A Developmental Study of Photosystem I Peripheral Chlorophyll Proteins

Abstract

An isolated "native" photosystem I (PSI complex) contains three spectral populations of chlorophyll a antennae (Mullet, Burke, Arntzen 1980 Plant Physiol 65: 814-822). It was hypothesized that nearly one-half of these antennae ( approximately 45 Chl/P(700)) are associated with polypeptides of 21,500 to 24,500 daltons. The present study utilizes two developmental systems 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 nanometers at 77 K as compared to 735 to 738 nanometers emission maximum in the respective controls. Both the mutant and ImL chloroplasts were deficient in polypeptides of 21,500 to 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 to 24,500 molecular weight range paralleled the appearance of PSI Chl species fluorescing at long wavelength ( approximately 735 nm).The PSI spectral properties of the control membranes were retained in isolated PSI particles containing 100 to 120 Chl/P(700) (PSI-110). Detergent extraction of PSI-110 removed polypeptides of 21,500 to 24,500 daltons plus approximately 45 Chl/P(700). The antennae-depleted PSI particle mimics PSI properties exhibited by incompletely differentiated mutant or ImL chloroplasts.