lhe role of high-light-induced chloroplast movement in the photoprotection of the facultative shade plant Tradescanfia albiflora was investigated by comparison with pea (Pisum safivum L.) leaves, both grown in 50 pmol photons m-' s-'. Photoinactivation of photosystem II (PSII) in vivo was induced in 1.1 % CO, by varying either duration (0-2 h) of illumination (fixed at 1800 pmol m-* s-l) or irradiance (0-3000 pmol m-' s-') at a fixed duration (1 h) after infiltration of leaves with water or lincomycin (an inhibitor of chloroplast-encoded protein synthesis). At all photon exposures, PSll of r. albiflora leaves showed a greater resistance to light stress than pea leaves, although both utilization of absorbed light by photosynthesis and psbA gene product synthesis were smaller than for pea leaves. This greater tolerance was not due to differences in PSll antenna size or the index of susceptibility of PSll to light stress, because these two parameters were comparable in both plants. However, the transmittance increase mediated by chloroplast movement was greater in r. albiflora than pea, resulting in a 10%