Population biology of Ammophila breviligulata and Calamovilfa longifolia on Lake Huron sand dunes. II. Ultrastructure of organelles and photosynthetic properties

Abstract

Organellar ultrastructure and photosynthetic properties of two grasses, Calamovilfa longifolia (Hook) Scribn. and Ammophila breviligulata Fern., growing on Lake Huron sand dunes were compared. Thylakoids of C. longifolia contained a relatively greater complement of the photosystem I (PSI) – chlorophyll a – protein complex, whereas thylakoids from A. breviligulata had a relatively greater complement of light-harvesting chlorophyll a + b complex. The chlorophyll a/b ratios of the mesophyll chloroplast thykaloids reflected the content of chlorophyll–protein complexes present in the membranes. Digitonin fractionation of mesophyll thylakoids from C. longifolia revealed that the PSI-enriched fraction contained more chlorophyll than the photosystem II (PSII) enriched fraction. Conversely, the PSII-enriched fraction accounted for the larger proportion of total chlorophyll in thylakoids from A. breviligulata. Whole chain electron transport (PSII + PSI) activity was greater in C. longifolia mesophyll thylakoids, at all light intensities. Chloroplast and mitochondrial ultrastructure were compared. The bundle sheath chloroplasts of C. longifolia contain extensive grana stacking and are distributed throughout the cell. The mitochondria of the bundle sheath and mesophyll cells are strikingly dimorphic. A suberin lamella is apparently absent from the bundle sheath cell walls. These results support the designation of C. longifolia as a C4 species of the nicotinamide adenine dinucleotide – malic enzyme type.