Effects of nitrogen starvation on the function and organization of the photosynthetic membranes in Cryptomonas maculata (Cryptophyceae).

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, O2 evolution in nitrogen-deficient (-N) cell suspensions never reached a positive value; in control cultures (+N), O2 evolution increased and was saturated at about 6.4 W·m(-2) with about 100 μmol O2·mg chlorophyll(-1)·h(-1). During fluorescence-induction experiments at room temperature, Fo and Fmax were significantly increased in-N cells whereas the Fvar/Fmax ratio 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, Protoplasma 129, 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 Fo in 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 affected.