Nitrogen deficiency affects both photosystems and the antennae pigment systems in the photosynthetic apparatus of the marine alga,Cryptomonas maculata. Under increasing energy fluence rates, O2evolution in nitrogen-deficient (-N) cell suspensions never reached a positive value; in control cultures (+N), O2evolution increased and was saturated at about 6.4 W·m-2with about 100 μmol O2·mg chlorophyll-1·h-1. During fluorescence-induction experiments at room temperature, Foand Fmaxwere significantly increased in-N cells whereas the Fvar/Fmaxratio decreased from 0.6 to 0.1. These observations can be correlated with a significantly decreased population of 12.5-nm-size particles in the exoplasmic-fracture (EF) faces of freeze-cleaved thylakoid membranes in-N cells (Rhiel et al., 1985, Protoplasma129, 62–73). The EF particles are suggested to represent photosystem II associated with chlorophyll a/c-protein complexes (LHCP). The banding pattern of isolated and Triton X-100-solubilized thylakoid membranes of both +N and-N cells in sucrose gradients showed that the LHCP is still present in-N cells. The same applies to sodium dodecyl sulfate-polyacrylamide gel electrophoresis of these membrane fractions. The reduced number of the 12.5-nm particles in the EF faces of-N cells may be a result of decoupling of the LHCP constituents of the photosystem-II complex rather than their degradation. This is supported by high values for the initial fluorescence Foin fluorescence-induction experiments and, in part, is indicated by the shift of the maximal fluorescence emission from 693 nm in +N to 684 nm in-N cells. The lack of the CP1 band in the gels of sodium dodecyl sulfate-solubilized thylakoid membranes from-N cells after electrophoresis demonstrates that photosystem I is also severely aff
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