A Developmental Study of Photosystem I Peripheral Chlorophyll Proteins

Abstract

An isolated native photosystem I (PSI complex) contains 3 spectral populations of chlorophyll a antennae (Mullet, Burke, Arntzen 1980 Plant Physiol 65: 814-822). Apparently, nearly one-half of these antennae (.simeq. 45 Chl/P700) are associated with polypeptides of 21,500 to 24,500 daltons. Two developmental systems [cucumber (Cucumis sativus L.) or barley (Hordeum vulgare) seedlings] to verify this association. Chloroplasts were isolated from a Chl b-less barley mutant and from partially-developed cucumber cotyledons (greened under intermittent illumination [ImL] chloroplasts) and were compared to control chloroplasts isolated from wild-type barley and mature cucumber. Both the mutant and ImL chloroplasts exhibited a long wavelength fluorescence maximum at 724 nm at 77.degree. K as compared to 735-738 nm emission maximum in the respective controls. Both the mutant and ImL chloroplasts were deficient in polypeptides of 21,500-24,500 daltons which were present in control membranes and in PSI fractions isolated from control membranes. In light-induced maturation of the ImL cucumbers, the synthesis of polypeptides in the 21,500-24,500 MW range paralleled the appearance of PSI Chl species fluorescing at long wavelength (.simeq. 735 nm). The PSI spectral properties of the control membranes were retained in isolated PSI particles containing 100-120 Chl/P700 (PSI-110). Detergent extraction of PSI-110 removed polypeptides of 21,500-24,500 daltons plus .simeq. 45 Chl/P700. The antennae-depleted PSI particle mimics PSI properties exhibited by incompletely differentiated mutant or ImL chloroplasts.