaves and cold-acclimated leaves of spinach due to a pronounced initial phase. On the other hand, the slow, probably D1 related phase dominated in mature canopy leaves and non-acclimated leaves of spinach. The fast phase of recovery and epoxidation of zeaxanthin via the xanthophyll cycle were closely correlated in all leaves studied. In addition, recovery following photoinhibition in the presence of dithiothreitol, which prevented formation of zeaxanthin, occurred only in a slow phase. On the other hand, leaf incubation prior to photoinhibition with streptomycin, an inhibitor of chloroplast-encoded protein synthesis, eliminated slow recovery by preventing resynthesis of the D1 protein. The young tropical sun leaves and the cold-acclimated spinach leaves exhibited a higher pool of xanthophyll cycle pigments per chlorophyll and in response to strong light converted a higher percentage of violaxanthin to zeaxanthin than the mature and the non-acclimated leaves, respectively. Quantification of D1 protein in photoinhibited spinach leaves by means of electrophoresis and Western blotting revealed a strongly diminished D1 protein degradation in the cold-acclimated compared to the non-acclimated state. High xanthophyll cycle activity and pool sizes observed in response to high light with young canopy and cold-acclimated spinach leaves may serve to protect these leaves against inactivation of the D1 protein.